IS tranny confusion

[shooter]

It's harvest season so..........

I've used an IS tranny as PI twice, sketching up a 3rd.  I was reading over the paper n got hung up where it talks about: "either || fed or push pull"
I sketched up what my brain "see's" from that statement, I know I'm wrong, just can't get to correct 

[jjasilli]

It seems your top 2 drawings are correct. 


Bottom Right is Single Ended with DC:
Power:  BLUE 
Plate:  Brown
Primary CT:  NC
Tube cathode > Ground; NC to Tranny

[shooter]

The top left is the one I currently use
the top right, possible, guessing the 2 in phase 1/2's would "add"
the bottom right, not sure why, if I already phase split with a tube, why use a tranny?

[jjasilli]

Your bottom right drawing is wrong:  There is no phase splitting at the tube.  Because there is no cap, this Single-ended  WITH DC.  Follow those wiring instructions near the top of the instruction page when no cap is used on the primary side.

[shooter]

there is no cap

The sketches were quickies, so they might need a cap, but I'm not that far yet.  still hung on HOW, you feed the tranny ||, or PP, I'm pretty sure it's an English thing vs an electronic thing 

[PRR]

> got hung up where it talks about: "either || fed or push pull"

[shooter]

the brain cataract is gone! thank you!
last minor point of understanding (amps in general, not guitar specific)
what benefit is there using a tube PI to drive a tranny to drive the PA?

[PRR]

> what benefit is there

Did you read the puff-page?

Typically this type of transformer is used with a low-gain tube such as 12AU7, 12BH7, 6CG7, 6SN7 or 6J5 to drive output tubes such as 6L6, 6550, 2A3, 45 or 6B4G. The advantage of using this type of transformer in certain applications is that it gives a different type of clipping behavior, the output tube grids can be driven somewhat into the positive range (because of the low DC resistance in the grid circuit), if a low impedance bias supply is used. It works great for a lot of early (pre-war) jukeboxes.
http://triodeelectronics.com/unintrui.html

The original purposes:

1) To make a push-pull drive without an added tube (in days when transformers were cheaper than tubes)
2) To drive power tubes VERY hard, into grid-current

If you review the history of the thousands of guitar amps made, you find like 6 which use an IT. It mostly does not make sense.

[mresistor]

PRR they were used in tube organs, and now I'm thinking as a cost saving measure.  There were some in the Chord Organ I took apart and some in the Baldwin. Mostly the ones I have sit on a shelf looking at me. LOL

[jjasilli]

+1 to PRR.  Interstage trannies were useful in the distant past to boost signal voltage when tube mu was low; even power tubes were low mu triodes needing huge signal drive voltage, like 115 VDC.  With latter day hi mu preamp & power tubes, interstage trannies are unnecessary.  However they are still beloved by small niches of advocates for nostalgia; or by some hi-fi purists who wish to avoid caps in the signal path, claiming that caps: i) color tone; and ii) cause phase shifting which puts the hi frequency band out-of- sync with the lo frequency band. 

[shooter]

Thanks guys the info is great!

and you hit all the reasons too!;
simplicity, cost, niche, HiFi-ish, AND, really old discarded  .

From guitar guys, it adds "magic sauce"
I'm thinking now doing an audio, using the IS to drive a quad of EL84's PP, but I'm still leaning RC coupled, which won't get me in with the speaker sniffer guys