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Old 20th June 2011, 06:48 PM   #1
mfaughn is offline mfaughn  United States
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Default Why two GZ34 in this schematic?

Hi,

Here is a schematic from an amplifier that I own. It is a Knight KA95 integrated EL34 PP. I am trying to educate myself about power supplies. Why were two rectifier tubes used like this? Correct me if I'm wrong (which is entirely possible) -- the diodes from each tube are simply paralleled and it is a conventional full wave rectifier, right? It appears that other EL34 based PP amps usually get away with a single tube for a full wave. Did the added load of the preamp circuitry necessitate this arrangement?

Thanks,
Michael

PS -- the PS is in part 2 of the schematic.
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Old 20th June 2011, 06:56 PM   #2
kevinkr is offline kevinkr  United States
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Probably down to the amplifier power output rating and the additional circuitry. Stereo amps like the ST-70 just squeaked by with a single 5AR4. Pairs were sometimes used in higher power amplifiers where more than 250mA was needed, and relatively low forward drop (for a tube) along with reasonably good regulation was also wanted.
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Old 20th June 2011, 07:13 PM   #3
mfaughn is offline mfaughn  United States
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Thanks for the help. Kinda what I figured but its good to hear it from somebody who knows.
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Old 20th June 2011, 09:27 PM   #4
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The GZ34 was designed to drive one pair of EL34 - not two.
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