Interstage transformer

[ubxf]

I have an old Inca custom interstage transformer that came from a leslie tube amp.
One of the primary and one of the secondary test open . Is there a way to analyze  the good side  to  spec a replacement  transformer ? 

 

[abbey road d enfer]

I have an old Inca custom interstage transformer that came from a leslie tube amp.
One of the primary and one of the secondary test open . Is there a way to analyze  the good side  to  spec a replacement  transformer ?

Since you have one good half-pri and one good half-sec, you can measure them. However measuring is not super easy, as the inductance varies considerably with level and frequency. You should test it as close to possible to the nominal operation. I would suggest you use a generator delivering about 10V at 50 Hz, and use the two complementary measurements shown attached.Only one measurement should be necessary but they should be a tad different; take an average.

 

[ubxf]

Thanks Abbey
I will do the measurement you suggest. I have to find a better generator. I have a Loftech TS-1  but it looks like it generates a maximum of 18dbv so about 8 V  not quite 10 V. Would that be close enough ?

 

[emrr]

Since you've one of each side remaining, as he said, you should get an idea of ratio easily.    I would also think this info might be out there already, being Leslie related.    After ratio, you know it needs to pass the lowest note on an organ successfully, so that's an easy spec to look for in a possible replacement.    Ratio may not be a critical piece either, depending on what you are going to do with it.  A 10K:10K with center taps may be fine here.  There's no DC through it, so that's not a worry.  The primary cap may have to change in value with a replacement.  I don;'t know if this amp is common, or cheap/expensive, but it may also be worth looking for a beater to rob the correct interstage from if you are of that mind.  A 'good' replacement may be as expensive as a beater amp for all I know. 

 

[abbey road d enfer]

Thanks Abbey
I will do the measurement you suggest. I have to find a better generator. I have a Loftech TS-1  but it looks like it generates a maximum of 18dbv so about 8 V  not quite 10 V. Would that be close enough ?

Yes, close enough. Level is not critical. This interstage xfmr drives 6L6's that require about 25V rms. 8V is only 10dB below.

 

[ubxf]

This amp is not really documented because it was one of the first made during the war. Then they changed the design and did away with the interstage transformer. I don't think there are a lot of them around left.
I will do the measurement and try to investigate some more.

 

[emrr]

Yeah, Inca is a name that doesn’t show up post-war, and not much before that. 

 

[gridcurrent]

the tube preamps at ElectroVox on Melrose had Inca transformers,
labels proudly stating division of Phelps-Dodge.
https://www.latimes.com/archives/la-xpm-2000-jun-27-me-45292-story.html

the interstage transformer listings in the Inca catalog is rather sparse of details.
one of the Hammond (Canada) transformers should perform well  in the Leslie 30.

 

[emrr]

the tube preamps at ElectroVox on Melrose had Inca transformers,
labels proudly stating division of Phelps-Dodge.
https://www.latimes.com/archives/la-xpm-2000-jun-27-me-45292-story.html

the interstage transformer listings in the Inca catalog is rather sparse of details.
one of the Hammond (Canada) transformers should perform well  in the Leslie 30.

Hammond 800 or 850 series is what I always think of in a new IT that’ll truly behave like a quality old wind.  And more $$$ than most people want to spend. 

I’ve a push pull 45 recording amp made by Universal Microphone Co in the mid 1930’s that’s all Inca transformers, all an equivalent scale and package to UTC LS series parts.

GREAT article there, one for the archives.  Hadn’t heard of that place.  Love to see pictures. 

 

[ubxf]

Thanks for the ElectroVox article , i'll look at the Hammond transformer lineup

 

[CJ]

what kind of output xfmr?

flip. resize, png>

 

[ubxf]

The output transformer is also a custom Inca transformer

 

[ubxf]

Didn't get a chance to do the measurement yet but here is a picture of the transformer

 

[emrr]

It always stands out that era of Inca have cases just like the earliest Altec/Peerless.  Likely from the same outside supplier. 

 

[ubxf]

Actually i was just told that this transformer might not be an Inca but in fact a Peerless. Some units with a serial # close to mine were fitted with a Peerless because they had trouble sourcing Inca transformer at that time. The power and output are for sure Inca because it is engraved on the shell.