Servicing a VOX Super Beatle V1142 this weekend.

[SoulFetish]

A friend of mine asked me to help him out with a Super Beatle V1142 he’s had for a while and been working
on here and there. He’s an engineer and a pretty competent technician as well, but he’s hit a roadblock in the project. He’s already done a fair amount of work on it, but says there’s a short somewhere. Bottom line is he’s starting a new job and won’t have time to work on it, so we’re Going to try and get it up and running this weekend. He’s giving me a BK 830B for helping him out
Apparently he’s Says he can’t really find a schematic for V 1142, I was wondering if anyone has the schematic for this version or if there’s much of a difference between that and the 1141? Also if there’s any experience with this particular amp any advice/things to look out for would be really appreciated. Thanks.
He sent me some good pics of the current progress and condition of the amp as well so I can pop those up if anybody is interested.

[Enzo]

What does the short do? Blow fuses? Kill the audio? "Short" used as a generic term of any intermittent sound?

[Tom Phillips]

Have you searched out the Thomas Vox amp information posted at New Page 1? {I wish the forum SW would not re-assign the link name. Just click on it to get to ...geofex . com...} There is a treasure trove of detailed information there.

[SoulFetish]

What does the short do? Blow fuses? Kill the audio? "Short" used as a generic term of any intermittent sound?

Yeah, it has taken on a generic definition of "something wrong". It was a good question, so I asked him. I assumed it was a real short type short. I asked him if it was blowing fuses and he said it wasn't. He mentioned that the filter caps were getting hot, so I think he was using the term in a generic way (I didn't want to get into it any farther than "what do you mean, 'hot'?" in a txt message). Bottom line is I really wont know where we're at until we put it on the bench and I can take a look.

[J M Fahey]

Ox, what´s the actual problem?
"Hot caps" by itself is not a problem (unless they boil electrolyte off and pop a cap or explode) .
"Normal channel distorts at all volumes/hisses like a steam locomotive/motorboats" is.

As of amp version, old Vox amps (like most other brands, for sensible reasons) didn´t have that much variation inside (think Kustom/Peavey/Fender) , so I think that Super Beatle "should" have the same transformer driven totem pole 120W power amp used in many others (including the big Bass amps and the PA ones) and 1141 vs 1142 difference might mean different cabinet configuration, added effects, stuff like that, but nothing beyond.

[SoulFetish]

Ox, what´s the actual problem?
"Hot caps" by itself is not a problem (unless they boil electrolyte off and pop a cap or explode) .
"Normal channel distorts at all volumes/hisses like a steam locomotive/motorboats" is.

As of amp version, old Vox amps (like most other brands, for sensible reasons) didn´t have that much variation inside (think Kustom/Peavey/Fender) , so I think that Super Beatle "should" have the same transformer driven totem pole 120W power amp used in many others (including the big Bass amps and the PA ones) and 1141 vs 1142 difference might mean different cabinet configuration, added effects, stuff like that, but nothing beyond.

Yeah, I agree. It was an odd response. When I read it, I was like "...the hell is he talking about?". This is a big tease and I apologize. I jumped the gun and won't really have anything substantial to report until tomorrow.

[52 Bill]

Not sure, but most of the Thomas Organ model changes were based on preamp changes, different effects, bipolar versus fet input transistors, etc. I have a copy of R.G.'s book somewhere here, it might list the actual differences in each of the models. I'll see if I can find it. My schematic book only has the V1143 schematic.

These amps are not really any harder to work on than other solid state amps of the same time period. Thomas Organ chose to use a construction method that they were familiar with from building their organs, which was not as easy to service as it could have been. If you have ever worked on a Fender solid state amp from the '60s, it's not much better.

[R.G.]

First the detailed stuff. I have written up both an overview of the electronics in the entire Thomas Vox line (The Vox Owner's Safety Net) and a supplement on the V1141 specifically. Both are available through the links at thomas-vox-repair .com and contain all I could think coherently about for the line and amp respectively.

The V1142 is exactly like the V1141 except that the bass channel has been hacked to put the E-tuner into it. However, the bass channel will not work at all unless the tuner is in there, because the tuner completes the emitter-to-ground path for the input transistors. All 'splained in the VOSN.

