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Welcome to MyTubeAudio. A truly different kind of repair shop. TRANSPARENT!

MyTubeAudio, LLC., is a West Michigan-based company that offers “While You Wait” service for tube amplifiers of most any make and most any vintage.  I’m licensed, insured, legal and experienced – I have been involved with tube amplifiers for over 25 years. I work by appointment only, two evenings per week. If you’re looking for quick service in West Michigan, give a call to the number above and make your appointment now. 2017 saw 58 appointments completed, several of which were multiple-amp jobs completed in one night. This is THE BEST way to see what’s been done and learn more about your particular amp.

Considering the deep inventory of parts, a solid collection of test and measurement gear and the experience of hundreds and hundreds of documented amp repairs, you shouldn’t be surprised to discover that most tube amps can be repaired in just an hour or two.  Retail music shops often charge 50% repair markups to an outside tech, often resulting in a three week wait or more. Why not head right to the bench with your amp?  You’ll see your amp get worked on, you’ll get your questions answered, and you’ll KNOW what’s been done. You’ll know your amp tech, and be able to let him know what’s important to you. This is my philosophy – a fully transparent, open exchange of knowledge and service. I learn from every repair, also. Many of my returning customers are very knowledgeable, skilled musicians, which makes this kind of work really pleasant and rewarding for me as well.

All work is performed “live” by appointment only – no drop-off work is accepted at My Tube Audio, LLC.  Do you have an important show coming up but can’t risk dropping your best amp off somewhere not knowing when it will be done?  MTA LLC can help you. The business model is ultra-simple and ultra-transparent: $40/hr for bench time plus parts and tax. Warranty is provided – 30 days on parts and 60 days on labor.  NO BENCH FEES. NO MINIMUM CHARGES. NO SECRETS. NO PROMISE DATES.  I buy parts wholesale and my markup is a standard 35%, making most items pretty close to typical “street prices”.  Yes, you can certainly bring your own parts if you prefer, and I’ll install them happily, but keep in mind I can’t warranty your items back to my suppliers if I did not purchase them…I’ll honor the workmanship only in that case.

What? You’d rather have something retro and custom?  You’re covered.

My Tube Audio is also an official dealer for Mojo products, who make an impressive  line of vintage-inspired classic tube amp kits.  I can build to order / custom modify anything you find on their website, so if you’re looking to buy a classic amp but would rather have something in like-new condition without the boutique-amp price, check out http://www.mojomusicalsupply.com/ and let me know what you’d like to do. It’s a good way to get a great amp for less cost than finding/buying/shipping/repairing a vintage unit.

I also offer electric guitar service – just about anything you might need outside of frets and paint. Wiring, mods, pickup changes, setups, intonation and hardware updates. You can even bring in your own purchased “goodies” and let me do the tricky part. What? you bought new tuners but they are a larger diameter?  No problem. MTA LLC has a well-equipped wood shop that can help.

Amateur Radio fans, please take note. I have a great deal of radio restoration experience (domestic AND European) and can help you get that vintage transmitter, receiver or transceiver back up and running. I have added whole second work bench full of gear to support radio repair, including test equipment for measuring alignment and sensitivity.

Hi-Fi friends, MTA LLC has you covered, too.  Beyond the basic performance checks, I can measure THD and Intermodulation distortion values, and a host of other aspects to make sure your tube HiFi gear is really operating like it should.

As for the site – Well, I don’t get enough free time to be doing a proper job of it, but I  add things when I can.  Up here on the front page I am going to continue to add more repair and project photos, with small comments here and there. It’s not as good as full pages dedicated to each item, but it’s better than nothing.  Enjoy what you see and feel free to contact me via the Email address shown in the photo above.

Thanks for stopping by – Dan, N8ZJV

MyTubeAudio LLC., Holland, Michigan

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Seems like I’ve played with a lot of SABA radios in recent times.  I was introduced to them when I was first given one in the early 2000’s by a work colleague back in Germany, where I spent about 8 years of my career.  Nice radios, and WAY overbuilt. The SABA ”greencone” drivers enjoy a good reputation among certain european audiophiles who are big into single-driver, wide-range speaker systems.   A few months ago I had a SABA come into the shop for general repair – just the radio chassis –  and that unit was in pretty good shape except the FM section was dead.  A few power supply caps were replaced as well as one very critical cap in the FM oscillator section, plus a full alignment on each band put that unit back in order.

