continuing to work on the design of the SET I'm going to make.
It took me a while to sort it all out in my head, but I FINALLY figured out that I want to use only tubes with thoriated tungsten filaments. Partly for the fun of it, partly for the look of it, partly for the challenge, partly for honoring the past, and partly for the purity of the sound - although I don't really propound that there's any one "best" sort of tube (but secretly, in my heart of hearts, I do....
)
I have put together a list of DHT's that use thoriated tungsten filaments - NOT coated tungsten filaments, and, of course, not indirectly heated. You might think I want power DHT's, but actually not - I'm looking for those rare tubes that are in-between preamp tubes that run tiny Iq's and power tubes that run over 15 mA - that is, 2nd stage amplifier stage type tubes - but only in thoriated tungsten.
Mu is not critical, at all. Plate voltage not very important either, although from 185 volts to 500-ish volts is the range I'm looking for; ideally 250 volts, I think. Plate current between 5 mA and 15 mA is the sweet spot I'm looking for, because, irrespective of plate voltage except for extremes, of course, I'm looking for sufficient Iq to have driving power for the 3rd stage, not too much, not too little. The puuuurrfect one would probably be about 250 plate volts at 8 mA for a Pd of 2 watts. Of course, in a pinch I can use one of the smaller power tubes, such as the 25T, but I'd rather not waste all that power. And, finally, it would be SWEET if there was some forgotten one that was CHEAP LOL.
Here's my list so far of thoriated tungsten triodes, with a tetrode, etc, mixed in, from preamp tubes to smaller power triodes (I am not completely opposed to triode-strapping a tetrode or pentode, so you know):
01A $50 3 mA - classic, beautiful thoriated tungsten triode, but a touch shy on Iq to be a good 3rd stage driver...although I could double it, but then
the price gets really high
3C24 $17
45 mA - nice price, but too much wasted power
841 (really low current) $29 2.2. mA
4-65A (power tetrode) $70 30 mA (I could triode-strap this, but price too high and Iq too high)
10Y 45 mA (not listed on vacuumtubes.net ????)
15E $12 (no datasheet except intended for 15 KV )
25T $55 (wish there was a 10T or 15T) 43 mA
35T 45 mA
100TL $100
80 mA
801A $75 18 mA (this one is close, probably the best of the list here, but expensive)
Are there any more that are not huge power triodes, especially in the 5 mA to 15 mA Iq range?
I'd also welcome any Russian tubes smaller than the GM70 and GM100
Very Best, Synchro27
It took me a while to sort it all out in my head, but I FINALLY figured out that I want to use only tubes with thoriated tungsten filaments. Partly for the fun of it, partly for the look of it, partly for the challenge, partly for honoring the past, and partly for the purity of the sound - although I don't really propound that there's any one "best" sort of tube (but secretly, in my heart of hearts, I do....
)I have put together a list of DHT's that use thoriated tungsten filaments - NOT coated tungsten filaments, and, of course, not indirectly heated. You might think I want power DHT's, but actually not - I'm looking for those rare tubes that are in-between preamp tubes that run tiny Iq's and power tubes that run over 15 mA - that is, 2nd stage amplifier stage type tubes - but only in thoriated tungsten.
Mu is not critical, at all. Plate voltage not very important either, although from 185 volts to 500-ish volts is the range I'm looking for; ideally 250 volts, I think. Plate current between 5 mA and 15 mA is the sweet spot I'm looking for, because, irrespective of plate voltage except for extremes, of course, I'm looking for sufficient Iq to have driving power for the 3rd stage, not too much, not too little. The puuuurrfect one would probably be about 250 plate volts at 8 mA for a Pd of 2 watts. Of course, in a pinch I can use one of the smaller power tubes, such as the 25T, but I'd rather not waste all that power. And, finally, it would be SWEET if there was some forgotten one that was CHEAP LOL.
