[HBR] Cost Of Homebrewing?

[hbr@mailman.qth.net]

Jim, this was mostly written before your recent post.  

I said:

>> Ask yourself this:  with W6TC's excellent work all over QST,
>> why didn't it make to our handbook?   
<Stuff snipped>
>> Why was it not *improved* in the ARRL lab and published in the 
>> handbook?   

Jim answered ... 
> That's what the DCS-500 was.  

Thank you.  When I look at it with the proper squint, I can see that 
the DCS-500 is indeed HBR knock-off -- basically, an HBR-11 done 
with 10 tubes.   However the only improvements I can find are in the 
IF section: 4.5 Mcs half-lattice crystal filters replacing the 1600 kcs 
first IFTs and adjustable selectivity via coupling variation between 
pairs of 50 kcs IFTs.   They did provide a transistorized 100 kcs 
calibrator in place of the 3.5 Mcs marker.  And the RF stage is a 
6BA6 -- a better choice than the (sharp cutoff) pentode section of a 
6AZ8 as used in the HBR-11.

They deleted the 6BY6 product detector of the HBR-11 in favor of a 
diode -- a definite step backward -- and replaced the 6BJ6 IFs with 
6BA6's.  Otherwise the tubes are pretty much the same types as the 
HBR-11. 

The 2nd detector isn't the only weakness.  The BFO is coupled 
directly from the oscillator cathode -- unless you keep the signals 
very small at the 2nd detector, you're going to have distortion caused 
by BFO pulling.

They used a truly crummy tuning cap -- a National HFD-30-X.  Boy 
the thing must have been a joy to tune.   There's not that much 
backlash in the sleeve bearings -- the rear is a friction finger type -- 
but the torque is pretty high.   And pinch/planetary dials don't 'do' 
torque.   

The 1st oscillator is the triode half of the 6U8 1st mixer, with no 
buffer.   Only the HBR-11 had that configuration -- the others of the 
series used a 6BH6 ECO.

And they kept the worst feature of the HBR-series.  Having worked 
for a few weeks with a receiver with a tuning rate of  28 kcs/knob 
revolution (the 1MHBR) I have a very hard time picturing the use of a 
National ACN/ICN/SCN dial -- 2.5 revolutions to cover 500 kcs = 200 
kcs/revolution ... is it even *possible* to tune in an SSB signal on 
such a receiver?   That's double the tuning rate of a 3-6 Mcs 
command receiver, for goshsakes.  The only thing that can be said 
for those dials is that compared to other new-purchase dials they 
were pretty cheap in 1960. 

"Improved in the ARRL lab and published in the handbook"?   Only 
the latter, I'm afraid.   Overall, the DCS-500 isn't as good a design as 
the HBR-series.

Walt
KJ4KV