Scott AW 15 Finicky Oscillator

[Michael J Boessen]

Hi, All:

I've been working on a Scott AW 15, with a lot of help from folks here, and I really appreciate it!!

I have the cabinet looking awesome, most of the chrome polished up, and everything working right up to the High band, and there I am stuck. 

Based on a suggestion here, I ordered 3 NOS 56 tubes of 3 different brands: a Tung Sol, an RCA, and a NU.   I also have an Arcturus that tests about 70%.  I'm not concerned about the blue band.  The RCA seems to do the best across all of the other three bands.  Good sensitivity on white and red, and works on the green band  from 22 MHZ down to 13 MHZ.  I've been 3 days, on and off trying to get this band to work.  I have tinkered with the values of the resistor and capacitor on the grid of the oscillator.  I put on the 2 .05 caps on the filaments as someone here suggested and cut the cathode ground wire as short as I can make it, about 1 1/2 inch.  I have even tried tinkering with the lead dress, but have not had any success with that and have everything back to as original.  I have even tried 3 different 2A7 mixer tubes.

I am stumped.  Other than fooling with the windings on the oscillator coil of the band switch wheel, I don't see what else I can do.  If I were missing the high end of the band I wouldn't worry about it.  Nothing above 18, usually anyhow, but 10 to 13 mhz is pretty busy.

I can't imagine what anyone can suggest to fix this, but would sure appreciate any suggestions.  

Best

Mike

[David C. Poland]

The AW-15 was designed to use 2A3's. Note - the tube sockets have the tube numbers embossed.

The prior 12 tube models used type 45 output tubes. 

The amp circuit design, output transformer and speaker voice coils were specific to the intended output tube pair.