Mine appeared in post 131 of this thread. Similar except that I have this thing for LTP splitters. I have tweaked a few resistor values and used 2 6SN7's in this version, but the schematic is the same. I plan to experiment further later on this weekend.
Thanks. Any tips on choosing OPTs ... or rather, any tips on choosing tubes to use with the pair of 2K5:4 OPTs I already have? 20W to 30W (or less really) of actual power is fine.
Also, since my power requirements are modest, is using a highish mu tube as an initial gain stage and leaving out the second gain stage reasonable to simplify things a tad. Something like the attached.
Also, since my power requirements are modest, is using a highish mu tube as an initial gain stage and leaving out the second gain stage reasonable to simplify things a tad. Something like the attached.
Attachments
I just noticed that AES has increased the discount on some tubes to 75%. Mostly on triode/pentode combo tubes and oddball ones.
The 12BQ6's dropped to $0.43. I just received some 6jg5 tubes this morning and they have dropped to half price now (50% off -> 75% off). I called, but they wouldn't retro the price. Maybe I should ship them back.
I see that vacuumtubes.net also has their $1 sale on again.
dsavitsk:
The interstage xfmr will have to handle rather high voltages for screen grid drive. If you are going class A output operation, I would put a CCS under the cathodes to split the signal at the outputs. Then delete the interstage. Getting enough gain for screen grid drive in one stage will be hard, to say the least. Maybe with a pentode input stage.
Don
The 12BQ6's dropped to $0.43. I just received some 6jg5 tubes this morning and they have dropped to half price now (50% off -> 75% off). I called, but they wouldn't retro the price. Maybe I should ship them back.
I see that vacuumtubes.net also has their $1 sale on again.
dsavitsk:
The interstage xfmr will have to handle rather high voltages for screen grid drive. If you are going class A output operation, I would put a CCS under the cathodes to split the signal at the outputs. Then delete the interstage. Getting enough gain for screen grid drive in one stage will be hard, to say the least. Maybe with a pentode input stage.
Don
Looks like they want me to repeat my order... 🙂
Thank you Don! 😉
Now, wait for a new fashion in bass guitar amps' design... 😀
Thank you Don! 😉
Now, wait for a new fashion in bass guitar amps' design... 😀
OK, someone just had to tell me this, so now there are more tubes on order (not many). I didn't order any "output" tubes this time.
I got the same email today, but no confirmation of last night's order. I'm guessing that some tubes will turn up "unavailable" again.
Tubes I didn't order:
The 31JS6C is a rather healthy sweep tube rated for 30 watts of dissipation. I already have some.
The 25CD6 is not a damper diode as stated. It is a 25 volt 6CD6 which is a sweep tube that responds well to screen drive. I already have plenty of these as well.
The 6JZ8 is a little triode - pentode vertical sweep tube. It can be used to make a 2 tube per channel P-P amp. Yep, I already have some.
Some other interesting tubes I found:
6AH6 nice high gm small pentode, good for an input stage or preamp.
7543/E130L/6AU6 another small pentode, well regarded I think
6LE8 a true oddball for the experimenter at heart. Has dual control, meaning g3 is a fine mesh instead of a course suppressor type grid. One can alter the characteristic curves of this tube by putting a positive voltage on g3. About +15V on g3 makes it into a high rp pentode with flat curves. Can also use g3 modulation for a remote volume control. Michael Koster has posted an audio compressor circuit using a BDT (beam deflection) tube that might work with this tube too. The 6LE8 can be seen as a sort of cheesy BDT tube.
Don
6AH6 nice high gm small pentode, good for an input stage or preamp.
7543/E130L/6AU6 another small pentode, well regarded I think
6LE8 a true oddball for the experimenter at heart. Has dual control, meaning g3 is a fine mesh instead of a course suppressor type grid. One can alter the characteristic curves of this tube by putting a positive voltage on g3. About +15V on g3 makes it into a high rp pentode with flat curves. Can also use g3 modulation for a remote volume control. Michael Koster has posted an audio compressor circuit using a BDT (beam deflection) tube that might work with this tube too. The 6LE8 can be seen as a sort of cheesy BDT tube.
