[TMC] GPR-90RXD stuff

[Richard Knoppow]

    If you have the coils AND a Q-Meter you can measure the Q and 
also the distributed capacitance. There is a technique in the 
handbook for this. Its a bit tedious but works.
    In the past I read a number of comments on the BFO in the 
GPR-90, which I gather has problems. The RXD version is quite 
different. However, the RXD was probably intended to be used with 
an external SSB adaptor so the internal BFO would not be used 
other than perhaps for tuning.
    I am another who thinks the GPR-90 is very sexy looking. 
Actually, all TMC stuff has a special style. I wish I had some.

On 8/6/2021 2:15 PM, James A. (Andy) Moorer wrote:
> If somebody has an L38 from a parts unit or is willing to 
> unsolder theirs, you can use a modern ohmmeter to figure out 
> where the tap is. There won't be a lot of resistance, but the 
> ratio of resistances from tap to end points should be related 
> to # turns. That plus the overall inductance should be all you 
> need. Hmm. I wonder how critical the winding technique is? 
> Basket-wound versus pi-wound? The point of those 
> "loose-looking" winding techniques is to reduce the 
> self-capacitance of the windings. You can wind one by hand, or 
> on a vintage Miller coil winder if you can find one and figure 
> out how to make it work.
> -A
>
> On 8/6/2021 5:01 PM, John Poulton wrote:
>> Just for the heck of it, I looked up the drawing for this coil 
>> (L38, BFO
>> output coil).  From the parts list, it's TMC part # CL-231, 
>> which is also
>> the TMC drawing number.
>>
>> Here's the drawing URL (I've scanned most of the drawings for 
>> smaller coil
>> assemblies):
>>
>> https://tmchistory.org/tmc_drawings/drawings_db/cl/cl_200_299/cl-231.pdf 
>>
>>
>> The drawing is singularly unhelpful.  It shows a 3-rank 
>> pi-wound coil with
>> an inductance of 585uH (in agreement with the schematic, but 
>> not the parts
>> list) with a powdered iron core, but it doesn't even mention a 
>> tap or
>> indicate where it might be..  Arghhh.  Maybe the wire type and 
>> Q will be
>> useful to you.
>>
>> Chris, hope you're able to find a photo of the coil.  I'd be 
>> interested to
>> know what you find out from it.
>>
>> 73, John K4OZY
>
>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL