[R-390] final word on audio deck saga (long)

[wli]

Guys:

After much rumination and thought re the many responses to my audio deck *saga*, I had some second thoughts and redid a few things again (!)

(a) restored some negative feedback  
     increased R612 to 330K
(b) removed R612 with a wire bypass
     eliminates positive feedback
(c) took out the 10M resistor
(d) reinstalled a new C609 electrolytic
     restores V601A cathode bypass
(e) kept the wire bypass of R101 
(f) removed R102 so T601 outputs straight to phone jack
(g) added F102 and F103 (this particular unit was originally a one-fuse unit) 
      mounted a small box over the reserved squelch area
      added pin jacks along side so I could check on B+ easily
(h) kept the #14G copper ground bus down the middle, grounded at only one point, no grounds to chassis ground lugs
(i) all new caps and resistors, each checked for value and leakage
(j) new ceramic tube sockets (I had them already so why not?)

So in the end, these changes are minor, and the deck is *almost* stock. 

I know some would object to having the fuses *hidden* on the deck. However, I did not want to take apart the chassis cabling or drill new holes in the rear panel. Anyway, if a B+ fuse blew, one should be prepared to pull the receiver out to discern the cause before replacing the fuse. Wiring up the additional fuses was real easy in that location. I sleep better knowing that B+ is fused.
      
Works swell. Loud audio, excellent speech intelligibility, nice low-fi music (I can't hear anything over 7KC anyway). Stable audio running all day. No squeals.

OK, next was an objective evaluation of noise:

Stuck in the lowest noise tubes that I had
Usual warm-up interval
Best ones for V601, V602, V603, V501 and the other IF amps
Isolated the IF-AF deck from the RF deck
Set the URM to 150µV at 455KC, modulated at 30% at 400cps
Injected IF modulated signal into J513
Looked at dB across the 600 ohm load resistor
Centered the URM frequency on my particular Xtal (mine is 454.698KC)
Reset bandwidth to 2KC
Set AF and RF gains to 10
Set IF gain for -7VDC at the diode load
Saw that my output was now +23dB
Switched the URM back to CW
Changed no other controls (important)
Saw my output dropped to -13dB
The difference is 36 dB (WOW)
Repeat x4
No change
Go to bed and do it all over again the next day
No change
I believe these numbers

Thanks

W. Li
Mercer Island