by erichayes » Sun Sep 16, 2007 12:19 am
The 680Ω resistor has been popularly thought to be a safety device to keep a load on the OT in case of speakers or other loads not being connected. I've never bought in to this theory, as 470Ω is way to high to offer any real protection. My gut feeling was that it was a snubber to suppress high frequency ringing.
I've never given close scrutiny to the MK-II circuit, but if what you say is hanging across the secondary is factual, that reenforces my feeling. Usually, snubbers are put on the primary of the OT, between the plates, I guess there's no reason it can't be done on the secondary--just a little less efficient.
In any event, I'd go with the 680Ω for starters, and , if you have access to a scope and a 1000~ square wave source, take a look at the output waveform. If you don't, give me a call and I'll see what we can work out.
Eric in the Jefferson State