[ARC5] Receiver Tube Substitution

[Kenneth G. Gordon]

On 15 Dec 2016 at 9:51, Rich Post wrote:

> Plug-compatible but 12SJ7 is sharp cutoff versus 12SK7 being remote cutoff.  If in an AVC 
> circuit, remote cutoff is needed. 

Right. It was probably what the original user had in stock. The R-23 and the R-23A do have 
AGC, so using a 12SJ7 as the RF amp would make the receiver more prone to overload by 
strong signals.

The effect probably wouldn't be noticed much in normal operation though.

Another common sub was the 12SG7. This results in lower noise.

At frequencies below about 20 MHz, there is no advantage to using them.

Ken W7EKB

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