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 Post subject: Re: Old Rectifier?
PostPosted: Jun Fri 22, 2018 11:53 am 
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Joined: Jun Wed 06, 2018 6:07 pm
Posts: 9
Peter Bertini wrote:
AleutGerl wrote:
Peter Bertini wrote:
AC on the DC output might be just ripple voltage. An AC meter on the output of a DC rectifier may give you a misleading idea of what you are seeing.

Pete


I've already tested it with a single diode (half wave) and with a full wave and I got 1 volt difference. The full wave is just providing much less pulsating DC (ripple).


Just curious, did you keep the 180 ohm resistor in series with the new rectifier?


I haven't started to put things back together yet to really get a chance to decide if I will or won't use the 180 ohm resistor. Been side tracked away from hobby projects again. Hopefully next week I'll be able to get back to working on it.


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 Post subject: Re: Old Rectifier?
PostPosted: Jun Fri 22, 2018 12:01 pm 
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Joined: Jun Wed 06, 2018 6:07 pm
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Usually Lurking wrote:
Thanks for the schematic link!

This is a "one tube" audio amplifier. Two stages. It does have a power transformer.

The B+ supply was half wave using the selenium rectifier. 160V filter caps imply a pretty low B+.

Since the AC source for the B+ supply is an isolated transformer winding, a four diode bridge is OK to use in place of the old selenium.

Using the bridge should reduce hum, and also reduce heating in the transformer.

With a silicon bridge, it would probably be safe to reduce or eliminate the 180 ohm series resistor. The transformer will provide enough series impedance to keep peak currents reasonable.

You might want to go to 250V filter caps.

Ted


I actually purchased 300v caps to replace the old 160v firecracker cap. When I get back into it, get the new caps and bridge rectifier installed, and see what the plated voltages, etc are I'll double check to see if the 180 ohm resister is needed or not. There is only a handful of the old carbon comp resisters in it, all of which have strayed, so I also purchased carbon film resistors to replace those. I'm trying to keep it as close to the original as possible, while making some changes/replacements that really don't alter the original circuit much. The reality is if I want to enjoy using it and make it the best it can be somethings are going to have to change in it I guess...


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 Post subject: Re: Old Rectifier?
PostPosted: Sep Wed 22, 2021 10:51 pm 
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Joined: Sep Wed 22, 2021 10:31 pm
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I am new to this forum and world of old electronics. I have started rebuilding old tube equipment and such and I have a similar situation as this person did.

I have a Webcor Fonograph with a 25l6gt tube and a selenium rectifier. The SR is a 8J1(C?). I have replaced all of the caps and now want to replace the SR with a diode such as the one that had been suggested to this person.

My setup also has a 47k resistor immediately connected to the positive terminal. Would I still have to add another “step-down” resistor or will the 47k one installed already be adequate?

Thank you for your time!!
Ryan


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