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These are lovely radios, made from the mid-50’s to the the later 60’s, and they were good examples of a German cultural tendency for engineering for engineering’s sake. Lots of features like: animation/indicators, flying ferrite antennas, optional remote control (wired) and an approach to designing a radio to out-engineer the competition are all present to be sure.  Most recently, I was contacted by a gentleman who inquired if I  could support a full restoration effort on a 400.  I agreed, and after locating a suitable candidate, a SABA 400 Automatic 10 (export version, going up to 108 MHz) he purchased it. He had to drive out of state (to Wisconsin) to find one that was physically in good shape with just a few mechanical and electronic issues.  The chassis was quite clean – very well stored over the years and quite complete in condition save a few minor things.  This restoration ran a total of about 25 hours of work to accomplish.  Four evenings working with the customer together plus a few evenings on my own were invested. A similar model is seen here:

https://www.radiomuseum.org/r/saba_300_automatic_stereo_11.html

Looking at the radio on the bench for the first time, it was clear that the automatic tuning, arguably the most intriguing part of this type of radio, was not working.  The motor looked good – not burned up as some of these typically are.  The various radio bands all received at least something, but weakly and they could clearly be improved.  All the dial strings were intact, a real relief to me, as the last SABA I worked on had most of them broken, a job that took a couple of really tedious tweezer-and-needlenose hours to rework with new dial cord and some springs.  These units are so over-engineered that they are not easy to work on – many things are not out in the open, totally buried or just not easy to get at with tools. On the other hand, from an alignment standpoint, they are very well designed and if you have the original documentation to go by (we did), getting the performance back up to snuff is rather easy. Those adjustment items are out in the clear and really well organized. They also use a 7-pin miniature tube socket to bring out all the relevant test points, which, after making an adapter, really makes the setup easy.

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You don’t need an oscilloscope with these to do a full alignment, but you WILL need a bi-directional (zero center) MICROamp meter. No issue, my Fluke benchtop meter has a uA scale and does +and- current.

Getting back to the Automatic, after some discussion we decided to first replace the iffy power supply cap situation that someone had soldered in to keep the radio going. It was a ratty affair, a old-stock 60’s American two- section electrolytic had been cable-tied and taped into place. The poor install and lack of insulating the B+ line was not as much of an issue as the overrating of the unit. It was more than twice the original unit’s ratings in uF, which, while it WILL keep the hum away,  also really stresses the rectifiers for the huge surge of current it needs to fill at turn-on, and the 60 Hz peak currents of normal hour-to-hour use are also higher than the power supply was originally designed for. That, and the fact that the original rectifier was a selenium unit, indicates to me whoever worked on this didn’t have a strong background in theory.  The only way I could see clear to add that much capacitance would be to upgrade the rectifier to a modern bridge and way over-rate the current in selecting a unit.  But none of this improves the radio.  The original was already engineered to a high standard, so the only thing to do was rip it out and  rewire it back to the factory standard.  Since a similar German-style 3-unit multi-section cap with stud mount is hard to source, and we did have some extra room in the area, we went with a large terminal strip that could support 3 individual caps for each section. That will also make future servicing much easier.

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Because they used a 2-section cap, not three, the old repair also had wrongly combined two of the sections, which is a recipe for feedback between the various sections that were supposed to be isolated, power-supply wise.  That sorted, I made sure that the isolation transformer and Variac I had set up nailed exactly the 125VAC line voltage under load that the radio voltage selector was set for.  We then set about looking at all the voltages around the tube sockets to compare with the factory documentation. The customer had made the wise step of ordering documentation from a gentleman in Belgium. It was all in the original German, but having worked in Germany for about 8 years in automotive engineering, I’m quite fluent and can handle that.  Most of what we measured was in tolerance, but some were clearly not. We noted everything down on the schematic and sat back and took a look at what we had.

One thing was clear, something was very wrong in the motor drive circuits – these voltages were so off that I immediately pulled the tube, intending to measure it. It was an ECL80, which is a pentode/triode combination. But what I pulled out was clearly a large-plated dual power rectifier, NOT an ECL80.  Someone had just filled the socket with whatever they could. There is not a tube power rectifier present anywhere in this circuit.  ECL80’s are not used in a lot of radios, so they are still relatively easy to get and not very expensive, but they are only available as NOS.  The customer ordered a few Telefunkens and we moved on with other repairs while we waited for parts.

