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.
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
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.
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
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.
Some brass plumbing pipe skirts:
Some plate curves (Sylvania) 50ma/div Vert. 50V/div. Horiz. 140V screen grid, 2V steps grid1
Some brass plumbing pipe skirts:
Some plate curves (Sylvania) 50ma/div Vert. 50V/div. Horiz. 140V screen grid, 2V steps grid1
--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
Note: The Sylvania --KV6 has a little higher Rp than the 6HJ5, however the RCA --KV6 has lower Rp, similar to the 6HJ5.
http://www.pmillett.com/DCPP_MB.html
6HJ5 50ma/div Vert. 50V/div. Horiz. 108V screen grid, 2V steps grid1
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 would very much like to watch this thread though I probably won't be able to add much of anything as I'm sooooo much a noob. Lol (munching popcorn) haha!
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
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 )
6HJ5 in triode configuration: (same setup 50 mA/div, 50V/div, 6V steps grid1 )
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 )
Here are some curves that I have:
17KV6A in triode configuration: (50 mA/div, 50V/div, 6V steps grid1 )
6HJ5 in triode configuration: (same setup 50 mA/div, 50V/div, 6V steps grid1 )
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 )
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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
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.
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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You guys are awesome! Now I feel like it's time to move on from the simple and straightforward old generation SE amps to the modern ones.
Planning to try the 6KV8 pentode section in triode (among others promising tubes) - which was mentioned here in our community as a high linearity tube. All my sources are more or less modern DACs with decent output level. We'll see...
Well, I've just realized - there is no problem with sourcing a Novar socket.
It took me about five minutes to move pins from the cheap flimsy black bakelite socket into the Magnoval ceramic base (already modified on the photo).
Both sockets are sourced directly from China.
You don't even have to disassemble the compactron [ceramic] sockets as it was proposed earlier.
Resulting socket feels pretty solid.
Welcome to the world of the wonderful Novar compactron power tubes LOL!
It took me about five minutes to move pins from the cheap flimsy black bakelite socket into the Magnoval ceramic base (already modified on the photo).
Both sockets are sourced directly from China.
You don't even have to disassemble the compactron [ceramic] sockets as it was proposed earlier.
Resulting socket feels pretty solid.
Welcome to the world of the wonderful Novar compactron power tubes LOL!
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The last ones I got from vacuumtubesinc.com were actual 9 pin compactrons. They fit properly. I bought several dozen last time I ordered tubes. Some of which were Novar.
I’m sure they are sourced from the same place in China that all of them are.
I’m sure they are sourced from the same place in China that all of them are.
Attachments
Do they have 1.02mm (or 1.016mm) ID pins already?
What I throw out of ceramic bases in my particular case were the 1.27mm ID pins definitely.
What I throw out of ceramic bases in my particular case were the 1.27mm ID pins definitely.