16309 output transformer in the Heathkit W5m

[michaelsamra]

I have many of these amps,25 to be exact and I was aware there were issues with the output transformers as well as some of the power transformers.

The problems with the 16309 output transformers don't stem from bad quality,they are pushed beyond their limits due to under voltage rated 1uf@400v coupling caps.These caps should be 600vdc because it measured 440vdc across the cap and that is after turn on..The voltage during warmup could easily see 500vdc plus.This caused dc leakage in the cap therefore making the KT66s draw grid current and overheat and pop the wire inside the transformer.
Four of my amps have open primaries on one half the primary. Being there is continuity between the plate and UL tap of each side independent of the other,that told me that the repair is probably simple. I unpotted one of the transformers and pulled back the fish paper and there it was,the primary on the one side was disconnected from the B+ red wire..I was able to reconnect it and and get continuity from side to side so now I have to put it back in and repot it.

 

[DanO55]

How did you get 25 of these? Can you say "KaChing".

 

[dcgillespie]

Granted, a 600 volt cap would have been more prudent, but the Heath manual shows there to be ~ 250 volts across these caps after the tubes are warmed (255 volts on the driver plates, minus ~ 5 volts on the output tube grids). Given these numbers then, how is it that you are measuring 440 volts across these caps?

Dave

 

[audiofred]

I'm a little cornfused...there is always DC volts on the primary of an output transformer. That's what brings the operating B+ to the plates of the output tubes. Coupling caps as on the control grids?? If they are defective the tube will draw excess current and could take the output transformer with it.
It doesn't matter about warm-up. If the coupling cap is good it will ALWAYS block the DC volts. The problem seems to be poor design or wrong voltage rating of coupling caps not the transformers. The coupling caps break down and the tube runs out of spec drawing excessive current.