Magnatone Troubadour 113 Output Transformer Repair/Replacement

[FPALB]

A 113 came in with a damaged output transformer (see pictures) primaries measured (with a Fluke DMM) 400k on one side and 500ohms on the other - both to C.T.. Once I dissembled the OT, cleaned up the burns, and found the lead now both sides measure around 500ohms to CT. To my knowledge a push-pull 6v6 transformer should have around an 8k to C.T. primary side - my question: this 500ohm to C.T. im measuring from the 113 isn't normal is it? Want to find if this is repairable or if I should replace it with a clone or with a hammond 1750E ( link also below), which is a 15W 8500 C.T. Princeton output transformer and what I feel like is a bit more standard for this type of amp.

The clone is pricey from Mercury Magnetics, but im unsure if the hammond would work at all!

Only schematic I could find is for the 213 troubadour which has a stage that includes the Magnatone varistors. - the 113 does not have this stage.

https://www.hammfg.com/part/1750E

THanks!

 

[fazer]

Your measurements are dc resistance you quote. 8k is the primary impedance. It’s turns ratio derived from knowing impedance (not DC resistance) of the secondary. Search testing an output transformer on internet. Plenty of articles.

 

[Rusan]

On that type of transformer, you'll see anywhere from about 300 to 500 ohms from the CT to the ends, but they'll never share two precisely identical ohms readings because of the way the primary is wound. As fazer said, what you want is the reflected secondary-to-primary impedance, not the DC resistance. Here's a good, well-written resource explaining it.

Personally, I'm not a fan of Mercury OPTs and would only use one here if no other option existed. If there's not a Hammond cross-reference and the repair time isn't critical, I'd call Heyboer with the physical dimensions and desired leadout colors, and have them build one. CJ is the resident expert on guitar amp iron; maybe he'll chime in here with a better solution.

 

[FPALB]

Thanks for letting me know about measuring and calculating correctly.

Sent in 5V on the primary got .160V on the secondary
Turns Ratio: 5/.160=31.25
Impedance ratio = Turns ratio squared = 961
Load impedance x transformer impedance = 8 x 961 = 7688
and there is our 8k.

thanks folks.

In this case it seems like when I cleaned up the transformer's burns the measurement also cleaned up - would I be safe to re install and try it out again? Ive already added a new lead, dressed the outside and re coated in polyurethane.

The hammond 1750E is 8500 ohm impedance is that close enough?