Need OT advice, PP47 amp

[Diverted]

Hi all, could use some advice.
I have a very old PP 47 amp here (Type I Rickenbacher) that has a bad OT. One half of primary reads about .5M.
From what I've read I'm assuming it has somewhere around 10K primary resistance. It also has a third tap on the secondary for the humbucking coil. 4 ohm voice coil.
I am trying to source a replacement and don't have much. But I do have a PP Magnavox OT from a 6V6 amp that I would guess has around 6-8K primary impedance.
Can I get away with this? I realize I will have to forego the humbucking coil without that extra tap on the secondary.
The 47 tube data sheets don't say much about 47 tubes in PP.

Thanks!

[shooter]

I became addicted to schematics in '72 when TTL was born and bits were the cool kid on the street 


without an original wiring diagram showing Field 1, Field 2, and the relevance to the whole circuit, i'm gonna pass on the guess.

[Diverted]

I became addicted to schematics in '72 when TTL was born and bits were the cool kid on the street 


without an original wiring diagram showing Field 1, Field 2, and the relevance to the whole circuit, i'm gonna pass on the guess.

Field 1 and 2 is just the two leads off the FC.

[shooter]

you're using a field coil or you've replaced with Resistors?

[Diverted]

I am running it with the field coil and original speaker. Replaced OT.
The voltages shown in the schematic are current, with FC speaker being used.

I previously had been running it with a different OT and resistors in place of field coil. There's no difference in volume now with the repaired original speaker than there was when I was using a 10K primary OT. Thanks.

[pdf64]

Why guess at the primary impedance of the replacement OT, rather than checking its ratio?

[AlNewman]

Is it strange there's no grid leak on the preamp tube?

[shooter]

 


it's all sorta strange.


but ya, i'd probably want the input cap coupled to removed any DC and I'd want the grid to be referenced to ground.

[pdf64]

Is it strange there's no grid leak on the preamp tube?

In most scenarios, the signal source that's plugged into the amp input provides a suitable grid leak resistance.
Bear in mind EVERYTHING was expensive back than; if a part was a 'nice to have' then to reduce cost of parts and assembly, it might get omitted.

[AlNewman]

It is funny how things have changed, they were trying to save money on a couple resistors, and added another few lbs in transformers.

The humbucker coil is kind of a weird thing.  So it's 4 Ohm, and your speaker is 8 Ohm? 

There are quite a few push pull transformers in the 10-25k range, with multiple taps and fairly reasonable value.  I wonder if it's possible to manipulate those to work with what you have.  I would think 6-8k is kinda light for push pull, considering a single tube likes a 7k load.  But it probably isn't being used at maximum efficiency, so maybe it's not a big deal.

[pdf64]

I can't get my head around a humbucking coil on the OT 

[shooter]

 
ya, me neither.


think it musta been of of those "special sauce" things from the 40's

[AlNewman]

I wonder if it's more like a humbucking coil for the field coil?
I have seen videos with an extra coil on guitars with single coils or P-90's where they're just an extra coil inset in the back near the pickup.  I'm not sure if they're wired through the guitar electronics, or they have a battery connected?
Your guess is as good as mine.