[Milsurplus] BC-669 Project XTALs

[David Stinson]

On 10/12/2019 8:24 PM, hwhall at compuserve.com wrote:
> Hi,
>
> How's the crystals for the project coming? I have an FT-243 on 3885KC 
> (originally BC-611 TX xtal) and found some HC-6 size ones: a few for 
> 3495KC and one 1500KC.  IIRC, those were freqs you were looking for.
>
> Wayne
> WB4OGM
Morning, Wayne!
Nearing completion.  Got all six receiver crystals etched and 
installed.  Still lack the 1885 and 1985 KC Transmit crystals.  The ones 
I had close enough to etch turned-out to be fractured.  I may have to 
get it to him without 160 meters for now.  Four TX channels are 3665, 
3880, 3885 and 3890, which should give him plenty of traffic here in 
Texas in the mornings and evenings.  I have found there is enough 
"width" in the receiver front-end that one can listen to favourite BCB 
stations; just install the appropriate "subtract 385" crystal or 
oscillator.  For instance- one of my favorite "oldies" locals is on 1400 
KC, so I pipe-in 1785 KC, tune the dial all the way down below 1700 and 
it sounds excellent.  Still fighting an intermittent problem in the PA 
output tuning, but I hope to have that whipped today.   My scope is 
saying unmodulated carrier into a 50-Ohm load is 180V PTP, but I don't 
believe that.  I have put a DC supply on the scope and confirmed that 
180 VDC moves the trace to 180V on the graticule.  180V PTP is  63 V 
RMS, which would equate to almost 80W out.  I don't believe that for a 
minute, especially since with 450V B+ at 200mils, input is 90W (my watt 
meter calibration is hosed so using the scope).   Wondering how this is 
happening.  Is it possible some RF is coupling into the scope's Vertical 
amp and adding to the "real" figure?  I'm using a 1970s Textronix x10 
probe properly grounded and the scope is connected to my extensive 
station ground and AC line ground.  So why the exaggerated  reading?

In any event- using a Motorola TMN6054 mobile mike and with a change of 
two resistors (already-modded when I got it so "fair game") in the Mic 
Amp, 100% clean modulation with excellent reports.  The two resistors 
are a voltage divider from the output of the microphone transformer to 
the grid of the 12J5 Mic Amp.  100k from transformer secondary to grid, 
50K from grid to ground.  This impresses only 1/3rd of the available 
audio voltage on the 12J5 grid, so I flipped those two over- 50K 
secondary to grid, 100K to ground, effectively doubling the drive and 
reports indicate this was an improvement.

Heading out to "the Cave" to finish-up.  Need to "clear the decks" for a 
final "check out" of the RAK and RAL receivers before shipping them off 
the the U.S.S. Wisconsin for installation in their period-correct Radio 
compartment.  Not sure how much the shipping is going to be, but their 
club is going to help with it.  I'll come begging if I need a little 
extra, LOL.

TNX OM ES GL DE Dave AB5S





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