U73b from scratch

[DaveP]

DaveP,
could you give us more information about this 1-2V max?...where specifically does this happens in the circuit?

What transformer is supporting these 160V DC?......does not need to have this transformer any GAP for DC current flow?

The 1-2V was talking about the audio input level.

The interstage has the 160V.  Push-Pull transformers don't need a gap, but tube currents have to be matched pretty well.

@Ruairio
Re hum:  I now build my stuff with the earth busbar grounded at Pin 1 and link on the input socket, not at the power socket, this might be worth trying. (Merlin Blencowe's idea)

I made the decision to build it as close as possible to the original spec (given that the transformers are no longer available)  This was probably a bad idea as it has caused you a lot of work.  I could have modded it from scratch to a modern spec, but then their is no vintage vibe...........what to do for the best?

DaveP

 

[ruairioflaherty]

@Ruairio
Re hum:  I now build my stuff with the earth busbar grounded at Pin 1 and link on the input socket, not at the power socket, this might be worth trying. (Merlin Blencowe's idea)

Great, I'll add that to the list.

I made the decision to build it as close as possible to the original spec (given that the transformers are no longer available)  This was probably a bad idea as it has caused you a lot of work.  I could have modded it from scratch to a modern spec, but then their is no vintage vibe...........what to do for the best?

You build for the challenge and the fun of it, and I offered to help test it out for the same reasons.  No stress.  My friend Kyle is a fantastic engineer and if he can get a great compressor that is unique, I can learn something and you can get some funds back we all win.

 

[opacheco]

The 1-2V was talking about the audio input level.

The interstage has the 160V.  Push-Pull transformers don't need a gap, but tube currents have to be matched pretty well.

DaveP

DaveP sorry but Are you talking about of the secondary voltage in terminals of your "extra" transformer (no considered in the TAB original schematic) for feed the Side Chain network??.....


Thanks for your help!
Opacheco.

 

[DaveP]

Are you talking about of the secondary voltage in terminals of your "extra" transformer (no considered in the TAB original schematic) for feed the Side Chain network??.....

1-2V is the audio input level.  The input transformers are all 1:1 in parallel so they all have almost identical levels.  I have found that most audio transformers are about 94% efficient so the secondaries will be slightly less than the primaries.

DaveP

 

[opacheco]

1-2V is the audio input level.  The input transformers are all 1:1 in parallel so they all have almost identical levels.  I have found that most audio transformers are about 94% efficient so the secondaries will be slightly less than the primaries.

DaveP

Ok DaveP excellent note!!

More quetion(sorry!) soon.

Thanks a lot again,
Opacheco