Two different preamps (one octal and one regular) in a Tweed Delux "clone"

printer2

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Completed schematic.

bfbDY2s - Imgur.png
 

NTC

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Printer2 for posterity, can you add the transformer manufacturers and part numbers? Or at least the PT secondary specs and the OT impedance ratio (which is probably 8k to 4-8-16) ? That way, anyone referring to this schematic has a better idea of how to get the correct results.
 

printer2

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Printer2 for posterity, can you add the transformer manufacturers and part numbers? Or at least the PT secondary specs and the OT impedance ratio (which is probably 8k to 4-8-16) ? That way, anyone referring to this schematic has a better idea of how to get the correct results.
No idea what the parts were, JG could probably tell you. What is correct? What sounds better to you might not to me. Depends on the type of playing you do. There is a range of voltages these amps ran at from 250V to 350V. Fender went to the Cathodyne PI because of the faults with this one. Same with the grid bias on the pentode, not a great way to do things. Unless it gives you the sound you want.

If you were really into getting the most out of the circuit I would make the 4.7k resistor a 20-25k pot and twiddle it around until it sounds right for you. You could then replace it with a fixed resistor of the same value. Or just keep a trimmer pot in place. Same goes with the NFB resistor, put a pot in and season to taste. You might want to mark down the PI pot position and adjust both to see if there is a sweet spot. How far do you want to go? I played around with an input pentode with a pot for the plate, screen and cathode resistor. After spinning the three I found one spot where the combination sounded best. I could have taken it one step further and adjusted the supply voltage, might just do that when I make a pentode input amp. The values may change depending on tube also. I can not remember if that was the case for certain, I did that over ten years ago. At some point I will get caught up on things and will be making an amp that has some of the good qualities of this amp and giving it more functionality. Not a beginner project though, looks like a dogs breakfast at first glance.
 

Jerry garrcia

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Printer2 for posterity, can you add the transformer manufacturers and part numbers? Or at least the PT secondary specs and the OT impedance ratio (which is probably 8k to 4-8-16) ? That way, anyone referring to this schematic has a better idea of how to get the correct results.
Away for a while. Will give you the info when I’m back home.
 

Jerry garrcia

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Printer2 for posterity, can you add the transformer manufacturers and part numbers? Or at least the PT secondary specs and the OT impedance ratio (which is probably 8k to 4-8-16) ? That way, anyone referring to this schematic has a better idea of how to get the correct results.
Hi. The trafos are both Hammond:
PT = 290BEX
OT = 1750E
If any other questions just ask. I know more about that amp than I know of my children.
For the theory of the circuit just read the thread since the gurus @andrewRneumann and @printer2 are the ones thar actually designed it. I was like a hammer in their hands. But it was my idea. No one can take that away from me :)
 




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