[Amps] input/output transformer switching

[Steve Thompson]

> Thanks for looking over the design.  I didn't consider the impedance change of 
> the relay, maybe somehow tune it out?
> 
>>I've wondered before if you could use the two halves in parallel 
>>at lower frequencies, with the rf in and out from the centre tap 
>>of the transformer primaries.
> 
> I think what you describe is similar to this example, which is used in the THP 
> HL-2.5Kfx
> http://www.arrl.org/qex/2006/09/qx9ohsawa.pdf

Sort of. The rf path in that amp is push pull all the way. I was 
thinking of feeding rf into the centre tap of the low Z side of the 
input transformer (where R9/10 connect in the article), and taking it 
out at the centre point of the low Z winding on the output end - you'd 
have to use E/I cores with semi rigid or binocular cores rather than the 
transmission line types used in the QEX article.

I think that Tempo did a similar sort of thing with the 6N2, and there 
was a lovely amp using a pair of 3CX800s on the amps projects web site 
(the address escapes me) using the same idea.

I've no idea how well/if it might work. You might be much better off 
building a low bands amp from some cheap plastic fets. Kill a MRF141G in 
the experimenting and it's a big hole in your pocket.

Steve