Here's my list so far of thoriated tungsten triodes, with a tetrode, etc, mixed in, from preamp tubes to smaller power triodes (I am not completely opposed to triode-strapping a tetrode or pentode, so you know):
01A $50 3 mA - classic, beautiful thoriated tungsten triode, but a touch shy on Iq to be a good 3rd stage driver...although I could double it, but then
the price gets really high
3C24 $17
45 mA - nice price, but too much wasted power841 (really low current) $29
2.2. mA4-65A (power tetrode) $70
30 mA (I could triode-strap this, but price too high and Iq too high)10Y 45 mA (not listed on vacuumtubes.net ????)
15E $12
(no datasheet except intended for 15 KV )25T $55
(wish there was a 10T or 15T) 43 mA35T 45 mA
100TL $100
80 mA801A $75
18 mA (this one is close, probably the best of the list here, but expensive)Are there any more that are not huge power triodes, especially in the 5 mA to 15 mA Iq range?
I'd also welcome any Russian tubes smaller than the GM70 and GM100
Very Best, Synchro27
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Skipping Pentagrid converters, Super Control tubes, etc:
22 Scree-Grid RF amp, listed for AF amplification also 1.7-3.7ma
26 Probably the most used DHT for preamp stages. very linear 2.9 - 6.2mA
30 Detector amplifier 2.5 - 3.1mA
31 Power amplifier 8 - 12.3mA
32 RF Amplifier, specified as AF amp also
33 AF Power Amplifier Pentode, 14.5 to 22mA
44 Class B amplifier specified for class A driver operation at 22mA
49 Dual Grid Power Amplifier, also serves as a class A driver at 6mA
71A Power Amplifier 10 - 20mA only rated at 0.79W
112A Detector amplifier 5 - 7.7mA
3A5 twin Triode
6A4 specs listed for 9-22mA, considered a PA, but only 1.4W out
I'm sure there are others as well.
22 Scree-Grid RF amp, listed for AF amplification also 1.7-3.7ma
26 Probably the most used DHT for preamp stages. very linear 2.9 - 6.2mA
30 Detector amplifier 2.5 - 3.1mA
31 Power amplifier 8 - 12.3mA
32 RF Amplifier, specified as AF amp also
33 AF Power Amplifier Pentode, 14.5 to 22mA
44 Class B amplifier specified for class A driver operation at 22mA
49 Dual Grid Power Amplifier, also serves as a class A driver at 6mA
71A Power Amplifier 10 - 20mA only rated at 0.79W
112A Detector amplifier 5 - 7.7mA
3A5 twin Triode
6A4 specs listed for 9-22mA, considered a PA, but only 1.4W out
I'm sure there are others as well.
300 B thoriated tungsten version fresh from Elrog in Germany.
Ok maybe not perfect candidate but interesting triode
VinylSavor: ELROG ER-300B, First Impressions
Have fun !
Ok maybe not perfect candidate but interesting triode
VinylSavor: ELROG ER-300B, First Impressions
Have fun !
I have a little practice using thoriated tungsten tubes (continuously -but slowly- develop my /P/SE amplifier), so some advice:
841/VT-51: great tube (5-9ma), with amplification factor about 20, but very sensitive to impedance of the next stage (not less, than 500k! otherwise HF band being to fall). Unable to properly drive power tubes without second stage -CF, source follower-. Huge anode voltage: I use it at 500V.
10/10Y/VT-25: Ideal anode current range is 20-30mA (about 300V). Great preamp or driver (cathode follower) tube. I don't use it as power tube, because it has limited power capacity (1-1.5W), and load resistance is minimum 10k.
801/801a/VT-62: Similar as the 10Y, but more powerful. I use them as PSE amplifier (841 amplification, 10Y cathode follower, A2 mode), 600-620V B+, 30mA anode current, with 5k output transformer (about 8-10W).
Each of thoriated tungsten tubes I own made at forties (1940-50), thus varies in parameters. 841 tubes parameter spreading is more significant (due to the greater mu -more grid wires!-), than 10Y/801's. The latter are more stable, but pairing (PSE: same operating point, same anode voltage, same mu) is painful (and very costly).
Each DHT is sensitive to the quality of the heater PSU, especially these tubes. I use DC filament supplies, Rod Coleman regulators, heater bias at preamp tubes, so overall cost is significant.
841/VT-51: great tube (5-9ma), with amplification factor about 20, but very sensitive to impedance of the next stage (not less, than 500k! otherwise HF band being to fall). Unable to properly drive power tubes without second stage -CF, source follower-. Huge anode voltage: I use it at 500V.
