opinions on sort of Williamson build?
So I recently grabbed a pair of affordable 3x7x12" BUD industries aluminum chassis, and have decided to finally build a pair of monoblocks to use some extra parts that I've been hanging onto.
Plan so far was to go for something of a Williamson based design, but with pentode connected (150 volts on G2) 12AV5GA as outputs, since I have a bunch and they don't require herculean drive voltage for decent power. I was planning on using 6FQ7/6CG7 (cleartop, BTW, for cool points, since I have a bunch) for the front end. I have a couple older Radio Shack 12.6 volt 3A filament transformers, and a couple RIB industrial control transformers I was planning to use for power. I have a couple no-name 6K:8 push-pull transformers to use as well, rated for 30 watts. This is a sweep the floor build, intended to use only extras as a cleanup of the parts bin
The power transformers were discussed in another thread a long while back, but I had planned on using the 240 or 277 volt output (bridge rectified) of these for my power supply, so I would be able to make up for a bit of loss in the windings when run this way to get somewhere 300-ish volts., problem is I only get about ~270 or so rectified and at the input to my mosfet ripple filter, which ideally should drop 15 volts or so to give a nice smooth output. That leaves me with maybe 250~260 or so volts supply to my driver stage, which is a little lower than I would prefer. Fortunately, I load tested the transformers all yesterday evening, and found that they run barely warm with 120mA DC draw, so they can handle the build just fine power wise.
With the way that my outputs will be run, I will be at ~20-25 volts per grid, so I don't need a tone of voltage swing, but would this be adequate voltage to run the 6CG7 as intended, with some adjustment of parts values, of course? I'm thinking that I should probably be fine, because the driver will not be asked to swing much voltage in the first stage (assuming that I have an unbypassed cathode, I may get a gain of ~10 or so, and for a 1.5 volt peak onput this should be well within the capabilities of a 6CG7 running with ~160 volts on the plate, and linearity doesn't look to be an issue around this area. I'll likely run a DN2450 cascode CCS to maximize the load impedance up here, and then use a step network (as in my flea amplifier) or self-bias for the concertina section. Sounds good, right?
For the driver tubes I was thinking that the 6CG7 types wouldn't be a great for this position at this supply voltage, but I do have plenty of the russian 6N1P on hand, that I think would be a better fit given the limitations of a good load impedance at this voltage. MY only real question here, is should I go with the original Williamson scheme of having unbypassed cathode resistors here, or would I be better off bypassing them, ar even running something like an LM334Z CCS tail under each pair? I have several of the 334Z on hand, and when built as a temperature compensated CCS they work well enough for an LTP that has both grids driven, and I think would probably be a better choice than running the drivers separately. If there's a "gotcha" here that I'm missing, I'd love to hear some ideas.
So, in summary, the amp is tentatively 6CG7-->6N1P-->6AV5GA Williamson, with solid state rectification and smoothing, fixed bias, and let's say ~260 volt supply.
Feel free to shoot me ideas (no, I'm not going for triode connected
) and If you have any suggestions let me know.
So I recently grabbed a pair of affordable 3x7x12" BUD industries aluminum chassis, and have decided to finally build a pair of monoblocks to use some extra parts that I've been hanging onto.
Plan so far was to go for something of a Williamson based design, but with pentode connected (150 volts on G2) 12AV5GA as outputs, since I have a bunch and they don't require herculean drive voltage for decent power. I was planning on using 6FQ7/6CG7 (cleartop, BTW, for cool points, since I have a bunch) for the front end. I have a couple older Radio Shack 12.6 volt 3A filament transformers, and a couple RIB industrial control transformers I was planning to use for power. I have a couple no-name 6K:8 push-pull transformers to use as well, rated for 30 watts. This is a sweep the floor build, intended to use only extras as a cleanup of the parts bin
The power transformers were discussed in another thread a long while back, but I had planned on using the 240 or 277 volt output (bridge rectified) of these for my power supply, so I would be able to make up for a bit of loss in the windings when run this way to get somewhere 300-ish volts., problem is I only get about ~270 or so rectified and at the input to my mosfet ripple filter, which ideally should drop 15 volts or so to give a nice smooth output. That leaves me with maybe 250~260 or so volts supply to my driver stage, which is a little lower than I would prefer. Fortunately, I load tested the transformers all yesterday evening, and found that they run barely warm with 120mA DC draw, so they can handle the build just fine power wise.
With the way that my outputs will be run, I will be at ~20-25 volts per grid, so I don't need a tone of voltage swing, but would this be adequate voltage to run the 6CG7 as intended, with some adjustment of parts values, of course? I'm thinking that I should probably be fine, because the driver will not be asked to swing much voltage in the first stage (assuming that I have an unbypassed cathode, I may get a gain of ~10 or so, and for a 1.5 volt peak onput this should be well within the capabilities of a 6CG7 running with ~160 volts on the plate, and linearity doesn't look to be an issue around this area. I'll likely run a DN2450 cascode CCS to maximize the load impedance up here, and then use a step network (as in my flea amplifier) or self-bias for the concertina section. Sounds good, right?
For the driver tubes I was thinking that the 6CG7 types wouldn't be a great for this position at this supply voltage, but I do have plenty of the russian 6N1P on hand, that I think would be a better fit given the limitations of a good load impedance at this voltage. MY only real question here, is should I go with the original Williamson scheme of having unbypassed cathode resistors here, or would I be better off bypassing them, ar even running something like an LM334Z CCS tail under each pair? I have several of the 334Z on hand, and when built as a temperature compensated CCS they work well enough for an LTP that has both grids driven, and I think would probably be a better choice than running the drivers separately. If there's a "gotcha" here that I'm missing, I'd love to hear some ideas.
So, in summary, the amp is tentatively 6CG7-->6N1P-->6AV5GA Williamson, with solid state rectification and smoothing, fixed bias, and let's say ~260 volt supply.
Feel free to shoot me ideas (no, I'm not going for triode connected
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