The power stage in this radio is another example of German over-engineering.  Since it was technically a “stereo” unit, meaning you can connect a stereo turntable or tape deck, it has 2 separate power amp stages, each running a class A EL84 pentode.  But the radio itself was only a mono circuit, and dual class A is not as efficient as push-pull class AB1, right?  Right. So these clever guys decided to go from 2 x 5W  stereo to a 12 watt push-pull mono configuration whenever a (mono) radio band is selected up front. So, let’s get this clear.  This radio operates stereo class A or mono class AB1 depending on the audio source selected. It switches from two independent output transformers to essentially one big mono output transformer  via some complicated switching and cross-wiring of transformer windings.   You would never see this on an American radio, if only for the extra costs involved. I love it. It does make the schematic a bit messy to follow, as those front piano key switches are involved all over the place getting things switched over.

The original European EL84 power tubes tested fine on the Hickok 6000A, so we left them in place. We started going though the unit cap-by-cap with the LCR meter, looking for out-of-spec values or leaky high-dissipation caps.

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At some point, the customer decided that it was in his scope to just replace all of the aging paper and wax caps. I did that work on a solo-night as it’s a slog and best done in concentration.  I stock a lot of orange drops and other high-voltage film caps, so it was just a question of banging them out, one-by-one.

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There were a couple really deeply-buried units, and in one case, two special “shielded” three-wire types I could not replace, but everything else came out and was replaced with new. You are probably thinking: “That is going to throw things off a bit alignment-wise…” but that wasn’t going to be an issue, since we had the factory alignment instructions.  I finished up the cap work and set up the bench for alignments with the HP8648A  RF generator. I use a radial AM coil (yellow) I made for radiated adjustments, and the factory-spec’d coupling and artificial antenna circuits were soldered up to do the conducted tests.

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These are specific cap-resistor combinations on 4mm banana plugs, which are connected to the female antenna jacks on the rear of the radio.  The radio uses a 460 kHz IF frequency, so that alignment is done first. That sets the fundamental sensitivity of the radio overall.  Once that is done, the local oscillators for the LongWave, MediumWave and ShortWave bands are individually adjusted for equal strength across the high and low ends of each band, as well as the frequency accuracy, which is set so that the dial lines up perfectly with each of the number markings at all points for each band. Something was a little off with two of the oscillators, because the shortwave and mediumwave oscillators did not peak out quite the way the instructions indicated they should – it felt like the coils for those two were not resonating or perhaps open.  We dug into this (none were open) and then analyzed the schematic to see what was common to both affected bands.  We later localized it to a single cap deeply buried under the switch bank sheetmetal that was a important bypass for all of the AM oscillators. One end was flying free. It wasn’t clear to me if perhaps I had un-soldered it to measure or if it had been that way all along – hard to say but there were other components in that immediate area that someone had soldered on since factory.  Either way,  it needed to be put back in-circuit. Trouble was figuring out which of many possible tie-points it went to.  There were dozens nearby on the bottom of the switch bank, all un-labelled.  After reading the prints and testing a few things, it became apparent where it was supposed to go. Once that was tacked back down, the oscillator coils were immediately responsive, so we knew we had nailed it.

That misplaced rectifier tube had done some damage. It didn’t take long to notice that it had burned up a couple of resistors, which were duly identified on the schematic for value, and then replaced.

There is a link to this radio series on radiomuseum.org that has an excellent write-up on the theory of the self-tuning mechanism, in German, and I printed that out and studied it for many hours, and later I even translated it into English to be sure I had understood all the details correctly.   It can be found here:

https://www.radiomuseum.org/forum/reparaturmanahmen_zur_saba_automatic_steuerung.html

I won’t go into it in great detail here, but it’s essentially an extra discriminator circuit (and gets aligned like one) driven by either the AM IF (460 kHz) or the FM IF (10.7 MHz) that drives a special AC motor with dual pairs of windings set in opposition. There is normally AC over all four of the windings, so the net forces all balance and the armature does not move. When the discriminator is either side of the IF (both the 460kHz and the 10.7MHz feed it in tuned circuits), a phase difference develops that allows a small 60-Hz signal, specially coupled in from the power transformer, to be amplified and driven into one or the other of the motor winding pairs, but which one depends on the phase imbalance being above or below the target frequency. It’s a beautiful bit of engineering considering it was accomplished with tubes and analog signals, and once setup to spec it works pretty darn good. It looks like a ghost hand on the tuning dial.

