[Collins] 75S-3B audio output tube

[Dr. Gerald N. Johnson]

On Sat, 2008-12-13 at 20:14 +1300, Dave Brown wrote:
> IIRC the filament current is different but this is not an issue unless 
> operating them from an external supply.
> The other matters to address have already been mentioned.
> DaveB, NZ
> 
Since the 75S receivers make no provision for running on anything but
the normal AC input, there is no problem of series/parallel current in
the heaters. That's not true of the 32S, KWM-2, and 51S equipment.

The heater (no filament here) current of the 6AQ5 is 450 ma and for the
6BF5 its 1.2 amps.

I searched with google last night and found a few references, especially
to K5UGM's mod, but I didn't find it. His web page is no more as he died
in 2006.

I searched my indices to ham radio magazine for one reported 6AQ5 mod
that was supposed to be there but it wasn't indexed as such. It might
have been in a Ham Notes Column about the receiver line, I didn't dig
those out.

I've seen more than one 75S without mods but running a 6AQ5 apparently
successfully. A couple years ago a member of this forum proposed a solid
state replacement, but I've not tested that either.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer