Peavey valveking 50 watt repair issue

[nandrewjackson]

Hello. I haven't been here in a year or 2, I'm glad to see the board still thriving.


I have a peavey valve king 50 watt combo with an intermittent crackle.


Here is a link to the schematic.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.thetubestore.com/lib/thetubestore/schematics/Peavey/Peavey-Valveking-112-Schematic.pdf&ved=2ahUKEwifvoH5y_L3AhURG80KHV6xD9UQFnoECAcQAQ&usg=AOvVaw0-dnleba2IQBCeqUvxplSH


The crackle starts after the amp is up to temperature. It crackles about 10 seconds out of every minute, not super loud like a thunderstorm but bad enough to be concerned about.
The crackle is not dependent on either channel volume, gain, or any other pot or switch.
I have swapped out all tubes, doesn't change the crackle.
The preamp tubes cannot be pulled one by one because the heater circuit is series DC.
I have pulled the signal wire that goes from preamp board to the grid of P.I. tube, crackle doesn't change whether or not that signal wire is connected.


I did a full recap of all electrolytics in all 3 power supplies, main, heaters, and -VDC bias supply. I also replaced all preamp tube plate R's and the power tube screen R's to higher wattage metal film.
I did a full solder reflow on all 4 boards.


If you're looking at the schematic, you'll see the HT line has "plate" , "screen" , "B++" , and "B+" . If I touch anywhere on the "B++" with a metal probe (multimeter tip) it sounds just like the crackle and seems to stir up the crackle into action by touching the "B++". That made me think it was C205 so I changed it, twice, didn't stop the crackle.


"B++" feeds the last triode of the preamp and both triodes of the P.I.
Could the crackle be a coupling cap on that last triode of preamp or P.I.?
Is it ok to assume it has to be something on the "B++" since touching "B++" seems to start up the crackle?


I really like the sound of the valve king, this one is in good shape and I'd like to keep it up and running.


Thanks in advance to any opinions. And if you're going to type something like "made in China crap" save yourself and the rest of us some time and don't bother.

[Latole]

Did you check power tubes bias ? Real power tubes dissipation ?
A too hot bias could perhaps produce these cracklings ?

The reading of the negative bias voltage is insufficient, it is necessary to confirm that the tubes work within the specs.

What is the plate voltage ?
Is R1 and R2 are good ?
 

[tubeswell]

Crackle can be


Old output tubes
Bad/cold solder joint
Oxidised connection terminals or tube pin clamps
Dirty switch contacts in FX Loop jacks

[chee16]

I don't remember what the inside of the Valveking was like.  Are there are ribbon cables? Push on connections?  I'm guessing you poked and prodded with something nonconductive?

You've done all the things that make sense so far. 

What are the voltage measurements at the different nodes?

[Latole]

Google

[pdf64]

I fixed a friend’s amp that had an annoying staticy crackle recently. On examination, one of the HT caps was loose, the crackle happened as it made intermittent contact with its pcb pad.
A complete reflow of the whole pcb may be a good move, if nothing easy fixes it. .

[Latole]

I fixed a friend’s amp that had an annoying staticy crackle recently. On examination, one of the HT caps was loose, the crackle happened as it made intermittent contact with its pcb pad.
A complete reflow of the whole pcb may be a good move, if nothing easy fixes it. .

OP wrote ; " I did a full solder reflow on all 4 boards. "

The problem with repairing at a distance AND not knowing the member's skills is that you can't be sure of anything.
 Whether it's done right or not.

Just recently a member was having DC voltage problems on his amp until we found out that the DC voltage, this member was reading in AC scale !!!!!

[nandrewjackson]

I've cleaned all of the 1/4" jacks.


The only push on connection is to/from reverb tank. There are ribbons, but they're soldered.


I failed to mention that I added 1R 1W cathode resistors to the 6L6's and I'm getting 25mA +/- for the idle cathode current.  I cut the pin 8 trace with Dremel, scraped off green coating and laid down a fair amount of the resistor lead on the scraped trace, it's a solid connection. The other side of the cathode R is wrapped around the through-board pin.


I have swapped out all tubes, that doesn't change the crackling.


