Could you be more specfic here? Are you talking about C9, R25, and D1 in my schematic?
Noted... I'll have to buy a few different kinds once it's up and running.
C9 is the bootstrapping cap. I also tried the R25/D1 thing to protect the cathode follower, but ended up removing it also. It's said that it has no effect on tone but I though I could hear/feel a difference. I have my heaters elevated to 70Vdc and I'm not terribly concerned about damage at power-up since my B+ is only 280Vdc at the DCCCF. Not sure if it was already covered, but are you planning to elevate your heaters? If your transformer has a centre-tap on your heater winding then it's super simple to do.
The Antek transformers have two separate 6V windings.
In my last amp I created a virtual CT with a couple 100R resistors and elevated them that way. For this amp I was thinking about going with regulated DC heaters for the preamp section on one winding, and the power tubes on the second winding running on the straight AC. This will be another thing I won't worry about until after I have it up and running. I don't want to add complications for no reason. If the amp doesn't hum with the elevated AC heaters and a good layout, I see no reason to go any further.
In my last amp I created a virtual CT with a couple 100R resistors and elevated them that way. For this amp I was thinking about going with regulated DC heaters for the preamp section on one winding, and the power tubes on the second winding running on the straight AC. This will be another thing I won't worry about until after I have it up and running. I don't want to add complications for no reason. If the amp doesn't hum with the elevated AC heaters and a good layout, I see no reason to go any further.
I agree, keep it simple. My main point wasn't so much about hum, but about heater to cathode maximum voltage on the cathode follower. I'm sure you're aware that the max is +/-200Vdc+pk.
Good luck with this project. It sounds very similar to what I just built (high gain pre-amp with quad-6v6 output).
Good luck with this project. It sounds very similar to what I just built (high gain pre-amp with quad-6v6 output).
Here is the power supply schematic:
Pretty straight forward; the "HV" and "LV" transformers are actually going to be a single Antek AS-2T300, which should give me a B+1 of about 410V - 420V with tubes. The caps should probably be 500V, which means I'll probably use 47uF instead of the 100uF shown for each of the main filter caps. Between the choke and the cap multiplier I think it will be plenty stiff/quiet enough.
Pretty straight forward; the "HV" and "LV" transformers are actually going to be a single Antek AS-2T300, which should give me a B+1 of about 410V - 420V with tubes. The caps should probably be 500V, which means I'll probably use 47uF instead of the 100uF shown for each of the main filter caps. Between the choke and the cap multiplier I think it will be plenty stiff/quiet enough.
Again, that depends on the sound you want. Many tube guitar amps purposely allow the power supply to sag, which adds another source of compression with another more controllable time before distortion sets in and time before the gain recovers and a different kind of "old-amp" distortion as the bias dips and the tubes get outside their linear range. It's not my "cup of tea" but you might consider a really hefty switch to throw another bank of caps in parallel, so you can have it both ways. You can put a large-value resistor across the switch which won't affect the power supply sag when you want a smaller capacitance, but the 'extra' caps will charge slowly (like a few seconds) so the switch contacts don't weld together when you decide you want the extra dynamics instead of compression.
The sort of sound I'm going requires very little power supply "sag", and a very clean B+. Hence the over-sized toroidal transformer, large caps, choke, and cap multiplier. When it comes to extremely high gain amps for modern metal, I think you almost need to think in terms of hifi for the power supply. If I was designing an amp for classic rock/blues I would be thinking in much different terms.
I dont understand why you choose to have passive output, by the tone control/eq/vol , and not at last use one of the tubes for that ?
and further you use a 1M ohm pot
is that good practice ?
6 tube stages, and then passive out, I dont get it
???
anyway, I think it would be better to use mosfets
as I understand it you should be able use almost similar schematic
and further you use a 1M ohm pot
is that good practice ?
6 tube stages, and then passive out, I dont get it
???
anyway, I think it would be better to use mosfets
as I understand it you should be able use almost similar schematic
Are you suggesting he use mosfets through the whole amp or just the output buffer? If you mean for the whole amp, you're crazy.
