[HBR] AA2YV Lollygags, HBR Proj Languishes

[Walt Hutchens]

Bill said:
> The recent traffic on the reflector, (re: IF transformers) has set
> my head to thinking. I don't have the 1600 IF's, so will have to
> scrounge or build.

The 1415 kcs IFTs from the 3-6 Mcs 'command set' receivers retune to
1600 kcs just by replacing the internal fixed caps. They're not small,
but they're easy to work on, and you do have plenty of space on that
chassis.

> ... why did Ted feel that an IFA was needed in that one HBR example?
> I'd would have thought it would screw up the gain distribution, why
> so much gain, and why risk overdriving the second mixer?

The gain of the 6BJ6's is significantly lower than most other common
IF tubes: I'm guessing he felt that with a diode detector (meaning a
need for high IF output voltage) more overall gain was needed. In that
case one might think first of putting the added gain at a different
frequency, to simplify construction. But there is the potential to
overload that second mixer. In fact, I'd say that unless the gain
control on the IFs is backed down, the 2nd mixer WILL be overloaded
under common 80 and 40 meter band conditions.

I like to keep the IF output lower and use plate detectors, putting
the gain in a frequency conversion stage to minimize overall feedback
issues, but plate detector part values may have to be tweaked to get
best performance. Designing for absolute maximum ease of construction
he would have chosen the diode/infinite impedance route.

Considering the skill level, parts availability, and economics of the
time, it's darn hard to find anything wrong with these designs.

Walt
KJ4KV