UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

yestertech · 1st Jan 2012, 5:48 pm

I assume you're using the AKG N60 PSU with it ?
Is yours the version using the AC701K valve ?
If so, do you have the correct +4 v DC on pin 2 of the PSU output. ?
The heater supply to this rather rare valve is provided by a regulated PSU which could
be the cause of the problem if unsmoothed DC is getting to the valve heater.
The 'HT' supply has 3 R/C sections for smoothing, so if faulty is less likely to cause hum, but one or more caps could be tired.
Time to get the 'scope out ....

Andy

1st Jan 2012, 5:48 pm	#5
yestertech Nonode Join Date: Dec 2002 Location: Coulsdon, Surrey, UK. Posts: 2,130	Re: AKG C60 valve mic I assume you're using the AKG N60 PSU with it ? Is yours the version using the AC701K valve ? If so, do you have the correct +4 v DC on pin 2 of the PSU output. ? The heater supply to this rather rare valve is provided by a regulated PSU which could be the cause of the problem if unsmoothed DC is getting to the valve heater. The 'HT' supply has 3 R/C sections for smoothing, so if faulty is less likely to cause hum, but one or more caps could be tired. Time to get the 'scope out .... Andy