Well max Anode is 60W,
I am told that 400mA is pushing it (tube life) ..The higher the bias current the shorter will be the tube life..Then again up to 60 Watt is the design..
The heat will be very high..In the box temp will be higher than with it open..
What power out are you getting now what bias current are you running?
Probably a good idea to check mains power taken just so your aware of the electric meter rotation speed....
Have you used chassis as a heat sink?
Regards
M. Gregg
I am told that 400mA is pushing it (tube life) ..The higher the bias current the shorter will be the tube life..Then again up to 60 Watt is the design..
The heat will be very high..In the box temp will be higher than with it open..
What power out are you getting now what bias current are you running?
Probably a good idea to check mains power taken just so your aware of the electric meter rotation speed....
Have you used chassis as a heat sink?
Regards
M. Gregg
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To descride sound is hard.
More distinct don´t wonders of when driven harder.
Now i can turn it up more before it gets ugly.
The power is enough for my needs but the russians are capable of twice as much.
I´ll try raising B+ for PI by adjusting the reg i got 30v more before regulation starts dropping.
More distinct don´t wonders of when driven harder.
Now i can turn it up more before it gets ugly.
The power is enough for my needs but the russians are capable of twice as much.
I´ll try raising B+ for PI by adjusting the reg i got 30v more before regulation starts dropping.
My first approach was a 1ohm resistor and a servo that adjust the bias but space is not there for it.
This is a brilliant KISS solution Alistair has a good eye for the nononsence approach of things.
Next step is higher b+ for PI.
For another go i´d like to raise the rails a bit higher for more OP.
I´m running 350mA right now keeps the cost for firewood down.
This is a brilliant KISS solution Alistair has a good eye for the nononsence approach of things.
Next step is higher b+ for PI.
For another go i´d like to raise the rails a bit higher for more OP.
I´m running 350mA right now keeps the cost for firewood down.
At 320V on PI with 47K loads, I get around 65V P-P from the PI before it starts to clip.
This should be enough to drive the O/P pair to the point where they would start to conduct G1 current,--although this PI cant source that sort of current.
Worth remembering, When running 150V +-B rails, the O/P pair are only 'seeing' 110-120V each, as the bias voltage is coming off the full +B value.
To get More power, a higher +-B volts to o/p would be needed to compensate for the Bias loss--With the attendant Extra Heat, both in the valve and the cathode-components and possibly reliability issues--Is it worth it?
--Alternatively, you can try out fixed-bias, but you'll need an extra neg supply referenced to the neg rail for bias of the bottom valve....
--The top valve could use a well de-coupled supply from the neg rail....
Ah--Thanks for the compliments!
I will be very interested in your findings of raising +B for the PI. I have a nice oil-filled Tx that i could use for the pre-amp supplies, and calculated I would get around 410V after a bit of RC smoothing...
Trouble is,--like everything--Fitting it!
Interesting you're Increasing the current!--Guess its pretty cold in your part of the world at this time of year!
Ive gone the other way--Still running the 2x PL509 I'm running 70mA, although sound has suffered slightly--but not as much as you would have thought suprisingly--These seem best at around 120mA-150mA
Higher B+- is on the list for next version including a bigger chassi.
Specs say 250 is ok for dissipation over 30w.
I have some industrial stepdown toroids 400-240 run it backwards some nice chokes and the recipe says +-250.
Fixed bias is cheating
.
Another choice of tube for PI ? with better drive capabilitys
Specs say 250 is ok for dissipation over 30w.
I have some industrial stepdown toroids 400-240 run it backwards some nice chokes and the recipe says +-250.
Fixed bias is cheating
.Another choice of tube for PI ? with better drive capabilitys
Higher B+- is on the list for next version including a bigger chassi.
Specs say 250 is ok for dissipation over 30w.
I have some industrial stepdown toroids 400-240 run it backwards some nice chokes and the recipe says +-250.
Fixed bias is cheating
Another choice of tube for PI ? with better drive capabilitys
Fixed-Bias....Cheating! I like that!
Experience of the 6C33C suggests 250 May be a bit high. You'll need around 50-80V drop across the cathode devices, depending on the current draw--LOTS of dissipation there....
A 12BH7 is apparently a good choice of PI tube according to some guys for best swing/drive, Sadly--I dont have any though...
Looks like 15-18K and 380-400V +B using the 12BH7 is a good op-point for the split-load PI....
12BH7 has similar characteristics to 6SN7, but higher Transconductance....
Measured it and it puts out ~10 watts.
More then enough to fill my livingroom.
Have some grounding to sort out, change a couple resistors then it´s time for assembly and introduction to the living area of the house.
Was your final circuit for your FET load just the sudo zener?
What bias current did you decide to use?
Looking forward to a pic of the assembled amp.....
Regards
M. Gregg
I have built them in 1993 and they're still working as they should...but their power performances are modest : only 20W RMS / 8ohms... for 25Kg, per unit.
Original pics from 1993 :
Today :
These OTL amps are now relegated as "Sacred Monsters", as do not take the time to use them much...
A+!
, per unit.Original pics from 1993 :
An externally hosted image should be here but it was not working when we last tested it.
Today :
An externally hosted image should be here but it was not working when we last tested it.
These OTL amps are now relegated as "Sacred Monsters", as do not take the time to use them much...
A+!
Question..
If you set the bias current to 200mA with one heater and then switch on two heaters does the bias remain 200mA or does it increase?
Regards
M. Gregg
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