I have this unit in for repair, it was supposedly repair by the High end pro shop due to clicking sound when it is first turned on and was not as loud as it used to be.
I turn it on and can hear the relay clicking away for about 1/2 minute and then stop, I can get the sound from the amp through the speakers OK.
Open it up and it looks like the filter cap for DC power supply for the filament and the audio source selector relays has been replaced. I look on line and see that the some of them has 4700uF 25V some of them has 10,000uF (this one has 10,000uF 35V installed by the repair shop).
I check the DC voltage it shows about 4.5VDC which seems to low for 6V filament. Check the AC ripple with my Fluke RMS, it shows >1VAC. The AC output of the transformer is just a little over 6VAC, so I expect the DC to be higher than that and should be close to 6VDC at full load by the tube filaments. So something is not right, I check the ripple frequency, it show 60Hz instead of 120Hz for full wave rectification. It means the diode may be shorted of have leakage, checking with meter show reading in high Meg Ohms range, so I use my LC75 leakage current test, two of the diode show off scale leakage current at 50V scale (GI854 is rated at 3A, 400V https://cdn.badcaps-static.com/pdfs/...1d66e2faa5.pdf), seeing 3A rating and the location where these Diodes are which the board turned brown so they have been running hot. I look up the spec of the tubes, the 4 output tubes alone draw 1.5A each, so add another about 2A for the smaller tubes, the current draw is exceeding the rating of the Diode.
I temporary hook up the bridge and use 4700uf cap (per Conrad Johnson, CJ told me to send in the unit for repair and will not provide me the circuit diagram) to test and see if the voltage will be normal, now I do have 6VDC, with about 200mV 120Hz ripple frequency.
So now I will install new bridge in heatsink and mount it to the chassis, I can find 10A diode but it will not solve heat problem.
By the way, I saw a lot of suggestion on line for people to upgrade the cap to 10,000 uF to fix the relay chatter and to improve sound. It seems to me that instead of finding why the relays are chattering in the first place and check the ripple frequency, voltage, look up the spec of the diodes, the they would have known the real reason of the problem.
I am surprised that for such an expensive amplifier, they did not use the correct rating diodes to do the job. It does sound good though.
I turn it on and can hear the relay clicking away for about 1/2 minute and then stop, I can get the sound from the amp through the speakers OK.
Open it up and it looks like the filter cap for DC power supply for the filament and the audio source selector relays has been replaced. I look on line and see that the some of them has 4700uF 25V some of them has 10,000uF (this one has 10,000uF 35V installed by the repair shop).
I check the DC voltage it shows about 4.5VDC which seems to low for 6V filament. Check the AC ripple with my Fluke RMS, it shows >1VAC. The AC output of the transformer is just a little over 6VAC, so I expect the DC to be higher than that and should be close to 6VDC at full load by the tube filaments. So something is not right, I check the ripple frequency, it show 60Hz instead of 120Hz for full wave rectification. It means the diode may be shorted of have leakage, checking with meter show reading in high Meg Ohms range, so I use my LC75 leakage current test, two of the diode show off scale leakage current at 50V scale (GI854 is rated at 3A, 400V https://cdn.badcaps-static.com/pdfs/...1d66e2faa5.pdf), seeing 3A rating and the location where these Diodes are which the board turned brown so they have been running hot. I look up the spec of the tubes, the 4 output tubes alone draw 1.5A each, so add another about 2A for the smaller tubes, the current draw is exceeding the rating of the Diode.
I temporary hook up the bridge and use 4700uf cap (per Conrad Johnson, CJ told me to send in the unit for repair and will not provide me the circuit diagram) to test and see if the voltage will be normal, now I do have 6VDC, with about 200mV 120Hz ripple frequency.
So now I will install new bridge in heatsink and mount it to the chassis, I can find 10A diode but it will not solve heat problem.
By the way, I saw a lot of suggestion on line for people to upgrade the cap to 10,000 uF to fix the relay chatter and to improve sound. It seems to me that instead of finding why the relays are chattering in the first place and check the ripple frequency, voltage, look up the spec of the diodes, the they would have known the real reason of the problem.
I am surprised that for such an expensive amplifier, they did not use the correct rating diodes to do the job. It does sound good though.
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