High Power Princeton?
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High Power Princeton?
I have a client who is inquiring about a higher powered Princeton build. He wants to retain the cathodyne phase inverter. Any ideas???
Thinking about 30-45 watts, used as a clean amp only...
Thanks!
Thinking about 30-45 watts, used as a clean amp only...
Thanks!
Learning to learn...
Re: High Power Princeton?
That would be a sorta Princeton Boogie, although my "Prune Boogie" has an LTP.fusionbear wrote:I have a client who is inquiring about a higher powered Princeton build. He wants to retain the cathodyne phase inverter. Any ideas???
Thinking about 30-45 watts, used as a clean amp only...
Thanks!
There's no reason a cathodyne couldn't be used on a higher power amp.
The Sunn 2x6550 (80W) circuit has cathodydne.
The difference is it's a higher current triode than a 12AX7, either 7199 or 6AN8.
If you use the 12AX7 with 2x6L6 just follow Merlin's grid stopper suggestions for both the output grids AND the PI grid.
rd
Re: High Power Princeton?
You might want to raise the resistor values from 56k to 100k as the larger output tube needs more voltage swing on the grid.
Re: High Power Princeton?
Would a 12AU7 provide more voltage swing at the grid than a 12AX7?… Isn't there a tube that is half 12AU7 & half 12AX7?
Re: High Power Princeton?
The cathodyne phase inverter stage runs at a gain of just under one, so whatever is at the input you have the same signal size at the output. So if you had a 12AX7 or a 12AU7 in that position because of the 100% negative feedback both tubes will give the same output, both produce a gain of one.
The problem with using a 12AU7 is that the other triode in that tube is used in the preceding stage. Rather than having a 100X triode there you only have a 20X triode (theoretical gain, in the actual circuit there is less gain). So you do not gain anything in the cathodyne stage by using the 12AU7 but loose in the preceding stage.
With increasing the plate and cathode resistor it develops more voltage across the resistors and less across the tube. When the cathodyne follows the input voltage it have more room to swing the signal across these resistors. The voltage swing across the resistors is what gets translated through the coupling capacitors, effectively giving you more signal capability. Ampeg used the cathodyne in some of their high power amps and they were running 100k resistors.
The problem with using a 12AU7 is that the other triode in that tube is used in the preceding stage. Rather than having a 100X triode there you only have a 20X triode (theoretical gain, in the actual circuit there is less gain). So you do not gain anything in the cathodyne stage by using the 12AU7 but loose in the preceding stage.
With increasing the plate and cathode resistor it develops more voltage across the resistors and less across the tube. When the cathodyne follows the input voltage it have more room to swing the signal across these resistors. The voltage swing across the resistors is what gets translated through the coupling capacitors, effectively giving you more signal capability. Ampeg used the cathodyne in some of their high power amps and they were running 100k resistors.
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Re: High Power Princeton?
isnt this a 12DW7 tube?brewdude wrote:Would a 12AU7 provide more voltage swing at the grid than a 12AX7?… Isn't there a tube that is half 12AU7 & half 12AX7?
"It's like what Lenin said... you look for the person who will benefit, and, uh, uh..."
Re: High Power Princeton?
12DW7... Thanks.
When I read Merlin's pre-amp book (1st ed.) I thought he implied that a 12AU7 would provide enough voltage swing to drive a pair KT88's. Did I misunderstand.
When I read Merlin's pre-amp book (1st ed.) I thought he implied that a 12AU7 would provide enough voltage swing to drive a pair KT88's. Did I misunderstand.
Re: High Power Princeton?
Sure it would. But you still have to have enough gain to give the 12AU7 something to swing.brewdude wrote:12DW7... Thanks.
When I read Merlin's pre-amp book (1st ed.) I thought he implied that a 12AU7 would provide enough voltage swing to drive a pair KT88's. Did I misunderstand.
Re: High Power Princeton?
would a 12DW7 work with AX7 side driving the AU7 side?
Re: High Power Princeton?
Look at the bigger Fender 5e circuits, like the low power tweed twin and bandmaster.
Re: High Power Princeton?
Sure.brewdude wrote:would a 12DW7 work with AX7 side driving the AU7 side?