Peavey Bravo PA plate supply voltage

[NPP]

Hi there,

I'm currently working through the schematic of my Peavey Bravo (late 80's 25W all-valver) in an effort to understand how it works and how everything interacts.

Generally speaking, I'm getting to grips with most things but one thing that is not sitting right is the voltage to the transformer tap in the output stage. I've measured it at 380V quiescent. However, the output tubes in this amp are a pair of EL84 and the maximum rated plate voltage on these is 300V.

Is this overvoltage condition a common one in guitar power amps or has someone in Peavey made a design error here?

Cheers
Gareth

[Chuck H]

Very few MFGs run el84s at or below 300 Vp. In fact, it's more common to see them at or around 400Vp. I'm not familiar with that amp, but I'll wager it's correct.

Many MFGs run tubes VERY high above the rated Vp. In fact, some are so high that amps built with a 110 or 115v power transformer primary that are now being plugged into 120 or even higher in some cases, have real issues with too much voltage. The old Traynor Guitarmate plugged into a modern US wall socket will put over 420 volts on the plates of it's el84s.

Chuck

[Enzo]

The Bravo is a great little amp, not overly complex, though the schematic layout might not be perfect for a learner.

As general advice, when you encounter something that doesn't seem right, "design error" should not be the first thing comes to mind. There are some marginal designs out in the world, but for the most part, if a major maker like PV or Fender puts something onthe market, it is well past the "Oh geez look at our goof" stage. The first thing to mind should be "what am I missing?"

When you read the tube manuals, consider that the specs were for general applications like TVs and table radios. They wanted the product designers to stay within certain limits so that RCA or whoever could warrant that the tube would last a year or two or three. Mom and Dad were not interested in a table radio that needed new tubes every 6 months. And a bad TV tube usually meant calling the TV guy to the house and getting charged for a service call. Not good.

But guitar amps are not common consumer goods. we drive the tubes to death. We EXPECT to change tubes once or twice a year. Mom and Dad expected 40,000 miles or more on a set of tires, but if they ran the car racing every weekend, they would expect to change them more often. Just so with tubes.

The design max voltages in the tube manual is for polite reliable designs, guitar amps regularly exceed them. For that matter, consider distortion. We all love distortion, but in reality it is the result of running tubes past their recommended specs.

Note that this amp is very typical of PV design, it shares a lot with the Classic 30. You might get the C30 schematic and compare. On fact there are plenty of mods published for the C30, many of which ought to adapt well to this amp. Check that out over at Steve's www.blueguitar.org.

There is really one path through the amp, and switching to the lead channel adds in V2's two stages for extra gain.

[NPP]

Fantastic, thanks for the responses. After I wrote up the original question I read something similar on the London Power site in the FAQ question, although Kevin advises against operating EL84s over 360V. Everything now makes sense...

I'll take a look at the Classic 30 information as well. I sonically know this amp inside out so it's a good starting point for me - and the schematic holds no fear, although I'm a tube newbie, I have a good amount of general electronics experience to draw on.

Thanks again, and expect more questions as I work my way through it.

Cheers
Gareth

[dexterity]

Hi there,

I'm currently working through the schematic of my Peavey Bravo (late 80's 25W all-valver) in an effort to understand how it works and how everything interacts.

Generally speaking, I'm getting to grips with most things but one thing that is not sitting right is the voltage to the transformer tap in the output stage. I've measured it at 380V quiescent. However, the output tubes in this amp are a pair of EL84 and the maximum rated plate voltage on these is 300V.

Is this overvoltage condition a common one in guitar power amps or has someone in Peavey made a design error here?

Cheers
Gareth

Hi there. I've got a Bravo that has a problem with the effect loop and would like a copy of the schematic you have. Can you post a link to it or email it or is it a hard copy? Cheers.

[Enzo]

Send an email to parts@peavey.com and ask politely for the schematics. If you have your serial number, include that in case there were any production changes. You could also call them on the phone.

Peavey is a very customer friendly company.