Consequences or wiring reverb Tx primary backwards?

[galaxiex]

I have a B1270 SF PR come to me making weird sounds.

Amp warmed up, all knobs at 0, speaker connected, no guitar plugged in.

Turn volume up and at approx 5 it makes crackling noise and high pitched whistle.
Go past 5 to 8 and above and all noise stops.

Found with voltmeter anywhere after the volume wiper
there begins a fluctuating negative voltage (couple of volts) all the way to the reverb driver grid
when vol knob is in area where noise starts.

The fluctuating neg voltage also shows up at the reverb recovery and the grid of the next stage.

Saw something that didn't look quite right and found the reverb Tx primary red and blue were swapped.

All info I could find show the Red to power supply and Blue to plate on the driver tube.
This amp had Blue to power and Red to plate.
Secondary side has Black to gnd and Green to tank.

Swapped the primary Red and Blue and noises went away, as did the fluctuating neg voltage.

Is it possible the backwards primary caused some kind of "flyback" voltage in prior and later circuits?
Any other damage that might have occurred from this that I should be aware of?

The amp now plays ok, but if cranked it makes a rattle/crackle like a blown speaker.
Quiet playing is ok.
Tried a different known good speaker and the rattle/crackle is still there.
Reverb sound is distorted and the rattle/crackle is much louder when the reverb control is turned up.
Maybe tank got damaged?
Tried different reverb drive and recovery tubes, no change.

Thanks for any and all help.

Edit; meant to have Title say...Consequences OF not or.

[J M Fahey]

Your symptoms hint at oscillation, most probably caused by non shielded (or poorly shielded) reverb return wire from pot wiper to next grid.
When set to 0 or 10 itīs either grounded or connected to a relatively low impedance (earlier tube plate) so shielding is not critical, but a pot shows maximum impedance electrically halfway and there problems appear.
I bet when rewiring the transformer leads you also displaced the offending wire, sometimes 1 inch this or that way makes all the difference.
Notice even puting a meter or scope probe *near* the wire made it oscillate, a quite unstable circuit or layout.
I would tape/glue wires in the "safe" position so problem does not reappear in the future, when amp "travels".

[Sowhat]

What tank are you using? is it a 4AB3C1B? if so then the input impedance should be 8 ohms and the output impedance should be 2250 ohms. A DC resistance check of those tank coils should indicate if there is something amiss. It's not DC resistance but is AC impedance that's stated here but the DC resistance should be in the ballpark of the impedance. If you don't see these values or there abouts then the tank is damaged, if not then I don't know and I would have to signal trace down a problem like that.

[The Dude]

Actually, the DC resistance will be quite different from the impedance. The 8 ohm input will measure about 1 ohm DCR and the 2250 ohm output will measure around 215 ohms DCR.

Chart here for future reference.

[Sowhat]

Actually, the DC resistance will be quite different from the impedance. The 8 ohm input will measure about 1 ohm DCR and the 2250 ohm output will measure around 215 ohms DCR.

Chart here for future reference.

Well... you never seen my ballpark... Guess that was a little misleading, give me a break, I was only off by a factor of 10. Maybe I should have said proportionally.

[The Dude]

It's all good. I just didn't want the OP throwing away a perfectly good tank.

[galaxiex]

Thanks for the great reply's!

JMF hit the nail on the head. Oscillations.

I noticed a somewhat long run to the vol pot wiper.
I have some RG-174 on hand so used that and grounded one end at the vol pot.

Bingo!
The amp is much quieter now but still has some other noises.

Moving various wires around with a chop stick changes things but still a bit noisy,
so I think I will need to shield a couple other runs that seem less than optimal.

I only had a small piece of RG-174 and need to order more, or,
is there a better option for shielded wire for amps?

I found this stuff...

https://tubedepot.com/products/mogam...erconnect-wire

Advice and experience please.


@ Sowhat, yes it's a 4AB3C1B and the tank is a new replacement.
DC resistance checks out for the impedance specs as The Dude posted.
I was concerned that the noise/fault may have damaged it, but it seems ok.

[Sowhat]

Mogami W2330, I've used thousands of feet of that cable for stage and studio harnesses. When it was suggested to use this cable I scoffed... that stuff is too thin for long runs, but I used it anyway and I was not disappointed. It is indeed thin but it's incredibly flexible and sturdy to boot. I never used it in a chassis but I don't see why it can't be. Probably a good idea to use the correct stripper for this cable and not your pliers.

[galaxiex]

Mogami W2330, I've used thousands of feet of that cable for stage and studio harnesses. When it was suggested to use this cable I scoffed... that stuff is too thin for long runs, but I used it anyway and I was not disappointed. It is indeed thin but it's incredibly flexible and sturdy to boot. I never used it in a chassis but I don't see why it can't be. Probably a good idea to use the correct stripper for this cable and not your pliers.

Thanks!
I'll order some.