This is a great hobby and if you keep it simple tube amps is the greatest way into understanding how amps work. I built things way above my knowledge too, and still do. I've always figured if things are built on an assembly line by old women I can build it too. And since everything is built by old women on assembly lines, I can build anything.
***PS Please note my correction that the suggestions on the output tube is for triode connected, not pentode. Pentode you keep the original values for cathode resistor.***
I have this tube in a small shop amp. I happened to take a serious listen last night. Oh man it is so sweet I cannot believe it. I stayed up way too late just listening to track after track. But that is trioded running on 235V on the plate. The b+ supply is 275V (10V drops on the OPT, and ca 30V on cathode, leaves 235V for the tube). Of course I was sitting rather close and the volume was very moderate, the rest of the house was sleeping. The amp was probably idling along and peaking at less than 1/10 of a watt.
As have been noted by others, pentode mode should include global feedback, and this complicates matters. I know it sounds insane, but 1.5 - 2W is plenty for sane listening within reason. And the potential 4W in pentode is barely 3dB more volume, barely perceptable.
I really recommend this in a simple as possible triode configuration. The sonics will hook you forever, and you will really enjoy this hobby.
Included is a slightly redone schem, for the 180V you will have on the plate. Oh this is for TRIODE by the way.
Another thing I forgot to look at is the cathode bypass. I would increase C3 to at least 470uF, I use 1500uF in my amp.
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scott17,
That is a good looking amp, and a nice circuit.
I use the 900V IXYS current source in some of my amplifiers.
I used to have a 2 stage SE amp with a 6N1P first stage; sounded good to me.
How many volts is the Green LED?
The screen maximum voltage is 150V.
You have 274V on the screen, minus the drop in the 100 Ohm screen resistor.
But yours seems to work because it is in Triode Wired mode.
I hope nobody modifies that circuit to Pentode/Beam power mode for more power,
with 274v on the screen, when the plate swings to 50V, there might be smoke.
That is a good looking amp, and a nice circuit.
I use the 900V IXYS current source in some of my amplifiers.
I used to have a 2 stage SE amp with a 6N1P first stage; sounded good to me.
How many volts is the Green LED?
The screen maximum voltage is 150V.
You have 274V on the screen, minus the drop in the 100 Ohm screen resistor.
But yours seems to work because it is in Triode Wired mode.
I hope nobody modifies that circuit to Pentode/Beam power mode for more power,
with 274v on the screen, when the plate swings to 50V, there might be smoke.
6A3sUMMER,
Thanks. The green LED is a 2V. Yes, I've read that for this particular tube, 12 or 6W6GT, since the screen exactly tracks the plate voltage in triode mode, the screen rating can be abused because there are no wild screen current swings in relation to the plate. I've also read that UL mode would be a problem, but I never tried it.
I chose the 12W6 version due to the heater current, and how nicely it works out with the Antek PT. I don't think anyone will be modifying the circuit easily, I used a PCB. If I remember correctly when I built it, I was getting about around 5W output. The speakers I built for this are 90dB and it gets plenty loud if needed.
Thanks. The green LED is a 2V. Yes, I've read that for this particular tube, 12 or 6W6GT, since the screen exactly tracks the plate voltage in triode mode, the screen rating can be abused because there are no wild screen current swings in relation to the plate. I've also read that UL mode would be a problem, but I never tried it.
I chose the 12W6 version due to the heater current, and how nicely it works out with the Antek PT. I don't think anyone will be modifying the circuit easily, I used a PCB. If I remember correctly when I built it, I was getting about around 5W output. The speakers I built for this are 90dB and it gets plenty loud if needed.
Indeed looks like a nice ckt. I have very similar voltages in mine, see ckt in post 41. The amp has been running with no prob for several years.
Yes, nice circuit, similar biasing. Love the front end, cool. I guess you found out too that the published curves don't necessarily reflect real world. I started out with calculations at around 800R in the cathode but found it needed more. It is a very nice sounding tube in SE triode.
Actually the 1kohm is from published data, graphically derived by me. But the voltage on the 1kohm is 27V, so I can go down a bit on the resistor value, yours is probably spot on. The value on the schem is calculated, but I should have put down the actual measured. Not sure what I was thinking.
