Dynaco ST-70 Power issues

Posted by mjstriker5@yahoo.com (A) on February 24, 2014 at 17:11:37

Just picked up a Dynaco ST-70 which was in good working condition. It had the the new power capacitor mod but other than that was stock. The unit seemed to run fine. I decided to replace the board capacitors with Orange drops and install diode mod to replace selenium rectifier. I also removed the power capacitor mod and reinstalled a new multi can capacitor with new bias caps and new resistors in the bias and power section.

The unit ran great for a few weeks. I could never get the bias up to original 1.56 as it would max out before but I read I should have the bias set to a lower value so I kept it around 1.4 or so (can't remember of hand what other threads advised).

I also noticed later that it appeared there was some sot of diode mod on the rectifier tube which I thought at first was a mistake but realized upon further reading some people recommend this mod. Unfortunately, it appears that one of the diodes was soldered across so effectively removed it from circuit.

A few days ago I brought the unit inside to see how it sounded with the living room set up. I ran the unit for a few hours without issue and it sounded great. I had the unit at almost half volume with the cover on and it didn't seem to run hotter than it usually does. In the garage i never had the cover on but inside there is more potential for burns.

The next day I went to turn on the unit and there was nothing. No sound or even a hum from the transformer. I checked the fuse and didn't seen any evidence of it being blown but it is white so I can't see the filament. I put a new one in and still nothing. I found a few places on the internet that talk about testing the transformer. I'm not getting any AC reading across to black filaments.

Thinking I may have fried to transformer but I am unsure. I was wondering if anyone had some insight into where the source of the problem may be and how I can go about testing the transformer.

Thanks

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Topic - Dynaco ST-70 Power issues - mjstriker5@yahoo.com 17:11:37 02/24/14 (3)

RE: Dynaco ST-70 Power issues - xaudiomanx 15:27:59 02/27/14 (2)

RE: Dynaco ST-70 Power issues - mjstriker5@yahoo.com 15:48:44 02/27/14 (1)

RE: Dynaco ST-70 Power issues - xaudiomanx 22:48:06 02/27/14 (0)

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