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In the picture above, you can see the typical clutch shaft (brown-brass-brown cylinder in the middle) which shuttles the tuning motion from the AM to the FM sections depending which band key is pressed.  To the right is the tuning motor, acting on the same tuning shaft. Under the clear cover is the gear reduction. If you look carefully you might notice the whole section sits on rubber isolators. There is factory red threadlocker all over this radio to keep adjustable things nailed down. I stock the original red material from Germany,  known as “Schraubensicherungslack”  for reasons like this.

Once the tubes came in, we just had to place it and see if every thing auto-tuned as expected – we pretty much figured it would, as I had borrowed a tube from another German radio in my collection to do the control system alignment with while we waited for the new one to arrive.   The German document stressed that a really good tube was necessary for the circuit to work well, and our new old-stock Telefunken tube did not disappoint. I could not tune a station any more perfectly centered than the automatic system did, as confirmed by the onboard magic eye tuning meter. I guess we nailed it.

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I was a little sad to see this unit go home – after so many hours you kind of get attached, but every project has it’s end. I learned a lot, as this was the first automatic tuning unit I’d seen first-hand. This radio should provide years and years of fine service to it’s new owner, and sound really good doing it. To that end I added a stereo 1/4″ TRS jack on an unused chassis hole in the back – to allow the connection of a Bluetooth adapter or a simple stereo cable to connect to an audio device.

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Most folks in the US don’t have access to DIN to RCA adapters, they (DIN inputs) were never popular audio connectors on this side of the pond.   All said, this was one REALLY fun project!!

-Dan

Addendum –  I received the following comments and pictures from the radio’s owner, and thought it would be fun to include that material here as well…..

Dear Dan,

I just want to drop you a note about my experience at your shop, MyTubeAudio. I am so grateful to have found your place, as without your expertise, knowledge, and experience my Saba 400 would be just a memory.   Now it’s going to be a family heirloom. I was glad to have front row seat watching you do your magic on each and every section of the radio. Replacing capacitors and resistors, setting the alignments of AM and FM waves, it was a sight to behold.

I remember how overjoyed I was when you powered it up a got a heartbeat out of her! The sound was wonderful, the automatic motor tuning was amazing to watch, and the length of the dial was full of stations! I couldn’t be more pleased with your efforts on the Saba radio! Thanks so much for making this possible Dan. I had a great time at your shop.

Gratefully yours,

Tim V.

 

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20180324_130818 chassis parts cabinet

20180324_130809 chassis cab and parts

20180329_122309 rear overall

Tags:

SABA, Automatic 400, Autotuning, German Radio, Luxury Radio, German Hi Fi, Radio Restoration, Radio Repair, Old German Radios, Radio Cap Job,

 

 

 

