I Know It's Only A Tube Hybrid 4x10 But Please Help

[Reli-Tele]

I picked this 73 Peavey Classic 100 4x10 up in a trade a couple of months ago. The dude took really poor pictures and I thought it was some rad all tube 4x10...NOPE! It's SS with 2 6L6 tubes in the power section. With the parts I put into it and and gas money to get this pig I think I have about $40 invested. I don't count the time I have in it. I consider this to be a learning experience because I'm very new at electronics repair in general. Anyways, I brought it home and it sounded like dry farts when you turn it up plus tons of crackling and hissing on the bright channel. The Normal channel was tolerable at low volumes, and it made a bit of noise while powering down. I don't have a meter for checking capacitance yet and pulling each one and checking it seemed daunting. I replaced all the electrolytic caps and one ceramic that was visibly damaged. Now it's all cleared up no noise in the bright channel but the normal has some slight noise, and they both sound like a GIANT BM if you turn them up just past 1/2 or so. I don't really have the cash to take it somewhere and I have no electronic back ground. What does it sound like to you guys. Is there and Idiots guide to diagnosing? Any input would be greatly appreciated. Thanks
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[Leo_Gnardo]

Good progress so far. Are you sure the speakers all are good?

[matt h]

(deleted)

[vibratoking]

...Now it's all cleared up no noise in the bright channel but the normal has some slight noise, and they both sound like a GIANT BM if you turn them up just past 1/2 or so....

It sounds like you fixed quite a bit. I don't think you'll find any debugging manual that addresses "slight noise" or "my amp sounds like a GIANT BM". We need a more detailed description. Perhaps it is normal behavior? I don't have any experience with that amp. Sounds kinda like the same topology as some of the early Music Man amps...which were pretty damn good amps. Can you post a schematic?

[Reli-Tele]

with no electronics background, I'm a bit hesitant to send you poking around the the inside of the amp. So, er, not silly, quite serious, but dead simple suggestion: use the "divide and conquer" strategy to confirm that it's the amp that's the problem and not the speakers. Run a different amp into the speakers and/or run the amp into a different (known good) speaker cabinet. Make sure to take some readings of the speakers with you r multimeters first to make sure there's not an obvious wiring issue that could damage a good amp.

Once you've ruled out the speakers as the cause, divide the amp in two again. In this case, pre and power amps.

If there's a power-amp-input somewhere (or you can safely figure out how to bypass the preamps of the amp to send in a signal into the preamp.) That'll let you test the PI and power tubes. If that checks out, move onto the preamp sections.

That's a basic troubleshooting strategy that should get you started.

Thank you that was helpful. I can definitely rule out the speakers but I believe it got worse during my trouble shooting. The output level was very quite and just as if not more distorted than before. It kind of sounds like a distortion pedal that has a 9 volt battery going dead in it. I noticed when I would strike a note on the guitar the one power tube GLOWED HOT and shortly after that I noticed it smelled very hot...I turned it off and felt defeated for a short while. Just that alone makes me think it's something in the power section.

It sounds like you fixed quite a bit. I don't think you'll find any debugging manual that addresses "slight noise" or "my amp sounds like a GIANT BM". Very Happy We need a more detailed description. Perhaps it is normal behavior? I don't have any experience with that amp. Sounds kinda like the same topology as some of the early Music Man amps...which were pretty damn good amps. Can you post a schematic?

I was wondering myself how much of it was the amps design. My experience with Peavey Hybrids is limited to modern ones. After an exhaustive search, I can't find the right schem. I did find a Forum post where a fella had a similar amp but had 4 tubes instead of 2. And his similar symptoms were cured by changing out one of the resistors in the tube socket. What is the general rule of thumb for failed electronics. For instance 40 year old Electrolytic caps should be changed right off the bat. What other components are prone to failure from this era. Oh I also changed the two film caps on the power switch, one was ballooned quite a bit. That probably cleared up the on/off noise I had.

What is this dooflingy?
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[vibratoking]

What is this dooflingy?

That's a multi-section electrolytic cap that needs replacing. If you can't find an exact match, you will have to substitute several caps in it's place. You can read the cap values and ratings off the device.

There are so many possibilities. Have you checked the bias current to the power tubes? Many times the bias circuit cap fails. Have you replaced it? There could be more than one. This could cause the overheated tube. I am guessing the amp has a preamp section based on opamps. These could be a little harder to troubleshoot because many of the details aren't common knowledge to tube amp builders, but there are guys here that can help you with those. I suggest taking it to a tech based on your questions. If you really can't, then keep asking questions and we'll try to peel the onion with you.

[eddie25]

That's a really old multi section capacitor with 4 different caps inside. It 'could' be related to your problem.

I would very carefully check to see if the tube that doesn't glow even gets hot at all. Sounds like you have a bad tube(s) or something like a bad screen or cathode resistor.

[Stevem]

Your issue with the output tube red plating as it's called is likely due to pin 5 either not holding tight in the reciver ( female) in the socket or a bad solder connection feeding the needed negative voltage to that pin 5.
Two other things are happening along with this.
1)
The red. Plating issue may have damaged or very much weaken that tube that has red plated output capability.
2) this tube if weak and or red plating is not outputting one half of the audio sign wave,this is the worst form of what's called crossover distortion a audio amplifier could have and will indeed sound like a BM when played loud enough.
At low volume levels if the other output is working good the amp is outputting may be 2 watts of power in what's called class A, like a Fender Champ does by design with its one output tube, but above this 1 or 2 watt level the amp will sound like pure crap!
That amp with all it's speakers being good and working right should sound loud and quite good for clean tones, but for distortion you should get a good tube stomp box, and may be even build one of the many that can be had in kit form that will provide the distortion that you are looking for!

Note that you do not want to over drive the amps preamp section with said tube stomp box, but get the lead tone, distortion and sustane you want.

[vibratoking]

Back in the day, I had a Music Man HD130. Opamp preamp with 6L6 outputs. Much like your amp I think. That amp had a great clean tone! One the best cleans I've ever experienced. Distortion and fuzz boxes sounded bad with that amp, but an MXR Distortion + with a nearly dead 9V battery made that amp sing. That was great tone. Too bad I was young and dumb. I traded it for a van with a bed and carpet on every surface. Thinking about it, maybe I wasn't that dumb. BTW, the battery had to be almost dead or the magic would not happen. Just my experience with this type of amp.

[Stevem]

That is the whole key to good distortion, you do not need hot signal level, but good distortion along with a good dynamic range.