Don
I'll look around a bit at the heavily discounted tubes, but I'm all tubed up/out for the time being. I was away for a family emergency until yesterday in Mobile, Al, with no internet. To while away the time, I sketched out schematics for 4-5 amps using the tubes I've bought so far. that's enough to keep me busy for quite some time.. To add to the fun, my Edcor order came in while I was away.
Yeah, I have a warehouse full of tubes and I keep buying more.
This time I decided that $1 each was my limit. These are my thoughts:
I have large quantities of both of these and a few other of the TV RF - IF types. They generally work well for high gain as a pentode or moderate gain as a triode. They are highly inconsistent as to noise and microphonics. I decided to delay further testing until my home made noise and microphonics tester is complete.
The 6JG5 was already mentioned here, but when I tried to order some there was only 7 left. Probably none now.
The 6GN8 claims to be a 6JG5 and a small triode in the same bottle. I got a few to play with.
The 6GU5 has been mentioned by Steve Bench as useful for phono stages. Triode wired it has a Mu of 140 with low Miller capacitance. For 65 cents I can afford to experiment.
http://members.aol.com/analogengineer/6gu5ph.html
The 6JW8 has very flat pentode curves. May be useful for a sand free CCS. 66 cents.
"The 6JG5 was already mentioned here, but when I tried to order some there was only 7 left. Probably none now."
George, if you want some of these, I bought way too many of them. Unfortunately half at the 50% off and half at the 75% off price. I didn't think anyone would want these oddballs. Let me know how many you need. Same for anyone else. OHh..., $0.82 each was my average price ($(1.10 +0.55)/2) + shipping extra. I can part with 80 pieces or so.
Don
George, if you want some of these, I bought way too many of them. Unfortunately half at the 50% off and half at the 75% off price. I didn't think anyone would want these oddballs. Let me know how many you need. Same for anyone else. OHh..., $0.82 each was my average price ($(1.10 +0.55)/2) + shipping extra. I can part with 80 pieces or so.
Don
I was only trying to order 10, so 7 is close enough, assuming that is what I actually get. I may be interested after I test the ones that I get. Shipments from AES take 7 to 10 days to get here (Ft. Lauderdale). Oddly, stuff from California is usually quicker.
My experience with the last of the lot from AES has not been good. All of the first 10 98 cent 6BQ6's were good, so I ordered 20 more. So far I have 4 bad ones from the second batch and I haven't tested them all yet.
17KV6A
I mentioned this tube (on sale at AES $1.92) in another thread, so I'll put a mention here too.
9 pin Novar base (no plate cap) and rated at 28 Watts. Appear to be plenty available. The data sheet for it is lacking curves, but it's the same tube as the 6KM6 which does have curves. (Look at the old 6KV6 non A data sheet, where it's rated at 80 mA, to be convinced that the two are indeed the same. Or use the formula gm = k I^.6666 for converting gm to different DC currents)
17KV6A/6KM6: gm 6000 at 40 mA or 9500 at 80 mA
rp 10K Ohm at 40 mA or 6K at 80 mA
Mu_triode 4.0 28 Watts/20 Watts
Should be useful for g2 drive experiments.
Don
I mentioned this tube (on sale at AES $1.92) in another thread, so I'll put a mention here too.
9 pin Novar base (no plate cap) and rated at 28 Watts. Appear to be plenty available. The data sheet for it is lacking curves, but it's the same tube as the 6KM6 which does have curves. (Look at the old 6KV6 non A data sheet, where it's rated at 80 mA, to be convinced that the two are indeed the same. Or use the formula gm = k I^.6666 for converting gm to different DC currents)
17KV6A/6KM6: gm 6000 at 40 mA or 9500 at 80 mA
rp 10K Ohm at 40 mA or 6K at 80 mA
Mu_triode 4.0 28 Watts/20 Watts
Should be useful for g2 drive experiments.
Don
Don
I was also looking at the 17KV6A, nice looking, powerful and capless valve. AES also has the socket, so that is no problem either...think I am going to get some.
Besides they have the 34CD3, a 12 pin damper compactron, I think the most powerfull ever made. The 6V version draws 2,5A! Further it is rated at 350mA continuos, 20V drop at 680ma and 11W dissipation. All this for 40 cents...