10/10Y/VT-25: Ideal anode current range is 20-30mA (about 300V). Great preamp or driver (cathode follower) tube. I don't use it as power tube, because it has limited power capacity (1-1.5W), and load resistance is minimum 10k.
801/801a/VT-62: Similar as the 10Y, but more powerful. I use them as PSE amplifier (841 amplification, 10Y cathode follower, A2 mode), 600-620V B+, 30mA anode current, with 5k output transformer (about 8-10W).
Each of thoriated tungsten tubes I own made at forties (1940-50), thus varies in parameters. 841 tubes parameter spreading is more significant (due to the greater mu -more grid wires!-), than 10Y/801's. The latter are more stable, but pairing (PSE: same operating point, same anode voltage, same mu) is painful (and very costly).
Each DHT is sensitive to the quality of the heater PSU, especially these tubes. I use DC filament supplies, Rod Coleman regulators, heater bias at preamp tubes, so overall cost is significant.
...and don't forget to rectify with thoriated tungsten vacuum diodes
Thank you for the reminder. Good idea! And you thought you were kidding....
Thank you very much for this list, and even with the Iq's.
Wow! I'll be making up a master list and adding this. 
I think these are all coated tungsten filaments, not thoriated tungsten, no?
I'll check. But even so, you're right, there's a TON more selection - and some truly great tubes, some of the best of all - with the coated tungsten filament tubes, it's just that for this amp I want to stay thoriated tungsten non-coated. NEXT amp, though, this list is fabulous.
Very Best, Synchro27
thanks!!! knowing that the 15E = 3C24 = 25T is INVALUABLE information.
At $12 for the 15E or $17 for the 3C24, what's not to like!!!???
I'll look at 'em again.....
Very Best, Synchro27
Thanks, Andreas
I've added some notes and links for the tubes you suggested:
Note: "ct" = coated filament (oxide on tungsten):
ct 4P1L 4P1L triode mode | Bartola Valves dh pentode
ct 6P21S http://tdsl.duncanamps.com/pdf/6p21s.pdf dh pentode
ct 6P23P 6P23P | Tubes Information dh beam pentode
ct 2J27L Ïåíòîä 2Æ27Ë dh pentode
ct 2P29L Ïåíòîä 2Ï29Ë dh pentode
Very Best, Synchro27
PS: as far as I can tell, except for big transmitting tubes, the Russians very intelligently went with coated filaments for practically everything else.
knowing that the 15E = 3C24 = 25T is INVALUABLE information.
3C24 and 24G are 100% identical - they differ from the 25T only in the fact that the 25T has no grid pin.
15E is similar, but not 100% the same - mu is 25 (vs 23), filament voltage/current, and pin out are radically different.
However, the 3C24's curves are 'close enough' that you can make reasonable operating guesstimates.
Please note: all of my experiments with the above tubes are as A1 front-end tubes.
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Thanks, dowdylama. I did some checking on TDSL, and found out that all the following are approximately equivalent, except the details as you noted, and things like whether the grid comes out the side, etc (the ones with a "G" I think have grid pins out the side):
3C24=24G=24=25T=25TG=VT204(army)=CV745=sorta 15E
3C24, VT204, 24G all are $17 at vacuumtubes.net
15E is $12 at vacuumtubes.net
Yes, I agree, these are best output stage tubes...I'm starting to think along the lines of a type 10 driving a 15E or 3D24 (but the type 10 in CF stacked on top of a type 10 CCS, bipolar supply - I LIKE bipolar supplies - since I plan to go into grid conduction territory on transients).
Very Best, Synchro27
cooling fins for pins for plates, grids, etc, part of this topic
Just a quick note:
the pins on these tubes, for the plate, and for some of the grids, don't bother me a bit. (Alfred E. Neuman "What me worry?" emoticon here)
I plan to make up on my lathe finned connectors from aluminum or brass that slide onto each pin and are secured with two tiny set screws - and LOTTSA big, very thin fins for extra cooling of the plate and grid. Hey, can't hurt, right?
