• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube Power Amp OA2 Tube used as Voltage Regulator

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Zenith 5B24

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Joined 2018
#1
Hello,


New to forum and have a question. I have a valve stereo power amplifier,
it is very old and homemade, one of a kind, as far as I know. It came
with an old Heathkit preamplifier SP-2 and a tuner.


The power amplifier is in service. It has an unusual circuit, in that it uses two (2), AO2 voltage regulator tube, functioning like Zener diode.


Tubes are 4 6Bq5, 2 12AX7 etc. Does anyone have an idea who could have designed it. The Heathkit Model AC-11 channel separation device has a tag
Smitty's Radio Lab Repair tag, Midland, Texas.


Thank you very much.


Zenith 5B24
 
#2
Nothing in the least out of the ordinary. Regulating screen grid B+ at a fraction of anode B+ is a good way to maximize open loop linearity of full pentode mode O/P tubes. The 0A2 gas discharge regulator is a "150" V. device.

Very carefully trace out the schematic for the power amplifier. There is more than 1 way the builder could have used the 0A2s.
 
#3
Dear Eli D.,


Thank you very much. I am listening to the amplifier now, using a Pioneer SX-9000
Receiver for the preamplifier, one can separate the pre and main. When she cools
down will send an image of the power amplifier and attempt to carefully trace out the
schematic and post it.


Clay
 
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