[R-390] R392 Audio

[Meir WF2U]

The original, military contract plug-and-play solid state replacement module
for the 26A7GT audio output tube is here:
http://www.roveroresearch.info/home/boatanchor-radios/r392/r-392-technical-d
ata/r-392-hints-tips-and-mods/r-392-official-solid-state-audio-module .
The military depot upgraded R-392's had a modification to accommodate the
module:  R629, a 8.2 megohm resistor that provides feedback to V606, the
first AF amp, is used in receivers that use the original 26A7GT, are removed
in receivers with the "official" SS audio module. This feedback is provided
inside the solid state audio module.

One of my R-392 receivers came with the original plug-in SS module and it
works great. 

73, Meir WF2U
Landrum, SC


-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Tom Frobase
Sent: Friday, January 24, 2014 7:06 AM
To: Charles Steinmetz
Cc: 390 list
Subject: Re: [R-390] R392 Audio

Charles was there not a solid state module developed by the military for
the 392?  How did it work?

On Friday, January 24, 2014, Charles Steinmetz <csteinmetz at yandex.com>
wrote:

> Perry wrote:
>
>  Perhaps a simpler alternate to Charles tube re-design of the audio output
>> circuit would be to use one the LM series of audio output IC's.  They
range
>> from 2 to 70 watts or so output and many have been designed for high-end
>> audiophile equipment so they have low THD.  Besides needing minimum
>> additional components to use, most are under $10.
>>
>
> Perry, you have no idea how involved (or not) the R392 audio mod is.  In
> fact, installing a power amp IC would be much more work.  And while power
> ICs are fine in a lo-fi application like a communications radio, the idea
> that power output ICs are useful "for high-end audiophile equipment" is
> simply laughable.  Even halfway-decent mid-fi consumer products don't use
> them.
>
> In the context of an R392, which has a unipolar power supply, using a
> power IC would require either (i) a whopping big output capacitor or (ii)
a
> bridge-type output with a DC offset of 1/2 the power supply voltage.  Both
> are problematic (the latter is a great way to blow up the IC and/or a
> speaker when you forget about the offset).
>
> Best regards,
>
> Charles
>
>
>
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