A bigger plate load on the input 12AX7 as the plate resistance is 62.5K for the 12AX7 which 120K is about twice the plate resistance.
The 6SL7 plate dissipation looks to be too high and it might run out of gas before it drives the 6550’s to full power
The 157Q is designed for a much higher current so I’m going to try a 157G (30H, 40mA)
1) The Hammond 278CX PT has a center-tap on the heater winding. It looks like you've balanced the heater windings manually using the 100 ohm resistors. Why didn't you use the centre-tap either grounded or biased to a DC voltage instead?
Why didn't you Zener-regulate the bias voltage (pre-20K bias pot)? Does regulation matter here?
What's the bias voltage range you were targeting?
What's the current draw for the bias voltage?
Why 1N5408's instead of 1N4007?
The filtering section looks like a giant Pi filter, but I don't know why there are caps in series, and that are parallel with the 100K resistors. Is this some method to allow you to use lower-voltage caps? Maybe you could give me a brief explanation or point to where I might find the answer
The 157Q choke is good for 400V, according to the Hammond site, yet it appears you've got 535V "going into" it. Is this right?
I really don't want to wreck any of it, or kill myself, or burn the house down!
dhuebert wrote:Here's how I prototyped my first bass amp BTW:
4) Why 1N5408's instead of 1N4007?
Gingertube wrote:Guys,
Note those Octal Relay Sockets Don uses in his prototype set up. They are about 1/3 the price of an output tube and provide screw terminal connections rated at 10 Amps to each pin.
A truely great way to prototype power stages using octal tubes - RECOMMENDED. Every hobbiest should own 4 to 6 of these things.
Cheers,
Ian
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