[ARC5] Why the differences between the R-23 and BC453

[Kenneth G. Gordon]

On 17 Sep 2017 at 14:52, J Mcvey via ARC5 wrote:

> 
> While dealing with a bad screen divider resistor chain in a R-23, I noticed that the 
> low side of the of the second resistor did go to ground as it does in all of the other 
> radios! The overall bias is different. There is an additional 3K
> resistor between the second divider and ground. This makes the screen bias 
> higher approx 140V ( assuming 240v in) and the 3k is supplying a 42V bias to the 
> cathode of the 12SR7.
> The entire det/cw osc circuit is different in the R-23 than any of the others. ( 
> including the other ARC series)

That is very interesting information, Mac. I have not examined the few R-23s I have here to 
noitice that. 

For one thing, the screen voltage to the 'SK7s should be at least 150 VDC according to all 
the tube manuals, yet that voltage was always lower than that in all other "ARC-5" receivers, 
which was always a mystery to me. So, that 140 VDC you are seeing is far closer to what it 
should be for best sensitivity. In point of fact, the sceen voltage CAN be as high as 300 
VDC, as long as dissipation ratings aren't exceeded.

> Anyone have a guess why they would do this?

Not yet. I'll have to examine the circuit more closely to figure it out.

Others here may know already.

I DO know that the AGC circuits were improved first for the "navigation" receivers (R-23 and 
R-24) , and then the "communications" receivers.

Ken W7EKB



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