The Home Studio

Posted: January 18, 2018 in 1

I’ve been a big fan of recording since I was a kid.  I remember sometime around age 13 I had bought a pair of Realistic mics and was experimenting at length with mic placement on our piano in the basement, trying to get a decent stereo recording on my trusty Pioneer CTF-500 tape deck. I thoroughly pissed off my mom when she discovered I had stolen every metal thumbtack from the desk and a few from my grandparents next door – having heard that you could put them into the felt hammers to get a honky-tonk sound.  To me it was like a harpsichord, RIGHT THERE in OUR basement!  I delayed their removal as long as I could, knowing that she’d probably never stick her hands in there and take them out.. and by the time I did I had my recordings anyway.  (Sheesh! What A Rotten Kid!)  I have always been fascinated with recording sound, and over the years I have collected a barrage of tools to do so, some cool, some funky, some weird.  My current project studio started in a real sense in the 90’s when the band I was in (The Voice) was working on CD projects and needed to have a good pre-production situation that we could use to minimize the cost of going into a professional studio.  You can save a lot of cash if you know before-hand EXACTLY how each track should be played and then pay just to re-record the parts in a better room and use their mixdown facilities.   We used it well for that cause, and along the way I recorded demos for several young bands and other musicians in th area.  I began with a Fostex R8 1/4″ 8-track  reel-to-reel machine,  (a package deal which included a  Fostex mixer) and later bought 2 new ADAT XT20’s. and  a new Mackie 8-bus 32-channel console with Meter bridge.  I would later expand that setup with another XT-20 for 24 tracks in total.  This setup was used for many years and tracked several CD projects for bands I was involved in and others.  Meanwhile, I was collecting mics and outboard gear – nothing too exotic, but good-sounding  standard stuff wherever I could find it.  Sometimes the gear seemed to find me.. I stumbled into many deals from friends and colleagues. I collected dBx compressors, Yamaha reverbs, cheap but useful Behringer gates, Alesis reverbs and other oddball bits and pieces.  I did invest in a pair of matched CAD E200 dual-element large condenser mics, which have proved useful and musical for lots of tracks over the years. I also have a Neuman condenser, a Shure SM91 condenser, and a handful each of SM57’s ad 58’s , and examples of beta 57 and beta 58 mics. Lot’s of headphones, too, but I have 4 pair of AKG 240M monitor phones that I tend to prefer.   Speaking of monitors, I use Yamaha NS-10’s and Hafler M1’s both driven by a Crown DC150 amplifier, no fan of course.  In recent years I have been using hard-disk based recording, mostly because I was working for 7 years in speech recognition for automotive OEMS and we were using Adobe Audition for all of our prompt editing. Since I got used to that I’ve been “mixing in the box” on an HP 8560 Elitebook with an SSD, and  I find that works pretty well. This older recording gear is not being used much anymore as a result, but it still looks cool.It’s a little sad to think how much investment is tied up there that I will probably never recover.

I got an M-Audio Lightbridge to use all those ADATs as digital/analog converters. My recording room is set up to be non-reflective, with about 16 each of  2 foot by 4 foot absorber panels placed along the walls, so it’s pretty dead. These are not the dangerous foam types, but a special  heavy 60 or 70 mm thick recycled cotton that does not burn (unlike foam)  and does not out-gas crap into the house.  They are surprisingly effective and I’d recommend them to anyone.   As I said, they will not catch fire (self-sustaining) like foam, and if they do manage to burn, the result is not anywhere as toxic as any foam would be.  I have no idea why these aren’t used more often in home studios, they cost just a bit more per square foot, but are a far better solution.  My thanks to my friend Ed Walters of The Solution LLC – audio consultants – he’s the one who turned me on to them, as well as handled the order once I’d decided what I needed. No regrets there.  cimg9854

I keep a lot of instruments and amplifiers on hand for the studio, mostly American stuff, such as  Fender, Gibson and Rickenbacker guitars & basses.  For amplification, there are many choices as well : ’79 Super Reverb,  ’66 Vibrolux Reverb, ’96 ProSonic,  1980’s Marshall JCM 800,  ’79 Hiwatt Custom 50, ’73 Traynor Mark III,  ’73 Ampeg VT-40,  ’66 Ampeg Gemini I,  ’66 Ampeg Reverberocket,  Peavey Triumph 120PAG, 60’s Gibson GA-9 , 60’s Valco, 40’s Electromuse, and a  rare 1936 Epiphone Zephyr art deco  amp.  A 1970’s Ampeg portaflex B-15S is  now present, with an additional Ampeg 4×10 cabinet for bass sounds.

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I have set up the room for recording everyone at once since the ADAT/Lightbridge combo can handle 24 inputs simultaneously, and it’s possible to set up  4 to 6 separate headphone monitor mixes.  The idea was to be a place where good 100% live recordings can be made.  To that end, I still would like to run some permanent mic lines into the adjacent rooms for use as isolation areas – guitar amps, vocalists, etc.  I have the 1000′ spool of mic cable now, just need some spare time and a mess of XLR wallplates :o)   .

A flicker of hope for those DT-50 owners who have suffered a blown power transformer (or two)…

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If you read the forums, even on Line 6’s own support pages, you will quickly recognize that something went quite wrong with the DT50 amplifier. It has also mysteriously disappeared from their catalog without explanation leaving its little brother, the DT25, behind.  I find it especially odd, since the owners of DT50 amplifiers speak so well of them.  Let me relate my recent experience with a customer’s DT-50 and the long road to putting this amp back into service.  I’m not a big fan of modeling amps in general, but I will happily admit that the latest generations have really improved in terms of real, usable tones that actually approach what they claim to mimic.  I’m also not a big fan of overseas contract manufacturing on so many levels, but especially on quality control. Questionable tooling, non-existent quality systems, using cheap hand labor to replace more reliable automated assembly, rampant intellectual property theft, and ongoing counterfeit parts supply chain issues all leave me feeling the best amps are still made in the west. Things can go wrong, and do.

