[ARC5] BC453 FET BFO Success!!!

[Kenneth G. Gordon]

On 18 Dec 2017 at 15:19, J Mcvey via ARC5 wrote:

> I have succeeded in implementing a FET driven BFO in the BC453 using
> the the original BFO coil and a minimum of wiring changes. It uses the
> original BFO cut-off circuit too! Total parts count = 6 Basically the
> mod disconnects the 12SR7 triode and replaces it with the FET The BFO
> supply is clamped to 24V with a zener. 

OK. Sounds good. How about BFO injection level? Is it sufficient?

> There are some bias and stability parts that are added to make the FET
> happy. It's not a "direct changeover". The "grid leak" setup on the
> triode is not used with the FET 

OK.

> Looks to be very stable .

Details?
 
> I'll write this up sometime in the next couple of weeks if there is any interest.

Of course there is.

However, one thing that I have felt was missing from this project from the beginning is the 
EXACT amount of real drift, in what direction, over what length of time, and whether or not it 
ever stabilized. None of this information, as far as I can remember, was ever forthcoming.

>From your original post, it appeared to some of us that the drift in the BFO was very 
excessive. I have never experienced what I could possilby term "excessive" drift in ANY of 
the BFO circuits in any of the "ARC-5" receivers I have used, even in that hacked-up 
BC-454 which was converted to cover 10 meters.

Even at the time that I used Spectran software coupled to the output of my BC-453 all lines 
in the waterfall display were straight after the receiver was allowed to stabilize. There were 
very slight drifts back and forth, of course, since at the time I was not using stabilized 
voltages, but there was most certainly no continual sideways drift of any of the lines in my 
waterfall display.

Please fill us in on these details.

As I said, to many of us, the drift you mentioned in your first post appeared to be VERY 
excessive. Unusually so, in fact.

Ken W7EKB

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