[HBR] Anyone tried these tubes?

[hbr@mailman.qth.net]

In a message dated 10/7/03 9:56:31 PM Eastern Daylight Time, 
Bill@LizCurtisHiggs.com writes:


> July 1966 QST where he sings the praises of the 6EH7 and 6EJ7 frame-grid
> pentodes, I have obtained several to play with in the front end of an
> HBR-16. His focus seems to be noise figure and other factors rather than
> cross modulation performance, but he places these little bottles in the same
> ballpark as the legendary 7788. 

I have used the 6EH7 as an RF and IF amplifier in a homebrew transceiver for 
over 10 years. Great tube. No experience with the 6EJ7.

Balogh used the 6EH7 as the RF amp (remote> 
> cutoff) and the 6EJ7 (sharp) as a mixer, claiming good results. One drawback
> is that the tubes are run at about 15-20 ma cathode current,

Not really a problem unless you run them wide open, which is almost never 
done.

 and with some
> 
> degenerative cathode feedback to cut the overall gain down a bit. 

The unbypassed cathode resistor thingy did not work well for me. I had to 
bypass cathode, heater and screen right at the socket to get the stages 
stabilized.


Also not a
> 
> drop-in replacement; the tubes have 9-pin bases to accommodate a pin for the
> internal shield (which may mean you can get away without an external shield
> if the layout is well-spaced).

I needed all the shielding I could get. Tube shield, piece of flashing copper 
across the socket, etc. The 6EH7 is really hot and will take off if all 
precautions are not taken. 

The excellent high Q coils of an HBR make it that much easier for 
oscillations to start..


> 
> Looks like the 6EH7 might be worth trying as an IF amp, as that was its
> original intent (for TV receivers). 

Even better for RF. In the HBR designs there is quite a bit of gain ahead of 
the IF so the improvement may be mild. 

I used multiple bypasses of different sizes on each nonsignal pin to get the 
low Z required for good bypass at all freqs. Small parasitic suppressors also 
helped. Lotta gain, very low noise, hard to overload. Heater current is a lot 
more than a 6BJ6, tho.


I believe either Swan or Drake may have
> 
> used it at one time in some of their IFs.
> 

Drake R4 line used the 6EH7 as RF amp and 6EJ7 as first mixer.



> Anybody tried these tubes? BTW, Antique Electronic Supply has the 6EH7 on
> sale at fifty cents (!) each if anyone wants to give it a try.
> 

A steal at that price!

73 de Jim, N2EY


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