The Crack is Back.....Ongoing Intermittent Crackle/Sizzle in HR Deville

[Perkinsman]

What I thought was repaired by resoldering the PI socket pins has returned. Changing tubes, replacing filter caps, resoldering & tightening all the tube socket pins hasn't worked. Someone mentioned a method to isolate the preamp from the amp by plugging into the "Amp In". Could that be explained so I can try to determine whether the crackle is in the preamp stage or amp stage.

[Perkinsman]

Anybody??

[HaroldBrooks]

What I thought was repaired by resoldering the PI socket pins has returned. Changing tubes, replacing filter caps, resoldering & tightening all the tube socket pins hasn't worked. Someone mentioned a method to isolate the preamp from the amp by plugging into the "Amp In". Could that be explained so I can try to determine whether the crackle is in the preamp stage or amp stage.

How about the PI or preamp plate resistors ? I think that was mentioned. That's quite common in older amplifiers (and some newer) and definatly causes crackling and sizzling when they are bad, and I wouldn't automatically rule that out in any amp, even if the resistor looked ok visually. Another tech claims he replace many in your prior post.

I had two amps that suffered from bad plate resistors and they exhibited the same "cat and mouse" symptoms you described. Replaced them and all is well now for a year or more. I'm also assuming you chopsticked and verified virtually every solder joint in the amp. This is easy and quick, and should always be done for a crackling issue, twice. If that checks out, I would replace the Plate resistors.

Just a thought, since you've done / changed other things.

[The Dude]

What I thought was repaired by resoldering the PI socket pins has returned. Changing tubes, replacing filter caps, resoldering & tightening all the tube socket pins hasn't worked. Someone mentioned a method to isolate the preamp from the amp by plugging into the "Amp In". Could that be explained so I can try to determine whether the crackle is in the preamp stage or amp stage.

Not sure why you started another thread? Now history of what you did or didn't do is in another place, so we're destined to repeat ourselves. Anyway, if you want to see if you can determine preamp or power amp, do as you state. Plug a source into the amp in. This disconnects the preamp via the switching jack. If the noise goes away, it's likely a preamp problem. If not, it's likely a power amp problem. You can also run the preamp out to another amp and see if the preamp is noisy. Of course, it could always be a power supply problem causing both power amp and preamp noise, but it's worth seeing if you can narrow it down.

[Perkinsman]

Not sure why you started another thread? Now history of what you did or didn't do is in another place, so we're destined to repeat ourselves. Anyway, if you want to see if you can determine preamp or power amp, do as you state. Plug a source into the amp in. This disconnects the preamp via the switching jack. If the noise goes away, it's likely a preamp problem. If not, it's likely a power amp problem. You can also run the preamp out to another amp and see if the preamp is noisy. Of course, it could always be a power supply problem causing both power amp and preamp noise, but it's worth seeing if you can narrow it down.

I wasn’t sure if anyone would follow that thread since i had ended it with what I thought was a fix. When trying “amp in”, is plugging my guitar in good enough? When trying “ preamp out”, do I run a cord to the instrument input of another powered on amp?

If the 6 plate resistors measure to spec, do they still need to be replaced or can I assume that they're ok & just reflow the solder joints? I see that each of the plates have TP's with corresponding voltages. If those are within spec, should I still replace the resistors?

[Enzo]

Please understand, you are chasing down the source of noise, not a dead amp. Your meter will not detect noisy resistors. In other words, the amp is not crackling because some 100k resistor measures as 112k. Likewise, while way off voltages could be stressing something, it is likely your test points will all measure more or less as they should. In other words just because 250v TP is dead on at 250v, that does not mean it can't still be noisy.

Yes. Play into your amp, and run a cord from preamp out to the input of some other amp. On the other amp use either the FX return or power amp in jack, or if it lacks that, just use the input. REmember, in that other amp, we are not listening for tone, we are just listening to see if the noise is present.

The way to track this down is to isolate the problem. Use a scope or listen with a signal tracer to find out just where in the circuit the noise originates.

[Mick Bailey]

When trying “amp in”, is plugging my guitar in good enough?

Yes, I frequently do this when troubleshooting these amps.

[Perkinsman]

[QUOTE=HaroldBrooks;543962]How about the PI or preamp plate resistors ? I think that was mentioned. That's quite common in older amplifiers (and some newer) and definatly causes crackling and sizzling when they are bad, and I wouldn't automatically rule that out in any amp, even if the resistor looked ok visually. Another tech claims he replace many in your prior post.

