[ARC5] BC-453 + Converter

[Kenneth G. Gordon]

On 29 May 2011 at 12:10, jsloss wrote:

> I'd like to add a small SS crystal controlled 80/40M converter to the
> rear deck of a BC-453.  Being somewhat challenged in SS design perhaps
> you would like to share your favorite circuit.

Although I do not have an SS version, I do have this version:

http://www.w7ekb.com/glowbugs/rx/NoviceQ5er/NoviceQ5er.pdf

which you may find interesting.

> Also is there a convenient way to incorporate switchable AVC although
> that may not be necessary as the set will be used only for CW on 80/40
> and gain can be controlled w/ the usual RFG pot addition.

IMHO, that depends on the particular version of "ARC-5" receiver you are 
using: the early versions had a pretty rudimentary AGC, and the later (R-
23/ARC-5) versions had a bit better one.

However, again IMHO, neither were really very suitable for CW or SSB. They 
were designed for AM reception.

For one thing, the BFO injection was kept very low in order not to have it 
effect the AGC, and this low injection into the detector results in considerable 
distortion at higher signal levels.

There have been several modifications to the ARC-5 AGC circuitry published 
over the years in the various ham literature, NONE of which (again IMHO) 
are really suitable for CW or SSB reception, and almost all of which require 
extensive modification to the receiver. 

I don't like extensive modifications to ANY military gear, and especially at this 
late date.

However, in my opinion, there is one, recently developed, AGC circuit that 
requires very few components, could very easily be mounted entirely on one 
small piece of perf board, could be added to practically any receiver with very 
minimal changes, and which works extremely effectively: that circuit, 
designed by a Mr. Chuck Hatch after many years of research, was published 
in Electric Radio magazine some time ago (I'll dig out the reference and 
publish it here asap). He designed it specifically for the R-390 receiver, but it 
is very simple and could be added to nearly any receiver with minimal 
modifications.

It basically consists of a voltage-doubler using SS diodes, a couple of 
resistors, capacitors, and a switch. But the key, the most important difference 
from other such circuits, is that its input from the IF strip is taken from the 
CATHODE (a very low-impedance point) of an AGC amplifier tube.

Although none of the ARC-5 receivers have an "AGC amplifier", one could 
either include an AGC amp using a transistor in the emitter-follower 
configuration on the same bit of perf board, or simply connect the input of the 
SS voltage doubler througn a capacitor to the cathode of the last IF stage, 
since, as I remember it, that stage uses cathode bias and thus is not 
connected directly to ground.

The resulting AGC voltage might be enough to achieve the result we wish. 
Further experimentation is necessary.

I hope this info helps.

Ken Gordon W7EKB