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Output Transformers

11/7/2005 10:50 PM
Justin Output Transformers
I recently aquired a 1947 Fender Dual Professional  
amplifier. It is missing both output transformers.  
Would anyone know for sure what I could use to  
replace them with? It uses two metal 6l6 output  
tubes and very light weight 10 inch speakers.  
Thank You,  
11/8/2005 12:40 AM
mark h

To further clarify. You say output transformers. Were there two? Were they mounted to the speakers and not the chassis originaly? You say the speakers are light weight so they must not be field coil type.  
I guess I would measure the resistance of the speakers and determine the nominal impedence (likely 4 or 8 ohms each driver) if the combined load is 4 ohms, a new manufacture pro, bandmaster or tremolux ot should be about right. If you want to use one ot per speaker and mount on the speakers, maybe two tweed deluxe or two princeton ot's might be the ticket. Good luck. Nice amp...M
11/8/2005 2:10 PM
I'm Sorry,Mark,  
Yes, it appears that each speaker had a output  
transformer on it. There are six wires hanging down from the chassis. The speakers seem to be 4 ohm.  
Thank You,  
11/8/2005 11:26 PM
mark h

My best guess is that each output transformer gets three wires from the chassis. Two out of each set of three would come from pin 3 on each 6l6 output tube and go to opposit ends of the ot primary (often blue and brown).The third would go to the ot center tap (red wire), comming from pin 8 of the rectifier tube (B+). The secondary of each ot (2 wires) would go to the speaker + and - terminals. You might have to play around with the blue and brown connections to get the phasing correct.  
As far as matching impedance, I guess I might try to use two tremolux type ot's, one at each speaker. Something similar but smaller in size might be better though.  
The above advice seems logical to me but I wouldn't swear by it. Maybe someone else out there can concur or revise this post. Good luck...M
11/9/2005 9:19 AM
Chris/CMW amps

Hi Justin  
Cool purchase! There are some pictures from the old Dual prof. in a Fender amp book, also showing the speakers and OTs.  
Try contacting Paul at , maybe they do have some replica OTs for your amp.  
11/23/2005 2:09 AM
Thank You for the help.  
I found someone here in Colorado Springs that can help me. He has a full time music electronics repair business but is always willing to help out the do it yourselfer. No one in town like him.  
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