Randall Amp Problems

[tanusgreystar]

Hi. I have a Randall Diavlo 5 watt amp that has very little output, new tubes and everything. When I first turned it on it heated up and smoked, and I found the power tube was faulty. New tube, no smoke, but there is barely anything coming out of the speaker. I was suggested to check the preamp transformer, but I'm not sure how to do that. I looked at the transformer and there is a red cable tied off and not hooked to anything. Would that have anything to do with it? I don't have a lot of money to bring into the shop and I'm semi handy with a multimeter and soldering iron, so any suggestions are greatly appreciated. Thanks!

[Phil_S]

Sorry to hear of your trouble.

Handy is one thing. Familiar with amp safety is another. No amount of money saved is worth your life. Even unplugged, there could be a stored lethal charge. If you aren't familiar with tube amp safety, you may want to rethink this. Tell us a little more about what you mean by handy. People here may be willing to walk you through this.

I think we'd like to see pictures of the inside of the chassis. If you aren't already familiar with how to discharge the filter caps, read up on that before you attempt to access "no user serviceable parts inside."

[tanusgreystar]

I have read about how to discharge filter caps, although I've never done it. I'm willing and able to however. I mean semi handy, I've never had any instruction on how to use a multimeter and I'm ok at soldering. But with instruction I could be better at it. I can provide pics of inside the chassis. I'll do that tomorrow. Thanks for your reply!

[Stevem]

You need to open up the amp and get at the bottom side of the 6v6 output tube socket and with a dc volt meter check for voltage on pin 3 and pin 4 , these voltages will be in the 300 volt range to take a guess off the top of my head!
Note that these will be the highest voltage locations in the amp so do a web search and first read up on working safely in the voltage environment that tube amps have in them.
The fact that you had smoke and killed a output tube without the amps fuse blowing is a concern to me!

[Gibsonman63]

You need to open up the amp and get at the bottom side of the 6v6 output tube socket and with a dc volt meter check for voltage on pin 3 and pin 4 , these voltages will be in the 300 volt range to take a guess off the top of my head!
Note that these will be the highest voltage locations in the amp so do a web search and first read up on working safely in the voltage environment that tube amps have in them.
The fact that you had smoke and killed a output tube without the amps fuse blowing is a concern to me!

Be sure to check for dc volts, not ac on your multimeter.

[Phil_S]

Basic safety info here: http://ax84.com/safety.html
Useful info here, too: http://www.rru.com/~meo/Guitar/Amps/Kalamazoo/

Take your time. Hurry is not your friend when safety is concerned. By take your time, I mean read this stuff first, ask questions, make a plan.

[tanusgreystar]

When I look at a socket diagram, is it showing the pins from the top or bottom of the socket? Do I check it with a tube in it?

Nevermind I figured it out

[rock_mumbles]

Tube socket diagrams are looking at the bottom of the socket ... at the solder connections.

Measure voltages with the tubes installed, DC voltages are made to ground ... measure the heater voltage across the heaters instead of to ground most amps have AC heaters, some have DC heaters

[tanusgreystar]

Here's a dumb question...to check for dc voltage for pins 3 and 4 do I put the multimeter leads on both pins at once, or do I put one lead on a pin and the other to the chassis and do that for each pin?

[Structo]

Are you sure you want to do this?

[tanusgreystar]

Yes, I just need a little guidance (and patience).

[sluckey]

to check for dc voltage for pins 3 and 4 do I put the multimeter leads on both pins at once

no

or do I put one lead on a pin and the other to the chassis and do that for each pin?

yes

[tanusgreystar]

ok

[vibratoking]

Be sure to inform us if you get electrocuted. At least we'll know to make stronger discouraging statements in the future.

[tanusgreystar]

I will