[ck81144]

Hi

I have a Dynaco FM-1 that is in pretty good shape.  I was thinking about building a FM2-A amplifier for it so I could use the receiver at work.  Does anyone know any of the specs for the transformers or if there are any suitable replacements available? 

Chris

[baldrick]

Wow, that's an ambitious project.

The amp circuit in the FM-2A is pretty decent.  A 12AX7 input / phase splitter and a pair of EL84 tubes for the output.

You will need a pair of transformers to make it.  A 6.3 V filament transformer and a decent output transformer. Luckily, Hammond makes both at reasonable prices.  In fact there are several that are appropriate for use with EL84s.

[avahifi]

I built one of these new years ago for a client.

Unfortunatelly, it ran so hot it cooked the circuit boards black in a year or two.  We just could not keep it running reliably long term.

So, my advice is don't, it is not a good idea.
Regards,

Frank Van Alstine

[baldrick]

I think the problem of heat comes from the design of the plate that supports the transformers.  It totally covers the circuit board and partially stifles the three tubes.  Plus, having the solder components underneath the circuit board does not help either.

I think with a careful redesign (someone without a kit would be free to fabricate things differently and rearrange things more logically - like not covering the circuit board with a solid metal plate) it would run cooler and more reliably.