Seems 6LU8 is a sweep tube, here's a thread about them:
Vertical deflection tubes for audio output?
Vertical deflection tubes for audio output?
The pentode inside the 6LU8 and 6LR8 (same guts, different base) is not equivalent to the 6L6GC. It's more like a 6EZ5 or 6W6. The triode inside is like a 12AT7.
That said they do make a decent little audio amp. You will get 2 watts or so in triode mode, or maybe 5 watts in pentode in a single ended amp. A pair in push pull will make at least 25 watts.
I used them to make a single ended HiFi amp a dozen years or so ago. This started out with a Tubelab SSE board and a bag full of clip leads. I did make a PC board for it, but it never got beyond the prototype stage.
These tubes like other TV sweep tubes have a fragile screen grid, respect its maximum voltage spec and they will live long and prosper.
That said they do make a decent little audio amp. You will get 2 watts or so in triode mode, or maybe 5 watts in pentode in a single ended amp. A pair in push pull will make at least 25 watts.
I used them to make a single ended HiFi amp a dozen years or so ago. This started out with a Tubelab SSE board and a bag full of clip leads. I did make a PC board for it, but it never got beyond the prototype stage.
These tubes like other TV sweep tubes have a fragile screen grid, respect its maximum voltage spec and they will live long and prosper.
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Thanks George, I was asking two different questions, one is the 6LU8 beam pentode really like a 6V6 which you answered pointing out that it is more like a 6W6. I've looked into this a bit more and it seems that most of the 6V6 guitar amps pushed the 6V6 way beyond the spec with 420V on the plates and nearly as much on the screens. I have to wonder if they got STR tubes for those 6V6 s? Odd thing is that they only claim 20-22W for those designs which I think you can do with much lower voltages.
I have to wonder if old NOS 5V6 or 12V6 will take plate and screen voltages up around 400?
The other question was if there is a compactron with similar beam power section specs to any 6L6 and more so the GB or GC. Or really any cheap tube, doesn't have to be a compactron.
The 6GB6 or 19GB6 (not the special ones with GC guts) might make a good 6L6GB alternative. I don't really like the cap on top. It is interesting that the 5881 has a screen rating of 400V which seems to make it a good choice for these amps - I have a bunch of
them that were given to me.
Nice project there George, where did you run the screens?
I have to wonder if old NOS 5V6 or 12V6 will take plate and screen voltages up around 400?
The other question was if there is a compactron with similar beam power section specs to any 6L6 and more so the GB or GC. Or really any cheap tube, doesn't have to be a compactron.
The 6GB6 or 19GB6 (not the special ones with GC guts) might make a good 6L6GB alternative. I don't really like the cap on top. It is interesting that the 5881 has a screen rating of 400V which seems to make it a good choice for these amps - I have a bunch of
them that were given to me.
Nice project there George, where did you run the screens?
If I would have known about 5V6's back befor mail to Canada was going up I would have bought some. But my supply of 12V6's should last me my life. If not I have my 12AB5's. I built a 390V PS amp with them. With nice polite sine waves turned into square waves I think the voltage might have dropped to 360-370V, clean the tube never even blinked at those voltages. I think Harman Kardon used the 12AB5 in one of their amps at these voltages, but hifi is a little more polite to their tubes.
Oh my, I am a little short on voltage it seems. Sorry for the big picture, thought it would resize. Wonder what the impedance ot the OT was?
Oh my, I am a little short on voltage it seems. Sorry for the big picture, thought it would resize. Wonder what the impedance ot the OT was?
Fender and others ran 6V6's in the 350+ volt range on the plate. Feed that amp the typical 120+ volt live voltage we see today and they are near 400 volts. I have fed several different kinds of old 6V6 metal envelope, 6V6GT, and 6V6GTA glass tubes plate voltages in excess of 400 volts without issue, but I kept the screen down in the 300 volt range.
The 6BD5GT is a 6L6GB with it's plate fins trimmed to fit into 6V6 size glass. These are somewhat hard to find.
I ran the 6LR8 amp in triode mode or UL mode. This puts the screen grid at nearly the same voltage as the plate, which was about 320 volts in these tests,
Aww shucks, your worth it. Seems my big picture ain't so big any more. a direct link. Seem to recall them running at 25mA.
http://www.audiophool.com/Schem_A/H-K_A-1040_sch.gif
http://www.audiophool.com/Schem_A/H-K_A-1040_sch.gif
Thanks for that, amazing that they ran them at such high voltages, especially the
screens. So for now I'll assume that I can try 5V6 and 12V6 at very high voltages.
5V6 is neat because you can add a resistor to the 6.3V winding or use a 5V rect
tube winding. Interesting that the 5V6 has a 4.7V heater when most rect tubes
are 5.0V.
screens. So for now I'll assume that I can try 5V6 and 12V6 at very high voltages.
