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.

[Lars Edwards]

Finally back on the AW-12!

At a very reasonable price I purchased 2 used 45's that test very close to each other and work very well in the radio.

I have good sensitivity on the BCB now - solved after some tube swapping.  All tubes tested very good but some of the 58's did not do as well as others.

Replaced the mica capacitor in the 1st IF.  This helped some with the alignment but the "peak" on this IF is still very broad - not a sharp peak like the others.

I'm pretty satisfied with where this stands now and I'm looking for some more advice.  The voltage on the plates of the 45 is a little high at ~ 393 volts vs. the 375 stated in the manual.  Also the voltages on the large power resistor are now a little high as well.  Is this anything to be concerned about ?

Does anyone have a circuit diagram of the antenna tuner ?  I think there may be a problem with the internal switch. It is relatively hard to turn and I suspect that it needs to be cleaned. Does anyone know how to open this up or how to get some Deoxit into the switch contacts?

Again, thanks in advance for any advice on these questions.

Lars

[Thomas Day]

Lars Edwards said:

Finally back on the AW-12!

At a very reasonable price I purchased 2 used 45's that test very close to each other and work very well in the radio.

I have good sensitivity on the BCB now - solved after some tube swapping.  All tubes tested very good but some of the 58's did not do as well as others.

Replaced the mica capacitor in the 1st IF.  This helped some with the alignment but the "peak" on this IF is still very broad - not a sharp peak like the others.

I'm pretty satisfied with where this stands now and I'm looking for some more advice.  The voltage on the plates of the 45 is a little high at ~ 393 volts vs. the 375 stated in the manual.  Also the voltages on the large power resistor are now a little high as well.  Is this anything to be concerned about ?

Does anyone have a circuit diagram of the antenna tuner ?  I think there may be a problem with the internal switch. It is relatively hard to turn and I suspect that it needs to be cleaned. Does anyone know how to open this up or how to get some Deoxit into the switch contacts?

Again, thanks in advance for any advice on these questions.

Lars

[Thomas Day]

V

Thomas Day said:

One of these switches came with my Allwave 23. There are 2 nuts on the back that line up with the rivets in the cover. The switch nut may also need to be removed. I have not taken mine apart, since I don’t use it. 

Lars Edwards said:

Finally back on the AW-12!

At a very reasonable price I purchased 2 used 45's that test very close to each other and work very well in the radio.

I have good sensitivity on the BCB now - solved after some tube swapping.  All tubes tested very good but some of the 58's did not do as well as others.

Replaced the mica capacitor in the 1st IF.  This helped some with the alignment but the "peak" on this IF is still very broad - not a sharp peak like the others.

I'm pretty satisfied with where this stands now and I'm looking for some more advice.  The voltage on the plates of the 45 is a little high at ~ 393 volts vs. the 375 stated in the manual.  Also the voltages on the large power resistor are now a little high as well.  Is this anything to be concerned about ?

Does anyone have a circuit diagram of the antenna tuner ?  I think there may be a problem with the internal switch. It is relatively hard to turn and I suspect that it needs to be cleaned. Does anyone know how to open this up or how to get some Deoxit into the switch contacts?

Again, thanks in advance for any advice on these questions.

Lars