The 2nd harmonic distortion that tubes produce when pushed to grid current limit has no equivalent in the solid state world. It's all hard clipping and lots of odd harmonics.well, yeah, I reckon it have been so, for many years
but I think its more of a myth today
those days might be over
you may not have noticed, but the ace might have changed hands over night
If you mean for the whole amp, you're crazy.
hmm, no(yes
)I would suggest a 'hybrid', to give even more options
and further, in that respect, I put my money on a 2-channel system(not stereo), through out, speaker and all
well, yeah, I reckon it have been so, for many years
but I think its more of a myth today
those days might be over
you may not have noticed, but the ace might have changed hands over night
Really? Has the response curve of transistors suddenly changed? I know there are lots of solid state amps out there with modeling to approximate the sound of classic tube amps, but it's still not the same. I know there are lots of great FET based amps, but there's a reason tubes are still produced today.
I agree, I was grew up on SS. It's amazing I stuck with guitar after playing all that crap. I had lot's and lot's of "tube" effects over the years.
In my opinion, it is not practical to emulate tubes, it cost way too much and falls way to short. If your trying that hard, it's cheaper to just go tubed.
In my opinion, it is not practical to emulate tubes, it cost way too much and falls way to short. If your trying that hard, it's cheaper to just go tubed.
Good practice? I don't know, but this is how many of the great classic amps are wired. The schematic doesn't reveal that the wiper of the 1 meg pot is usually connected to the grid of the PI.
I am not going anywhere near the tube VS solid state argument in the guitar amp domain. I have been building both for 45+ years, and I currently use both. Tubes and mosfets do behave quite differently when purposfully operated in their nonlinear regions. I have found that using a mosfet as a follower in an otherwise tube guitar amp design doesn't hurt the tone, and in some cases helps since the usual 12AX7 is a crappy follower. I often use a mosfet to drive the tone stack and maybe as the PI.
You can even use a mosfet buffer on a 12AX7 gain stage to increase the gain, but it DOES change the tone and overload characteristics. It makes for a more defined edge that might be good for a metal amp. It's up to the builder to find the sound he want, and it may take a good bit of tinkering to get there.
Geez... I forget to check a thread for one evening and you guys go all OT on me.
Right, the tonestack will just feeding a typical cathodyne or long tailed pair phase inverter, not a power tube. As shown above is how it is done in pretty much all guitar amps I've seen. If I go with a cathodyne PI, I will have a free half of a 12AX7 to try a follower or gain stage after the tone stack.
I also have no interest in debating the SS vs Tubes argument. Both devices have their uses, and faults. When I do the layout for the turret board, I'm going to be leaving room for a FET based input buffer, and one to replace the cathode follower before the tone stack to free up V3B. This design will not be finalized for quite a long time, and will be my "test bed" for high gain preamps. The schematic above is merely my starting point.
Right, the tonestack will just feeding a typical cathodyne or long tailed pair phase inverter, not a power tube. As shown above is how it is done in pretty much all guitar amps I've seen. If I go with a cathodyne PI, I will have a free half of a 12AX7 to try a follower or gain stage after the tone stack.
I also have no interest in debating the SS vs Tubes argument. Both devices have their uses, and faults. When I do the layout for the turret board, I'm going to be leaving room for a FET based input buffer, and one to replace the cathode follower before the tone stack to free up V3B. This design will not be finalized for quite a long time, and will be my "test bed" for high gain preamps. The schematic above is merely my starting point.
George, ever used a CCS for increasing the gain of a 12AX7 gain stage? Would it be worthwhile to try for the first stage in a preamp like this?
I would say go cathodyne, and use the other half to boost the signal before the PI since the cathodyne has slightly lower than unity gain. You'll also want the anode voltage as high as possible on the cathodyne PI to keep your headroom up. If you don't already read "The Valve Wizard" site, there are a few good points to be careful of with the cathodyne PI shown on this page.
Sorry guys, I shouldn't have gone there. I wasn't going to, but I was full of energy early this morning. haha
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