• 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.

Stromberg Carlson ASR 220C blowing fuse

jprisco

Member
2013-05-11 5:32 pm
Hello - first time poster here ...

I have a SC ASR-220C that a year ago I pulled off of a shelf it had been sitting on for 17 years. Powered it up slowly and found everything working except one the 7408's. Got a new (used) one and it played great for 10 months. Developed the dreaded 60 cycle hum two months ago - ordered and installed new filter caps and all was well. About a month ago I started getting occasional, random clicks in the output ... last week it started blowing the circuit breaker. I took out all of the tubes and it still blew. I then removed the wire to first cap after the rectifier and it stopped blowing the breaker. When I measure from that disconnected wire to ground I get 270 volts AC (pin 8 to ground on the 5AR4 - no tubes in any sockets)- it's been a lot of years since I shot a circuit but I'm thinking the power transformer may be shorted. Any opinions would be welcome plus any info about where I might get a replacement transformer.

Thanks in advance.
 

Attachments

  • ASR-220C.pdf
    680.8 KB · Views: 40

Rundmaus

Member
2005-08-21 10:46 pm
If it does trip the circuit breaker after you opened the connection to the 1st filter cap, something in the PSU or amp downstream of the rectifier is faulty.

If the transformer was to blame, it would have tripped the breaker even without the rectifier or filter chain.

Rundmaus
 

Rundmaus

Member
2005-08-21 10:46 pm
So it trips without the rectifier tube, but doesn't with the first cap disconnected.

That's strange.

If there is a shorted cap or something in the amp or power supply, there should be no difference in behaviour between pulling the rectifier or disconnecting the first cap.

Check for shorts (continuity) between the different pins of the rectifier socket, also between the HT winding including the center tap and ground/transformer chassis. Same for the rectifier heater winding.

Rundmaus