However, it is very likely that the amp is having ... wait for it... dying electrolytic caps problems. That's what the "hot caps" probably means, high leakage and heat. Best advice: stop mucking about with trying to figure out this, that or the other until you have replaced 100% of the electro caps in the amp. Just don't waste the troubleshooting time until you do this.

Once you have new caps in at least the power chassis, you can debug and get the power chassis working entirely independently of the preamp. The power amp will happily work without the preamp at all power levels, but DO NOT OVERDRIVE IT INTO A SPEAKER OR DUMMY LOAD. It's OK to run it up until you see a little flattening of a sine wave, but massive over drive will cause the output transistors to die. Don't mess with the preamp until you have the power chassis functioning perfectly.

Once you have the power amp running correctly, start on the preamp. Again, don't waste your time on debugging until you have replaced all the caps. It's futile.

Flexing the wires by raising the PCB is what breaks wires. When you take the PCB loose at the back, prop it up at about a 45 with some folded cardboard or paper so you're not flapping it up and down. Broken wires are a super danger with these amps, and one reason amp techs won't deal with them very often.

Much advice available for free here.

[olddawg]

If the guy has been messing around with it already, good luck! Been there.

[SoulFetish]

First the detailed stuff. I have written up both an overview of the electronics in the entire Thomas Vox line (The Vox Owner's Safety Net) and a supplement on the V1141 specifically. Both are available through the links at thomas-vox-repair .com and contain all I could think coherently about for the line and amp respectively.

The V1142 is exactly like the V1141 except that the bass channel has been hacked to put the E-tuner into it. However, the bass channel will not work at all unless the tuner is in there, because the tuner completes the emitter-to-ground path for the input transistors. All 'splained in the VOSN.

However, it is very likely that the amp is having ... wait for it... dying electrolytic caps problems. That's what the "hot caps" probably means, high leakage and heat. Best advice: stop mucking about with trying to figure out this, that or the other until you have replaced 100% of the electro caps in the amp. Just don't waste the troubleshooting time until you do this.

Once you have new caps in at least the power chassis, you can debug and get the power chassis working entirely independently of the preamp. The power amp will happily work without the preamp at all power levels, but DO NOT OVERDRIVE IT INTO A SPEAKER OR DUMMY LOAD. It's OK to run it up until you see a little flattening of a sine wave, but massive over drive will cause the output transistors to die. Don't mess with the preamp until you have the power chassis functioning perfectly.

Once you have the power amp running correctly, start on the preamp. Again, don't waste your time on debugging until you have replaced all the caps. It's futile.

Flexing the wires by raising the PCB is what breaks wires. When you take the PCB loose at the back, prop it up at about a 45 with some folded cardboard or paper so you're not flapping it up and down. Broken wires are a super danger with these amps, and one reason amp techs won't deal with them very often.

Much advice available for free here.

Thanks you guys for getting me prep'd with some good advice and resources to look to.
RG, I did make my way to here:
Tech Tips and Resources
and the other literature available at GEOFEX. Great stuff. I'm curious though; it seems you've compiled a catalog of service data for these amps over quite a long time and have become the defacto authority on this line of amplifiers.
So, my question is: How did you fall into that? Did this develop because there was no relevant information available when you began servicing these? Or Is there something unique to the design or sound of this amp that you've always been drawn to? Just curious.
I've never played a TV Super Beatle or worked on one. I'm trying to dispel my old unfounded prejudices and snobbery against solid state amplifiers. I remember a point when I thought fuzz pedals were total dogshit, and had no use for them. I couldn't understand why it seamed every pedal builder had to have at least one fuzz pedal they produced. My experiences with "fuzz" pedals up to that point consisted of probably playing a couple of horrible sounding fart box pedals and wrote the effect off. But, I'll never forget being at a buddy's place and he just finished building a fuzzface so I had the guitar and he asked me to plug it in to test drive it. So I dimed the volume and it was pretty good with a bit over the top hairy distortion. But I rolled back the guitar volume to like 8, and it cleaned up like an AC30. It was like I immediately understood why people have a fuzz thing. It was a total moment. Everything changed. I mean, it isn't perfect but it is magic. Now I'm this guy ->


with the Fuzz voicing module with built in transistor tester for gain and leakage and a collection of vintage Ge's (and Si's).
that's a little bit of a tangent, but the point is... (..what were we talking about again?) Oh yeah. So, for you was the Super Beatle like my Fuzz experience?

