In the Seeburg amps these are not being used as simple rectifiers.
For bias they are used as temp sensors. Using only one diode results in too little idle bias, though this can be adjusted in TSA6-on.
Beginning with TSA-7 they were used as active gain attenuation in the AGC. A single diode will result in too much attenuation for a given AGC voltage.
In the earlier amps using the packaged selenium (red and yellow cap) using three in series for each leg more closely replicates the attenuation ratio of the originals. I use only 2 there as well since it makes the AGC more effective. This brings the max. attenuation from only about 8 db up to about 12 db gain reduction.
FWIW: I add some R&C decoupling to the AGC amp transistors to boost the range to 19DB max which is similar to the tube units using 6SK7 and 6BJ6. The TSA amps are still slightly less effective at leveling due to a softer knee as compared to the harder tube type.
Regards, RobNYC On Thursday, March 21, 2024 at 12:40:54 AM GMT-5, Jay Hennigan via Jukebox-list jukebox-list@lists.netlojix.com wrote:
Rick, what's the voltage drop across the stabistor in the working channel? If it's around 0.7 volts, use a single silicon diode.