Both tubes call to be combined: find a surplus toroidal with 2x 18V secondaries, unwind some and you are king!
Erik
I was also looking at the 17KV6A, nice looking, powerful and capless valve. AES also has the socket, so that is no problem either...think I am going to get some.
Besides they have the 34CD3, a 12 pin damper compactron, I think the most powerfull ever made. The 6V version draws 2,5A! Further it is rated at 350mA continuos, 20V drop at 680ma and 11W dissipation. All this for 40 cents...
Both tubes call to be combined: find a surplus toroidal with 2x 18V secondaries, unwind some and you are king!
Erik
The 6KV6 may be the same tube as the 6KM6 but is specified for an entirely different application. The 6KM6 is a typical sweep tube. The 6KV6 was the first of an entirely different animal called a pulse regulator. What is a pulse regulator?
Black and white TV sets had unregulated high voltage power supplies in the 10 to 18 KV range. When color TV came to be, the requirements got tougher. The color CRT needed more voltage and nearly 3 times the current, and regulation was required to keep the image converged. The first color TV sets used shunt regulator tubes operating on the 25 to 27 KV line (look up the 6BK4). This was popular for at least 10 years until it was discovered that the shunt regulator tube made X-rays, often an unsafe amount of X-rays. There was a lot of media coverage about "unsafe TV's" in the late 1960's. New shunt regulator tubes were invented that used leaded glass and composite envelopes to shield against X-rays.
Someone discovered that the shunt regulator could be moved to the primary side of the flyback transformer where it would only have to deal with a few KV eliminating the X-ray issue. It also only conducted during a short interval to control the amount of HV being generated, hence the term pulse regulator. The first ones were pentodes like the 6KV6. They were probably derived from ordinary sweep tubes.
Shortly the beam triode regulator took over this duty. The 6HV5 is the most common (and expensive) of these. These look like sweep tubes with the screen grid left out. None have plate caps. All have very high Mu, like 300. I have not been successful at making a decent sounding amp with them yet. Very high plate resistance for a triode.
Black and white TV sets had unregulated high voltage power supplies in the 10 to 18 KV range. When color TV came to be, the requirements got tougher. The color CRT needed more voltage and nearly 3 times the current, and regulation was required to keep the image converged. The first color TV sets used shunt regulator tubes operating on the 25 to 27 KV line (look up the 6BK4). This was popular for at least 10 years until it was discovered that the shunt regulator tube made X-rays, often an unsafe amount of X-rays. There was a lot of media coverage about "unsafe TV's" in the late 1960's. New shunt regulator tubes were invented that used leaded glass and composite envelopes to shield against X-rays.
Someone discovered that the shunt regulator could be moved to the primary side of the flyback transformer where it would only have to deal with a few KV eliminating the X-ray issue. It also only conducted during a short interval to control the amount of HV being generated, hence the term pulse regulator. The first ones were pentodes like the 6KV6. They were probably derived from ordinary sweep tubes.
Shortly the beam triode regulator took over this duty. The 6HV5 is the most common (and expensive) of these. These look like sweep tubes with the screen grid left out. None have plate caps. All have very high Mu, like 300. I have not been successful at making a decent sounding amp with them yet. Very high plate resistance for a triode.
Hi George! -How you doing!
How about those so-called Beam-Triodes I've seen in the Compactron lists....
Things like..6HV5A and 6HZ5, 6JH5, 6JK5--That sort....
Never had anything like Those here in the UK, What do you make of them...?
How about those so-called Beam-Triodes I've seen in the Compactron lists....
Things like..6HV5A and 6HZ5, 6JH5, 6JK5--That sort....
Never had anything like Those here in the UK, What do you make of them...?
"The 6KV6 may be the same tube as the 6KM6 but is specified for an entirely different application."
Yes, I had observed that. Unfortunately I don't have a 6KM6 handy to compare one with, but the two 17KV6A I have are virtually identical to a 21JV6 and 21HB5A (HOs) in appearance, which are both rated at 18 Watts.
