More filament noise questions

[Randall]

65 Deluxe Reverb in for some problems, one of which is noise. Same thing as in the Bassman I just fixed, noise that follows the Volume knob, same noise in both channels as well as the reverb volume pot. So I investigate the filament supply. This amp also has a replacement PT, and appears to have a filament CT, although it's mostly an educated guess because the HV CT is red/orange, and the other wire is solid orange. Plus, the wire going to the bias board is red/blue. So, I'm thinking, is there any way the red/blue is actually the CT and the orange wire the bias? I can't think of how that could work since the bias circuit is working, I just set it (it was at 42mA for 6V6!).

Then I trace the filament wiring and discover every socket is wired reverse from the one after it. The power tubes look like they mat have been messed with, but the preamp tubes look factory. Did Fender ever do this on purpose? I always thought they should all be wired the same right down the line?

What is going on here I wonder?

[mozz]

Is that a reissue? I have seen some newer fenders with noise and hum, (pro junior or blues junior?, i forget) which had the filament wires swapped, on a circuit board. I actually cut the traces on one and ran jumpers to keep it in phase.

[Randall]

No, this is the holy grail.

[nosaj]

65 Deluxe Reverb in for some problems, one of which is noise. Same thing as in the Bassman I just fixed, noise that follows the Volume knob, same noise in both channels as well as the reverb volume pot. So I investigate the filament supply. This amp also has a replacement PT, and appears to have a filament CT, although it's mostly an educated guess because the HV CT is red/orange, and the other wire is solid orange. Plus, the wire going to the bias board is red/blue. So, I'm thinking, is there any way the red/blue is actually the CT and the orange wire the bias? I can't think of how that could work since the bias circuit is working, I just set it (it was at 42mA for 6V6!).

Then I trace the filament wiring and discover every socket is wired reverse from the one after it. The power tubes look like they mat have been messed with, but the preamp tubes look factory. Did Fender ever do this on purpose? I always thought they should all be wired the same right down the line?

What is going on here I wonder?

Well you could always desolder and ohms test them the CT of a leg will be approximately half, instead of just wondering about it.

nosaj

[Enzo]

They wired the 12AX7 sockets for heaters with whichever wire came out closest. it doesn;t really matter. Each triode of each tube is doing a different job, so there is no balancing to be done.

[g1]

Agree, and consider why you would even want the heaters in phase, what would the benefit be?
I think you also asked in another thread about power tube heaters phasing. In this case I believe it was sometimes done to make the power amp 'humbucking' of certain heater induced hum.

edit: to clarify, in a push-pull power stage, power tube heaters are better kept in phase.

[pdf64]

Yes, in the balanced sections of an amp, eg power tubes, there's a (tiny) theoretical benefit in keeping the heater wiring pin to pin.
But for the rest of the amp, I suspect that the 'wire all heaters in the same phase' thing is another one of those myths which the internet has acted to propagate widely.

...the HV CT is red/orange, and the other wire is solid orange. Plus, the wire going to the bias board is red/blue. So, I'm thinking, is there any way the red/blue is actually the CT and the orange wire the bias? I can't think of how that could work since the bias circuit is working, I just set it (it was at 42mA for 6V6!)...

Try measuring the eg 320-0-320 Vac at the input to the rectifier; if the Vac are closely similar, then the CT is correct, whereas if they're >50Vac apart, then the wrong wire has been used for the CT.

[Randall]

"Try measuring the eg 320-0-320 Vac at the input to the rectifier; if the Vac are closely similar, then the CT is correct, whereas if they're >50Vac apart, then the wrong wire has been used for the CT."

It's the filament CT I wonder about, not the HV. Curious they would not have made it green like the filament winding, but with a stripe.

Edit: I lifted one side of the filament wire, and it has no relationship with chassis ground, so I guess that orange wire is not a CT, as well as why it isn't some type of green. So I will install a couple of resistors on this amp as well. But this raises another question, what is it's function here, is it a ground fault connection? The PT turns out comes from Magic Parts, a TF-105, but I see no documentation on their site.

[Enzo]

COntact them and ask. The extra wire could well be an internal shield connection. If ti has no continuity with any other winding, I would bet on that.

[Randall]

"COntact them and ask."

Holidays and all, I am going to assume it is a shield or fault ground. I installed virtual tap resistors, and problem solved!

Interesting though, what are the odds of getting back to back identical issues? I have gone my entire life and not run up against this, and then two amps in a row are repaired by installing virtual taps on replacement transformers. Just weird.

Anyway, case closed

[Enzo]

It was more a general suggestion. it may come up in the future.

[Randall]

True. I will make an inquiry and report back.