[Boatanchors] Tube reciever design banter

[Carl]

----- Original Message ----- 
From: "Drew P." <drewrailleur807 at yahoo.com>
To: <boatanchors at mailman.qth.net>
Sent: Wednesday, December 23, 2009 1:08 AM
Subject: Re: [Boatanchors] Tube reciever design banter


>
> Carl wrote:
>
> "Dual triode mixer in a Pullen circuit. 6ES8 preferred as its a very
> unique variable mu tube."
>
> Presumably since the mixer section of the tube in a Pullen circuit is 
> biased in a very non-linear portion of its characteristic curve, use of a 
> variable mu triode would make operation even more non-linear.  More 
> non-linearity would make for a mixer having better conversion gain.
>
> How much better in conversion gain and other performance parameters is a 
> variable mu triode as compared to a (relatively) constant mu triode when 
> either is employed in a Pullen mixer circuit?

Ive no idea since I went from the older 12AT7 basic dual triode circuit to 
the 6ES8 Pullen for 9 pin tubes. There the NF dropped slightly on 10M and 
the various signal handling parameters improved substantially and this was 
with a 6GM6 in front in a single band setup. It wouldnt be fair to compare 
with a 6SN7, 7F8 or similar or even a 6J6.


> How much better is the Pullen circuit with its intentional biasing for 
> non-linearity as compared to a non-Pullen triode mixer (such as the mixers 
> in the R-390 series)?

See above



>
> Carl, thank you for your insights on these topics.  It is good to get 
> information from someone like you who was in the field and obtained 
> practical knowledge in tube electronics.
>
> By the time I took EE courses, tubes were regarded as hopelessly passe, 
> and none of the professors cared answer my tube questions (even outside of 
> class time), instead they invariably expressed relief that they didn't 
> have to deal with thermionic technology anymore.

I went from tech to engineer in the tube days without a degree. It wasnt 
untill much later that I formalized it and I had a few gray hair professors 
who used to sit down with me informally and impart tube knowledge that I had 
overlooked or blissfully ignored. They were glad to relive those days.

I didnt really get back into vintage gear seriously until about 12 years ago 
altho I dabbled regularly with restorations for others ever since the 
National days. Sorry to say now but I had sold off a rather substantial 
National collection in the mid 80's.  I then slowly lost interest in the 
nightly brawls chasing DX on SSB/CW and needed something different than the 
daytime microwave R&D work that paid very well. So I reverted to my 
childhood and got wound up with old radios and hot rods again. Full circle!

Carl

>
> Drew
>
>
>
>
>
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