SA-134 frequency Correction

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ecaltd

Active member
Joined
Apr 21, 2014
Messages
36
... while waiting on parts for the other projects on the bench I decided to revisit this one. A few years back I had a pair of these that I went through and re-capped etc..

One of them I racked up on a 3U shelf with remote gain an Daven attenuators on the output. Time to do the same with this one, additionally I will install a Hammond 369AX power transformer to make it worldwide compatible.

Question to throw out there is : has anyone changed the C9 and C13 values to get a different curve out of the unit ? What do you think about a two or three way switch to change the caps depending on the source material being amplified. If I used shielded cable to a front panel switch would that few inches of wire make a difference or would it be better to mount it on the chassis ?

gb

IMG_9744D.jpg

IMG_9745D.jpg
 
I just went through mine and lowering Just the NFB resistor without the proper cap (C9) associated caused motor boating the final tube stage.

I too am about the rack up one of these and pan to just use the current gain pot and add a meter. The schematic doesn’t specify the buffer circuit for the meter or which meter model was used in the rack version. That being said I believe the Gates meters used in these were the big 3” Simpson models.

Doug would know.

Im curious how you did the out attenuator?
 
Last edited:
I just went through mine and lowering Just the NFB resistor without the proper cap (C9) associated caused motor boating the final tube stage.

I too am about the rack up one of these and pan to just use the current gain pot and add a meter. The schematic doesn’t specify the buffer circuit for the meter or which meter model was used in the rack version. That being said I believe the Gates meters used in these were the big 3” Simpson models.

Doug would know.

Im curious how you did the out attenuator?
I did the attenuator post output and meter post attenuator so you can get that lovely round distortion !
 

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