[Heath] Mohican question

[JF]

On 9/1/2012 1:17 PM, Alexander N. Gerli wrote:
>
> /Got my Mohican running after cleaning the bandswitch and controls.
> I have both the AC and battery packs for it too. But, go figure, no
> manuals. I’ll get a reprint from Manualman Pete for the radio so I
> can realign it (it needs tweaking something awful), but I can’t find
> the model number of the AC pack. Must be GC-1-something, but what?
> Does anyone on the list have this little gem of a manual that I may
> borrow to copy?/

The XP-2 AC power pack info seems to be online at at least
2 places:

http://www.mods.dk/manual.php?brand=heathkit
   and
<http://elektrotanya.com/heathkit_xp-2_power_supply_for_gc-1_receiver_sch.pdf/download.html>

Unlike the battery pack, the AC pack uses the 2 dial lamps as
part of the voltage regulator circuitry, so they will be on all
the time regardless of the position of the front panel light
switch and must be replaced if they burn out, and perhaps also
their series resistor (R93) to chassis ground if it has
deteriorated.

Examine various owner comments and test the power wiring
polarity closely before applying power - for example, in an
apparently erroneous warning (depending on how you read it)
posted by a Mohican owner some time ago (copy below), he said
he found the polarity of his AC pack was backwards at the
radio's muting terminals; however, the chassis actually is B+
(positive ground) and the muting terminals B-, so if he really
found -12V on the muting terminals then that was the way it
was supposed to be. The radio uses all PNP transistors so the
chassis is +12V, but the many circled voltage readings on the
schematic do not have polarity indicators - there is only a
small note at the bottom saying all voltages are negative in
respect to chassis ground.

(Quote from erroneous-looking post:)
 >...with an installed XP-2 power pack, when I powered it up,
 > I got a lot of hum from the speaker and nothing else. A
 > quick check of the voltage on the muting terminals showed
 > that I had -12 volts where +12 volts was supposed to be!
 > A bit of investigation revealed the problem... the plugs on
 > the XP-2 and the Mohican are both wired according to the
 > assembly manuals, but DO NOT CORRESPOND with one-another.
 > The Mohican manual/schematic shows that the receiver expects
 > + 12 VDC on pins 4 & 5, with ground on pin 6. The XP-2
 > manual (both schematic and assembly instructions) has the
 > plug wired with +12 VDC on pins 3 & 4 and ground on pins
 > 5, 6, & 7.

73
John   KE5ZB