Stromberg Carlson Push Pull Output Transformer Solution

[Ralph Spracklin]

Hello All

While I have a long way to go on the restoration of my Model 925 or the Model 1025 (both models the same) 14 Tube Stromberg Carlson Radio-Phono Unit, I did go ahead and check out the power transformer and chassis mounted smoothing choke. Both metered out OK. So then I also went ahead and metered out the very dirty, tar dipped, Push Pull Output Transformer. Things did not go too well, it was/is a dud. This set was originally equipped with a single ten inch, Permanent Magnet Speaker. The speaker itself did not come with the unit.

The output transformer had a three wire primary winding, which is centre-tapped. The secondary consists of just a single two lead output to the single speaker.

My question is this. As this is a Push Pull Setup using the two, 6F6 Power Output Tubes, and, should I have to replace this Transformer, would I be able to wire-in two like single winding primary type, output transformers, in series as to the primaries of the two said transformers. Of course I would use two matching speakers, which I already have, and still receive the same, or close to the same results.

I know this shows my inexperience & my ignorance on this particular subject. Your thoughts please!

Ralph

• This topic was modified 2 years ago by Ralph Spracklin.
• This topic was modified 2 years ago by Ralph Spracklin.

[engineer]

You said:
“would I be able to wire-in two [like?] single winding primary type, output transformers..”
Bad idea, I would not do that. Buy a proper P-P OPT (about 6,000 primary impedance) and rebuild the original circuit. .
Cheers,
Roger

[Ralph Spracklin]

Helo Roger

Push Pull Two O/P Transformers

Roger, much thanks for responding to my query.

After much research, I think I have also come to the conclusion that this is not a great idea. However, your reply leads to another question n regards to my acquiring a proper replacement transformer. Your suggestion was a transformer with a Primary Impedance of about 6000. However data for the 6F6 suggests that for the use of 6F6s in a Push Pull setup the impedance should be around an impedance in the range of 10,000. Any thoughts on this. I don’t want to purchase the wrong transformer.

Regards

Ralph

• This reply was modified 1 year, 12 months ago by Ralph Spracklin.

[John Greenland]

Hey Ralph,
You are correct about the impedance according to the RCA tube manual RC20.
The plat to plate impedance is 10, 000 ohms.
The single ended amplifier impedance is listed as 7000 ohms.

I have attached to page from RC-20

Good luck

BTW there are other alternatives but it will require more mods to the radio.
For example replacing the 6F6’s with 6v6’s !!!!

• This reply was modified 1 year, 12 months ago by John Greenland.
• This reply was modified 1 year, 12 months ago by John Greenland.

Attachments:

1. 

   RC20-1960.pdf
   

2. 

   RCA-RC-20-6F6.pdf
   

[Ralph Spracklin]

Hey John
Yes, you have reinforced my thoughts regarding the required impedance. I feel confident that I am headed in the right direction. Hopefully I can locate a 10000 impedance O/P Transformer that will match up with the 6F6 Tubes. I am also thinking thar as for the speaker itself, the voice coil on that speaker should be 8 ohms??? I have acouple of those, quality speakers, kicking around, As i said on my first post regarding this problem, I am in no particular rush to physically correct this problem as I have much other work to do on this set. In the meantime, if anyone has a good O/P Transformer that was pulled from a a 6F6 Push Pull Set, at a reasonable price, and hopefully close by, (Barrie, ON) please advise.

Regards
Ralph

• This reply was modified 1 year, 12 months ago by Ralph Spracklin.

[John Greenland]

Ralph,

A lot of newer output transformers will have 2 or 3 taps for the speaker, 4 or 8 or even 16 ohms.
You can match just about any speaker or combination of them to these transformers.
Two 4 ohm speakers in series ( phased properly) will be 8 ohms just as in reverse , two 8 ohm speakers in parallel ( again watch the phasing) will be 4 ohms.
Look up a Hammond 1609.

Good luck with the restore.

Regards John G.

[John Greenland]

Ralph,

I meant to include this;

https://www.hammfg.com/electronics/transformers/classic/1608-1650?referer=790

[Ralph Spracklin]

Afternoon John, Lee/All

As you know I am in the market for the output transformer we have been discussing above. I have ran across an Outfit in KItchener, Ontario, that, seems to have what I am loking for at the great price (new in box CTL, B320) for the price of $25.00. They seem to have many transformers, including Hammond. They also have a variety of of Grommets, Felt knob washers, Antenna coils, IF Transformers, Dial glasses and silk screened radio dial scales, a variety of Grill Cloths, as well as Vac Tubes. The site is ” antiqueradiosandparts.com ” also goes under the name Merry Tunes. Has anyone had any dealings with this outfit. Indeed they sem to have a lot of products/items that us restorers would need. Yet they never show up in supplier links. So my question is, Are they reputable???

Ralph

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