[Milsurplus] SCR-183 TX (was GF/RU)

[David Stinson]

Thanks for writing, Neil.

Glad to hear your set is making contacts.  Been poking-around on a couple

of them lately to determine if an alternate tube- 6S4 TriodeTV Vertical-Deflection

Amplifier  with cathodes connected to pin 4- will work as well as the 6AQ5s.  

6S4 is cheap, plentiful and doesn’t suffer from “audiophool-itis”- at least, 

not yet.  So far, they make good RF output- around 7 Watts at 300V B+

(regulated) with about 30 mills cathode current- but the bias developed

in the “stock” circuit is too high for the pair in the Modulator.  Will look for

a non-destructive way to moderate that when time and work permit.

 

With a regulated B+ and running MOPA, the 6S4 MO exhibits a very 

slight chirp on both 80 and 40 meters.  This could be an artifact of the 

old Heathkit regulated supply I’m using.  Need to scope it and see if

can catch a “droop” on key-down.  A FET regulator would fix that.

The difference in some MOPA transmitters with well-regulated 

supplies to the MO can be enlightening.  With a “standard” MO B+

power supply ( a DC-DC mobile supply by Halliscratchers) running the

Australian AT-5 transmitter, the chirp is pronounced.  With a simple 

FET regulator inserted in that B+ lead, the note is steady and solid.

 

Time for me to get to work.

GL OM ES 73 DE Dave AB5S

 

From: AKLDGUY [mailto:neilb0627 at gmail.com] 
Sent: Tuesday, March 26, 2019 1:17 AM
To: David Stinson
Subject: Re: [Milsurplus] Wanna Build GF/RU?

 

Hi David

Re: SCR-183. I have the BC-230 transmitter which works well on 40m with 4 x 6AQ5. Had terrible modulation with a ton of FM until I ran across one of your old posts blaming improper neutralization. Listeners said my modulation was perfect if copied in FM mode!

 

Was not sure how to adjust the trimmer (manual calls it a balancing condenser), so unbolted it and partially removed it and found I needed a quarter inch socket. With a germanium diode to my multimeter at the antenna terminals, and with only the VFO running, adjustment for null was easy. This made a remarkable difference to the modulation.

 

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