The 6SL7GT spec for heater elevation is + 90V relative to the cathode. If your upper cathode is sitting at 150VDC, then you have a window of 240VDC~60VDC that the heater can be elevated to. In SRPP for a 6SL7, I usually run it at around 100VDC, which makes it -50VDC in spec terms.
This is now what I have come up with. Using a single 5V 10A transformer for both the 2A3 filament DC supply modules.
Thanks for your input. Is the back-feed issue in all cases or just when two regulators are powered by a single winding?
The point to point thing is nice if you do changes to the circuit after the fact. You can control stray capacitance pretty well (usually a board is better) but you had better not make a rat's nest out of it for that to be the case
The B+ is getting a double whammy as AC line Voltage changes. As it does so not only does the high Voltage change but so does the filament supply for the rectifier. So this makes the circuit more prone to AC line Voltage problems as it will result in greater variation of the B+.
In properly designed equipment, this is a moot point. Gazillions of tube type equipment have been produced and are still around being restored.
There are more benefits to point-to-point than that. Ease of repair. I recently had some resistors fry on the input pcb of my Dynaco ST70. The board was totally fried and needed to be replaced along with all the mounted components. Took a fair amount of time and money to fix. If it had been fully point-to-point, it would have been a simple diagnosis and fix for $2 worth of resistors.The point to point thing is nice if you do changes to the circuit after the fact. You can control stray capacitance pretty well (usually a board is better) but you had better not make a rat's nest out of it for that to be the case
I would not worry about using solid state to regulate the filament. However, in your schematic:
The B+ is getting a double whammy as AC line Voltage changes. As it does so not only does the high Voltage change but so does the filament supply for the rectifier. So this makes the circuit more prone to AC line Voltage problems as it will result in greater variation of the B+.
If you are making a hifi amp as opposed to a guitar amp, there's really not a good argument for the tube rectifier unless the B+ will be too high for the intended circuit using solid state. The trick is to make sure the solid state rectifiers are properly silenced, which is really more a matter of silencing the power transformer when the rectifiers are installed. To this end you need to keep the transformer leads as short as possible. To silence the circuit the best means is a resistor and capacitor in series, placed across the input to the rectifiers. Usually a 0,01uf cap is a good place to start. A variable resistance can be placed in series with that cap and the ideal value dialed in.
Tube rectifiers look cool but unless that's the reason for using them or the B+ will be too high otherwise their day has come and gone.
Bear with me a bit longer Nick. Due to constrained chassis real estate space, I have been looking for a single transformer with dual secondary windings. Lots of 6.3v but next to none in 5V with appropriate amp load. Could a 10V CT 20A work using half for each module? Or would that common leg (CT) still be considered a single winding? I am looking at this one HERE. I dunno.
Yep. Not many 5VAC candidates out there and they would be perfect for regulating down to 2.5VDC. The 266PA12 is a bit overkill, but as a general rule, I use a transformer that has at least double the needed DC current.
Pete recommends 4A as a bare minimum for a 2A3 so your 2X A makes perfect sense.
Hawk had me a bit confused because of the 'drop ship' info that had me believing it would come direct from Hammond. Either way, I placed an order with them. I have ordered Hammond transformers from them in the past and they do have the lowest prices.
Yes, did that. I was also going to use taller heat sinks but space didn't allow. I did also mount the trim pot on the bottom of the pcb for easy access.
Not yet because I am just mocking up at this point. But thermal compound will be used at final assembly.
