[Milsurplus] BC-9: Back to Head Scratching.

[antqradio at sbcglobal.net]

Well Dave, I have offered the loan of a few VT-1's a week or two ago but you refused.  Offer is still there; it is just a matter of logistics.  I am about 250 miles from Nevada, TX.  We make the trip to the DFW area several times a year, the wife likes to shop at Ikea and I don't mind the drive.
Have a delivery to make to a museum in Oklahoma City of some avionics so I can go the short route or the long route.   Pretty sure I have a few used VT-1's and know I have just as many NIB.  I don't know their viability so they may or may not work in the BC-9 but they will have good filiments.Jim



      From: David Stinson <arc5 at ix.netcom.com>
 To: milsurplus at mailman.qth.net 
 Sent: Saturday, February 18, 2017 6:18 AM
 Subject: [Milsurplus] BC-9: Back to Head Scratching.
   
Well, I'm flummuxed again.
No matter what "frequency compensation" cap
I use, I can't seem to net the thing closer
than about 3 KC.  Going below about 220 pFd
actually makes it *worse.*  Duh......

I'm beginning to wonder about the silver micas
in my junkbox.  They test OK on the ZM-11.
And there is an "antenna effect" when using the 
tank-and-link output.  I haven't defined it yet.
Maybe it's the triode-connected 6AQ5.  Maybe
there's just a limit due to its quirks.  None
of the other tubes I've tried work on receive
nearly as well and some, not at all.  I even
plugged-in a VT-25A.  Good on transmit,
but no will regen.
I'm going to assemble the loop this weekend
and see how it behaves with that.  We'll see.

One other thing for those thinking of tinkering
with a "replica."  A very old bug-a-boo with 
regens and oscillators like this:  If you use the
link-coupled output and your antenna is 
resonant exactly at the freq of operation, 
the oscillator can't handle the load and 
it will quit.  I  don't remember what this effect
 is called but it's in all the best regen literiture.
I've been fiddling around 3550 KC.  
If I use a tuner to present a flat 50-Ohms 
to the link at 3550, when I tune the transmitter 
freq. it will actually "jump over" the resonance 
area- it will tune up to about 3540 and then 
"jump" to about 3610.  I have to tune the 
antenna to about 3525 to get it to behave.
Even with that, I was still able to make a nice
QSO between here and South Texas with the
mighty 2 Watts.  (Not last night.  No chance
with that CW contest).

Mike Hanz contributed an excellent, 
non-destructive suggestion:  Use a 100-volt
Zener, resistor and reed relay on the DC
side of the 120 VDC line.  Switch-in a small
Receiver compensator that will certainly, finally
net the radio.  I mean, I'm never going to have 
a VT-1 to actually test it under original condition,
and I don't usually object to such "non-hacks."
But I'm not sure I'll go that far.  I'm very pleased
to have gotten the radio back into a condition 
where its preservation long-term is likely.  
It's still fun to play with as a receiver or as a
transmitter using an external receiver.  

Maybe I should count myself lucky that, with 
the help of our outstanding community of 
"Smart People," the radio is alive and kicking
again after almost 100 years.  I even had the 
correct Hi-Z 12,000 Ohm headphones.  
Maybe I should "quit while ahead"
 before I screw it up good.
Still want to see how it plays with the loop.

Going to try to make a few contacts with it
for Novice Rig Roundup (no; it's not a
"Novice rig" but it is cool ).
Will likely use an external receiver.  
The transmit freq is still surprisingly stable 
and chirp is minimal.  Just for fun.

Have a great weekend, y'all.
73 Dave AB5S


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