I have scribbled out a few configurations. I was originally thinking of introducing one diode clipping between a standard v1 and v2 stage, but I figured it should follow the logic of the first solid state version. That one works really well. So starting off with a single clip adjustment on V1. The op amp version biased either side of the wave through NPN PNP, but here can be done on V1 and/or V2 cathode bias. I also had a gain adjustment so that can be done easily. I would like to switch between normal and hot ''channel".
So variable pot added to cathode resistor for bias. The clip here is towards cut-off. Add a switch to ground on the pot's bottom for normal and hot channel. Tone stack will be a classic one after V2.
Now regarding those tube diode clippers. I want to put them after V2. We need to move their forward bias points away from zero or we get no sound. Simplest from what was discussed is to drop their heater supplies right? Do we go for adjustable with pot or switched resistors? I have enough leftover current from the 6.3 v transformer supply, to drive the added diode heaters.
I could put a DC regulated supply with variable volts. The lazy way would be to series wire them to go to 1/2 supply, but I don't want exact symmetrical post clip.
D1 and D2 can tie in to signal line with simple switch again for hot channel
What do you think so far?
Now regarding those tube diode clippers. I want to put them after V2. We need to move their forward bias points away from zero or we get no sound. Simplest from what was discussed is to drop their heater supplies right? Do we go for adjustable with pot or switched resistors? I have enough leftover current from the 6.3 v transformer supply, to drive the added diode heaters.
I could put a DC regulated supply with variable volts. The lazy way would be to series wire them to go to 1/2 supply, but I don't want exact symmetrical post clip.
D1 and D2 can tie in to signal line with simple switch again for hot channel
What do you think so far?
hmm, would a tone stack after v1 give you enough gain? i might consider adding an EF95 on the input if not, but that cathode idea sounds good, should probably be bypassed with a 100uF cap to make sure it only affects the DC bias, or at high resistance settings a lot of gain would be lost.
As for diode heaters, i was going to use aa 12v regulator for the 12ax7 and 12at7/au7 and then a 6v zener, pot and MOSFET. where one side of the pot goes to the zener 6v, the wiper goes to the MOSFET gate, the other side of the pot to ground,the drain of the MOSFET to 12v and the source to the heater, could use 2 of those, 1 for each side
As for diode heaters, i was going to use aa 12v regulator for the 12ax7 and 12at7/au7 and then a 6v zener, pot and MOSFET. where one side of the pot goes to the zener 6v, the wiper goes to the MOSFET gate, the other side of the pot to ground,the drain of the MOSFET to 12v and the source to the heater, could use 2 of those, 1 for each side
Yeah, the triodes will have AC bypass caps. As for the classic tone stack, being a subtractive circuit we lose some dB overall whether at V1 or V2 , the position of it will change what bands get overdriven and where. I am going for mild DC bias changes, maybe 20 to 30% into cutoff.
I need to look at the diode bias clip points, I think at grid of v2 is a good suggestion.
Your heater control will work, and should be nice and quiet.
If you get into 2 watt range with yours, you will have a real sweet amp for university. Maybe you could put a switch in to drop the output stage watts to 1/4 watt or so. On the right speaker, 2 watts still is loud!
I need to look at the diode bias clip points, I think at grid of v2 is a good suggestion.
Your heater control will work, and should be nice and quiet.
If you get into 2 watt range with yours, you will have a real sweet amp for university. Maybe you could put a switch in to drop the output stage watts to 1/4 watt or so. On the right speaker, 2 watts still is loud!
hehe, yeah, im using an old HH invader i pulled from another amp i swapped with a celestion tube 10, not a bad speaker really. though i may add a VVR in the HT supply so i can change the power that way, i found everything i need just waiting on the EB91 (though currently testing some things with LEDs), 275v on the power section, biased around 5ma per triode, the V1 voltage is 241, and V2 voltage is 246. and i have 150v running an EF95 which i may make switchable for boost. I ended up using mains power in this box, il probably add a few other things too (delay, compressor, noise gate, effect loop) and make it as versatile as possible.
by the way, it might be good to try the tone stack in both positions, or maybe (overkill?) 2 tone stacks?
by the way, it might be good to try the tone stack in both positions, or maybe (overkill?) 2 tone stacks?
Ok, on a quick test, a normal 12ax7 gain stage, 220k plate resistor, 2.2k anode resistor, with a 10n coupling cap and a 1u cathode bypass, is barely enough to drive an LED array (marshall jcm900 style diode config.) i measured the voltage drop to be about 3v so it doesnt give us alot of room for a tone stack, il play some more tomorrow and add a switch, and check the trace on a scope. if you want to start a new thread, should probably do so soon!
I hope to get the thing running and play with tone stack positions, I may do something similar to the simple tone control I added on the SS version for the hot channel (hi boost /cut).
Run with a relatively clean boost up front to push everything to ( or past) the limit, you probably won't need the compressor!
Run with a relatively clean boost up front to push everything to ( or past) the limit, you probably won't need the compressor!
ok, I think im definately adding the boost, that might be a good place to put the tone stack, and then have v2 and 3 do the clipping, i really cant get much at the moment. the stage after the diodes may need less gain too, or all i get is the triode overdrive, not the diodes. How have you arranged your build?
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