06-30-2015, 10:49 PM
You wrote: Once you have established the B+ power and your filament voltages are OK (easily detectable), start mapping voltages across the tubes.
OK, filament voltages check; 5v on the rectifiers, 6v elsewhere.
You wrote: It is normal for anodes of most tubes to be at high enough voltage (100V-250V, or a bit more in case of audio output ones), the screen grids should be also fairly high, almost equal or a bit less than anode voltages, control grid is at low DC potential, and Suppressor grid is at Cathode potential.
Absence of Anode voltage is a good indicator of the load open, like the primary of an interstage RF/IF transformer.
This. Voltage on the 6L6 power tubes, but none on the 6F6 or 6J5. This is a good indicator of an open interstage primary. But I’m getting continuity across that primary, and just got it back from Heyboer.
You wrote: Start your check with pulling the rectifier and checking the AC outs.
Done. Getting about 340VAC on one transformer HV secondary, about 280 on the other. No voltages on this schematic so I don’t know if that’s correct.
You wrote: Power down.
Then measure the load across the rectifier output, check if short is present.
No shorts, far as I could see.
You wrote: If not, put rectifier in, put the loads (speakers) in, power up, briefly see if the DC develops and where it goes, once reached about 500V it should go down a bit and stabilize. Watch for smoke.
No smoke. Voltage starts at about 530, slowly tapers down to about 330 (reading this on the 6L6 outputs).
You wrote: Power down AND watch the DC going down. If very slow, you have no load. If fast (second or few) - OK.
Goes down pretty quick.
You wrote: Once this is OK, start measuring voltages.
Done. No voltage on the driver tube and 6J5.
You wrote :Check the transformers' continuities, check speakers.
Checked transformer windings, seem OK. Speaker field coil good, checked audio output transformer. All windings appear OK. Transformer 178 gets warmer to the touch after being on for extended period than 179, which stays cool.
OK, filament voltages check; 5v on the rectifiers, 6v elsewhere.
You wrote: It is normal for anodes of most tubes to be at high enough voltage (100V-250V, or a bit more in case of audio output ones), the screen grids should be also fairly high, almost equal or a bit less than anode voltages, control grid is at low DC potential, and Suppressor grid is at Cathode potential.
Absence of Anode voltage is a good indicator of the load open, like the primary of an interstage RF/IF transformer.
This. Voltage on the 6L6 power tubes, but none on the 6F6 or 6J5. This is a good indicator of an open interstage primary. But I’m getting continuity across that primary, and just got it back from Heyboer.
You wrote: Start your check with pulling the rectifier and checking the AC outs.
Done. Getting about 340VAC on one transformer HV secondary, about 280 on the other. No voltages on this schematic so I don’t know if that’s correct.
You wrote: Power down.
Then measure the load across the rectifier output, check if short is present.
No shorts, far as I could see.
You wrote: If not, put rectifier in, put the loads (speakers) in, power up, briefly see if the DC develops and where it goes, once reached about 500V it should go down a bit and stabilize. Watch for smoke.
No smoke. Voltage starts at about 530, slowly tapers down to about 330 (reading this on the 6L6 outputs).
You wrote: Power down AND watch the DC going down. If very slow, you have no load. If fast (second or few) - OK.
Goes down pretty quick.
You wrote: Once this is OK, start measuring voltages.
Done. No voltage on the driver tube and 6J5.
You wrote :Check the transformers' continuities, check speakers.
Checked transformer windings, seem OK. Speaker field coil good, checked audio output transformer. All windings appear OK. Transformer 178 gets warmer to the touch after being on for extended period than 179, which stays cool.
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