[Drake] Drake 2B modifications

[windy10605 at juno.com]

This is still a fluid design but here are some Drake 2B items implemented
and being considered:

1) Add a .005ufd cap from pin 2 of V6 to pin 6 of V7. This comes from
K5LN, increases the BFO drive level in the AM (diode) detector mode.
Allows better copy of CW and SSB in the "diode" position which works well
with the NL circuit. Also there is no signal level change between Prod
Det and Diode Detector. You still use the Product Detector for SSB
reception. 
2) Add a .01ufd cap across R2. Gives the RF amp a little more gain.
3) Replace the 6U8 with a 6EA8. Provides a better HF oscillator for those
40 year old "tired crystals".
4) Replace the 6BZ6 RF amp with a 6GM6 (direct substitution). Is supposed
to give better S/N ratio due to higher Gm (but really GOOD 6BZ6 works
too). Needs measurements to confirm.
5) Move C71 to across R40, not across the output of the Audio Output
Transformer. I never understood why the cap was across the output. More
audio, better lows.
6) K6JEK is evaluating several other audio changes and making THD
measurements. Data from Jon later.  
7) The W7ZFB audio modification distributed earlier which improves and
greatly increases audio output (maybe a little too much). Need
measurements to see actual results ...but "it sounds good".
8) Add a .001ufd bypass cap to ground pin 6 of V9 (normal screen bypass).
 
9) Raise the "Q" of L1-L4. Just received some coil forms to try.

These changes are all reversible, some very easily reversible, and I'd be
interested in any more suggestions and what you experience with your
Drake 2B. 

73 Kees K5BCQ