Help with AMPEX 350 noise issue

[MatthisD]

If you haven't checked the resistance of the coils, to me that would be the first step of diagnosing a faulty winding. If the two primary windings measure about equal but you still suspect them, then measure the DC voltage at pin 7 and pin 10 to check for a 10vdc drop total or 5v per winding; 320v down to 310v according to the schematic. If nothing seems wrong then I would connect each winding separately. I wouldn't bother with a resistor if the goal is to check whether or not that the transformer is the source of the noise. There is 10vdc dropped through the transformer primary so the plate voltage will only increase by a handful of volts if using just half of the primary.

 

[jwhmca]

Well, I swapped out the transformer with another and the problem went away.

1. Info on rewinding?
2. NOS anyway?
3. Bypassing the "power through" and just using it for the audio portion?

 

[jwhmca]

I just checked the resistance of the pri coils... TOTALLY OPEN!!! What the heck? Why was it working at all!?!

Maybe, just maybe they "heated off" when I pulled the transformer out!

Could it have been heated up in use and semi curing itself?

 

[riggler]

Maybe moving things around was the straw that broke the camel's back on the primary winding.

I just wanted to note--- I have a 300 machine, and I found a cause of intermittent noise / dropped level to be a dirty input transfer switch!

Too bad about your transformer, really!!

 

[MatthisD]

It could be the wiring to the binding posts has corroded, or the internal splices like shown in the photo on page 1 of the thread. If you'd rather replace it than try and repair it, Sowter list their replacement as 15k/600 and you can calculate the current from the volts dropped across your good transformer. Cinemag have a 7:1 that takes a few mA.

 

[jwhmca]

I'm thinking about doing a choke bypass, but I'm not really sure what it would look like...