The 21JV6 and 21HB5A are rated for 220 degrees C bulb temp though, while the 17KV6A is rated at 240 degrees C bulb temp. I have a 6HJ5 HO tube that has the same size plate as all these, but is rated at 24 Watts, and also has the higher 240 degrees bulb temp. rating. The two 17KV6A's that I have, also have g1 fin radiators on top. But just two tubes is too small a sample to know if they all do. The 21JV6 and 21HB5A tubes seem to randomly have these radiators or not, even within the same brand.
So maybe 24 Watts is a resonable HO tube rating (instead of 28W) for the 17KV6A. A little fan ventilation up thru the chassis around the tube socket would probably extend the ratings on all of these.
Don
Yes, I had observed that. Unfortunately I don't have a 6KM6 handy to compare one with, but the two 17KV6A I have are virtually identical to a 21JV6 and 21HB5A (HOs) in appearance, which are both rated at 18 Watts.
The 21JV6 and 21HB5A are rated for 220 degrees C bulb temp though, while the 17KV6A is rated at 240 degrees C bulb temp. I have a 6HJ5 HO tube that has the same size plate as all these, but is rated at 24 Watts, and also has the higher 240 degrees bulb temp. rating. The two 17KV6A's that I have, also have g1 fin radiators on top. But just two tubes is too small a sample to know if they all do. The 21JV6 and 21HB5A tubes seem to randomly have these radiators or not, even within the same brand.
So maybe 24 Watts is a resonable HO tube rating (instead of 28W) for the 17KV6A. A little fan ventilation up thru the chassis around the tube socket would probably extend the ratings on all of these.
Don
"How about those so-called Beam-Triodes I've seen in the Compactron lists...."
They look impressive with their 35 or 40 W plates, but I am very pessimistic about using them without multi KV plate voltages. You just can't get any emission out of them without the g2 grid to help, or you end up burning the g1 grid in positive territory.
Only possible chance I see would be to try putting some positive screen like voltage on the g3 grid. But g3 generally doesn't have much transconductance, and the "beam" properties sure would be wiped out. Probably act more like a tetrode then if at all.
Don
They look impressive with their 35 or 40 W plates, but I am very pessimistic about using them without multi KV plate voltages. You just can't get any emission out of them without the g2 grid to help, or you end up burning the g1 grid in positive territory.
Only possible chance I see would be to try putting some positive screen like voltage on the g3 grid. But g3 generally doesn't have much transconductance, and the "beam" properties sure would be wiped out. Probably act more like a tetrode then if at all.
Don
smoking-amp said:
Spiral filament 6AU6, for low hum.
I got some 7543 from AES a few years back. They were iron curtain junk that a well known tube relabeller sold to the government as 7543. Who knows what they really were, but they FM'ed so badly in the PTO's of my Collins gear, as to be unusable to me in the only application I have for 7543.
They might have been useable as a 6AU6, but real 6AU6 are still common as dirt.
Win W5JAG
tubelab.com said:
Also often seen dual marked as 6EB8/6GN8.
I think 6GN8 / 6EB8 would be a good spud amp, and I have a bunch of them, but only so much time.
Win W5JAG
I have about 7 or 8 different numbered Beam Triodes. They seem to be identical except for the plate size. They come in big (30 watt) or bigger (35 watt). I have some 6HV5's in both sizes. The cheapest way to go here is the 6JH5 at $3.50 or the 6JK5 at $2.70. both are 35 watt beam triodes without plate caps.
I did find that positive G1 voltage is required to get reasonable current at realistic (550 volts) plate voltages. With a Mu of 300 it doesn't take much positive G1 voltage. I made a single tube SE amp using an emitter follower to drive G1 from a CD player. There was plenty of gain but the bass was very boomy. It sounded like the thumpa - thumpa car down the block. I believe that this was due to a very high output impedance which could be cured by a bunch of NFB.
G3 is a pair of beam forming plates like those found in a 6550. I thought about applying a positive voltage and it didn't seem to make much difference, so I just tied G3 to the plate. Lots more current, but highly nonlinear and a serious propensity for oscillation. I may revisit these tubes for P-P operation.
I have several hundred. Still looking for a good application. I have at least 1000 6AK5's too. Same deal. Maybe I will find a good circuit for them.
- Status
- Not open for further replies.