5V6 is neat because you can add a resistor to the 6.3V winding or use a 5V rect
tube winding. Interesting that the 5V6 has a 4.7V heater when most rect tubes
are 5.0V.
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This claims to be a "complete" list of sweep tubes, nice that it has the screen voltage rating:
"Complete" list of sweep tubes
6JC5 is interesting with 300V screen, only .8A on the heaters, and they still seem to be cheap.
Well, not that cheap.
"Complete" list of sweep tubes
6JC5 is interesting with 300V screen, only .8A on the heaters, and they still seem to be cheap.
Well, not that cheap.
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The 6JC5 is very similar to the 6JB5 and the 6HE5. Late in the tube production era it was common to find all three type numbers on the same tube. The Sylvania data sheet also lumps all three type numbers together, but there were some differences in the early tubes. In some cases they look and perform quite like the pentode inside the 6LU8 / 6LR8.
GE's own "Compactron list" from 1964 gives the origin of what's really inside some of those 12 pin fat bottles. They show that the 6HE5 is really a 6EZ5, which was a decent audio amp, and on the dollar list at some tube sellers until someone read about it on this forum, and poof 7,000 tubes vanished in a few weeks. No more $1 6EZ5's.
The 6EZ5 is a somewhere between a 6V6 and a 6W6 spec wise. The 6JC5 / 6JB5 / 6HE5 can be a variety of things depending on what number is on it, and when it was made. If you are looking to buy some I would try to make sure that you get identical tubes, otherwise you might get some that wouldn't work well together in a push pull amp.
In post #248 in the long thread about Pete's Engineers Amp I stuffed some of the 6JC5 tubes into his board and cranked them up. I got 25 WPC without violating any specs. I never got to really squeezing them hard though.
https://www.diyaudio.com/forums/tubes-valves/151206-posted-power-amp-design-25.html#post2079822
I assume that since you are asking in the instruments and amps forum that you may be looking to make a guitar amp? SE or P-P? how much power, and what is your guess at supply voltage? Is a lower screen voltage than the plate voltage a possibility? In some cases it is still possible to bet into the 20 to 30 watt range with cheap (under $3) tubes.
This little breadboard uses some old radio tubes to make 20 watts. I let it run at full power overnight with no ill effects. It will be a guitar amp when I ever get around to finishing it. See posts #39 and 57 here:
UNSET is coming?
There was also some good discussion of making cheap guitar amps in this thread:
5E3 Blackface Single End Amp
GE's own "Compactron list" from 1964 gives the origin of what's really inside some of those 12 pin fat bottles. They show that the 6HE5 is really a 6EZ5, which was a decent audio amp, and on the dollar list at some tube sellers until someone read about it on this forum, and poof 7,000 tubes vanished in a few weeks. No more $1 6EZ5's.
The 6EZ5 is a somewhere between a 6V6 and a 6W6 spec wise. The 6JC5 / 6JB5 / 6HE5 can be a variety of things depending on what number is on it, and when it was made. If you are looking to buy some I would try to make sure that you get identical tubes, otherwise you might get some that wouldn't work well together in a push pull amp.
In post #248 in the long thread about Pete's Engineers Amp I stuffed some of the 6JC5 tubes into his board and cranked them up. I got 25 WPC without violating any specs. I never got to really squeezing them hard though.
https://www.diyaudio.com/forums/tubes-valves/151206-posted-power-amp-design-25.html#post2079822
I assume that since you are asking in the instruments and amps forum that you may be looking to make a guitar amp? SE or P-P? how much power, and what is your guess at supply voltage? Is a lower screen voltage than the plate voltage a possibility? In some cases it is still possible to bet into the 20 to 30 watt range with cheap (under $3) tubes.
This little breadboard uses some old radio tubes to make 20 watts. I let it run at full power overnight with no ill effects. It will be a guitar amp when I ever get around to finishing it. See posts #39 and 57 here:
UNSET is coming?
There was also some good discussion of making cheap guitar amps in this thread:
5E3 Blackface Single End Amp
Yes, the plan is to try to do a PP 15W guitar amp for the hundred buck challenge (maybe
$150 since prices have gone up). My son might use this as a practice amp since all of his
amps are 50 to 100W at this point.
Then also to do another amp in the 20 to 50W range, with parts that I have but with options
for cheap parts if possible. This might be to replace my son's Hot Rod Deville that he really
does not like. I've worked on this "modern" Fender amp and while it has lots of pieces that
look like the old Fenders it is different enough to probably explain why he doesn't like the
sound. People say that once you start doing mods to the cheap PC board, lands quickly lift,
and you end up with a mess.
I also happen to have a lot of the parts that could go into a PP parallel 80-100W 6L6GC type
amp. That might happen someday but we really have no need for so much power.
I have more common parts (not compactrons) to build these things but am always looking
in the spirit of the hundred buck challenge for ways to do them cheaply.
