[Collins] 75A-2 with 6AK5 as V1 - RF Amplifier

Gerald geraldj at ispwest.com
Sat Dec 31 00:19:04 EST 2005


On Fri, 2005-12-30 at 12:37 -0700, Bill Pancake wrote:
> Hello all.... I'm hoping some kind soul reading this has an 
> original or copy of a Sams photofact or the correct schematic
> for a 75A-2 receiver that uses a 6AK5 for V1, rf amplifier tube. 
> I'd gladly pay for the cost & postage of a copy or a copy-of-a-copy. 
> Can't seem to find one anywhere!  Thanks in advance, 73, Bill, 
> wd0x at arrl.net.

Well, I put my foot in it this time. There really were 75A2 with 6AK5
(and 6BE6). Early versions before about SN 1100 or 1200. I did a google
search and found several requests for the early schematic.

I checked BAMA and I checked the CCA archives. CCA has two 75A2 manuals,
one from 1951 and one from 1952. I'm downloading section 5 and already
downloaded section 6. Section 6 is the parts list and it shows V1 is
6AK5 and v2 is 6BE6. Section 5 should be the illustrations including the
schematic.
http://www.collinsradio.org/Manuals/75A-2(09-51)/75A-2(09-51)Sec5.pdf

I can envision heated debates over 6AK5 vs 6CB6 and 6BE6 vs 6BA7. For
sure the noise figure of the 6AK5 would be better, but the AGC action
poorer. The gain of the 6BA7 might be greater, but that comes with lots
of noise. The BA7 has more grids and in a mixer that tends to create
more noise.

And yes, the schematic in this section 5 shows 6AK5 RF stage and 6BE6
first mixer.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer



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