[ARC5] Fw: Getting ARC5 and SCR-274N Txs on 40 m

[Brian]

Hello Wayne,

You’ll need to change the PA tank coil, too. The 4 to 5.3 MHz one has too much inductance. If you try tapping down, that might work, but you definitely don’t want to unwind turns. Those coils and the VFO coils were wound with the wire hot so that when it cooled only the diameter of the former could alter the inductance – and I bet Dr Drake chose a grade of ceramic that would stay relatively constant over the required temperature range. When these sets were designed, maximum ceiling was probably 10,000 ft, enough for the pilot to require warm clothing, but there was no internal fuselage heating or pressurisation.

73 de Brian, VK2GCE.

On Thursday, December 31, 2015 1:36 AM, you said:

Brian:

I have a 4 to 5.3 MHZ transmitter that has had everything BUT the oscillator 
coil and associated cap taken out of it.  I thought I would put in a 7 MHZ 
osc coil and see if I could build a stand alone CW 40 meter transceiver in 
the case.

The dial for that transmitter - a metal one - is in fine shape and it will 
be used to replace a broken plastic dial on an absolutely beautiful and 
otherwise intact and original 4 - 5.3 MHZ SCR-274-N natural aluminum 
transmitter.  I paid $10 for it on ebay several years ago.

But I gather that you are saying that you cannot pad down a 4 - 5.3 MHZ transmitter to get it to 40M?

Now, I think I will ask the Group how much of this sort of thing is possible.  E.g., can you put a new osc coil in an otherwise original 4 - 5.3 MHZ set and leave 
the rest of it alone?

Thanks,

Wayne
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20160103/1ee4ec22/attachment.html>