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Valve king II 20 combo clean channel distorted

Posted: Thu Apr 08, 2021 2:27 pm
by skint
Hi guys

Just bought a valve king II 20 combo in second hand. It was selling has broken. The clean channel is distorted, but not a good distorsion, looks unbiased and broken sounded. The lead channel looks good but sometimes doesnt, i think its because of the lead channel distorsion. Just changed all the tubes with new ones and the problem is still there. Using another amp, connect the effects loop send to it and everything sounds good, connecting the guitar to the return the problem comeback. Also connected the effect loop with a patch cable, no diference. I have a multimeter and a scope (cheap chinese one) but i dont know what to do first. Any of you had this problem? Any thoughs?

Thanks

Re: Valve king II 20 combo clean channel distorted

Posted: Mon Apr 12, 2021 6:50 am
by skint
No one? Not even Peavey?

Re: Valve king II 20 combo clean channel distorted

Posted: Wed Apr 14, 2021 11:05 pm
by JamesPaul
skint wrote:
Thu Apr 08, 2021 2:27 pm
Hi guys

Just bought a valve king II 20 combo in second hand. It was selling has broken. The clean channel is distorted, but not a good distorsion, looks unbiased and broken sounded. The lead channel looks good but sometimes doesnt, i think its because of the lead channel distorsion. Just changed all the tubes with new ones and the problem is still there. Using another amp, connect the effects loop send to it and everything sounds good, connecting the guitar to the return the problem comeback. Also connected the effect loop with a patch cable, no diference. I have a multimeter and a scope (cheap chinese one) but i dont know what to do first. Any of you had this problem? Any thoughs?

Thanks
I have not experienced this problem in either my 20MH or my 20 Combo. From the troubleshooting you have already completed, the problem is somewhere between the effects loop return and the speaker.

If I'm reading your description correctly the amp was sold to you as broken. Did the previous owner experience this same distorted sound?

Are the T.S.I. LEDs green? Do they change to red, or flicker, when the distorted sound occurs?

Does the distorted sound change if you activate the reverb and turn the Reverb control?

Does the distorted sound change if you turn the Vari-Class control?

Do you have the schematic?

Re: Valve king II 20 combo clean channel distorted

Posted: Tue Aug 10, 2021 11:43 pm
by nortally
This happened to me as well. My ValveKing 20MH recently came down with this symptom. I have to think that it could occur in any of the 20MH amps.

A year ago, I turned on my amp and it was very low volume, very distorted. I tried swapping the preamp tubes and got lucky, it started working again. I've used the amp frequently since then with no issues.

Yesterday I decided to try playing with a volume pedal in the effects loop -- I had not used the effects loop in a long time. The problem returned when the effects loop was active. Now for the fun part. The problem now recurred with nothing in the effects loop, but went away when I put a footswitch in the REVERB/LOOP jack and toggled the LOOP button. On a whim I decided to try a jumper in the effects loop, no good. I kept experimenting with the effects loop and the footswitches and the problem kept moving until I gave up. I tried cleaning the effects loop inputs and the pedal inputs, no effect. Now the problem is intermittent and frequent regardless of the footswitch settings. The amp is low volume, muddy and fuzzy. The amount of muddy fuzz seems to respond to attack/volume of the guitar.

What next? My thoughts are:
- different pair of power tubes (although the diagnostic lights are green)
- different set of three 12AX7s
- ???

Re: Valve king II 20 combo clean channel distorted

Posted: Thu Aug 12, 2021 1:55 am
by JamesPaul
nortally wrote:
Tue Aug 10, 2021 11:43 pm
This happened to me as well. My ValveKing 20MH recently came down with this symptom. I have to think that it could occur in any of the 20MH amps.

A year ago, I turned on my amp and it was very low volume, very distorted. I tried swapping the preamp tubes and got lucky, it started working again. I've used the amp frequently since then with no issues.

