High pitched whistle in tube amp

[InbredJunk]

Have you guys ever experienced this? Only happens when I first turn it off of standby, and lasts, intermittently for 30 seconds or so. It's a high pitched whistle, that changes frequency, from high to low. After 30 seconds or so, the amp acts like normal. I fear it is a bad solder joint or bad cap. However, I do need to roll some tubes and check that out.

I never heard it before I biased the amp properly though, so it may be a power tube problem? The guy I bought it from said it may need some new tubes. Didnt know how old they were.

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[Blille]

Re: High pitched whistle in tube amp

I had the same symptom a couple years ago in a 5e3. It ended up being an issue with the input jacks.

Did you move the amp recently?

 

[InbredJunk]

Re: High pitched whistle in tube amp

I had the same symptom a couple years ago in a 5e3. It ended up being an issue with the input jacks.

Did you move the amp recently?

Yes. I took it out of the head box and cleaned it real good. Tube sockets, jacks, and scratchy pots. I sprayed the tube pins with electronic cleaner, shook the excess off, and inserted them a few times, used a dummy plug and done the same thing to all of the jacks, and sprayed all of the pots and rotated them. I then let the amp sit for a day or so before I put it back together and played it. While I was in there, I didnt see any faulty components, but I very well may have missed something. None of the caps had bubbles in them, and no sign of leaking, and no burned spots or nasty looking solder joints.
The amp is a peavey triple x 120 watt head.

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[Blille]

High pitched whistle in tube amp

Could be lead dressing, a couple of cables touching that shouldn’t or even a couple of components on top of each other (less likely).

So I would first just try to move internal cables around.

I always tap tubes softly to see if they are microphonic.

Hopefully it’s something this silly and not more serious.

 

[InbredJunk]

Re: High pitched whistle in tube amp

I will try that out.

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[dystrust]

Re: High pitched whistle in tube amp

In something as high gain as a Peavey XXX, my first thought would be a microphonic tube.

 

[Mincer]

Re: High pitched whistle in tube amp

Yeah, this is what a microphonic preamp tube sounds like. While it is making the sound, tap lightly on each preamp tube with a pencil eraser- you will hear the faulty one.

 

[ehdwuld]

Re: High pitched whistle in tube amp

I had that problem
It started as a whistle that feedback to a howl

It was a cracked solder joint on my reverb tube

Removed the pan and tubes
Touched all the tube socket solder joints with a hot iron
Reflowed the solder

All good

 

[Despair]

Re: High pitched whistle in tube amp

You've already tested some of the issues, but sounds like you started with obscure first. Even just swapping the first preamp tube with one later in the circuit can sometimes hide the issue, as microphonics tend to be worst earlier in the preamp, as they get amplified more.

Microphonic tube is the most likely of the possible issues, but microphonic capacitors aren't unheard of, poorly seated tubes, or bad solder joints on a tube socket, potentiometer, capacitor or jack are less common sources of whistling noises.

Power supply issues are a nasty one. Reverb circuit flaws or defective reverb pan/springs are another "fun" obscure one.

Microphonic capacitors often don't show any sign of defect. Some of them just start to squeal with age.

 

[RevDoom73]

Re: High pitched whistle in tube amp

Yep, as has already been stated, I've had the high whistling noise happen a couple of times, on a Peavey 6505+, and each time it wound up being a microphonic tube problem. It started out being a temporary issue and then the whistle got more prominent and long-lasting.

 

[Mincer]

Re: High pitched whistle in tube amp

Man, that whistling can get loud, too! Just replaced a preamp tube on my Mesa because of it.

 

[IMENATOR]

Re: High pitched whistle in tube amp

Yeah, this is what a microphonic preamp tube sounds like. While it is making the sound, tap lightly on each preamp tube with a pencil eraser- you will hear the faulty one.

Use a wooden chopstick, voltages in amps can be super dangerous. Don't touch with bare hands.

 

[InbredJunk]

Re: High pitched whistle in tube amp

I have an update. I havent bought any new preamp tubes yet, but I did take out the el34s, and popped in the 6l6s I had on hand, then the 5881s, and the squeal was gone with both of them.

I only had 2 of each, so i dropped the cab selector to 4 ohms and put the tubes in the middle slots.

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[ehdwuld]

Re: High pitched whistle in tube amp

Still could be a cracked solder joint in one of the outside slots

Try them on the two outside slots instead of the middle ones