[Hammarlund] Super Pro bias supply

[Carl]

You could also use a combination of fixed and cathode bias so that if the 
supply failed the tube wouldnt exceed its ratings enough to take out the 
transformer.

Or switch to three 6V6's, drop the B+ to a safe level, change cathode 
resistor in the output as needed, and get the same 14W at half the 
distortion and at less cathode current. Id also want to try a 6K6 driver to 
further reduce the load on the driver transformer since the 6V6's would be 
biased for AB1.

Others then may wish to change the driver to a 6SL7 or 6SN7 as a phase 
inverter/preamp and bypass the driver transformer.

These are radios that beg for little changes that help a lot.

Carl
KM1H



----- Original Message ----- 
From: "Brian Harris" <cosmophone at yahoo.com>
To: <wrcromwell at gmail.com>; "Al Santangelo" <ve3ajm at gmail.com>
Cc: "hammarlund" <hammarlund at mailman.qth.net>
Sent: Wednesday, July 25, 2012 8:26 AM
Subject: Re: [Hammarlund] Super Pro bias supply


If one installed a relay in the power supply which is energized by the bias 
supply and whose contacts, when closed, allow B+ to flow, would solve the 
scorched driver transformer. Seems simple enough to me.


Brian Harris
cell 214-763-5977
email cosmophone at yahoo.com


________________________________
 From: Bill Cromwell <wrcromwell at gmail.com>
To: Al Santangelo <ve3ajm at gmail.com>
Cc: hammarlund <hammarlund at mailman.qth.net>
Sent: Wednesday, July 25, 2012 6:37 AM
Subject: Re: [Hammarlund] Super Pro bias supply

On Wed, 2012-07-25 at 07:16 -0400, Al Santangelo wrote:
> OK on the further information.
> So then, what is the connection between the failure of the
> -50v bias supply and the failure of the audio driver transformer that
> I've read about?
> This bias supply is not connected at all to the audio driver
> transformer ie.T7 in the SP-400X receiver. Thanks.
>
> Al Santangelo
> ______________________________________________________________

Hi Al,

I went to BAMA and snagged a copy of the manual. If the bias supply
fails the audio driver will turn full on (zero volts at the control
grid) and it gets it's plate voltage through that transformer. The
transformer will be ruinated. You can't stuff tens pounds of baloney in
a one pound sack.

73,

Bill KU8H

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