[Hammarlund] Old Hammarlunds - the Geissler modifications.

[Carl]

He must have impressed somebody since in later years the USAF adapted and 
adopted the Nuvistaplug to the SP-600. Supposedly it helped but I can 
imagine it overloaded bad with a wide open first RF.

Carl
KM1H


----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: <Hammarlund at mailman.qth.net>
Sent: Sunday, May 15, 2011 4:11 PM
Subject: Re: [Hammarlund] Old Hammarlunds - the Geissler modifications.


> On 14 Apr 2011 at 17:18, djed1 at aol.com wrote:
>
>> ---Original Message-----
>> The Geisler mod involves more than the first mixer- there are changes
>> to the detector, RF and AVC also.
>
> I was re-reading that article this morning: Geissler modified BOTH RF 
> stages
> to a cascode circuit using 6SL7s.
>
> He modified the mixer also to a cascode circuit using a 6SL7. In fact, 
> except
> for inputs, the circuit is identical with the 2 RF stages.
>
> He modified the HFO to a 6SL7 triode oscillator and cathode follower.
>
> He completely removed the 6N7, and modified the 6H6 to a combined 2nd
> detector and noise limiter.
>
> He modifed the AGC circuitry, and reversed the wiring to the "S" meter.
>
> Lastly, he modified the audio stages, changing the first tube from a 
> triode-
> connected pentode to a pentode, and changing the biasing on other stages
> to provide "...10 more watts of audio...", and "...better tone".
>
> As far as I am concerned, his only mod that has any kind of merit at all 
> is the
> change to the HFO, but even that could have been done better and less
> intrusively.
>
> IMHO, the 6F6s run hot enough at 14 watts: they must have been red-hot at
> 24 watts output. Ye gods!
>
> And last, but not least, his documentation is incomplete.
>
> Anyone who considers the Geissler mods to be "reasonable" is, IMHO, quite
> simply, nuts.
>
> Ken W7EKB
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