I replaced OEM R1 and R2 with higher wattage metal film. Could one of those be faulty?


Thanks for the replies so far. . . .

[nandrewjackson]

I did measure the DC voltages. I didn't write them down, I can get the numbers posted here soon.

[Latole]

Did you check power tubes bias ? Real power tubes dissipation ?

A too hot bias could perhaps produce these cracklings ?

[nandrewjackson]

Another item of note, if it happens to be crackling while flipping off the main power switch, the crackling get very loud for a second

[tubeswell]

Another item of note, if it happens to be crackling while flipping off the main power switch, the crackling get very loud for a second

Hmmm, that kind of static noise is usually filter caps.

[nandrewjackson]

I've been a little concerned about that.  For the 2 100u/550V ones I used a JJ cap can. I've heard those can be junk. And it was $$.


For the 2 22u/500V ones I used F+T.

[tubeswell]

Did you also do the bias supply filter caps?

[nandrewjackson]

Yes. On the bias supply and on the heater supply I used nichicon caps. I've had good results with nichicon in the past with the lower voltage situations.

[tubeswell]

Closely inspect the PCB jumpers, ribbon cables, push-on connectors, and socket PCB mounting points (and trace pads for these) for signs of fragility or cracking, in case this happened during repairs. PV amps are a bit notorious for the fragility of the PCBs and the jumper arrangements. If you even screw the boards in too tightly, if can bugger  things up.

[Latole]

To note the lack of response, maybe you don't know how?
We could show you how.

Too bad that for an amp repairer it is indispensable

[nandrewjackson]

Latole, lack of response? Life gets in the way.
A: I don't have a dedicated workbench for this, my coffee table in my efficiency apartment needed to be a coffee table again.  It's also my dinner table and sometimes my footrest
B: with my job and family and friends also competing for time, valveking can wait.
C: I believe I already mentioned that I have measured the voltages and installed 1R cathode resistors to measure idle current. And while I didn't write them down and post them here I can assure you that they are within operating range and the 6L6s are actually running a bit cool if anything.

Yes, I know how to measure the voltages and plug the numbers into the equation to get the numbers.


If you're doubting my ability to pull the 4 boards, replace 15+ components, do a full reflow on hundreds of solder points, add 1R cathode resistors to the output tubes, reassemble a working unit , then perhaps do you also doubt that water is wet????

[glass54]

Hi nandrew,
If you have pulled the boards out of this amp, refurbished multiple components and it still goes, you can handle anything 
+1 with Tubeswell. I have had many Peavey's with terrible ribbon cable joints/fractures etc sometimes hard to pick the fractures until the amp warms up and responds to "chopsticking" or spray "Freeze".
I would try to break the amp sections up to eliminate the problem area. For example, put a shorted plug into J115 "Return" (or short out R166 at TS) and let the amp run for a while, Theoretically if all is well, you have eliminated the PA and Power Supply. Then work backwards in sections to the input. If it is a Power Supply problem, maybe monitor metering it would help BUT with your new caps upgrade and good soldering skills, I'd be surprised if it was the PS. (Famous last words?  )
Anyway all the best and we look forward to your success.
Kind regards
Mirek

[Latole]

   Latole, lack of response?   

 1-  C: I believe I already mentioned ......... installed 1R cathode resistors to measure idle current. And while I didn't write them down   andpost them here I can assure you that they are within operating range and the 6L6s are actually running a bit cool if anything.

 
 2-   If you're doubting my ability to pull the 4 boards, replace 15+ components, do a full reflow on hundreds of solder points, add 1R    cathode resistors to the output tubes, reassemble a working unit , then perhaps do you also doubt that water is wet????

1- I did not see that ,I see only you read voltage, nothing about  word "bias" .

2- I just ask ask.  We don't know you and write about some other post in forum

[nandrewjackson]

It was the JJ cap can that I used to replace the 2 power caps C202+C204 100uf/550V.


I can remember hearing about bad JJ cap cans years ago, that was the first and hopefully last one I'll be dealing with.


Thanks for everyone's input. It's appreciated. This board rocks.


I replaced that JJ with a F+T can.


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