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Beam Triodes

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#2
I got a pair of 6HV5 by mistake, thinking they were low voltage pentodes. Agh!
Now not too sure what to do with them? I'll either need 1000V B+, or see how
much cathode emissions can tolerate being diverted to grid in A2 with a lower
plate voltage...

www.davidberning.com shows a patented design that allows most of the amp
(relocating the power supply(s) to the loudspeaker side of the transformer) to
operate at much lower voltage, and does not require high voltage storage cap.
The only safe way I can think to play with 1KV+ plate voltage.

The triodes themselves look really nice. I should probably add them to my ever
growing gallery of X-Ray photographs. Is there a screen hardwired to the plate?
Or just G1 and a beam former? Only one way to find out without breaking...
 
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#4
Ironically, they use all the same parts (cathode, grid, plate, even the micas) as their respective beam tetrodes. They're just missing the screen grid. Such a shame, electrically speaking -- they've got huge cathodes, but not nearly low enough plate resistance to use for anything other than their intended purpose.

Maybe you could get something from them in class 2, but the grid current must be huge. Just the screen grid in a sweep tube is quite unforgiving -- the control grid must be murder!

Tim
 
#5
Has anyone played with the 30w plate dissipation beam triodes that were used as regulators in color TV's?
Click to expand...

Not yet, too many tubes, not enough time. Previous experience with these tubes revealed that they will gladly oscillate if given half a chance. This means a clip lead amp is out of the question. I tried it, it jams the TV set and distorted badly. I thought about trying them in the red board, but I think mosfets will be needed to drive the grid positive. The red board is stuffed with 35LR6's right now for some BIG power levels. The first attempt to add mosfets to the red board yielded smoke.

So, it looks like the beam triodes and a few other experiments will have to wait for a new driver board to be born.

Only one way to find out without breaking... Ironically, they use all the same parts (cathode, grid, plate, even the micas) as their respective beam tetrodes. They're just missing the screen grid.
Click to expand...

I break tubes so you don't have to. It had a white getter anyway so, WHACK! Yes, the guts look like a big fat juicy sweep tube that someone forgot to put the screen grid in, except for the control grid. It is a large frame grid with really tiny slits and it is very close to the cathode. This gives a high Gm and a Mu of 300.

Maybe you could get something from them in class 2, but the grid current must be huge.
Click to expand...

Maybe not, the Mu and Gm are high enough so that only a few volts of Vg1 are needed. I tried to make a true spud amp using only the tube and an OPT. I wired the headphone output of a portable CD player between grid and cathode and connected the power supply and OPT between cathode and plate. I had to crank the power supply to max (550 volts) to get some plate current and the sound was very boomy due to the high Rp. It was not very distorted though.

I haven't given up on these tubes yet, but I have many more interesting experiments to try first.

Last year I was visiting Stan at ESRC and I asked him why the 6HV5 cost so much while its siblings are cheap. He replied that there is an amplifier out there that uses them and they sell. I don't know if it is an audio amp or an RF amp. The similar 6JD5 is on the dollar menu.
 
#7
You should know first that one is an RCA and the other a Raytheon.
They look nothing alike... Other than part number...

What could I actually use most right now?
Any tube power transformer.
7591, 6CA7, or anything vaguely 6L6ishy...
One ГУ-50 and/or tank socket for same?
One real 7025 NOS or JAN...
Some Octal or 9p Novar sockets for PCB?
Any strange tubes for XRay peepshow.
Neutrik or Switchcraft 1/4 jacks.

I'll give you 6HV5 free, don't need trade.
But wouldn't turn away any the above.
 
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#9
I've been looking for a Schade-style project that I can build in time for this year's Burning Amp fest. I was thinking about a low power pentode-pentode sort of deal, but a beam power Schade using a triode-pentode dual and some 6HV5As wouldn't be all that hard to whip up, either. The characterisittics of the tube seem a natural for a partial feedback setup, and it would give me something to do with all that excess gain.
 
#10
TETRODE COMPACTRON AMP 6JD5

Got a little crazy last night and thought I should try a UL connected tetrode compactron design using 6JD5 tubes. Using the same board with mods, get rid of the 150 volt bias requirement, but then need UL output transformers. I guess another option would be to triode connect it, beam to plate. Thinking that it may require a little more drive I increased the bias current in the first 2 stages.
I have a matched set of tubes on order and started to do the PCB design.
Any advice on 6JD5 tubes???
 

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#12
The 6JD5 is not a tetrode, it's a beam triode. The second grid is a beam forming plate, not a screen grid.
Click to expand...

My experiments were limited to 550 volts since that was the biggest power supply I had at the time. The second grid is indeed a beam former. I did however tie it to the plate just to see what happens. Nothing blew up. The tube was able to pass about 80 mA with no bias and 550 volts on plate and supressor, however I could not control the oscillation. With the supressor grounded I only got about 20 mA of plate current. The entire test circuit was sky wired on to the tube socket, so better results could be achieved with a better layout.
 
#13
Hi!

I've built about a dozen amps and preamps with this family of tubes. Mostly SE. In Class A1 they need more than 1kV B+ to provide meaningful output. I never had any issues with oscillation. Careful layout will take care of that.
They are quite robust and can handle some abuse. Running them at or even slightly beyond the max plate dissipation is not a big issue. They have quite high plate resistance.

There is a SE output transformer available from Lundahl, which fits well. He developed that one on my request. It has 16k primary impedance, 30mA DC current. The transformer is the type LL2735B

Best regards

Thomas
 
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