[R.G.]

I'm curious though; it seems you've compiled a catalog of service data for these amps over quite a long time and have become the defacto authority on this line of amplifiers.
So, my question is: How did you fall into that? Did this develop because there was no relevant information available when you began servicing these? Or Is there something unique to the design or sound of this amp that you've always been drawn to? Just curious.

I was a teenager in the 1960s, and got attached to the Thomas Vox line for all the silly teenage reasons, but did not have the money to actually get one. Well, I did get one, a Cambridge Reverb. It sounded worlds better than the Princeton reverb that I had. But there were the Super Beatles, always out of reach. By the time I got my degree and a job, the Thomas stuff was passe, and I had too many other things to worry about to chase them.

But I was multiply smittten - teenage volume lust, British Invasion envy, and techie/electronic curious and capable. I wound up chasing them most of my adult life as an occasional thing. I did get a broken Beatle in about 1988 to fix. Still have it. It was so difficult to find service info on it that I just kind of grew into collecting Vox service info for myself. In the late 90s, I started designing effects PCBs and writing about effects on usenet. Then the internet happened, and I had a venue for the Thomas stuff. It just kind of grew on me. Like mold.

In my dotage, I have come to appreciate the Thomas amps more. They are arguably the best sounding of solid state amps before perhaps 1990. The high frequency response is limited, so they don't have a lot of ear-piercing treble if you'll get rid of those silly high frequency horns, and they don't have huge amounts of gain and feedback like simplistic opamp circuits so the clipping you do get isn't as obnoxious. But the real advantage is the "watchdog" limiter.

I think that Thomas included that because the Beatle and Guardsman are out at the edges of what the power transistors could take. It stops the output stage from going into hard clipping, which is rough on the output devices. Instead, it substitutes a well-set-up clipper/limiter that can be adjusted to cut in just before the power amp would itself clip. It's a soft clipping that the power amp reproduces linearly, but it sounds like the power amp is going into soft limiting. I think of it as an underappreciated "secret weapon".

I've never played a TV Super Beatle or worked on one. I'm trying to dispel my old unfounded prejudices and snobbery against solid state amplifiers.

Once you've spent the time to get a Beatle - or Guardsman, or Viscount or Buckingham - set up right, they do sound nice. But they are all 50-60 years old, and need the maintenance done.

By the way, while you're in there, think about replacing the input transistors with new 2SC1815s or 2N5088s (careful!! different pinouts!!) and installing a reverse-biased diode from emitter to base on the input transistors. Over time, input transistors get noisy from repeated tiny breakdowns of the base emitter. New ones fix the noise, and reverse biased base-emitter diodes make it permanent. The hiss no longer creeps in.

Do yell with questions about it as you go along. My stated purpose is to keep Thomas Vox stuff out of dumpsters.

[R.G.]

So how did the fixup go?

[SoulFetish]

So how did the fixup go?

My buddy totally flaked out on me! (and I was looking Forward to that getting that BK component tester too).
He started a new job this week, and I'm sure he put off everything he needed to do to get ready until Sunday. I was looking forward to working on it, though. We chatted a bit about whats been done already, and power supply/grounding. But he did sent me some pictures:


It looks like I'm just gonna' have to wait til a Super Beatle comes in the shop before I can get into one. But when it does, I'll be ready....

[drewl]

I have repaired and restored several of these over the years thanks to the incredible work of RG.
Can't thank you enough! Think I spent a couple hours trying to "fix" the bass channel with E-tuner removed once- before the website existed!

Always loved the look of the Super Beatle and all the TV amps, maybe it was from watching The Monkees as a kid.

Who wouldn't want a couple Super Beatles in their living room?

[52 Bill]

It was the Beatles for me, those were the biggest backline amps I'd ever seen. And that grill cloth!

It looks like the amp already has a bunch of R.G.'s fixes done to it. I think there are add on heat radiators on the outputs and a relay to replace the broken power switch. Also the new filter caps and all new resistors on the power amp board show signs of a lot of work.

R.G.'s new power switch pc board is lot more elegant than the rat's nest of wires that has been added here.