Fender Hot Rod DeVille III 2x12 volume drop issue

[SunDogAZ]

I have a similar issue. Mine is a Fender Hot Rod DeVille III 2x12. Board has 2009 printed on it. I bought it from a guy who said that the volume cuts in and out and prob needs new tubes.

I tried some old tubes that I thought worked (6L6-GC and 12AX7's). No change. My old tubes may be bad, but I would need to buy new ones to do a proper test.

I know my guitar cable is good, speakers are connected properly, input jacks are fine, and tubes glow orange. In fact, after I got it home, it worked fine for about 5 mins.

However, now my symptoms are:

- With guitar plugged directly into either input jack, very low volume on either channel. You can barely hear amp with volumes at full.
- With guitar plugged directly into Power Amp In jack, I get a full clean loud sound, and none of the controls work (which is normal).
- If I rock the amp back and forth, I hear the reverb springs bouncing sound come thru the amp at normal volume.

I know I need to take it to an amp tech to have it properly diagnosed / repaired, but wondered if, based upon my description, anyone has any insight. I do have a multi-meter, and also know of the dangers of working on a tube amp. So, I am open to testing a few things, but prefer to take it to a tech.

Any ideas?

[glebert]

As I said in the other thread, I would check continuity to the tube pins, specifically V1 and V2 since your PI and power tubes seem to be working since it works well at the power amp in.

Another test you can do is to plug a guitar into the input but with guitar volume turned down. Fiddle with the volume, gain, tone, and presence knobs and listen to hear if any of them change the idle noise coming out of the amp. This can help diagnose where in the signal chain the problem lies. For example, on the drive or more drive channels if you crank up the master volume and the noise to the speakers doesn't change at all that means the problem is after the master volume. If the noise increases with master volume the problem is probably before the master volume. This is a good excuse to go through the schematic and follow the signal path and see if you can localize the problem.

I can find schematics for the HRDv III Rev B, but that is 2010, so yours may be a Rev A. Rev B will likely be close enough, but if you can try to find the exact one that would be best.

I guess if you are planning on taking it to a tech why try to diagnose it yourself? Do you want to make sure he is honest about the repair?

[SunDogAZ]

As I said in the other thread, I would check continuity to the tube pins, specifically V1 and V2 since your PI and power tubes seem to be working since it works well at the power amp in.

Another test you can do is to plug a guitar into the input but with guitar volume turned down. Fiddle with the volume, gain, tone, and presence knobs and listen to hear if any of them change the idle noise coming out of the amp. This can help diagnose where in the signal chain the problem lies. For example, on the drive or more drive channels if you crank up the master volume and the noise to the speakers doesn't change at all that means the problem is after the master volume. If the noise increases with master volume the problem is probably before the master volume. This is a good excuse to go through the schematic and follow the signal path and see if you can localize the problem.

I can find schematics for the HRDv III Rev B, but that is 2010, so yours may be a Rev A. Rev B will likely be close enough, but if you can try to find the exact one that would be best.

I guess if you are planning on taking it to a tech why try to diagnose it yourself? Do you want to make sure he is honest about the repair?

If I can fix the issue myself, that would be preferable. And, yes, if I take it to an amp tech, I want to see what their diagnosis is.

I will test the tube pins for continuity later. But, I tried your 2nd suggestion and this is what I observed:

First, I plugged in the guitar with guitar volume all the way down, all knobs on the amp 1/4 the way up.

- Channel 1 (clean): only the Reverb and Presence seem to change the idle noise.
- Channel 2 (dirty): only the Reverb, Presence, and Master Volume seem to change the idle noise, the greatest change being the Master Volume.

[Jazz P Bass]

I would try the Preamp out jack by inserting a cable & 'sending' the signal to another amp.
If that works then you have an issue with the Power Amp In jack itself.
The fact that plugging in to the jack does prove that the power amp works but does NOT prove that the jack itself is capable of transferring the preamp signal to the power amp.
It may turn out to be a simple broken solder joint on the jack pads.

[SunDogAZ]

I sprayed all the jacks with DeOxIt contact cleaner and unplugged / plugged back into all of them a few times to work it in there, and let it sit for 1/2 hour.

Here are some things I tried:

- plugging into either guitar jack, very low volume on either channel.
- plugging into either guitar jack, using pedal patch cable from Pre Amp Out to Power Amp In, no change.
- plugging into either guitar jack, and running cable from Pre Amp Out to a 1x12 cabinet, no sound in that speaker, but low volume in amp.
- plugging into Power Amp In, I get full volume clean sound.

Something I just noticed when plugging into the Power Amp In to test for sound, I get sound as I mentioned before. But, when I plugged back into one of the guitar input jacks, I get full volume until I strike a chord, then the volume drops to much lower volume again. I was able to repeat this a few times.

Thx

[Jazz P Bass]

First off: "- plugging into either guitar jack, and running cable from Pre Amp Out to a 1x12 cabinet, no sound in that speaker, but low volume in amp."
The Preamp Out is a signal meant to go to another amplifier Input jack, not a speaker.
Regardless, it sounds to me like your Power Amp in jack is suspect.

[SunDogAZ]

First off: "- plugging into either guitar jack, and running cable from Pre Amp Out to a 1x12 cabinet, no sound in that speaker, but low volume in amp."
The Preamp Out is a signal meant to go to another amplifier Input jack, not a speaker.
Regardless, it sounds to me like your Power Amp in jack is suspect.

I meant to ask about that. I just ran a guitar cable from the Pre Amp Out to the input jack of another amp, and no signal going to that amp. I tested the 2nd amp first, with said cable, and it worked fine. Let me know if you meant for a speaker cable to be run. Also let me know if you meant to run to the Power Amp In of the 2nd amp. I may have another amp with efx loop to do that test with...

The Power Amp In and Pre Amp Out jacks are soldered to the main board, which will have to be pulled out in order to hit them with a hot iron and see if that helps. Prob for the tech....

But hold on, wouldn't it be the Pre Amp Out jack that is suspect? If it sends no signal to another amp, but plugging guitar into Power Amp In does produce full volume, seems like it would be an issue with the Pre Amp Out jack or going back from there.
Thx

[glebert]

If I can fix the issue myself, that would be preferable. And, yes, if I take it to an amp tech, I want to see what their diagnosis is.

I will test the tube pins for continuity later. But, I tried your 2nd suggestion and this is what I observed:

First, I plugged in the guitar with guitar volume all the way down, all knobs on the amp 1/4 the way up.

- Channel 1 (clean): only the Reverb and Presence seem to change the idle noise.
- Channel 2 (dirty): only the Reverb, Presence, and Master Volume seem to change the idle noise, the greatest change being the Master Volume.

Based on this I would look at the V2 tube solder joints and pads.

[SunDogAZ]

Based on this I would look at the V2 tube solder joints and pads.

Cool. I will check them in a little while.

[SunDogAZ]

Cool. I will check them in a little while.

I am guessing it is tech time. The other day I ordered a standard retube kit from Eurotubes. I followed the directions, meaning I sprayed the pins with contact cleaner (DeOxIt, the best), and worked tubes in and out of sockets a couple times. After firing up the amp, no change. :/

https://www.eurotubes.com/store/pc/F...Kit-94p203.htm

I did notice that, when I slightly wiggle either power tube, I hear popping, sort of crackling sounds. But it doesn't change the volume of the signal. I can still plug into efx out and get full clean volume. Not sure if that helps?