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Hi guys, Iīm currently making a P1 extreme. Iīve already made the box, itīs gonna be a 1 x 10" combo with vertical chassis a la Fender tweed, tinted and laquered pine:
Now Iīm defining the circuit. My target is a cleanish combo, not so much a distortion machine, so I arrived at the following schem:
The idea is to be able to use different power valves, to get different levels of saturation and power:
6V6--------more dist - aprox. 5W
EL34/6L6---mid dist - aprox. 10W
KT88/6550--less dist - aprox. 20W
To be able to use different valves, I have to change the cathode R and the OT impedance. To change the cath R Iīll use the ON-OFF-ON switch seen in the schem, by summing Rīs in parallell I get to the recommended values for each valve:
6V6:-------600R
EL34/6L6:--330R
KT88/6550:-200R
Of course with this method I wonīt have 100% optimal bias for each valve, but Iīll be in the ballpark. Also itīs easier in my opinion, when changing valves, to throw a switch and thatīs it, than fiddling with a pot, measuring...
Regarding the OT impedance, after reading the values proposed in the original schem and making some calculations, I arrived at the following speaker connections (names referenced to the schem) to adapt impedance to the different valves:
---------------OUT1---OUT2---OUT3
KT88, 6550------8-------4-------X
EL34, 6L6, 6V6--16------8-------4
Ok, so far my thoughts/mods. Tell me ŋŋŋare they OK???
I believe that this could work... my only worry is plate voltage with a 6V6. My (theoretical) voltage will be 275V x 1.4 = 385V. I know that the real voltage will be less under load... Datasheets recommend 350V max. plate voltage... I guess that if I stay below max plate dissipation, Iīll be safe.
Some other things to review:
- In the original, the heaterīs secondary doesnīt have a mid point tap. My transformer does have one, so that has to be connected to ground. But do I have to attach it to the power valveīs cathode, like in the original, to reduce noise, or to ground? Or it doesnīt matter?
- Regarding the fuse, in my country I have 220 V at the wall rather than 120, so, what fuse rating do I have to use? 1A, or 2A like the original?
- I connected pin 1 of the power valve to ground. Does that work with all the valve types involved?
Well, as you can see, I have many doubts... so any help will be greatly appreciated. If you see anything worth of comment besides what Iīve explained/asked, please do so!
I have posted all this in the AX84 forum, but I think, the more opinions on my schem, the better!
Thanks.
Now Iīm defining the circuit. My target is a cleanish combo, not so much a distortion machine, so I arrived at the following schem:
The idea is to be able to use different power valves, to get different levels of saturation and power:
6V6--------more dist - aprox. 5W
EL34/6L6---mid dist - aprox. 10W
KT88/6550--less dist - aprox. 20W
To be able to use different valves, I have to change the cathode R and the OT impedance. To change the cath R Iīll use the ON-OFF-ON switch seen in the schem, by summing Rīs in parallell I get to the recommended values for each valve:
6V6:-------600R
EL34/6L6:--330R
KT88/6550:-200R
Of course with this method I wonīt have 100% optimal bias for each valve, but Iīll be in the ballpark. Also itīs easier in my opinion, when changing valves, to throw a switch and thatīs it, than fiddling with a pot, measuring...
Regarding the OT impedance, after reading the values proposed in the original schem and making some calculations, I arrived at the following speaker connections (names referenced to the schem) to adapt impedance to the different valves:
---------------OUT1---OUT2---OUT3
KT88, 6550------8-------4-------X
EL34, 6L6, 6V6--16------8-------4
Ok, so far my thoughts/mods. Tell me ŋŋŋare they OK???
I believe that this could work... my only worry is plate voltage with a 6V6. My (theoretical) voltage will be 275V x 1.4 = 385V. I know that the real voltage will be less under load... Datasheets recommend 350V max. plate voltage... I guess that if I stay below max plate dissipation, Iīll be safe.
Some other things to review:
- In the original, the heaterīs secondary doesnīt have a mid point tap. My transformer does have one, so that has to be connected to ground. But do I have to attach it to the power valveīs cathode, like in the original, to reduce noise, or to ground? Or it doesnīt matter?
- Regarding the fuse, in my country I have 220 V at the wall rather than 120, so, what fuse rating do I have to use? 1A, or 2A like the original?
- I connected pin 1 of the power valve to ground. Does that work with all the valve types involved?
Well, as you can see, I have many doubts... so any help will be greatly appreciated. If you see anything worth of comment besides what Iīve explained/asked, please do so!
I have posted all this in the AX84 forum, but I think, the more opinions on my schem, the better!
Thanks.