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OT failure on a HRD - here is the procedure I used to test the OT (thanks Roly where ever you are 
)
First build the tester in this article: Transformer tests
Check for lethal voltages at the B+ filter capacitor C31 and discharge the supply if necessary.
Remove the blue, brown and red wires from the primary side of the OT. Remove the speaker cable from the output jack and put a cable (or blank connector) into the main speaker (8 ohm) output jack - closest to the fuse. Connect the two leads of the tester from the article onto red/blue, red/brown or blue/brown leads of the secondary - if the windings are okay you should see a momentary flash in the neon bulb when toggling the DC/battery. No flash and you have a shorted turn somewhere in the winding. I always monitor the B+ to make sure the capacitors are not charged up during testing.
Just worked on a HRD that was blowing it's fuse (complaint) - when the amp was connected to a light bulb limiter it was obvious there was a fault. Pulled the secondary wires for the HV supply (B+, etc.) and the LBL didn't light up. Pulled the connection off one side of the filter choke, with the secondary connected again, the LBL was brightly shining. Output tubes were okay and so were the flyback diodes - tested the OT and found the issue.
)First build the tester in this article: Transformer tests
Check for lethal voltages at the B+ filter capacitor C31 and discharge the supply if necessary.
Remove the blue, brown and red wires from the primary side of the OT. Remove the speaker cable from the output jack and put a cable (or blank connector) into the main speaker (8 ohm) output jack - closest to the fuse. Connect the two leads of the tester from the article onto red/blue, red/brown or blue/brown leads of the secondary - if the windings are okay you should see a momentary flash in the neon bulb when toggling the DC/battery. No flash and you have a shorted turn somewhere in the winding. I always monitor the B+ to make sure the capacitors are not charged up during testing.
Just worked on a HRD that was blowing it's fuse (complaint) - when the amp was connected to a light bulb limiter it was obvious there was a fault. Pulled the secondary wires for the HV supply (B+, etc.) and the LBL didn't light up. Pulled the connection off one side of the filter choke, with the secondary connected again, the LBL was brightly shining. Output tubes were okay and so were the flyback diodes - tested the OT and found the issue.
) .
yet nobody complains, after all the light 6" or even 8" speaker does not put out much below that.
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