[ARC5] ARC-5 receiver mixer mod attached as PDF

[Kenneth G. Gordon]

On 3 Jan 2017 at 11:42, Arden Allen wrote:

> >> Perhaps it's the Pullen Mixer you refer to.  No. This is a single-page of 
> >> information written up by my successor....
> 
> Now that's an interesting approach but I wonder if a 12SL7 would have worked 
> as well, not needing a socket adapter.

I had wondered the same thing. However, if you review the characteristics of the two tubes, 
you will find that the 12AT7 has a much greater transconductance than the 12SL7, resulting 
in less noise, better mixing action, and requiring far weaker input signals. Perhaps that is 
why he chose that one.

Also, I have on my website a reprint of an article from, I believe, 73 magazine, concerning 
the Pullen mixer, and both the 12SL7 and the 12AT7 were tried in that circuit. It was clearly 
shown that the 12AT7 resulted in far, far better performance than any other dual-triode tried.

To find that article, go here:

http://www.w7ekb.com/glowbugs/rx/receivers.htm

Scroll down to 9) The Pullen Mixer and then "A Like-New Mixer Circuit" PDF.

>  Also, was there worse oscillator 
> pulling?

I have no idea. I have not yet used the adapters I have here as I, so far, have not seen a 
need for them.

In any case, at the time (1974), the receivers were essentially "fixed-tuned" and were never 
changed from the frequency once set, so that problem, if it exists, was never seen.

Most of the adapters I have here were pulled from BC-453s or R-23(*)/ARC-5s which had 
been "convertered" to cover 22.3 KHz (!!!). They were literally hacked to ribbons. All IF cans 
were replaced with 239 KHz IFs, the RF amps were removed, the coil box was removed and 
replaced with a single Miller TV horizontal osc coil, etc, ad nausaeum. It makes me sick to 
even look at one of them.

They are restorable to use....barely...with copious quantities of JB-Weld applied to various 
places on the chassis. :-(

Ken W7EKB

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