Yesterday I decided to try playing with a volume pedal in the effects loop -- I had not used the effects loop in a long time. The problem returned when the effects loop was active. Now for the fun part. The problem now recurred with nothing in the effects loop, but went away when I put a footswitch in the REVERB/LOOP jack and toggled the LOOP button. On a whim I decided to try a jumper in the effects loop, no good. I kept experimenting with the effects loop and the footswitches and the problem kept moving until I gave up. I tried cleaning the effects loop inputs and the pedal inputs, no effect. Now the problem is intermittent and frequent regardless of the footswitch settings. The amp is low volume, muddy and fuzzy. The amount of muddy fuzz seems to respond to attack/volume of the guitar.

What next? My thoughts are:
- different pair of power tubes (although the diagnostic lights are green)
- different set of three 12AX7s
- ???
Given the current, intermittent and frequent regardless of footswitch settings behavior, I would next clean every jack, switch, pot and tube socket in the amp.

Then go back to troubleshooting and see if the symptoms are consistent.

Re: Valve king II 20 combo clean channel distorted

Posted: Sat Aug 14, 2021 4:12 pm
by nortally
Given the current, intermittent and frequent regardless of footswitch settings behavior, I would next clean every jack, switch, pot and tube socket in the amp.
Great advice, sincerely appreciated.

I've cleaned jacks & tube sockets by spraying contact cleaner on a plug or tube and inserted/removed about 10 times. The pots & switches are modular surface mount components and I'm ignoring for now -- I don't feel that I have a good procedure for cleaning them.

I've identified two distinct problems, testing with the clean channel only.

(1) The amp really wants the reverb/fx loop footswitch plugged in and set to OFF, or else the sound is fuzzy. This is with or without anything plugged into the fx loop send/receive jacks. With a pedal (BOSS DS-1) in the fx loop, it sounds normal when the pedal is on but fuzzy when the pedal is off and the fx loop is on.

(2) I let the amp really warm up, and after an hour the sound went to shit, fuzzy AND muffled/volume drop, regardless of the footswitch, loop, etc.

Regarding (1), the footswitch jacks are both switched as is at least one of the fx loop jacks. My cleaning routine may not be adequate to clean the contacts of the internal switches. I'll test them for continuity, but I really don't think that's the issue.

Regarding (2), this seems like a failing component. I'll roll the tubes and try to make it go away. After that I don't see any hope except factory service. Maybe it's time to call them.

Re: Valve king II 20 combo clean channel distorted

Posted: Sat Aug 14, 2021 6:55 pm
by rogue777
Look at the schematic. I think the stacked Mosfets are used as switches. Use some circuit analyses, maybe with the help of a voltmeter to determine which switch is off or on by measuring the gate voltage. Once you figure how the circuit works, you'll be able to fix your problem.

Re: Valve king II 20 combo clean channel distorted

Posted: Sun Aug 15, 2021 8:48 pm
by nortally
Look at the schematic. I think you have to figure out how those Mosfets work.
Unfortunately the problem is now worse. I sat down to test symptoms methodically:
no footswitch/fx loop empty/result
footswitch on/fx loop empty/result
footswitch off/fx loop empty/result
etc.

During this process, the problem got worse and finally quit putting out any sound regarless of the footswitch of fx loop. My theory is that some part has been failing and finally went out. The speaker a low hum that doesn't respond to the volume knobs, and pops when I shut off the amp.

I'll review the schematic with a friend and see if we can identify components to test, but this puppy may be off to the shop -- I feel that I'm over my head.

Re: Valve king II 20 combo clean channel distorted

Posted: Wed Aug 18, 2021 10:03 pm
by JamesPaul
nortally wrote:
Sun Aug 15, 2021 8:48 pm
Look at the schematic. I think you have to figure out how those Mosfets work.
Unfortunately the problem is now worse. I sat down to test symptoms methodically:
no footswitch/fx loop empty/result
footswitch on/fx loop empty/result
footswitch off/fx loop empty/result
etc.

