[HBR] Radio design advice

[Brian Hill]

Have any of you messed with a triode/hexode type converter?


Regards
B.H.
Brian's Radio Universe
http://webpages.charter.net/brianhill/500.htm

----- Original Message ----- 
From: "Mike Hanz" <AAF-Radio-1 at cox.net>
To: <ianmwilson at earthlink.net>; "HBR Receiver List" <hbr at mailman.qth.net>
Sent: Wednesday, May 31, 2006 3:45 PM
Subject: Re: [HBR] Radio design advice


> Ian Wilson wrote:
>
>>Pullen Mixer: you will probably need to increase the triode count. A 
>>Pullen
>>should have a cathode follower driving both sides of the mixer; so that's 
>>3
>>triodes (you can use the 'spare' triode of a dual triode as one of the
>>oscillators).
>>
>
> From a perfection seeker's standpoint, Ian is absolutely correct.  The use 
> of a second dual triode will completely isolate any pulling effects from 
> the two inputs, and Keats in fact noted this approach in his book as a 
> *disadvantage*.  On the other hand, others with a more pragmatic (or cost 
> cutting) view have observed that the mixer itself has a cathode follower 
> configuration with relatively high input impedances, and the elimination 
> of the second dual triode does not affect its operation to a degree that 
> bothered their perception of acceptability, especially compared with other 
> mixer designs.  I like Ian's observation because toobs are cheap in an HBR 
> design and it is a point of perfection that we tend to seek in these sets, 
> but if you have space difficulties in your particular chassis, you can 
> still use the Pullen approach in its "dumbed down" configuration and still 
> get good results from it.
>
> 73,
> Mike
>
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