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Old 6th August 2012, 07:29 PM   #1
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Default HP Model 712b Regulated Power supply

Any help appreciated. New to tube amps etc.
I am going to try to replicate this power supply but there are a couple of things that are confusing me.
http://www.hparchive.com/Manuals/HP-...prefix-511.pdf
The relevant circuit is on page 22 of the manual.

I noticed that the voltages across the anodes of the series pass tubes seem very high at 1000 volts and ditto for cathode and screen grid at 460v [- drop across 1500 ohm grid resistor] and 685v respectively . [185 of the volts on the screen is provided by selenium rectifier at bottom left of circuit]
How can the voltages applied be so high ?.
The data sheet for the tube has seriously lower maximum ratings at 400 volts max on anode. Is it ok to put such high voltages on plate, cathode and screen as long as voltages differences are within spec in relation to each other ?
TIA.
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Old 6th August 2012, 08:26 PM   #2
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Maximum voltage ratings in data sheets are allways referenced to the cathode of the tube, which in this circuit is not at ground potential. Thus the actual anode voltage in the circuit shown is 500V and the screen voltage is 185V , which are still acceptable for a good quality 6L6 (preferably the GC version which has a higher max.plate ratings of 500V).
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