[HBR] HBR-11/2000. Comments?

[N2EY at aol.com]

In a message dated 7/23/06 9:21:02 PM Eastern Daylight Time, Tuchueh7 at cs.com 
writes:


> Progress to date 
> on the test chassis (6AR8 mixer-6EH7 if): I was able to stabilize it 
> somewhat 
> by using resistive loading of the input and output transformers, and 
> reducing 
> the cathode bypass cap to .001 (if freq = 530kcs.) Still evidence of 
> regeneration; narrow nose BW and excessive gain. 
> Now I try capacitive bridge neutralization. 2.7 mmf neut. cap. and 1500 mmf 
> cap on the bottom of the input IF trans. gives me a fairly stable IF amp 
> w/out 
> the resisitive loading and normal value of cathode bypass. At this point, 
> trace goes south on the old TEK 454a necessitating some down time to fix it. 
> Looks 
> like neutralization is the ticket!!! 

It strikes me as odd that a single stage of 6EH7 is so hard to stabilize. Two 
stages can be fussy but a single stage was no problem for me when prototyping 
the Type 7. 

One trick was the use of unetched PC board material, with a copper flashing 
shiled across the socket and all bypasses soldered direct to the PC copper.



> Next item on the agenda is the audio amp and B+ supply built on a separate 
> chassis
> from the HBR. I got some nice solid walnut boards to house the amp/B+ 
> chassis 
>and
>a six inch commercial PA speaker. I have found that I need lots of loud 
clean 
>audio
>for hamming around.

Why such a small speaker? If you like audio, why not a 10 or 12 incher, in a 
nice big wood cabinet?

Some time back, in the search for cleaner audio, I went to an all-triode 
audio chain. Power stage is a pushpull 12BH7. Gives me a couple of clean audio 
watts at much less distortion than a single-ended pentode - without negative 
feedback. Power consumption is about the same as the 6AQ5 it replaced, and I have 
a much wider choice of output iron.

73 de Jim, N2EY