The DT-50 has, if you have read even a few forums, been plagued with a very high failure rate of power transformers. To Line 6’s credit, many were replaced under warranty, and (in a slight nod to the scope of the issue) they continue to offer replacements to some customers who have, by now, recently fallen out of the warranty period. They even offer, in some cases, to pay postage one-way.  The caveat here, is that, again if you follow the posts, many of these replacement transformers are ALSO failing some months later. The transformers that are failing are made by Chuang Meei in Taiwan, part number 11-30-0044.

Shipping an amp is an expensive, if not risky proposition, so I was not surprised when my customer told me he’d rather have the repair done locally, and preferably without using another Chuang Meei part.  The owner had not had much luck talking to Line 6 initially, and the offer to repair it out-of warranty apparently came a bit later in their conversations. It was also suggested that he might bring the unit to a Line 6 service center, and he was duly given a couple of contacts in Michigan, although not in our area.  When contacted, those shops were backlogged on repairs or “unable to get that transformer right now”, he was told. This customer really liked this amp, and had it integrated with a few other Line 6 products in a seamless way, and he was not about to give up easily.  Replacement parts are not something Line 6 sells much of – only about 18 items are available via their store, mostly knobs and pots and logos, unless you are a “service center”.

Having heard rumors that Mercury Magnetics actually make a DT-50 power transformer replacement, he contacted a MM distributor, JMI Music in Fort Worth, Texas (www.jmimusic.com; 817.284.5877).

While not a catalog item, it turns out that they DO make one, and told him they could wind him one on special order. So, order placed, and a tranny was delivered about two weeks later.  It is a model BOG-DT50-P and cost in the neighborhood of $218.  Not cheap, but MM has an excellent reputation for made-in-USA quality. I was disappointed to find that, when asked, MM specifically did NOT guarantee that the color codes of the unit would match up with the original, even though it was apparently specially-wound for the DT-50. That meant we had to verify every circuit and ground to make sure it would install correctly.

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There are 15 wires on this unit. Line 6 again disappointed us by repeatedly insisting, in multiple calls, that a schematic was not available due to “non-disclosure agreements” (not the lack of an NDA, as in, with me, but an NDA itself, leading me to think perhaps I was dealing with a contract service center and not an actual Line 6 tech department), and further, they would not/could not even verbally identify, by phone, just the color codes of the wiring of the original DT-50 transformer. (So those risky wire colors are secret now?)  Again, none of this would be a big deal, but MM effectively had told us the colors may not match up.

Here’s what we did to prove it one way or another.  Using an LCR meter, and knowing the original PT had a least a shorted primary, we shorted the primary of the new MM unit and made AC impedance measurements across all the secondaries and noted them down on the MM transformer’s supplied pinout documentation. We then measured the DT-50’s shorted unit’s secondaries and compared values. We found that it was pretty obvious which windings were which based on relative resistances at a test frequency of 120 Hz. To double-check the work, I followed those connections back to the PCB traces and to each of the diodes and filter caps to verify that the voltage of each secondary was compatible with it’s proposed power supply circuits. No surprises found here, folks.  In this case, everything matched up perfectly.  Well, except one thing.

The mounting feet of the new transformer do NOT line up with the original threaded PEM-nut inserts in the chassis. They are about ¼” off in one dimension.  Just enough that if I drilled 2 new holes, they’d be compromised in strength as they would be really close to the PEM-nut inserts. A better plan would be to swap out the mounting brackets from the original transformer and use them instead on the MM. Fortunately, the core spacing of the main bolts did match, so this actually works out pretty well. All four bolts must be completely removed to do this, and some new spacer washers placed in the top 2 bolts so the end-bells still retain a cooling air gap of about 2mm at the top (see pics) like it has at the bottom.  Pay attention to the MM paper and plastic insulators on the screws and get them all back into place, it’s tricky, but they are there for a reason. These pics show the Chuang Meei Feet now sitting under the MM iron:

Once that was accomplished, it was a simple matter of bolting it in place and splicing the matched-color wires together using the pre-tin, then sweat together, then heatshrink method, to keep the original molex-type connectors rather than soldering the new leads directly to the molex headers.

