6146 -3d21b as triodes
The 6146 is very difficult to use as a triode you can get 19 watts, but the drive requirements are very high Peak AF grid –no.1 to Grid no.1 200 volts. The 3D21 works very well as a triode and you can get a lot of power, very easy to drive. I have built two amps using 3D21b’s as triodes class AB2.
The 6146 is very difficult to use as a triode you can get 19 watts, but the drive requirements are very high Peak AF grid –no.1 to Grid no.1 200 volts. The 3D21 works very well as a triode and you can get a lot of power, very easy to drive. I have built two amps using 3D21b’s as triodes class AB2.
ok. so the power transformers are the TRA400 from Ask Jan First. potted chokes are some old chicago standard transformers, 8 henry 85 ohm. i can't remember where i got the output transformers. they're marked "A-405" on them and they're 6.6K a-a, no UL windings, with a 0-4-8-16 secondary. about the size of the 60 watt Edcors.
after a quick test run i have discovered that the 10M45S doesn't like dissipating 5 watts into thin air. i'm lucky i saw them unsolder themselves from that floating position soon enough to turn off the power.
i'm going to use mica and insulated washers to mount them to the front of the chassis and give it another try. other than that, just a few other resistor value tweaks and i'll be ready for a proper tryout with speakers.
i'm going to use mica and insulated washers to mount them to the front of the chassis and give it another try. other than that, just a few other resistor value tweaks and i'll be ready for a proper tryout with speakers.
living the poor artist lifestyle in berlin meant i didn't have the euros for new 10M45S' and trimpots for a couple months. but there is good news:
they live....
i slapped a heatsink on the front, used some arctic silver mx4 thermal grease, mica insulating wafers and the plastic insulating shoulder grommets, then tapped a few M3 holes to keep it all in place. the heatsink gets warm to the touch but not hot. output tubes are crusing easy at 400V B+, about 80V on top of the 10M45S at 55mA.
if anyone is interested i can post a cleaned up schematic. now i just need to find some speakers to test them on!
they live....
i slapped a heatsink on the front, used some arctic silver mx4 thermal grease, mica insulating wafers and the plastic insulating shoulder grommets, then tapped a few M3 holes to keep it all in place. the heatsink gets warm to the touch but not hot. output tubes are crusing easy at 400V B+, about 80V on top of the 10M45S at 55mA.
if anyone is interested i can post a cleaned up schematic. now i just need to find some speakers to test them on!
A decent screen regulator can run with its gate on a voltage divider, its drain to B+ and its source to the g2. At least for a PP amp running Class A. A screen stopper at each grid, and tie the B+ ends together, and from there to the source. Clamp the source with a Zener so it does not exceed about 15V positive to the source, and a diode drop negative. Enhancement mode types are plentiful. An FQP2N60 is good for 600V D-S....just cruise Mouser's sort function, and heat sink adequately.
cheers,
Douglas
cheers,
Douglas
the only thing i'm not sure about is the 130V on the anode of the 6J6. originally i wanted 100V on the plate to leave more room for the 6BZ7's to swing. i have an 80K/3.3uF RC filter between B+2 (390V) and B+3 but it's not dropping enough voltage. i think i might halve that to 40K, then put 80K to ground to make a divider to give the 6J6 200V to start, but then i might have to recalculate the plate load resistor.
not sure what you meant about screen regulators, i don't think i need one for triode mode, no?
if i dropped in a 6n6p i could probably get away with a plate load resistor of, what, like 15K? that would save me 50V of anode voltage and increase headroom, sounds like a good deal. do the various suffixes make any difference or can i just take the plain jane ones?
i had the 6BZ7's lying around and i had compassion for them, but in the end it seems like they just aren't making the cut.
haven't run the amps into anything but a dummy load but so far the 6P20S bias is holding steady so we'll see! no red plating or any wackiness.
if i dropped in a 6n6p i could probably get away with a plate load resistor of, what, like 15K? that would save me 50V of anode voltage and increase headroom, sounds like a good deal. do the various suffixes make any difference or can i just take the plain jane ones?
i had the 6BZ7's lying around and i had compassion for them, but in the end it seems like they just aren't making the cut.
haven't run the amps into anything but a dummy load but so far the 6P20S bias is holding steady so we'll see! no red plating or any wackiness.
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