[HBR] Another HBR Project -- Chapter 3

[hbr@mailman.qth.net]

Good progress this week.  Panel and chassis are done and power 
supply wiring is working.   The nearest thing to excitement was when 
the unused tap of one of the filament transformers shorted to the 
chassis and nearly cooked the thing.   The rest went smoothly 
including some tricky mechanical work for the command receiver 
plug-in coil unit -- glad that's behind me.

The 6EW6 looks like a better local oscillator than the 6BH6 -- higher 
transconductance (14,000 vs. 4600) means less coupling needed 
between tube and tank circuit which means the tank has relatively 
better control over the frequency.   The price is greater heater power 
... probably worth it since the layout allows keeping the heat pretty 
well away from the tank.

W6TC certainly knew his practical theory:  using a pentode ECO not 
only gives you some isolation from the mixer but there's a lot of 2nd 
harmonic output and that's used in the HBR-series (as in similar 
commercial designs of the time) to get injection for the higher bands. 
It is a potential source of 'spurs' on 80-40 where the fundamental is 
used but with high-Q front end coils that should be a tolerable 
problem.

Pictures -- captions follow each address:

http://www.collie-rescuers.com/ebay/cistern3.jpg

A first-rate workshop helps with these projects.  

http://www.collie-rescuers.com/ebay/hb1.jpg

Chassis, panel, liberated 6-9.1 Mcs command receiver tuning cap.

http://www.collie-rescuers.com/ebay/1stptst.jpg
http://www.collie-rescuers.com/ebay/1stptsb.jpg

Top and bottom views after 1st installation of parts -- +130 V, -160 V 
power supplies and filament transformers.   The negative voltage is 
needed for the AGC circuit.   Top view -- that's the output transformer 
between the two audio stages.   Other 'iron' L to R:  12VAC 1.2A 
xfmr, filter choke, 6.3-0-6.3 1.2A xfmr,  home made (primary x 
primary) 120VAC xfmr for plate supply.  Black objects in bottom view 
are filter caps.   The odd-shape socket (6U8 1st AF/phase splitter)  
is a Western Electric unit with three tie points mounted on each of 
two projections hanging off the sides -- very convenient when there 
are a bunch of parts to mount.   A flea market find ...

Audio stages next.   I have been working about 5 hours a day so this 
might indeed be a 1 week project if one could go at it dawn to 
bedtime.    

Walt 
KJ4KV