I had two amps that suffered from bad plate resistors and they exhibited the same "cat and mouse" symptoms you described. Replaced them and all is well now for a year or more. I'm also assuming you chopsticked and verified virtually every solder joint in the amp. This is easy and quick, and should always be done for a crackling issue, twice. If that checks out, I would replace the Plate resistors.

Just a thought, since you've done / changed other things.[/QUOT


Wasn't anything easy about this job, lol. After pulling all the knobs to get at the 4 plate resistors for V1 & V2 on the main control board, they all measured very close to spec but since others have suggested replacing them, I did. I then powered back up and crackle, pop...still no improvement. The last set of plate resistors for V3, the PI tube were on the other board of course so I had to take that one out as well. After replacing the 100K, which measured in spec, I finally got to the last resistor, the 82K all the way in the back. Sure enough, it measured 1.5M. I replaced it, put it back together and voila, the sweet sound of silence! This was a great lesson in troubleshooting, thanks for everyones assistance.

[HaroldBrooks]

[QUOTE=Perkinsman;544016]

How about the PI or preamp plate resistors ? I think that was mentioned. That's quite common in older amplifiers (and some newer) and definatly causes crackling and sizzling when they are bad, and I wouldn't automatically rule that out in any amp, even if the resistor looked ok visually. Another tech claims he replace many in your prior post.

I had two amps that suffered from bad plate resistors and they exhibited the same "cat and mouse" symptoms you described. Replaced them and all is well now for a year or more. I'm also assuming you chopsticked and verified virtually every solder joint in the amp. This is easy and quick, and should always be done for a crackling issue, twice. If that checks out, I would replace the Plate resistors.

Just a thought, since you've done / changed other things.[/QUOT


Wasn't anything easy about this job, lol. After pulling all the knobs to get at the 4 plate resistors for V1 & V2 on the main control board, they all measured very close to spec but since others have suggested replacing them, I did. I then powered back up and crackle, pop...still no improvement. The last set of plate resistors for V3, the PI tube were on the other board of course so I had to take that one out as well. After replacing the 100K, which measured in spec, I finally got to the last resistor, the 82K all the way in the back. Sure enough, it measured 1.5M. I replaced it, put it back together and voila, the sweet sound of silence! This was a great lesson in troubleshooting, thanks for everyones assistance.

Good news !

I have only old vintage amps at this point, so this plate resistor crackling problem appears more commonly for me, and I am of the mind now such that I replace any carbon Plate resistor that is more than 20% off, regardless of how good it looks. Some look nearly perfect, but I now know from some experience that when they are out of spec, changing them usually sets the plate voltage back to it's intended design level, and that's not going to hurt the sound one iota. I don't however advocate automatically shotgunning all old parts, that's a waste IMHO, just the ones that are bad, or suspect. Filter capacitors have a shorter life so they are some of the first to go, as you already know.

[DFuller]

I feel I should note - it's really not uncommon for the plate resistors in the Hot Rods to end up WAY out of spec. I've seen it more often than I care to count.

[g1]

when they are out of spec, changing them usually sets the plate voltage back to it's intended design level, and that's not going to hurt the sound one iota.

Just a note of caution. Whether you call it 'hurt', it may change the sound. If it's some vintage piece that the owner considers to have the 'magic tone', changing off spec. parts can sometimes get you in a fair bit of trouble.

[HaroldBrooks]

Just a note of caution. Whether you call it 'hurt', it may change the sound. If it's some vintage piece that the owner considers to have the 'magic tone', changing off spec. parts can sometimes get you in a fair bit of trouble.

Thanks for the insight g1, it makes perfect sense for customers that want their current gem to remain with it's current sound.

I agree, and fortunately I have no customers, so I get to do what I want, LOL. If I did have customers, I would ask them what to do, and as you correctly stated tell them than the magic tone is a result of the 40-50-60 year wear and tear on the amp, and if they will sign a "release" on leaving the old marginal parts in, I would be happy to comply, with the exception of a bad filter cap, or something that would lead to a bad short (dangerous conditions).

If I had unlimited funds (I don't !), I would actually and willfully keep some vintage amps in a state of disrepair, so I could use their funky, cool, and sometimes downright nasty sounds in my recordings ! I know this is probably done in studios all the time. Some great sounds come from amps that are "off" and maybe ready to expire.