I also plan to support them or suspend them somehow so they don't press on the tube or torque a side pin.
I was thinking of coating the connectors with high voltage clear coat, but that would cut down on cooling. OTOH, it would also cut down on arcs to me or the cat LOL.
the other plan is to make a sweet plexiglas cover that would insulate the whole she-bang, but then I gotta have forced air cooling inside it. Ventilation holes would just let the arc out in humid weather...however, all in all, the plexiglas cover is probably still a grrrreat idea..
Of course, all of it could go beneath a ventilated metal, grounded case, but that would take all the fun away of admiring the toobs...
Very Best, Synchro27
Just a quick note:
the pins on these tubes, for the plate, and for some of the grids, don't bother me a bit. (Alfred E. Neuman "What me worry?" emoticon here)
I plan to make up on my lathe finned connectors from aluminum or brass that slide onto each pin and are secured with two tiny set screws - and LOTTSA big, very thin fins for extra cooling of the plate and grid. Hey, can't hurt, right?
I also plan to support them or suspend them somehow so they don't press on the tube or torque a side pin.
I was thinking of coating the connectors with high voltage clear coat, but that would cut down on cooling. OTOH, it would also cut down on arcs to me or the cat LOL.
the other plan is to make a sweet plexiglas cover that would insulate the whole she-bang, but then I gotta have forced air cooling inside it. Ventilation holes would just let the arc out in humid weather...however, all in all, the plexiglas cover is probably still a grrrreat idea..
Of course, all of it could go beneath a ventilated metal, grounded case, but that would take all the fun away of admiring the toobs...
Very Best, Synchro27
I reckon the one you might want to look at is Type 71 aka CX-371 = UX-171 the 500mA thoriated tungsten filament type predecessor to the oxide coated filament CX-371A/UX-171A (71A)
mu 3, Rp <2k, Ip ~10 to 20mA.
Sets up real nicely at 150 to 180V with -30 to -40V bias, so your B supply ideal is near to spot-on.
Agree with your first paragraph at every point and would also add that the self rejuvenating nature of the TT filament means they last a very, very long time (and probably amongst other things the reason that they don't make them anymore!)
Shane
mu 3, Rp <2k, Ip ~10 to 20mA.
Sets up real nicely at 150 to 180V with -30 to -40V bias, so your B supply ideal is near to spot-on.
Agree with your first paragraph at every point and would also add that the self rejuvenating nature of the TT filament means they last a very, very long time (and probably amongst other things the reason that they don't make them anymore!)
Shane
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Thanks, Ceglar. You are spot on. I could wish for a bit more mu, even though I said it didn't matter, but the specs are right on for an interstage tube.
I like the looks of it at 160 volts, -33 V, 20 mA, 3.2 watts, 6K load line - a little higher load line and lower bias than spec'd in the datasheet because I want more excursion into grid conduction for transients.
The 10 and 10-Y and 841 are also candidates, I suppose, but the 71A is clearly the best choice of them all so far.
I had forgotten about the self-renewing nature of thoriated tungsten, thanks for reminding me. Another great reason to prefer thoriated tungsten!
Very Best, Synchro27
I like the looks of it at 160 volts, -33 V, 20 mA, 3.2 watts, 6K load line - a little higher load line and lower bias than spec'd in the datasheet because I want more excursion into grid conduction for transients.
The 10 and 10-Y and 841 are also candidates, I suppose, but the 71A is clearly the best choice of them all so far.
I had forgotten about the self-renewing nature of thoriated tungsten, thanks for reminding me. Another great reason to prefer thoriated tungsten!
Very Best, Synchro27
Mu is 3.. wish for more, I know. But, it can be set up biased quite deeply (-40V).. and therefore ability to sacrifice some headroom for maximum voltage swing with suitable drive.. find the best compromise. Even then the tube is so linear that even max voltage swing across plate load still quite ok. Also, quite low Cin compared with 45, 46 etc.. I think also that it is king.
Shane
Shane
they does exist, more like big ones for hv/transmitter duty
https://frank.pocnet.net/sheets/175/d/D0-1-30.pdf
https://frank.pocnet.net/sheets/175/d/D0-1-30.pdf
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