[Hammarlund] Bias supply zorching the audio driver transformer

[Al Santangelo]

Its weird that I haven't seen a one of the old SPs at any hamfests for
many years up here in Southern Ontario. I know they are many decades
removed from being surplused out here by military. One of those things
I guess..and as it seems to go, when you find one you'll find another
and so forth. So there is a bit of mystery there for me too.

Ken VE3MAW has a mint BC-779 variant..the BC-1004 with the original
matching PS all rack mounted. It has an issue with one of those caps
up in the IF cans and that caused a resistor to smoke in the can.

So a new project to get regenerated in radio again. I'm sure that once
gone through, they will perform well for 160 80 and 40m activities and
cruising around the BC bands etc.for my use. It will be a fun project.

Al Santangelo

On 25/07/2012, Todd, KA1KAQ <ka1kaq at gmail.com> wrote:
> On Wed, Jul 25, 2012 at 3:38 PM, Richard Knoppow
> <1oldlens1 at ix.netcom.com>wrote:
>
>>
>>   There is another change which might be of importance in getting old
>> Super-Pro receivers to work. The power supply for those before the
>> SP-400-X
>> were arranged to power a loudspeaker field which was also used as a
>> second
>> filter choke. If the supply is used without a speaker field it should be
>> replaced with a choke or resistor of the right value.  the SP-200 manual
>> says that there was a "special" supply for use without the fieldcoil
>> which
>> contained a second choke.  The military power supplies all have two
>> chokes.
>> The SP-400 supply is of this type. The terminals for the speaker field
>> should NOT just be linked since the lower voltage B+ will be too high. If
>> it is open no voltage will get to anything but the power output stage.
>
>
> That is certainly true of some SPs, Richard. But many omitted it from the
> start. Can't recall the exact correlation, but some had 600 ohm
> transformers (sealed type as I recall) while others had 8 ohm iron not
> requiring a field coil speaker.
>
> To make it more confusing, supplies tended to get mixed up along the way so
> a receiver needing the extra choke might show up with a supply that omitted
> these extra connections. There's a good shot of the back aprons on Henry's
> page not quite halfway down, under power supplies:
>
> http://www.radioblvd.com/hammarlund_super_pro.htm
>
> And the earliest supplies (SP-10) had a supply with a slightly lower B+,
> using a 1V tube instead of the type 80 used in later supplies. My SP-10
> lacks this supply (though for some reason I have a bunch of spare 1V
> tubes). The later versions can be adapted, but I'd still love to locate one
> before I die.
>
> Al's going to have a Super Pro overdose if we're not careful. (o;
>
> ~ Todd/KAQ
>