AW-15 Oscillator Circuit Question

[Joseph W Strickland]

In the All-Wave 15 oscillator circuit there is one coil identified as part no. 135-30. In that coil assembly there is one capacitor that I believe is a 1200mmFd or 1700mmFd. The copy is so poor that I cannot make it out. Could someone who has one identify that capacitor for me?

Thanks in advance.

Joe

[mike hadley]

Hi Joe, here is some more images, I can't send the pdf,

You are right about scott radio's, I had my allwave working, with it's cutting out problem before I started on the restoration,

the selectivity is second to none, no noticeable bleed between stations incredible for a 1930's design,

Mike

[Joseph W Strickland]

Mike;

Successful file transfers are completed. Thanks for these extra items.

Joe

[Joseph W Strickland]

Mike;

I have the redrawing of the All-Wave 15 with Wunderlich tube almost complete. There are a few items I need help on.

1) There is a 600 ohm control shown just below the antenna input circuitry. What is its function? Is it a sensitivity control?

2) The RF Interstage transformer and the IF transformers have a coupling capacitor from the plate of the preceding tube to a tap on the secondary of the transformer. I believe Scott used a .5MF capacitor for that but am unsure. It is certain that they would have to use a coupling capacitor, otherwise it would be applying B+ to the signal grid of the following tube. A .5MF capacitor is tremendous overkill for that application. Even a .01 or .001MF would probably be OK there.

3) There is a plate load resistor shown for the #56 1st Audio Amp. stage, but no value in indicated. I need its value.

4) There is a common cathode resistor for the two #56 Push-Pull Drivers, but its value is not legible.

5) There is a 750 ohm control that is ganged to the volume control. What is its function?

Thanks in advance.

Joe

[mike hadley]

Hi Joe

I have attached a couple of schematics that I have, my chassis is early and does not have the two preset controls shown on the illustration as 95 and 96, the 600 ohm control appears to adjust the bias on the screen grid of the if stages, is this an attempt at variable controlling local distant reception?

according to the late chassis diagram the plate resistor on the 1st audio is 50k

the common cathode resistor is 2k, the 750 ohm ganged control in my chassis appears to be the 600 ohm control mentioned previously,

I hope that the data will help clear things up a little,

Mike

[Joseph W Strickland]

Mike;

OK, I have them both. I may be able to make better sense from the extra information now.

Joe

[Joseph W Strickland]

Mike;

Wow! There is a lot of information contained in these two drawings! There is much to absorb. I believe you are correct in your assessment of the use of the variable 600 ohm control shown under the antenna input circuitry. It appears to be varying the screen grid voltage of the 1st and 2nd IF amplifiers, while the 3rd IF amplifier is left at a fixed gain (at least as far as the screen grid voltage is concerned). I now see that Scott used color codes for the different wavelength bands. As different bands are chosen other resistor values are added to the sensitivity control to change the gain adjustment range needed for the band selected. The Wunderlich chassis appears to have AVC/AGC being fed back to the IF and RF stages as do the later versions too. I will identify the AVC/AGC buss when I do the final version of the redrawn schematic.

Scott did not show a value for the capacitance coupling of the IF transformers. It was likely just some resulting capacitance from the over-laying of windings and while shown, was not measured, so I can remove the value I showed. I thought I had seen such a value, but it was likely just an illegible blob of ink from a poor scan. It is probably a good idea to add a note explaining that aspect of the design.

It is interesting that the April 10, 1934 drawing had B+ going to the plate of the 1st Audio Amp. through a 50K ohm resistor and the primary of the inter-stage transformer is DC blocked at the terminal that would normally be connected to B+. This was probably done in order to provide some degree of protection for the primary winding. Many of these inter-stage transformers used very fine wire, which was easy to damage if a tube shorted or corrosion developed from exposure to moisture, time and temperature cycling of the radio. These transformers have a history of going bad from those issues in all sorts of brands.

It is interesting to see that the later schematic has added component designations for all the parts. It shows the progress being made in the development of schematic standards by the Radio Manufacturers Association. This may also help me associate the parts from the parts lists you sent to specific components on the schematic.

More later.

Joe