Note that the center-tap of the B+ for this amp goes to ground. MM placed a flag sticker warning label on the B+ green/yellow wire about this. In some rectifier designs, shorting this to ground will result in a short-circuit through the diodes, but in the DT-50 on the bench here, it was used and grounded.

 

Before I connected the secondaries back up, I applied 12.5 VAC (via the variac) to the power input of the amp and verified I had 1/10th of the expected AC voltages on the each of the secondaries,  before I risked applying the wrong voltages to the PCB circuitry. Everything looked dead-on, so we connected all and powered up the amp. In this case, the output was a perfect 50 watts at clip into 8 ohms, the bias was very close to spec, and after all functions were verified a solid burn-in was completed. We then re-dressed all of the leads safely as per the original wire dress.  As a result, one VERY happy customer took his beloved amp home knowing that this problem should never return.

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Power transformers can fail for a number of reasons. Often, an internal, self-resetting thermal fuse is to blame when it fails to re-set. Other times, arcing across windings is to blame, insulation issues, or a shorted output tube connected without an HV fuse will take out the smaller-gauge B+ winding by drawing too much current. I like to do post-mortems on parts whenever possible. In this case, we tore the original unit open and found that one side of the 120/240 primary was simply shorted out. Hopelessly shorted, with no signs of heat or smoke. Perhaps a winding error, or a tolerance issue. Transformers get quite hot, and copper expands and contracts a lot with temperature cycling. It has to be accounted for in the design. To see an occasional tranny go bad is to be expected.  To have a whole group of them go bad is either faulty design or faulty manufacture, bad tolerance stack-up, poor materials or a combination of these.

 

I suspect Line 6 is acutely aware of what happened, but they are not talking about it and not being very helpful, either. If this case is typical, and they expect to keep their (once-loyal) customers, they should be providing better customer support for their products, especially at this price point of equipment ($1800 list). Simply sending in the transformer alone for an exchange/replacement would have been a low-cost $35 (OEM price) solution they should have offered (only 4 screws and 3 connectors to remove/replace).  Leaving the customers hanging or offering a $65 shipping bill and waiting weeks to get an unimproved replacement is not a good response to an obvious quality issue. My guess is that they simply did not have enough trannys to go around (some threads recalled being told they were out of stock) or the whole lot were so suspect that they just stopped DT-50 amp production altogether and tried to limit economic damage while they could. Sourcing from Asia is always risky.  Now you know.

 

I’m basically putting all this out there so other people, who until now cannot get their amps fixed, can know there IS a solution, and this is what it takes. Whether it’s worth it to you, well that depends how much you like the amp. For me, I‘d have to say it is one of the best-sounding modeling amps I’ve ever heard, and worth making it right. By the way, if you are brave, and just have to have one, I noticed Line 6 has “Refurbished” DT50’s quietly available via their online store for the time being, at $1,039.00.

I do wonder, at that price, which power transformer do they have in them?

 

Dan , MTA, LLC

 

 

 

 

 

 

 

 

 

2016 – The New Year!

Posted: January 20, 2016 in Uncategorized

Thanks for visiting MyTubeAudio. 2016 is off to a great start already!

The Business –

It’s been a busy couple of years – the daughters are growing like weeds, my career changed paths again, and the amps keep coming. About the only part of my life that feels consistent is the repairs. For a few years now I’ve been doing exclusively while-you-wait repairs for tube gear, one, two or sometimes three per week, and I’m get nothing but wonderful feedback from the customers.  As to stats, well, most repairs take around two hours, sometimes more or less, but the average bill seems to hover below $100 when I’m billing $40/hour plus parts.  I had some feedback that the site was looking a bit dated, so I figured I’d better take a rare quiet evening free and update things a bit.

The Bands  –

The Voice and Rocket 8 are both active these days – The Voice had a strong show at a local theater and just about filled it – we made well  more than enough to cover costs plus pay the professionals who took care of lighting, sound and serving the crowd.  During that show we showcased some new material that we’ve been working on the in the last year and released some new material on iTunes as well as our back catalog for download. We followed that up with a nice Christmas show and are starting the new year by doubling-down on the remaining unfinished mixes, which so far are sounding pretty tasty.

