[HBR] Another HBR Project

[hbr@mailman.qth.net]

Kees said:

> This business about using a turret tuner out of an old TV, like on
> this 1956 radio of Cliff's, looks interesting also. Toroids should
> make that very useable. 

Yeah, wonderful idea.   The problem with those TV tuner bandswitch 
designs in the past was that the coils were so small that you couldn't 
get a decent Q but with toroids, that wouldn't be a problem.   You 
might even put the toroid in series with the original coil and use that 
as a trimmer.   Somebody on the list ought to try it!

On the 'One Week HBR' project, I'm chewing now on the HV supply.  
I like to keep it to around 150 volts to reduce the power consumption 
(=heat) but nobody much made power transformers like that.  I have 
found a few 'isolation' transformers in the 20-30 watt range but even 
those are not common now.   I've done 'transformerless' designs but 
having to decouple the negative line is a source of design problems.   
Another trick I've used is to convert the primaries of two Radio Shack 
filament transformers of the right size into a single 1:1 transformer -- 
they are bobbin wound with equal bobbins for both windings so this is 
easy to do once you get the transformer apart.  

I have just tested a 15 watt 1:1 power supply:  with a capacitive input 
filter it gives 110 volts at 90 ma which should be enough power for the 
1WHBR.   The voltage, however, may be an issue.   I want to use a 
12BH7 (dual medium mu triode) for p-p audio output, driving it with a 
phase splitter; there may be trouble getting enough drive voltage.  

We'll see.  Have to get going on the chassis.

Walt Hutchens
KJ4KV