[HBR] IFT for BFO Coil

[waltah at earthlink.net]

Darrell, WA5VGO wrote:

> Thanks very much for the BFO advice. It sounds almost fool proof. 

You've been reading my adventures with HBRs, so you know how 
'fool proof' my ideas are ... Hi!

They may be proof against most fools but *I* get into trouble quite 
regularly.   Yep, I'm the guy who feels he has made progress with 
this receiver project because on *this* one, I only hooked up two 
tube filaments wrong.

> I had not considered the problem with the RF choke, but fully
> understand your point. It would take many mH to be effective at
> that low of a frequency. 

Since the original tank capacitor was 100 mmf, the coil must be 
around 20 mH for resonance at 100 kcs.  Thus unless you used a 
choke of at least a few hundred mH -- that is, maybe half a henry 
or so! -- a lot of the tank current would actually flow in the blocking 
choke.   You might get the oscillator working like that, but I 
guarantee problems.

> I assume my ratio between the capacitors is okay? 

It sounds right to me.  1:3 is a very common ratio for cathode 
section to grid section in these oscillators.

> I plan on using a 6C4. All of my experience with oscillators has
> been the tapped coil variety. 

A 6C4 should work fine and will be less trouble than a 'hotter' tube.  
Tapped coil or capacitive voltage divider makes no difference to the 
RF; it's strictly a DC issue and you can deal with that.

Walt 
KJ4KV