[Hammarlund] Bias supply zorching the audio driver transformer

[Carl]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "Al Santangelo" <ve3ajm at gmail.com>; "hammarlund" 
<hammarlund at mailman.qth.net>
Sent: Wednesday, July 25, 2012 12:31 AM
Subject: Re: [Hammarlund] Bias supply zorching the audio driver transformer


>> Hi Todd,
>>
>> Great to meet up with you here OM. Hope to hear/work you
>> soon on 75 or
>> 40m for sure. The group is still going strong.
>>
>> I know it was mentioned to be careful about the bias
>> supply and
>> damaging the audio driver transformer in the Super Pros.
>>
>> I was just looking at the schematic for the SP-400X and I
>> see that the
>> schematic shows the use of cathode bias on the PP 6F6s.
>> ie. the centre
>> tap of the secondary of the driver transformer is
>> grounded.
>> I don"t the SP-210 schematic here, so I'm thinking that
>> this is one
>> other difference between the 400 and the earlier SPs?
>>
>> Al Santangelo



>
>    The amplifier is the same in all the Super-Pro series.


** As I already stated yesterday

> Cathode bias 6F6's connected as triodes and running AB2. The
> transformer coupling to the grids can supply the small
> amount of grid current that they draw on peaks.
>    There is no bias going through the audio transformer in
> an unmodified receiver.
> The bias supply is used for the RF, and IF stage bias, it
> would be difficult to damage it.


** Bias also goes to the 6F6 driver.


>    There are schematics for the SP-400 and SP-100 at BAMA
> and for these and earlier versions at Nostalgia Air.


** This will eliminate the regular confusion on the WW2 Super Pros, its THE 
decisive manual for all in one place.
http://bama.edebris.com/manuals/military/bc779/


   The
> main differences over the models was the change from glass
> to metal tubes going from the 100 to 200 series and the
> addition of the new-type crystal filter in the 200 series.


**  The SP-100 has a majority of metal tubes, the SP-10 was all glass.


> The optional crystal in the earlier sets was of a rather
> crude design.


** Already covered a few days ago. The crystal filter was introduced for the 
SP-10 and was an option on all the SP-100 versions.
http://www.radioblvd.com/hammarlund_super_pro.htm

.

>    The BC-779 has different frequency coverage from the
> SP-200-LX. The LX has a single LF band covering 150 to 300
> khz while the BC-779 has two bands covering 100 to 200 and
> 200 to 400 khz in place of the two lower frequency bands.


** Both the SP-100L, SP-200L  and BC-779 had the same two range coverage. 
There is confusion in the advertising as mentioned in this same article
http://www.radioblvd.com/hammarlund_super_pro.htm



>    Older RCA tube handbooks will have the data for the 6F6
> tubes as operated in the Super-Pro.


** Plus all the data is readily available on line

http://www.tubedata.org/

Carl
KM1H



>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
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