Allwave 15 Voltage

[Doug Faubion]

I am Working on an  ALLWAVE 15 S/N f-303 and I could use a tube voltage chart ie the voltage on each pin of all of the tubes in the set. I do not have the speaker for the radio and had to make a resistor box to lower the voltage that the field coil would have done. The AM band works but the SW is very week.

[Doug Faubion]

The third tube back is a 55, no number in the socket and no red dot anyplace, does not appear to have any rework on the bottom of the set in that area.  Hope this helps.

[Doug Faubion]

I am looking at the Allwave 15 schematic trying to see how the BFO works, I have B+ on the tube with the button in    and a sign wave on the output, moving the trimmer on the back has no effect.  What frequency should I be looking for on the plate of the BFO tube, How does it get coupled to the IF strip if that is where it goes?  Any ideas.   

[Kent King]

For all our members...Doug's question prompted me to compare AW15 diagrams. The diagram for the 55 detector is missing a connection from the BFO to the last IF. This connection is shown in the Wunderlich diagrams....take a moment to compare them and you'll see the missing connection. When I get a chance, I'll try to correct the 55 diagram.

Kent

[David C. Poland]

Doug - if the 2nd detector tube socket has no number, then it was originally a Wunderlick tube set and has been modified. Perhaps in the field by someone. Or, Wunderlick sets could be returned to Scott for a conversion to use a 55 tube as 2nd detector and also change the 1st detector/mixer 58 or 57 tube to a 2A7.   The conversion involves a couple circuit changes and drillling a hole for a wire to the 55's grid cap. A Scott diagram has been found for the changes to use a 55 tube.

FYI - The Wunderlick tube is the pioneer AVC tube introduced in 1932. Manufactured by Arcturus using cobalt blue glass and a dark red Bakelite base - six pins, no grid cap, 2.5 volt filament and 2 control grids.  (There is also a 6 volt version that seems never to have found favor in radio production) The Wunderlick tube is used with a final IF transformer having a center tap on the secondary winding. The 2 ends of the secondary connect to the 2 tube grids. The 2 tube grids are co-planar (interlaced). The tube performs as a full wave detector and the tube also acts as an audio amplifier. The IF transformer center tap feeds the AVC circuit.  

Scott began using the Wunderlick tube December 1932 with the later version 12 tube "Allwave Deluxe with AVC".  The first version the model Fifteen introduced Feb 1934 continued to use the Wunderlick tube for several months before a design change to use the 55 tube and which time the additional 2 red shortwave antenna posts were dropped. Accordingly, you may find it helpful to refer to the several model 15 diagrams as you restore your example.

[Doug Faubion]

Thanks so much for the Information,  I will do some poking around to look for some solder work in that area.

[David C. Poland]

One hint is to inspect the hole for the 55 tube grid cap wire. Three version 55 type chassis I have inspected have a little brass sleeve around the hole to protect the 55 tube grid cap wire. The couple early converted examples I have seen just have the hole without any sleeve. 

I have not traced out my converted AW-15, but I would expect to find the  4th IF transformer has a center tap now disconnected. And that the tube socket lugs show later work to strap together the socket lugs 3 and 4 (for the diode plates of the 55 tube). 

[Doug Faubion]

On further inspection the tube socket might have a red center button but not too red.  It looks like a different shade of brown but not the same shade as the other sockets in the set, so one might call it red but looks different shade of brown to me, kind depends which flashlight I am using.  The grid cap hold does not have an eyelet or sleeve in it , just a hole.  There is one (not used) connection in side the 4 th IF can, (looks like the wire was cut off)  Pins 3 and 4 have a Light green jumper to tie then together.  Could this mod have something to do with my BFO not working. 

[David C. Poland]

The dark red, at least a red cast (not bright red). center button of that socket does indicate it was built as a Wunderlick 2nd detector set. There are 2 diragrams found (3 for the later 55 sets). 

Several versions of the Wunderlick sets have been found. All have the additional red  pair of antenna posts and a rear toggle switch to switch between antennas. A comparisons among some collectors a few years ago found these variations:

1) 57 1st detector/mixer, 5 position sensitivity, rear tone control.

2) 58 1st detector,mixer, 5 position sensitivity, rear tone control. (Escutcheon may say static instead of sensitivity).

3) 58 1st detector/mixer, continuous variable sensitivity switch, no rear tone control, additional outboard toggle static switch. 

Scott Fifteens  are noted for continuous evolution so other variations may be found. And some radios have been reassembled scrambling escutcheons. Referring to more than one diagram may be beneficial.

Factory converted sets - Wunderlick to 55 2st detector but still the unmarked tube socket, & 2A7 1st detector/mixer per Scott document found. But there may be others with just the 55 tube change. I have a Wunderlick Fifteen recently acquired having a 55 tube with grid cap wire running to and wrapped around one of the tube diode pins - haven't checked out this radio yet. 

The later production run sets built with the 55 2nd detector have the tube socket so marked, only one antenna post, no antenna toggle switch on the back, a tone control on the back and 3 position sensitivity control on the front. This later series initially used a 58 1st detector/mixer then later a 2A7. And earlier a 5 position sensitivity then later a variable control. I have a late example where the tone control on the back is a 5 step control affecting both bass and treble.

[Doug Faubion]

My radio has a 3 position static switch (sensitivity) on the front and 4 antenna post and a toggle switch on the back under the antenna post.  It has a 2A7 mixer.

 

[David C. Poland]

The 2A7 tube says factory update to me. Sets returned to Scott get returned with 2 inch brown paper packing tape wrapped around the receiver front right electrolytic cap.

Does the socket now say 2A7 and if so, show signs of later solder work?

[Doug Faubion]

It has 2A7 on the socket and shows signs of rework but no tape on the cap.

[Kent King]

Doug's questions about the BFO lead to some interesting results...see the attached file.