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.
The inductance Vs current for the 2:1's
Frequency response of the 2:1's note how loading does not roll them off.
Now for the 4:1's
dave
Inverting Interstage Transformers.
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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
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.
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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
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
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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!
A friend has that amp now and reports that it compared favourably to some expensive Audio Note Japan designs.
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!
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!