Sovtek 5881/6L6WGC physical noise

[Chuck H]

A tube with loose innards would, I suppose, be more suspect for other failures later. That said I have two pair of Ruby el34B's that are too microphonic to use in a combo cab and I was perfectly willing to put them in my Marshall 1959slp when the tubes it has wear out. In other words, I think you'll be ok if you just use that set of tubes in an amp that doesn't share the tubes and speakers in the same cabinet.

Side note: NOW I have to sell that Marshall to cover automotive repairs I was never really fond of the amp and I don't use it but I do like that I have it. If you get that. Still, it'll be better off in the hands of someone that will use it and make music than sitting on a shelf.

[Chuck H]

I thought he meant resoldering tube pins - not socket lugs?

Ah. I've heard of that but never seriously considered it. It seems daunting.

Apologies mozz.

[Helmholtz]

I have successfully resoldered loose electrode wires in the hollow tube pins.

[Chuck H]

Did you just re solder at the pins or did you have to remove the base? I don't know what adhesive is used between the base and the tube but it must be some pretty nasty stuff to adhere to glass and also take high temperatures. I don't know what it would take to remove a tube base.

[Helmholtz]

No, just solder pin ends. You typically can see the wire inside.

Won't work with EL84s, though .

[mozz]

I guess it wouldn't hurt to try and resolder the tube pins. I'm not saying to remove the tube from the base, just hold it upside down heat it up and see if you can get it to draw any solder in. I know some old radio tubes can be brought back to life, not many but it does happen to fix some of them.

[Chuck H]

It's an odd mechanical oscillation. Nothing to lose re soldering the pins. Why it does it at those frequencies when just sitting there idling is the odd thing. It would seem that those frequencies must be sympathetic to the power supply within the tube itself (50/100Hz?).

I've never had a power tube whistle while just sitting there not conducting signal.

[Chuck H]

No, just solder pin ends. You typically can see the wire inside.

Won't work with EL84s, though .

Yeah, well, I get that because el84's have solid pins straight through the glass. But I expect that's the reason for the winky face since you know I'm an el84 guy (and proud of it!). I'm not a repair guy so I haven't seen all that much. I haven't run across a big bottle that I thought might benefit from re soldering the pins yet. If it ever happens I'll go in with some confidence now. Thank you.

[htrd]

An OT is stressed by either:
- High current, causing excessive wire temperature. May melt wire insulation and lead to shorted turns in extreme cases.
- Very high voltage peaks (say>2kV) causing internal arcing resulting in carbonized wire insulation - also causing shorts.

Neither of the two seems to be happening in your case as the speaker noise is low.
If you have a scope you might check for additional ultrasonic oscillation.

I mean that this tube looks like it is prone to earlier failure due to some internal instability. With possible consequences on the amp itself if some electrodes will short internally for example. At this moment the tube works fine, sound is clear, headroom is great, just sporadic silent whistle from the chassis, not present in the audio signal. I haven't scoped the output, but OT is cold.

It would seem that those frequencies must be sympathetic to the power supply within the tube itself (50/100Hz?).

Yes, 230V/50Hz. But the frequencies are a bit odd - 2.96K and 8.88K, which is the 3rd harmonic of the first one. That confuses me. Why the 3rd harmonic?

I guess it wouldn't hurt to try and resolder the tube pins. I'm not saying to remove the tube from the base, just hold it upside down heat it up and see if you can get it to draw any solder in. I know some old radio tubes can be brought back to life, not many but it does happen to fix some of them.

Hmm, you mean desoldering the tips of the pins and resoldering them again, trying to add more solder inside?

[mozz]

Don't really have to desolder, just heat them up and try to add more. Watch getting solder on the outside of the pins, it's a pain to remove.

[Helmholtz]

In my cases I could see the wire because there was too little or even no solder in the pin.
Normally the wire should reach to the end of the pin.

No sense completely filling the pin with solder, so don't solder base-up.
Use just enough solder to catch the pin.

I think in production they used a solder pot.

I don't think a loose socket wire is the problem here as a bad/intermittent electrode contact should have nore dramatic consequences.

[Chuck H]

It might be worth trying some of those silicone tube damper rings. I've had pretty good luck with them in a couple of cases.. I've also used thin homemade silicone pads with holes punched in them between the tube and the socket itself.