[AMRadio] Homebrewing

W5OMR/Geoff w5omr at satx.rr.com
Sat Jun 10 11:01:44 EDT 2006

Donald Chester wrote:

>> Would be around 35w DC input (250v @ 125mA on the final).  What I'm 
>> wondering, will the BTCL 10-80 band switch handle that much power?
> I would say so.  You are talking about only 20w or so of  rf.

It's an interesting idea, Don.  One dual-triode in the final (balanced, 
link-coupled, push-pull) modulated by a pair of dual-triodes, in 
push-pull parallel.

250VDC @ 500mA should be plenty sufficient for a power supply.  One 
could almost simply recify 120vAC, and build a voltage doubler, for the 
necessary B+.
For saftey's sake, I would use a 1:1 isolation transformer.

I'm gonna mull this over, a while.  I've got some 6AS7's, and a good 
100w Modulation transformer (more is better!)  Then, when needed, that 
plate modulated signal could be fed into the current project, which is a 
single 450TL linear amplifier. That kind of power isn't needed on 15m or 
above, though.

Lessee... one-half of a 12AX7 for the mic input, outputted to the 2nd 
half of the same tube, with inverse feed-back back to the mic input 
stage, fed into a phase splitter, into another 12AX7 for push-pull 
audio, capacitivly coupled to the grids of the modulator tubes.

A Johnson VF-122 vfo into a 6AU6 for grid drive to the final, and a 
fixed bias supply on the final grids...

The whole rig (minus the power supply and mod transformer) could 
probably fit on a 9x12 cake-pan sized chassis.


Driving your AM Rig without a scope, 
is like driving your car at night, without headlights. (K4KYV)

73 = Best Regards,

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