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BTW.We should also add a pair of diodes across the plates of the OPT Sec. on the sockets to protect from any arching.
Tony
Moderators: pompeiisneaks, Colossal
That's another way to do it. Here's what I came up with.
martin manning wrote: ↑Sun Jun 03, 2018 1:57 pmI'm sure that's what those 270k's are there for, but I don't think they are doing anything except wasting power. The upper and lower cap pairs will get charged up to peak AC 30 times per second, which is much faster than the RC time constant with the balance resistors. To do this right, though, I think all of the other caps should be stacked to cover transients and power-up without tubes installed. I'd also put a Zener on the FET filter node to protect it.
If I had one of these to play with I think I would try an 8-10k resistor between the choke and the screen filter to see what the difference is. A 5W would be big enough, dissipating only ~1W at idle.martin manning wrote: ↑Mon Jun 04, 2018 7:22 amBTW, 700V on the plates with 5k5 Zpri or there about is good from a plate dissipation point of view, but I'm not so sure about the 350V screen. I think something between 250 and 300V would actually be a better match.
Martinmartin manning wrote: ↑Mon Jun 04, 2018 7:22 am Tony, I agree you should draw it up as in the original. I think the reason that it worked (works) fine for Dumble is that there was a bit more margin on the voltage limits. Without a load, the filters after the stacked one are seeing 450V+. These days components are designed more precisely (even the high quality ones), and it would be best to respect the stated maximums. That's where I was headed with the schematic I posted. Stacked filters can cover the required voltage capability with inexpensive and available parts. In the original, the voltages will be a little lower due to the 40k/820k divider and the 12k dropper. I'm seeing 355 for B3, 285 for B4 and 275 for B5.
BTW, 700V on the plates with 5k5 Zpri or there about is good from a plate dissipation point of view, but I'm not so sure about the 350V screen. I think something between 250 and 300V would actually be a better match.
As far as the screens go! Dumble uses 150 ohm 3 watt on the screens of the 6L amp, Music man uses the typical 1K5.(total) My guess would be due to the lower voltages (less protection needed) any other thoughts on why he might have lowered them down that far? TonyBTW, 700V on the plates with 5k5 Zpri or there about is good from a plate dissipation point of view, but I'm not so sure about the 350V screen. I think something between 250 and 300V would actually be a better match.
Thanks for that, Tyler. I guess that's another vote for stacked filters all down the line.
So which is which? I can't make sense of what you wrote there. I thought 470Ω for 6L6 amps ala Fender, and 1k or so for EL34. Above there is mention of 150Ω for the MM power supply.
There’s talk here, but whether it’s the correct one?martin manning wrote: ↑Mon Jun 04, 2018 10:25 pm Does anyone have details on the Musicman power transformer? I would like to know the DC resistance of the HV secondary. I can't believe or don't understand the specs posted above, since the current rating has to be quite high to work with the doubler. Maybe that's DC current listed?