[HBR] questions about HBR-11

[waltah at earthlink.net]

Joe LeKostaj wrote:
> Also, could you please point me to the hang AGC info?

If you have a *Handbook* from the 60's, it should be in there.   My 
1967 book has it on p. 106.  The vacuum diodes can be replaced 
by silicon units;  only the one shown as part of a 6BC7 needs any 
particular voltage rating and since this is audio-based AGC, you 
could use any of the popular 400-volt rectifier diodes there. 

Since you need one of the triodes to drive any audio AGC scheme, 
you're really just talking three more diodes, another triode, and a 
few other small parts to put in hang AGC.   It's a very nice addition.

Of course if you use a standard audio AGC circuit -- the HB-67 in 
the same book shows one -- you can wait until you have the set 
working and retrofit 'hang' AGC.   Just leave a little 'real estate' near 
the AGC driver tube and provide or leave room for an extra triode 
there.   

Boy, the HB-67 uses a rare tube.  The 6T9 is one of those 10-pin 9-
pin tubes, isn't it?  Has anyone *ever* seen the socket one of those 
things?
   
> 
> Regarding local AM stations, there's one on 1590 that may casue some 
> trouble. We'll just have to see how it goes.

You're in pretty good shape.    With the 85 Kcs IFTs I'd put the 1st 
IF about halfway between multiples -- 19 x 85 = 1615 and 20 x 85 
= 1700, so something about 1660.   That leaves you a couple of 
kcs to tune the 85 kcs BFO before the harmonic is centered in the 
1st IF and it is well away from 1590.   

Of course a well-filtered and shielded BFO running at just high 
enough power to do the job shouldn't leak harmonics back to the 
1st IF, but there's no point in making the job harder instead of 
easier!

Walt
KJ4KV