[rfeenstra]

That is the plan. The size was much larger than anticipated compared to the radios ive worked on but testing each section revealed a lot of consistency from cap to cap and there is a big block of them. Since there is no field coil to ac t as a choke, maybe they compensated with capacitance. I'm sure I could reduce a bit to lower the startup load on the 80 and still be hum free.

[Radioroslyn]

What causes the start up load is C1. Originally it was probably a rather small value perhaps 2mf or so. Max size for the 80 tube's specs is 40mf so the 2mf is well below this rating. If you have hum issues w/2mf in as C1 you can increase the value of C2 and C3 if needed. Between these 3 caps is where the filtering is taking place the others down the line are there to bypass any signal from being distributed thru the high volt circuits. Would recommend a mylar cap for C1.
GL

[rfeenstra]

Thanks all!

[Arran]

With regard to the speaker hardware, you could try what they used on RCA/G.E speakers from 1930-33, which had a series of socket head (hex) machine screws with nuts and lock washers on the other side, around the perimeter of the basket. The combination screws don't look too bad, but straight out Phillips ones are just too modern, but what would be even worse are those cap screws that require an Allen key, those are mostly used on modern bicycle parts and some aftermarket car parts.
Regards
Arran

[rfeenstra]

Power supply finished.  Had to have a way to mount the caps in the can so I built the terminal board using the terminals taken off from the old caps.  This was wired up, secured in the can and covered with the original wax.  Solder connections on the reisitors may look questionable but are as the original and are secure.  The exposed copper was so badly oxisidixed that solder would not flow.  A couple of the connections I had to file down to clean copper and flow solder there since the original wiring had so little solder contact area. Now to start the radio itself.  Don't know yet how much pot metal I'll run into but hopefully not too bad.

           

[rfeenstra]

things can never be simple!  another audio transformer with open secondary.  this one uses 40 guage wire for the secondary and there is probably close to 8000' to wind! the primary is about 500 ohms and the secondary should be 8000 ohms.  That's based on the other transformer which I believe is the same.

[Radioroslyn]

If the iron core is 1/2" AES has pre wound bobbins that can be fitted to the old core. They are 1:3 ratio.

[rfeenstra]

Thanks.  I'll look at it.  I suspect that my ratio is a bit different, though.  It may not be critical enough to care.  I just want the radio to work.  I won't be using it seriously.

[Phlogiston]

Is there a picture of your audio trans? What is the core size?

[rfeenstra]

I just measured the core and it's 13/16".  A little big for the AES unit.  To keep it looking reasonably original, I would prefer not replacing the TR. Do you have another suggestion or do I re-wind?  it shouldn't be too dificult to re-wind - just a lot of layers of 40 guage!

[rfeenstra]

Photos:

               

[Phlogiston]

The .75 (3/4") might work. You could remove and or file a few of the laminations.

http://www.arbeiii.com/Transformers/

[EdHolland]

I am really enjoying this thread, and admire the attention to detail, and the chance to peek under the covers at something of this vintage and understand the challenges it presents.

It is interesting to see that the transformers used round coil formers. It seems to have many, many layers!

If I might ask, are the laminations separate E and I forms, or are they one piece with a break in the center to allow assembly of the bobbin? I can't quite make it out from the pictures.

Best of luck with the restoration

Ed

[rfeenstra]

The laminations are 1 piece with the cut right at the end of the center pole.  You can just make it out where the rust is.  It appears that, when they wound the TR, they did not use varnish or shellac to set the windings in place.  They are loose on the paper.  I can push them side to side.  This would make it easy to unwind if I go that route.  The 3/4" core unit may be a possibility rather than rewinding but I would have to file down the laminations to make it fit.  Right now, I'm leaning toward a re-wind.  I have the wire on order.  It should be easy to put the old, round bobbin on my rewind rig and count the windings as they come off with the electrically actuated counter on the unit.  The no fun part is getting the wire wound with out crossovers and laying paper between every layer.  As per Ed's advice, I use shellac to secure each layer's windings in place before I start the next layer.  My initial measurements and calculations point to nearly 50 layers!  The primary is on the inside and measures fine so I can hopefully leave it alone.

[rfeenstra]

Well Russ, It looks like I'll have to do what you did with the linkage arms.  while mine are solid with no signs of breaking up, the threads for the setscrews are mostly stripped out.  this radio was worked on previously and the shafts jimmied up a bit to hold without the set screw.  One was completely missing. I suppose I could drill and tap but I'm afraid the pot metal won't hold up.  Plus, the thickness of the casting is only thick enough to get maybe 3 or 4  threads engaged.  Hopefully I can improve a bit on the original design.  As you pointed out on your Grebe, precision here is paramount for smooth operation of the 4 tuning caps.  It's an interesting setup.

What did you use as the foundation of your new linkage?  it looks like you may have used an L bracket that you bent and drilled. I'm picturing a piece of strap that I would bend and put the setscrew on the end instead of the side.