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Old 12th October 2006, 05:23 PM   #1
Bill*B is offline Bill*B  United States
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Default PP splitters again

Hi, I'm working on a low power PP amp, and am obsessing over the phase splitter. I need about 10V to drive the 6Y6 pentode outputs.

A couple of years ago, SY posted a thread called "fun little PP input" with a neat circuit I hadn't seen before. If anyone - SY?- has tweaked this further, I'd be interested in any late breaking developments / thoughts.
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Old 12th October 2006, 05:29 PM   #2
SY is offline SY  United States
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Default Time Marches On

Nothing new, it's the same circuit I've been using for decades. It works quite well and is the input stage of my "big" amp.

If I were to redo it, I'd probably combine it with an input transformer, use higher current tubes (e.g., ECC88), and replace the biasing resistors with LEDs.
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Old 12th October 2006, 05:41 PM   #3
zobsky is offline zobsky  India
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Default Re: Time Marches On

Quote:
Originally posted by SY
Nothing new, it's the same circuit I've been using for decades. It works quite well and is the input stage of my "big" amp.

If I were to redo it, I'd probably combine it with an input transformer, use higher current tubes (e.g., ECC88), and replace the biasing resistors with LEDs.

SY, .. you did have a Jensen input transformer in the original circuit Fun little P-P input stage

Could I use a CD player on the primary of the transformer, with a volume pot, or would I need a line stage.
I'm confused about how much current a jensen or cinemag input transformer can handle. . I don't need much swing on the secondarys and am pondering using an input transformer to drive the grids of a push pull EL84 pair


Thanks for any input.
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Old 12th October 2006, 07:48 PM   #4
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The tranny was in a bench circuit I was testing. My actual day-to-day amp still uses a "barefoot" input with a 6SL7 (actually, a 5691...). Modifying that is about number 15 on my List of Things To Do That I'll Never Have Time For.
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Old 12th October 2006, 08:17 PM   #5
zobsky is offline zobsky  India
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Thanks for the info. My push pull project will hopefully take off this year, as soon as my SE one works satisfactorily.
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Old 12th October 2006, 08:50 PM   #6
Bill*B is offline Bill*B  United States
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Thanks, guys! I love octal tubes, so I'll build mine with a 6 or more likely 12SL7. Still haven't decided about that 100 uf bypass .... Regards, Bill.
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Old 13th October 2006, 01:00 AM   #7
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Hey-Hey!!!,
I just put together a PP 6V6 amp. B+ of 260. It is two stage, a 6BK7B LTP/diff amp riding a DN3545N3 CCS. The negative rail is RC decoupled and reduced from the -30V bias supply to -15V.

The amp is two-stage, and runs a Chicago B0-series OPTx rigged for CFB with its tertiary winding. The front end runs the amp very well, with adequate gain to run a buffer linestage with the CD machine. There is no other NFB, and the front end is probably delivering 50-60V at full power.

For most listening I can put any valve I have with that base/pinout, all the way down the mu ladder to the 6GU7.
cheers,
Douglas
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Old 13th October 2006, 04:43 PM   #8
Bill*B is offline Bill*B  United States
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Fascinating. I'd love to see your schematic. How to bias the output tubes is a decision I haven't made yet.

Sy, when you bypassed the cathode resistors in your input stage / splitter: did you tie one end of the cap to cathode, and the other to signal ground? Or did the cap just go across the resistor? Forgive me for asking for so much hand holding.
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Old 13th October 2006, 06:01 PM   #9
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The caps just went in parallel with the cathode-to-source resistors. If you connect the caps to ground, you short out the signal.

No problem with hand-holding, this is not a normal circuit.
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Old 14th October 2006, 03:45 PM   #10
Bill*B is offline Bill*B  United States
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Default Yet another question!

Prehaps you will tolerate one more question, then. I confess that I'm lost when it comes to biasing transistors. Does the tube act as an active load for the JFET, and set the current flow all by itself? Can I choose a value for the cathode resistor - to set the bias for the tube - just like I would if it was connected directly to ground, or is there more to it than that ? (If the source follower wasn't there, I'd expect about 1.85ma of current in your 400V B+ 100k plate resistor 6SL7 1K cathode resistor circuit). Does the voltage drop of the follower come into play? I can't quite figure out how to look at this circuit to come up with the current flow.
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