Hot Rod Deville Crackling leaving Standby Mode

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Here goes another Rookie.

My Deville makes a crackling, poping noise when switching from Standby mode to On mode. A fellow ham helped me trace the signal to what we thought was a 22uf cap. I now have replaced all the Filter caps cleanly and found one of the power supply 100 uf caps to check at 70.

Noise is still present but as before, it fades after a couple of minutes and then might come back but never as strong as at start up.

Voltage at some of the 350 vt filter caps is in the 450 vt. range.

I have probed (with plastic) for cold solder joints till blue in the face for the noise but now suspect a resistor is breaking down but dont know for sure. I have replaced the tubes to no avail.

Since I have some high voltages in the later stages of the amp, should I start back at Test Point one and work forward or just in the stage where the high voltage occurs.

I can afford to get it fixed or replaced for that matter, but would rather learn how to do it myself.

Sorry so long.

ENB

[Enzo]

Just when switching or continuous after switching? The two things would have completely different reasons. SO it is an important question.

If it makes noise for a few seconds after switching on, geez, I'd just accept it.

The switch itself could have pitted contacts inside. SLap a .01uf 1000v cap across the standby switch contacts to see. Or leave it OFF and use a clip wire across it to CAREFULLY c0mplete the circuit.

But really my first thought is a tube waking up to the heat. Ever turn off your car on a hot day after a long drive, and hear the motor making pops and other little metal noises as it cools? Tubes are made of metal, and the inner parts get quite hot. SOmetimes tubes make litle noises for a minute until the thermal expansion of the metal parts settles down. Have you tried different tubes? Oh yes, you did.

Another thing to look for is broken solder joints. You can probe and often find many, but not always. Turn the reverb down first, ball up your fist and whack the top of the amp hard. Does the amp respond in any way? It shouldn't. That shouldn;t start or stop the crackles. If it does, then there is a loose connection.

Two places. get out a magnifier and look at the power tube socket pins where they solder onto the little circuit board. Any cracks? ANd bottom center of the main board are two power resistors side by side - R78,79. Poke them, any response?

I'd be willing to bet that those 350v caps with 450v on them are half of a series cap pair. That would mean 225v across each one. Look at the schematic. The upper one might have 450v on its + pin, but the other end sits at +225 above ground. Caps don;t care how high off the ground they are, only the voltage from end to end.

And of course ANY part can be bad, but having a filter cap like those way off value is not rare at all. They have notoriously loose tolerances - +80%/-20% caps used to be common in Fender amps.

If the noise is continuous, then isolate the problem. Is it always there? Is it there with ALL controls are ZERO? ANy control that affects a noise is after its source. COntrols that don;t affect it are before its source.

The main resistors I'd concern myself over at first would be the two plate loads for the phase splitter - R57,58. They like to open more than others in these amps.

I would doubt that was a filter cap, as you found out. Any spikey noise that comes out of the amp looking for a speaker can show up on the B+, that supply is not regulated, and the spike of noise draw a spike of current from the supply to make the noise.

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Thanks for your reply.

The Noise sound much like listening to an AM Radio during a sevier ligtning storm and is pretty loud. It does not correlate to any movement of any of the pots. Noise dies down after thirty seconds or so but will rear it's head after a little while.

I feel like a Dumb*** that I am forgetting that those caps were in series. I used have that in my brain but forgot that.

When tracing the noise with a signal tracer, we found it up to the V3 section and not after. I understand that V3 is the phaze inverter. I will scrutinize the resistors you mentioned for sure. I think we replaced one of them already.

You have game me something to work with and some things to check. Thanks for taking the time to respond and for your patience. All this is making me learn my way around the Deville Circuit board a little better. I guess thats a good thing.

ENB

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Update to leaving Standby Noise

Enzo, you were right on the mark in regards to R57 and R58. The 100k resistor was at 140k and the 82k resistor was at 4.someodd megaohm, both in circuit and when removed. I did not have an 82k handy but I did have the 25 watt 100k resistors. Installed them for now until I place another order. The amp is quiet now going from standby and sitting idle. I am grateful for your help.

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[Enzo]

25 watt???

The pair of 100k will work just fine until you find some 82k

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25 watt???

The pair of 100k will work just fine until you find some 82k

Typo, 1/2 watt is what I meant, not sure where I dreamed up 25.