[Amps] Ten Tec Herc 444 (original Herc)

[Steve Thompson]

John Popelish wrote:
> Jim Brown wrote:
> (snip)
> 
>>As it warms up, the voltage to which the power supply regulates 
>>drifts up and causes the protection circuit to engage, which 
>>prevents it from transmitting. TenTec told me this was a known 
>>problem, but that since they had to discontinue the amp (thanks 
>>to Motorola discontinuing the output devices), they had not put 
>>in the engineering time to fix the drift problem. 
>>
>>Mine is in good shape, but I need to fix the regulator drift 
>>problem. If anyone knows how, I'd love to hear about it so that 
>>I don't have to reinvent the wheel.
> 
> 
> Can you point me toward a schematic of the regulator?  This doesn't 
> sound like a very difficult fix.
There's a copy of the handbook with schematics at
http://www.qsl.net/tentec/ttamp.htm but some bits at the tops of pages 
(incl. part of the regulator) seem to have got sliced off. The regulator 
is unconventional and appears to rely on specific internal circuitry 
inside a 7924. A modern replacement with different internals, or 
different brand, might mess things up.

I'm puzzled by why there should have been problems with the rf devices 
causing the product to be discontinued. The rf amplifier section looks 
extremely conventional, and anything but device dependent.

Steve