[HBR] HBR-11/2000. Comments?

[N2EY at aol.com]

I don't know if I replied to this or not!

Please excuse the delay and possible redundancy.

In a message dated 7/16/06 10:11:37 PM Eastern Daylight Time, Tuchueh7 at cs.com 
writes:

> I especially like the idea of doing the power 
> supply and audio amp on a separate chassis. This sounds like a good place to 
> 
> start.

It's worked for me...

> 1) Speaking of the amp, I am thinking of LC audio bandpass filters at the 
> input, outside of the feedback loop. I like to think of the effect of 
> negative 
> feedback as not really widening bandwidth but rather equalizing gain at all 
> frequencies. Plus you can use the feedback to shape response if you pay 
> careful 
> attention to phase margin.

All kinds of possibilities without using up lots of space in the rx nor 
making lots of heat.

> 2) Devil 6EH7. I notice that W6TC used the 6BJ6 in his IF. Tube manual 
> shows 
> this
> bottle has low Gm than 6BA6. Do you suppose he chose this on the basis of 
> stability
> and ease of application? 

Lots of reasons:

By the time the signal reaches the second IF, there's not much need for low 
noise or enormous gM. What's the point of using a hotshot tube if it never runs 
anywhere near flat out?

There *is* a need for low Cgp and an unfussy circuit.

W6TC was designing a receiver that could be duplicated easily. The HBRs are 
about as unfussy a design as could be done in their time while still meeting 
all the design and performance requirements.

The 6BJ6 uses much less heater and B+ power than the 6EH7. Less heat and less 
power supply.

The 6EH7 may not have even existed when the HBRs were designed. If it did, it 
was a premium tube made by one or two manufacturers, and not to be found in 
surplus or the junkbox. The 6BJ6 was everywhere.

His design distributes gain more evenly amongst all 
> 
> stages than my proposed line-up. I am still playing around with the little 
> 6EH7 breadboard
> (included a picture of same). Right now I am going to try the following to 
> tame it
> a. Resistive loading of input IF tran. and output IF tran.

This isn't good for selectivity.

 If no result then 
> 
> add:
> b. Grid damper resistor. If no result then add: If no result then add:
> c. Reduce gain with increased negative bias: 

Which means running a hotshot tube way below full throttle.

If no result then add:
> 
> c. Screen damper (resistor or choke) If no result then add:
> d. Plate to bottom of input IF tran. capacitive neutralization:
> 3) See attached pictures of tuning caps:
> #1. This is an interesting piece with the stator split (cant see from 
> picture)
> It also has some curious piston trimmers across the stator. Finally, each
> rotor section is insulated and and has no electrical connection.

Avoids ground loops.


> #2. This piece is fairly straightforward 12-108 mmf nice silver plate. Can 
> be 
> 
> padded down to correct value and has advantage of being able to pad out a 
> lot of stray capacitance.
> #3. Not pictured. I have three pieces of GenRad 10-130 mmf. These will 
> require 
> some metal work to gang. they are very nice parts.
> 
> Mucho gracias, amigo.... I really appreciate your consultation!!!! Barney 
> 
> PS The attached pictures were rejected by QTH.com so email me direct if you 
> want
> to see 'em.
> 
> PPS Today I fooled around with the test chassis and found that I could tame 
> the 6EH7 somewhat by loading the IF transformers with resistance (390K on 
> the 
> input and 68k on the plate side. Also reduced the cathode bypass from .1mf 
> to 
> .001mf.
> Now I can peak the IFs without oscillation. There is still some regeneration 
> 
> I think;
> nose selectivity is about 750 cycles and voltage gain for the 6AR8  and 6EH7 
> 
> is about
> 60 dB. 

That's regenerative all right!

73 de Jim, N2EY



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