US Masters TVA30 schematic anyone?

[Prairie Dawg]

I've got one of these that walked in off the street with low volume. The usual external stuff (tubes, speaker) didn't produce any great change-my Princeton Reverb can kick sand in its face. This is a Chinese built import brought in by a firm in Wisconsin. I've emailed them for a schematic but no response.

It's a 30w head and cabinet, the head (so they say) is a fixed bias 4xEL84 setup with three 12AX7s and a channel switching setup with a gain channel. Sounds a lot like a Hot Rod Deville running EL84s. The reverb is very weak too.

I hope to heck this isn't another orphan.

I have a couple days

Does anyone know anything about this amp and the people who are selling them? Anything at all will be helpful before I pick up the phone and call them.

Thanks y'all.

[Enzo]

Never heard of it. Sounds more like a PV Classic 30.


Here's the amp, and here's the company. If I were you, I;d not wait long for email, I'd pick up the phone and call them. Unless I know a company sends out schematics already, I prefer to call on the phone, because I can get a human, and will know right now if they can help or not. As always, use the proper buzzwords. "A customer dropped off one of your TVA30 for repair. I;d like a schematic to aid in troubleshooting."

TVA30 Tube Amp - 30 Watt Class A All Tube Amplifier - Masters Design

[km6xz]

The only thing that concerned me about their web site was that is was last updated in 2010 so maybe no longer around.
But the photos suggest a pretty well made straight forward unit. The boards are all accessible so trouble shooting should be a snap.
Low gain....low reverb...you have done a stage gain test, if both of those symptoms are observed, look for a front end gain problem since that would effect both of those issues. You changed tubes before measuring anything? That will needlessly explode the cost to the customer. You will get to the cause a lot faster by doing diagnostics before randomly changing parts.

The stuffed parts on the main board looks like a lot better level of parts than of typical Chinese re-brands. I am going to guess that it is not a bad amp at all when it is back to normal operation.

[Enzo]

Yeah, but it could be on the back end too. If the front end is bad, the reverb will get low drive and be weak overall. But that means the recovery ought to be working. SO rock the amp to crash the reverb springs. If that comes out loud, the recovery and power amp are working. If that comes out low, the power amp end is bad.

In the absence of drawings, I often go down the tubes and check for B+ on each plate. And some evidence of current on each cathode.

[km6xz]

Yes, of course, but rather than jangle the pan I'd just try the insert return since it is of a known level for drive. A -10dbv at 1khz can tell a lot at the return jack. But anything that someone uses to divide and conquer is enough. I just try to encourage people to take measurements that can compare to what was expected before the reading was made, particularly before resorting to swapping parts randomly. It is best to measure with a strong idea of what the results should be, which requires thinking about the circuit and how it should work.

[Enzo]

Oh I think we are on the same page more or less. I guess I like to MacGyver it - see how much I can learn before getting out the tools. Front counter diagnostics perhaps.

[Prairie Dawg]

Well, it appears as if my friend is the proud pappy of an orphan amp.

The local number for US Masters was disconnected, the fax doesn't work, the email bounced and people on the US Masters facebook page are saying that USMasters/Regensberg Guitar are defunct.

This should be interesting. I have a couple orphan Judybox amps myself.

[Enzo]

SO just dig in and fix it. Tube amps really are all the same inside. You can find the power supply easy enough and see if everything looks reasonable. You can see if all the voltages are getting to the tubes. You know there will be input stages and other gain stages, a tone stack, and the power amp needs a phase splitter. All those should be recognizable inside.

Two powerful techniques then come to mind. One is to input a signal up front and trace it with a csope or signal tracer through the amp. The other way is to inject signal starting at the power tube grids and working back, listening to the speaker for results.

[km6xz]

That reminds of me of when I was a little kid, in the 50s, Popular Electronics has a schematic for a signal tracer which I built in a tube radio chassis. It had a input for a rectified AC for IF and RF. For two tubes and a 5 inch 3.2 ohm speaker it was very effective in fixing all sorts of things before I got my first scope when I was about 12. That sort of thing would be perfect for quick and dirty stage by stage tracing of unknown circuits. With a 500 volt input coupling cap it was pretty hardy at the input so could be touched to any part of a circuit without fear of blowing it up.
Years later I got a HP log amplifier. it was a small box that took an AC or DC input and output a log of it so you could measure signal levels from microvolts to 100 volts on one analog meter scale. Stage gain measurements were a snap.
Here is a link to the manual with schematic for the old Eico 147 tracer that used to be on every TV and phono repair shop bench in the old days: http://bama.edebris.com/manuals/eico/147a I am sure that will bring back memories for old timers....

[Enzo]

The old Heath and Eico tracers were great. They even had banana jacks on the panel for their output transformers, so you could sub it into a circuit. These days, I wind up with a bunch of the small crappy amps like they throw in with beginner guitars. All I need is that capacitor input probe, and it becomes a tracer. SOmetimes,just to show off, someone comes to my shop, and I demonstrate tracers by plugging a cord into my bench amp, and add the cap with clip wires.

Those old Eico and Heath things were sturdy, and will still be useful today. I have several of them here in my shop.

[Gtr_tech]

I had onna those many years ago. I already had a scope, and I picked it up in a thrift store for a coupla bucks. I ended up scrapping it for its pwr xfmr to build a tube preamp. The tracer is long gone, but I still have the preamp.

[Prairie Dawg]

Sometimes a bit of detective work and the power of the pen pays dividends. A bit of digging around on the Wisconsin secretary of state website gave me a mailing address for the registered agent of M-Tec Corporation which was the guitar amp arm of US Masters. Turns out I recognized the name and it was one of the principals. I scribbled out a note, dropped it in the mail, and more or less forgot about it. Yesterday there was an unfamiliar email in my inbox and it was a schematic diagram and a list of recommended mods for the TVA30.

It looks to be a relatively uncomplicated production.


As the future of the company and ownership of its IP is up in the air right now I am going to refrain from posting it, but anyone who would like a copy can email me at rwluedemanATmchsiDOTcom.

[jbltwin1]

I have one of the old Eico signal tracers. Use it constantly. Actually, just went in and re-capped IT so it's good for another 30. Had to build a bundle cap but hey, it's mine so it doesn't exactly get abused. I even used it once to record a guitar part in the studio. Great little tool. I use the little SS amps with the cap in front too but this sits on my bench and it's always ready. Has the cool little green eye too! Mike.

[oc disorder]

Hello.. does anyone have this schematic ? either a Masters TVA 30 or a (ha ha) Strauss SVC 30.
Both claim to design it and have it manufactured in China.

Very similar to the Peavey classic 30 perhaps a little too similar !
2 x secondary's 312v~ and 24v~
Reverb driven by chip - tube heaters obviously in series - DC heaters in Pre-amp
this could take a while so I'll stop here.

Have a badly damaged one , power transformer burnt out.

I have contacted the local agent who sent me user manuals ... Either they employ children or
they are embarrassed about the blatant rip off !

I intent to rewire it in a more traditional manner and a schematic will save me a lot of time.

spot the difference...