Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Mar Wed 20, 2019 8:41 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 3 posts ] 
Author Message
 Post subject: Silver Marshall Output Transformer
PostPosted: Feb Sat 09, 2019 7:28 pm 
Member

Joined: Aug Wed 04, 2010 5:40 pm
Posts: 346
Location: Tyngsborough, Massachusetts
Recently I acquired the chassis of a Crosley Model 57 that had been installed in a plain wood box. At some point, likely in its early years, the audio output tube had been changed from a 45 to a 47.

The radio came with a Silver Marshall 231 output transformer that does not look like it is original to the radio. The transformer has three primary connections and is marked on top for the full winding for use with a UX201A, UX112, or UX210, and for half the winding for use with a UX171. I tested the transformer for voltage ratio and got a 4 to 1 ratio on the whole winding and a 2 to 1 ratio for the half winding, indicating impedance ratios of 4 to 1 for the half winding and 16 to 1 for the full winding. The tubes indicated for the full winding have recommended load impedances of 10k to around 13k, and the 71 has a recommended load impedance of 4k to 5k, so it would appear that the transformer is designed to supply a speaker of around 1k impedance.

The only schematic I've found for this radio covers the model 53, 54 and 57, with only the 53 actually drawn, and the changes for the 54 and 57 described in text. The 53 schematic shows a high impedance speaker connected directly to the output tube plate. The text describes an output transformer for the model 57, and how it's connected an that it uses a field coil speaker, but nothing more.

Does anyone know about the speaker that would have been originally installed in this radio?

Jeff


Attachments:
IMG_0020a.jpg
IMG_0020a.jpg [ 138.35 KiB | Viewed 131 times ]
IMG_0021a.jpg
IMG_0021a.jpg [ 117.07 KiB | Viewed 131 times ]
Top
 Profile  
 
 Post subject: Re: Silver Marshall Output Transformer
PostPosted: Feb Sat 09, 2019 11:01 pm 
Member
User avatar

Joined: Sep Thu 14, 2006 3:27 pm
Posts: 11703
Location: Carmel, Indiana
Here's a description that I found in the 1927-1928 "New Radio Buyer's Guide" by the Barawik Co.

231 PUSH-PULL TRANSFORMER
For use in conjunction with No. 230 input push-pull circuits or as an output transformer for, by means of center tapped primary, its impedance may be adjusted to match accurately the plate impedance of the tube used. Wight, 4 lbs., 8 oz. Net........$5.88

_________________
Michael Feldt
www.indianaradios.com


Top
 Profile  
 
 Post subject: Re: Silver Marshall Output Transformer
PostPosted: Feb Sun 10, 2019 3:41 am 
Member

Joined: Aug Wed 04, 2010 5:40 pm
Posts: 346
Location: Tyngsborough, Massachusetts
Michael, Thanks for that information. I hadn't thought of it as a push-pull transformer, but the two sides of the center tap are pretty much the same.

Also, it seemed earlier than the radio, as evidenced by the output tubes it identified.

Jeff


Top
 Profile  
 
Post New Topic Post Reply  [ 3 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests



Search for:
Jump to:  


























Privacy Policy :: Powered by phpBB