During this process, the problem got worse and finally quit putting out any sound regarless of the footswitch of fx loop. My theory is that some part has been failing and finally went out. The speaker a low hum that doesn't respond to the volume knobs, and pops when I shut off the amp.

I'll review the schematic with a friend and see if we can identify components to test, but this puppy may be off to the shop -- I feel that I'm over my head.
Did the speaker defeat switch get bumped? Probably not likely, but would also explain no output.

You could try a new V3 and power tubes as they are downstream off effects loop and reverb. Although the TSI lights should indicate if there are power tube issues. If no improvement you can take the tubes back out and save them. You will eventually need them.

I once spent 3 hours chasing a switching issue, but it turned out to be whoever worked on the amp before me reseated a jumper off by 1 pin. As expected that was a consistent failure right when I got the amp. Agreed yours looks like something has gradually failed.

If you find it or your tech finds it, we would appreciate you sharing whatever it is.

Re: Valve king II 20 combo clean channel distorted

Posted: Thu Aug 19, 2021 12:46 am
by nortally
Good thoughts. Yes, I checked the Spkr defeat and tried rolling the tubes.

Final tests:
- Plugging a guitar straight in to the effects return works, sound is OK considering that there's no preamp.
- Plugging the effects send into another amp's effects return did not work, so I tried connecting the effects footswitch. I got some pops when I inserted the plug and worked the effects button, but no guitar signal.

Off to the shop, will post when I get it back.

Re: Valve king II 20 combo clean channel distorted

Posted: Thu Aug 19, 2021 3:35 am
by JamesPaul
That looks like the power amp is good.

You could try putting in preamp tubes, V1 & V2, but with all the switching weird behavior I am thinking switching logic.

Re: Valve king II 20 combo clean channel distorted

Posted: Wed Oct 06, 2021 7:45 pm
by Jkbaker81
All of this sounds like my problem. The shop replaced a fried op amp chip. Once they did that, something around the effects loop failed so they fixed that. I had it for two weeks and the problem is back.

Re: Valve king II 20 combo clean channel distorted

Posted: Sat Oct 09, 2021 11:09 am
by nortally
Sorry I forgot to post an update.

I took it to Pro Audio in San Francisco, a Peavey-certified shop. For $95 they diagnosed it as a blown/bad FET and estimated $300 total for the fix, which is more than the cost of replacement. The reason the repair would be so expensive is that the tech didn't know how many times he'd have to tear it down and reassemble to find the bad FET. The counter man said it was really hard to work on because "it has parts under parts -- no one does that". Also, he said that he'd been trying to contact Peavey for a while without getting a response. I took it home and threw it on a shelf.

According to Peavey's website, you can send them repairs without an RMA. They'll contact you with an estimate. If they decide its on them, they'll fix & send back at no charge. So my options are:
1. Send it to Peavey and hope for the best.
2. Buy another used one that pops up for under $300
3. Try to fix it myself (realistically, will never get around to this)
4. Use a different amp. I have a Super Champ X2 but haven't bonded. Maybe I'll just get a used VK112. Or save up and buy that Mesa Mark V short head or an Orange Rocker 32.

Re: Valve king II 20 combo clean channel distorted

Posted: Sat Oct 09, 2021 6:51 pm
by rogue777
I don't care for that shops response. Perhaps Peavey can give you a reasonable repair.

Re: Valve king II 20 combo clean channel distorted

Posted: Sat Oct 09, 2021 8:09 pm
by nortally
rogue777 wrote:
Sat Oct 09, 2021 6:51 pm
I don't care for that shops response. Perhaps Peavey can give you a reasonable repair.
Yeah. It boils down to the tech saying "I don't wanna." And of course I'm not going to have my equipment repaired by someone who doesn't want the job. I'm not particularly surprised, just a little disappointed.

For the curious, what the Peavey website says about factory repair: https://peavey.com/c/Factory-Repair-FAQ
Because this amp was not made in the USA, I want to call them first & make sure they work on these.