EH Scott Radio Enthusiasts

The Fine Things are Always Hand Made

Good morning everyone,

           This is my first time posting so please forgive me if I mess something up. I have recently purchased the radio stated in the subject line above and please see the attached pictures. Single tuner, Serial M-99, single speaker, and AVC with the Wunderlich tube. Before powering up the radio on a dim bulb tester, I notice the 80 rectifier tube was in one of the 45s' socket and the 45 was in the 80 socket. I decided I better start checking underneath the power supply before applying power. I noticed filter caps have been changed out in the past and some soldering on wires in different locations. I pulled the tubes out in the power supply and began tracing wiring and taking resistance measurements. The biggest GOTCHA so far is what I understand to be the audio interstage transformer. Please correct me if this is not the correct terminology. My Fluke meter shows an open circuit on all connections. I have never seen a transformer open like this. Anyway, I need a replacement. Performing research by looking at the grid and plate characteristics of the 45 and 56 tubes. I believe this transformer from Antique Electronic Supply could possibly work.

 https://www.tubesandmore.com/products/transformer-audio-interstage-...

P-T156

Any advice will be greatly appreciated letting me know if this part would work or I'm totally out in left field. I'm in and out of the house today so it may take time for me to respond. 

Thanks!

Views: 1376

Attachments:

Reply to This

Replies to This Discussion

Good evening everyone and happy holidays!   The grid caps on every tube that had a grid cap was broke off plus the grid cap wires inside the IF cans were cut. EACH ONE! Why, I do not know. I will attempt to make an electrical contact with any remaining wire sticking out of each tube in order to test each one to see if they are good. If they are good, I will attempt to solder each grid cap back on each good tube. I have performed this operation before with success. I plan to replace the cut IF wires that travel through each IF can and the replacements will be the same length as the original and maybe shorter. Is yellow cloth covered wire the correct color?  Please see the attached photos of the cuts wires. I have also attached a picture of a capacitor to verify its value. It looks like a .025uf at 400volt. Does this look correct? Thanks for the help.

Attachments:

FYI - the way I remove the rear IF covers is to unsolder the braided cable covering from the can at the eyelet and also unsolder the grid cap. Then the grid wire with braided covering will feed into the can. To rethread later, may need to temp solder fine wire to the end to start re-threading the wire through the eyelet hole in the corner.

Yes - .025 mfd @ 400 Volts for each IF . As per a Scott factory Wunderlich version Deluxe diagram I have.

Diagram shows the AF choke inductor in the B+ line to the 1st audio 56 tube, with a part # 2496 but no values. A parts chassis is your best hope.

opps - should have read .  ... eyelet hole in the cover.

Good morning David,

          That is great information on the re-threading of the wire and I will give that a try. I hope to reuse the steel braid that is covering the wire and your re-threading method could possibly help get the wire through the steel braid. Thank you on the verification of the capacitor value. I have been in touch with Kent and when he has time, he plans to see if he has an AF choke in his inventory. I keep searching eBay for a parts chassis and the current going price for a chassis seems a little high. I may be out of touch on a fair price for a parts chassis but will continue to look for a better deal than what I'm seeing now. The color of the IF wire is faded and I want to go back with the correct color (cloth covered) wire. Is yellow the correct color?

AS for wire cloth insulation, use your judgement based on what you find in yours.

My late production AW-12 AVC, all grid cap wire insulation was black including those with wire braid covering.

Keep in mind, Scott was a low production Custom Set builder. So materials were probably ordered periodically during a model run and may be inconsistent as to sources and details like insulation color in the early 1930's. Indeed sets evolved during a model run of a year or two, so Scott likely avoided over stocking parts and materials. 

Lastly, in watching for a parts AW-12, be careful. I have a diagram from the early 1932 production AW-12 single dial before the Dec 1932 AVC- Wunderlick and tube lineup upgrade, and it shows no inductor in the audio section of the receiver. FYI - photos would look the same but that the early version used 24A's instead of 58's in the IF stages and the 2nd detector is a 56.

That transformer you point to is the phase inverter.  If Kent doesn't have one, I would be perfectly comfortable trying that one from AES. 

Of course, I clicked on this not realizing that there were 2 pages of replies before this one, LOL....Glad you got the phase inverter transformer and all is well there. 

Scott Seickel said:

That transformer you point to is the phase inverter.  If Kent doesn't have one, I would be perfectly comfortable trying that one from AES. 

Good evening David,

       Thank you for the prompt response. Yes,  I will use my best judgment on the color of the IF wiring. I like to keep everything as original as possible and for the most part it seems just about anything goes when they manufactured these units. I will be careful on the purchase of a donor unit. In case I find a donor chassis, I could possibly have the seller remove the chrome can to verify if an inductor exist in case. Thanks again for all your help.

Good evening Scott,

         I appreciate the information you provided. There is a member of this website who has graciously provided the part that I needed. It is installed and ready to go. LOL! One step at a time.

All - So there is a large choke that feeds the B+ to the plate of the 1st AF 56. In the Scott diagram , it is marked 2496. However, the three units I have here are all marked 1796 (one is marked 1796E). However - 3 of the 4 units I have here are open or already replaced. Out of four AW12D sets here, only one has this plate choke original. I am hoping to find time to put this on a bridge to read the inductance accurately. The DC resistance is just shy of 11k ohms  - about 10800 on my most sensitive meter. If anyone has any other info on this particular part, please add to the thread. If I get a good reading of the inductance, at least we will know what can be used as a replacement. 

Kent

Good morning Kent,

           Thank you for going the extra mile to research this part. There was a patent number on the side of the inductor. I ran the patent number on the gov. website and the patent only covered the housing or shell of the inductor and not what was inside. I plan to draw out this circuit and research on the web for more information. Thanks again.

Lance -

I have ordered a Hammond P-T156C choke from Antique Electronic Supply. I'm going to test this in one of my 12s - the DC resistance is a bit less than the original, but should be close to the inductance needed. I'll let you know how the testing turns out once I get a unit here to try.

Kent

Good morning Kent. All this morning I have been researching the circuit attempting to understand the use of the choke. The information you provided above sounds dead accurate to what I have learned from the net. Out of curiosity, did you take into consideration the characteristics of the 56 before picking the Hammond P-T156C?

Reply to Discussion

RSS

© 2021   Created by Kent King.   Powered by

Badges  |  Report an Issue  |  Terms of Service