Rocket 8 has been keeping a steady clip, so to say, at about one show per month per the PLAN, and in the last year we added a second guitarist, which really filled things out and has allowed me to get more familiar with keyboards, adding more texture and breath to many of the danceable 80’s covers we specialize in. There is a demo on YouTube out there now – I’ve been mixing the live audio multi*tracks for the past  few months  as time has allowed while Glen has been putting together scraps of video to make a medley of material highlighting the band’s offerings. Hopefully it will bring us some new venues to ply our trade in.  There are rumors about a possible Mac Island show this year – we’ve committed to it but have to get the venue on board with it- there is a good chance it will happen for 2016. I think the last time we played there was summer of 2013. We’ve also invested in gear again – adding a digital board (Midas/Behringer X32) and picked up 2 x 18 JBL subs and 2600W of Crown power to drive them. Active monitors were also added, and the upshot of all of the investment was deleting the racks of gear we used to carry – a cleaner, simpler PA with tons of headroom and all of the FX we would ever need. We don’t clip anything anymore and are getting very good feedback on the sound overall. iPad access to system tuning is a wonderful thing – you can walk around a room and do anything you might want to, and save your changes too.

The Site –

I do have more repair pictures to upload -I’ll make an effort to get them out there this year, I promise!!  I get a lot of comments from customers that they have indeed taken a look at the site before calling, so it’s time worth spending.  I’m a bit hesitant to publish my contact details here, but let’s say that I can be reached most easily via CraigsList Grand Rapids where I have kept an active ad for years – Search Tube Amp Repair under For Sale – Musical Instruments for all the contact information.

The Studio –

On of the benefits of the Rocket 8 transition to a digital board is that all the rack gear came back home where it belongs. Not that I use it much but it’s nice to have everything back in place and wired up for service and not out in harm’s way.  As part of the new job I started in November of 2015, I took some severance pay and invested in a capable laptop, and that has resulted in a lot of recording and mixing “completely in the box” as they say. It’s addictive in some ways, but I too, like so many others have noted how it lacks warmth. I’m using Adobe Audition on that machine, as I used it with my former job doing voice-recognition prompts for so many years that it was a natural choice. I do miss my extensive plug-in library that we had on the corporate license, but that can be cured a little more investment. I’m finally happy with a PC that can handle multi-track audio gracefully without complaint. Funny to think I had to lose my job to get to that point.

The Day Job –

It took a couple of months, but after Visteon shuttered the doors in West Michigan, I landed on my feet (with more than a few former colleagues) at a good company, Gentex, just a short drive away. I couldn’t be more pleased, as it’s a well-run place. My current role is as a Senior EMC Test Engineer, so once again I’m playing with some really expensive toys, interesting antennas, and radio. My latest work will have me playing around well into the double-digit GHz domains, looking for truth and harmonic content above the noise. I love this kind of work, and the research that goes with it, I’m back into a learning mode and that feels great. Good to be employed, too!

I wish everyone a safe and happy 2016 – if you are considering having some tube amp work done, please get in touch – we can fix your amp together,quickly and have fun doing it, for less cash than you’ll likely pay elsewhere.  The best part is you take it home with you the SAME night. That’s what while-you-wait service means – NO WAITING, and exactly the things you want done get done, and done right.

-Dan Brasier, N8ZJV

MyTubeAudio, LLC

Holland, Michigan

 

 

Here is a random collection of photos from 2014 work.  I’ve been terribly busy, 2 bands, engineering day job, family (2 young girls + wife!) and tube work… lots of it.I don’t have much time to post here but I think I can upload a bunch of new pix and call it good for now!  (oops – I now see that they upload in a random order… if I get time I will try to sort them later. )

By the way, the “While-You-Wait” repair thing is going GREAT!  It’s so much more enjoyable and the customers are loving it. I should have done this years ago. I no longer take drop-off repairs of any kind, but I’m doing morework.  2015 started with a bang – usually 3 appointments per week. Let the solder fly!!

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Epiphone Electra needs a heart transplant

Posted: January 25, 2014 in Uncategorized

This Epiphone had an issue with a bad photocell/lamp combination – a special optocoupler that is no longer available – and so no tremolo.  I managed to retrofit a new lamp into the original assembly and only had to make sure the current driving it was within spec and still performed well in the tremolo circuit.

Epiphone Electra repair (25)

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Epiphone Electra repair (30)

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Epiphone Electra repair