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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6KV6/6KM6 SE triode

Discussions about 6KV6 and/or 6KM6 pop up here and there from time to time.
What I haven't found yet is an example of this tube being used successfully in a SE triode amp.
So what's the (preliminary) consensus on how to best use them?
Appreciate your input.
 
One reason is most likely the fragile screens. Doesn't mean you can't try it. It's not like these tubes are rare and expensive. 😉

It's just a lot easier to triode strap a 6L6 or EL34 if you just want a few watts. And, most people don't know what a sweep tube is anyway.

jeff
 
Thank you, Jeff.

I'm already scared enough to begin with LOL
So any input are highly appreciated.
What voltages and OPT primary do you think are best to start playing with?
Frankly, I find these tubes to be damn attractive (in appearance at least) - especially RCA black plates.

Dennis.
 
With power finals of this general type, a B+ of 250-300V and a plate load of 3kOhm is not going to be far off of 'quite good'. Enough core and turns to deliver 20Hy minimum primary L value and idling current at .45 of saturation at 100 mA should do it.

Then, whilst building, leave yourself the ability to install decent voltage amplifiers. TV sweeps tend to deliver a triode mu around 4, so plan accordingly.

Douglas
 
The Sylvania --KV6 tubes have a nice vacuum seal tit on top that give them an antique look. A Resistive Schade (plate to driver plate local N Fdbk ) setup should work well for a "Triode" mode, with the low screen V. Or you can use UnSet mode with a P Mosfet cathode driver and Schade N Fdbk. Or just plain B. pentode mode.

17KV6A.jpg

Some brass plumbing pipe skirts:
17KV6A_disguise.JPG

Some plate curves (Sylvania) 50ma/div Vert. 50V/div. Horiz. 140V screen grid, 2V steps grid1
17KV6A_SYL_50_50_2_140.JPG
 
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--KV6 (gm 9500 @ 80 mA, mu 4 ) is close to a 6HJ5 (gm 10,000 @ 80 mA, mu 4.2 ). The 6HJ5 saw a lot of resistive Schade builds on the Pete Millett Engineers Amp 50 Watt Monoblock PC board. Using a 4.3K OT. And George took them up to 75 Watts and more.... Using a 3.3K OT.
http://www.pmillett.com/DCPP_MB.html

6HJ5 50ma/div Vert. 50V/div. Horiz. 108V screen grid, 2V steps grid1
6HJ5_RAY_50_50_2_108.JPG


Note: The Sylvania --KV6 has a little higher Rp than the 6HJ5, however the RCA --KV6 has lower Rp, similar to the 6HJ5.
 
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I took it on a slightly literal, 'strap it as a triode' basis. s-a makes a very good point as to applying feedback to get even better-than-triode performance. Icing on the cake would be to see the ac plate curves with the un-set, super curves... 🙂

Douglas
 
I don't have a Schade curve set handy for the 17KV6A, but 6HJ5 is close to the same tube except for slightly higher screen V.
Here are some curves that I have:
17KV6A in triode configuration: (50 mA/div, 50V/div, 6V steps grid1 )
17KV6A_SYL_T_50_50_6.JPG


6HJ5 in triode configuration: (same setup 50 mA/div, 50V/div, 6V steps grid1 )
6HJ5_RAY_T_50_50_6.JPG


6HJ5 in UnSet: (6KV6 should be very close to this, nearly same gm, Schade resistors running the show ) Of course the mu will depend on the Schade resistor ratio. I have it set up for about the same mu 4 as native mode (for comparison ) (50 mA/div, 50V/div, 6V steps grid1 )
6HJ5_50_50_UnSET.JPG
 
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Easy R-Schade starter:

If you want to get something up and working quick, I would suggest just using the DCPP schematic with one output tube deleted, with R24 (220K ) just connected to B+. The differential input stage VT1, VT2, -could- be simplified to just one 6CB6 with a 7 mA CCS under it with a bypass cap across the CCS, but you won't have the option of trying out any global N FDBK then. Several different 7CM base tubes will fit the same sockets for the VT1, VT2 stage with different gm for more gain if needed (SE output tube grid drive, global N FDBK etc ). 6CB6, 8136, 6GU5, 6EW6, 5/6JK6

For more drive, some 9 pin driver tubes with high Rp for R-Schade: 6CL6 6JC6A

You will need a 3K SE OT for output with just one tube then. Output tube idle current would need increasing for class A SE (grid bias V adjust ), and then the output tube B+ will need reducing to stay within the output tube dissipation limits.

Lots of TV Sweep tubes could be used for the outputs as well. There is even a PC board for this design, not sure if still available.

schematic:
http://www.pmillett.com/file_downloads/dcpp_mb_sch.pdf

The PC board is still available (no affiliation here ) https://www.ebay.com/itm/163099242163
 
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George (Tubelab) might have a suitable PC board for trying UnSet with the 6KV6 or other TV Sweep tubes. You'll get a few more Watts out with UnSet.

R-Schade presents a low impedance to the driver stage, but needs a current drive. So high gm and high Rp driver tubes are needed. (or a triode driver with a series resistor output )

UnSet presents a high impedance (P MosFet gate ) to the driver stage, so is more like traditional designs. Getting the DC ranges right for the output cathode drive and P Mosfet power is more tricky however.
 
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