Best way to drop B+ 150 VDC?

[Xander8280]

Can it tap off between the PI and preamp? Another resistor/cap...can split one of your last dropping resistors to the preamp into two resistors that add to the same resistance. Cap-to-ground and loop tapping off the joint of the two resistors.

[Xander8280]

I noticed on another forum that the Silver Jubilee preamp tube plate voltages ought to be about 450 VDC. That sounds high, but what do I know? How do you raise it at the first filter cap without replacing the transformer?

What?

[ViperDoc]

What?

I had an errant train of thought regarding B+ and forgot I'd asked a question. I was wondering if there was a way to RAISE a transformer's B+ without raising the primary voltage, and I don't think there is, is there?

[jabguit]

What?

I had an errant train of thought regarding B+ and forgot I'd asked a question. I was wondering if there was a way to RAISE a transformer's B+ without raising the primary voltage, and I don't think there is, is there?

https://www.electronics-tutorials.ws/bl ... rcuit.html

[thetragichero]

bogen did this in a lot of pa amps (snagged four chassis for a good price last year, still in my "figuring out what to do" pile)
check out schematics for chb35 and chb50. understand that you're reducing your current capabilities with a doubler

[ViperDoc]

Very interesting, I appreciate the link and SCH recommendations, guys. Thanks!

The link mentions the voltage doubler. etc. circuit type raises voltage and reduces amperage. I can't see myself wanting to double a 600V HT secondary, so would this require using a higher amperage, low output secondary to hit, say 450? And if so, why wouldn't a designer just design a transformer that has the desired secondary output, other than it being cheaper? The Bogen CHB35 schematic shows 450V at the first node after the voltage doubler, so because the HT output is not listed on the SCH, I would assume the PT secondary has a 225-0-225 winding?

[Phil_S]

Please understand that I'm not a transformer expert even though I've invested a bit of time in trying to ramp up my knowledge. My thinking is, during the era these Bogen amps were made, that transformers were relatively expensive. (They remain relatively expensive.) It may have been more economically efficient to wind a lower voltage and higher amperage transformer with the intention of deploying it with a doubler. Winding a lower voltage transformer allows for smaller size E-I laminations and shorter wire coils. I expect this translates to lower manufacturing cost, in both time and parts. The only accommodation is that a larger wire gauge (a bit more costly) is needed to allow for an increased amperage rating. I want to say that Bogen had good expertise in value engineering.

I see an effort to guess at the primary voltage as it isn't given. Remember that "double" means roughly double or 2x sqrt(2) = ~2.88x, not simply 2x. Do your math accordingly and allow for maybe 5% voltage drop under load.

[ViperDoc]

Thanks, Phil.