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"My favorite Martian" VHF double tetrodes

Mike Stehr

Mike Stehr

Poverty Audio
I came across three RCA 3E29's, and a 829B way back when with some septar sockets.

I have two RCA CRC 3E29's that have good gettering, and the heaters work when connected to a power supply.

I've looked at the Pete Millet 829B schematic and have output transformers with a 5K primary tap, but don't have the odd tubes he uses for drivers.
I've did the net search thing with regards to a 829B/3E29 in amplifier form, I've seen one SE version using 12SN7.

I think the input grids have -18 volts, or 36 volts peak to peak for a certain anode voltage rating....not too sure...

The data for 829B mentions to use a separate regulated supply for the screens or a voltage divider. I could try single-ended tetrode and use two separate DC tube supplies, and use one to regulate the screens.
Maybe with some sort of plate to plate feedback, (RH84?).

On the Pete Millet schematic, he is using cathode bias, with the cathode cap tied to the OPT B+, a idea of Western Electric IIRC, I can't recall the technical term.
829B data mentions not to go cathode bias, and go fixed bias. Maybe that's when used in tetrode mode at higher voltages.....I dunno....

I've got everything to breadboard it up rather quick, they are interesting looking beasts.

I'm curious as if tubes like 12AT7 or 6SL7 would have the required voltage to drive the grids?

I would imagine so.....any thoughts?

Mike
 

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I'm thinking of using these in an amp... I'm thinking about white silicone high-voltage wire for the plate leads and some small ribbed ceramic insulators over the terminals... Mouser sells small socket pins by Mill-Max that will fit the plate pins.
 
I bought a pile of 815 dual power pentodes years back. I have no idea what I am going to do with them but they look cool.

2999157027_a8c69b0771.jpg


(pic from web)
 
Tom Bavis said:
I'm thinking of using these in an amp... I'm thinking about white silicone high-voltage wire for the plate leads and some small ribbed ceramic insulators over the terminals... Mouser sells small socket pins by Mill-Max that will fit the plate pins.
Click to expand...

Thanks Tom, I'll keep that in mind.

For breadboarding, I'll probably just cheat for now and use clip-leads. I won't be using the tubes for vertical high frequencies at 5000 volts anode voltage, and only limited to 350-400 volts. The clip-leads should be ok.

I have 6SL7 all set-up to use for drivers. Except I'm not sure if it would wise to drive the 3E29 with the cathode of the second half of 6SL7. I guess I'll find out...

I wanna mount some green LED's right under the exhaust tip on the bottom of the 3E29's. That'll make 'em look like something you'd be proud to park on the dashboard of your UFO....
 
Mike Stehr said:
I wanna mount some green LED's right under the exhaust tip on the bottom of the 3E29's. That'll make 'em look like something you'd be proud to park on the dashboard of your UFO....
Click to expand...

LOL, they sure do look cool, might as well do it up right. :D I don't think I ever said, but I love your avatar. :thmbsp:
 
Has anyone ever built around those 815s? I was thinking maybe paralell the sections and use two for stereo.:scratch2:
 
Check this nice little medium mu triode out. It's not a double, one top post is the plate and the other is the grid.
 
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Sorry about my skummy hand drawn schematic......

Any comments on whether this circuit will work or not?
Any ideas or value changes are welcome....

I decided to attempt negative bias from a separate supply, because I'm not sure what value of resistor to use for cathode bias.

Mike
 

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jaymanaa said:
Check this nice little medium mu triode out. It's not a double, one top post is the plate and the other is the grid.
Click to expand...

A buddy built a preamp using something that looks suspiciously like those. I will have to check. Whatever they were, they made a great preamp tube.
 
If I ever come across a Stromberg ASP-422, I'll probably convert it to 815s (I have a few, can get more, and 6DY7s are made of unobtanium). How many other octal dual power pentodes are there? It's not specified for AB1 but should do 20 watts fine. AB2 would require cathode followers...
 
Tom Bavis said:
If I ever come across a Stromberg ASP-422, I'll probably convert it to 815s (I have a few, can get more, and 6DY7s are made of unobtanium). How many other octal dual power pentodes are there? It's not specified for AB1 but should do 20 watts fine. AB2 would require cathode followers...
Click to expand...

I anxiously await your schematic.

;)
 
jaymanaa said:
Dang, I want to come over to your place.:yes:
Click to expand...

Bummer.....I think one just died. The heaters on one didn't glow as bright as the other, and it seemed to get worse quick. I dunno.....I got a hunch it's from lack of emission, and better not use it.
I fired up the heaters today, and it barely glows.

Seemed fine last night. All I did was power up the filaments on the supply to get the heaters going, and then powered up the negative supply to the input grids, and set the B-with a multimeter.
I hope I didn't ruin the grids by applying negative voltage without having the plate voltage applied.
I was going to power up the B+ today, after checking everything over again.

Oh well, I can tweak with one ala mono......

I could use one for stereo I guess.......the cathodes are tied together, so I suppose it'd be kinda like a maggotbox SEP 6BQ5 amp.......use a regulated screen supply......I dunno if the shared screens would matter....

I suppose I better find out if the one is worth listening to, or if it even works. :worried:
 
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