Inverting Interstage Transformers.

Design and use of the various types.
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dave slagle
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Inverting Interstage Transformers.

Post by dave slagle »

Hey guys,

I have been playing with some small ratio step down transformers lately (I know "gasp") and have finally come up with some designs that I'll actually call my own. In the process I think I partially cracked the Inverting Interstage nut for all of you A2 dreamers.

I have a pair of 2:1's and 4:1's and I'll put the data below. (one pair each @ $350 a pair)

First a pic they are 2 X 2.5 X 3" and weigh 1.7 pounds each. 49% nickel core all nonmagnetic hardware as always.
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The inductance Vs current for the 2:1's
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Frequency response of the 2:1's note how loading does not roll them off.
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Now for the 4:1's
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dave
dave slagle
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Post by dave slagle »

For the 4:1's how about a 6C45 cooking @ 25ma to drive an A2 211 @ 100ma

the gold gap will net a 10MA offset window and plenty of inductance.

For the 2:1's I like the thought of a 5687 @ 20ma driving an 801 @ 40ma.

For those of you lucky enough to be holding real PX25's... I'm jealous :-)

dave
DowdyLama
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Post by DowdyLama »

Cool stuff - way to go Dave!

Jim
jlsemrad
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Post by jlsemrad »

Dave,

How much grid current is there at the bias point you are using for the 211? It doesn't look like the positive bias point could be very high for 100ma of plate current. For true IIT operation don't you need to run a fairly significant amount of grid current to cancel the plate current of the driver tube? I'd say run the 801A at 100mA so you can get about 5mA of grid current and raise the Gm to near maximum.

Also, how about using these ITs to drive a DHT in normal class A using something like a 437A to minimize source impedance of the driver?

John
Last edited by jlsemrad on Thu Nov 19, 2009 10:20 pm, edited 1 time in total.
dave slagle
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Post by dave slagle »

Hey John.

OOPS. I wasn't clear

I was thinking cathode drive so the secondary goes in the cathode circuit so you have the full plate current working for you. I know the cathode is a bi-atch to drive but I was actually thinking to lust let the DCR of the secondary bias the tube wherever it falls and then enjoy the A2. The nice thing is you don't get the drastic difference in load when you drive the grid positive.


Agreed on the 437A, but for those I have a non-inverting design. How about a 416B through the 4:1 gain of 50, RP of 300 ohms OR maybe a 6HV5 if you really want to get sick :-)

dave
piotr_grzesik
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Post by piotr_grzesik »

Ooh! Nice one Dave.

A couple of years ago I built the Shishido 801A amp (as published in SP10) but with different filament supplies. I managed to luck into a complete set of iron on eBay. The Tango interstages (10672, I think?) were custom made with something like a 1:0.8 step-down. The data sheet reckoned they were flat to 100kHz or something! :shock:

A friend has that amp now and reports that it compared favourably to some expensive Audio Note Japan designs.
Too much stuff and not enough time!
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