Seems like a lot of tubes have gone up in price as you mentioned. I can't even find a $1
seller for tubes.
Thanks for the input George, I'll check out those threads in more detail, always a fun read.
It seems to me that if one wants to build a 6V6/6L6GB type PP amps with cheap tubes the
6BG6/19BG6 are a good way to go.
$150 since prices have gone up). My son might use this as a practice amp since all of his
amps are 50 to 100W at this point.
Then also to do another amp in the 20 to 50W range, with parts that I have but with options
for cheap parts if possible. This might be to replace my son's Hot Rod Deville that he really
does not like. I've worked on this "modern" Fender amp and while it has lots of pieces that
look like the old Fenders it is different enough to probably explain why he doesn't like the
sound. People say that once you start doing mods to the cheap PC board, lands quickly lift,
and you end up with a mess.
I also happen to have a lot of the parts that could go into a PP parallel 80-100W 6L6GC type
amp. That might happen someday but we really have no need for so much power.
I have more common parts (not compactrons) to build these things but am always looking
in the spirit of the hundred buck challenge for ways to do them cheaply.
Seems like a lot of tubes have gone up in price as you mentioned. I can't even find a $1
seller for tubes.
Thanks for the input George, I'll check out those threads in more detail, always a fun read.
It seems to me that if one wants to build a 6V6/6L6GB type PP amps with cheap tubes the
6BG6/19BG6 are a good way to go.
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Another list of TV tubes, especially the list from smoking-amp:
https://www.diyaudio.com/forums/tubes-valves/211254-magnificent-television-tubes-39.html#post4160682
https://www.diyaudio.com/forums/tubes-valves/211254-magnificent-television-tubes-39.html#post4160682
Way back about 10 years ago George mentioned the 20EZ7 as a replacement for the 12AX7
and they were available for $4 per tube, now they are $7 - $15.
Any other options, don't mind alternate pin out and voltage but I prefer to stay at 9 pin.
Any opinions on the Russian 6n2p? I'm aware that they are a different pin out and 6.3V
heater only but never tried them.
I've also never bought from the Ukraine or Russia.
Also, is there a 19-20V version of the 12AT7?
and they were available for $4 per tube, now they are $7 - $15.
Any other options, don't mind alternate pin out and voltage but I prefer to stay at 9 pin.
Any opinions on the Russian 6n2p? I'm aware that they are a different pin out and 6.3V
heater only but never tried them.
I've also never bought from the Ukraine or Russia.
Also, is there a 19-20V version of the 12AT7?
There are no obvious 9 pin equivalents for the 12AX7. The 12AX7 has a Mu of 100, which is not too common in something that wasn't intended for audio. Tubes that were used for audio have gotten more expensive due to the demand. There are quite a few lower gain options that were intended for TV or computer use. This may mean an extra stage in the preamp.
There are some 7 pin tubes that were originally used in radios that contain 1/2 of a 12AX7 available in several heater voltages, just ignore the extra diodes. The 3AV6, 6AV6, 12AV6 and 18FY6 all contain a 12AX7 triode. I have used the 6, 12, and 18 volt flavors in guitar amps with good results.
There is a 35DZ8 9 pin tube that contains a 12AX7 triode and a small output pentode. I got a few back during the HBAC builds, but never actually tried them. It also comes in 6, 9, 12, and 18 volt versions.
There are some other 9 pin triode / pentode pairs that are useful and often cheap. The 6EB8, 6GN8, 6JT8, and 6KT8 all have 1/2 of a 12AX7 paired with a high Gm pentode. The 6LY8 and 6MV8 each have a high gain triode that's similar to 1/2 of a 12AX7. Some of the pentodes are big enough for output duty at the 1 to 3 watt (SE) and 5 to 10 watt (P-P) level. All are relatively cheap. Look on the list I linked below.
There are a few Compactron tubes that contain 12AX7 guts, but some have become quite rare. The 6C10 is 3/2 of a 12AX7, but Ampeg used them in a guitar amp, so they are expensive now. The 6D10 is 3/2 of a 12AT7. The 6K11 is a 12AX7 (two of the three triodes) plus 1/2 of a 12AU7. I haven't priced any of these in a long time.
There were two Florida vendors that put tubes on the $1 list during the HBAC days. Unfortunately Stan at ESRC passed away about a year ago and I believe that his 4 million tube warehouse is tied up in a probate battle. It was one of my favorite places to visit on a Florida vacation to Orlando. I met Stan when his father ran the company maybe 40 years ago.
The other is VacuumTubes.net. They still have a cheap tubes list, but most of the "lots of power for low$$$" tubes are gone. I grabbed a bunch of 25DN6's when they were 50 cents each. I can squeeze 100 watts from a pair of them. The 17BQ6GT and 25BQ6GT's are still cheap. They are good for 35 to maybe 50 watts per pair. You can still get tubes from this list for 35 cents to $1 each depending on quantity.
Quantity Specials
