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

[Kenneth G. Gordon]

On 18 Feb 2017 at 6:18, David Stinson wrote:

> 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......

Well, since this exercise began, I have been wondering about "F"...

> I'm beginning to wonder about the silver micas
> in my junkbox.  They test OK on the ZM-11.

Well, I don't think those are the problem...

> 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.

That, as someone just said, is the so-typical "dead spots" and "suck-out" of simple 
regennies connected directly to an antenna.

> I'm going to assemble the loop this weekend
> and see how it behaves with that.  We'll see.

Well, when you do, I strongly suggest you mount the entire radio/antenna out in the clear 
somewhere, with nothing in even remote proximity to the loop.

> 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.

Yes. Very common problem. That can be minimized by making the coupling to the antenna 
VERY "loose".

>  I  don't remember what this effect
>  is called but it's in all the best regen literiture.

Yes.

> 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.

That sounds about right.

> 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).

Ha! Tell us about it!

> 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.  

Still, it would be very nice if it could be made to work as it, apparently, as intended.
 
> 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.  

Gee....where did you get those?

> Maybe I should "quit while ahead"
>  before I screw it up good.
> Still want to see how it plays with the loop.

Me too!!!

> 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.

Yes. LOADS of fun! :-)

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

Same to you, David.

Ken W7EKB

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