So You Want to Play With BIG Tubes...

[Kasanay]

I recently bought 3 boxes of tubes from a fella' through Craigslist. When I got to the guys house and saw the tubes, I nearly turned around and left. The boxes were nasty! Many of the tube boxes had been converted into rodent ranches. There was so much mouse crap in the mix, I didn't bother looking through them.
I did, however, see enough good tube numbers so I made the buy.
Once I got them home, I grabbed some gloves, a trash can and shop vac and got them sorted out. I was pleasantly surprised.

Check this out:

 

[primosounds]

Yep, high voltage heaven? Hopefully, not sending you there. Big ham radio tubes, 2 to 3 KV plate voltage. Although some of these can be used as audio finals at more "sane" voltages. You also got some nice triodes like 211, which could be powered by the 2A3 with something like a cascoded 6sn7 for the input. Still mostly around 1 KV for that. Some of the high power pentodes can be trioded to make nice SE amps. Lots of SE 813 amps out there.

 

[Retrovert]

To elaborate on primosounds' comment, the difficulty with running high-voltage tubes at the lower voltages common to HiFi is that the plate curves become very non-linear and the requisite voltages become scary dangerous.

Somewhat simplified, the crux of the problem is that vacuum tubes are designed for a certain amount of attraction between the cathode and plate so electrons may make the journey. That attraction is a function of the potential difference between the cathode and anode (plate). Think about how the screen potential in a tetrode or pentode accelerates electrons to the plate. So the higher voltage not only permits greater spacing between the tube structures, but actually requires such spacing to prevent arcing (aka flashover) between cathode and plate, no matter what the grid does. This means that as the voltage is reduced from the higher levels used for transmitting to the lower levels used in HiFi the electrons are less attracted to the plate and the tube's properties become peculiar. At some point the voltage is so low that electrons don't want to leave the space cloud. Poor agorophobic electrons...

Many years ago I was gifted some high-voltage transmitting triodes from a ham's estate. My discussions with tube manufacturers, including EIMAC, led me to understand the issues and that it was not possible to run those tubes below about 500 VDC and have any sort of linear characteristics. The manufacturers stated that audio uses were not common and suggested I select other tubes with better characteristics.

But it gets worse. Far worse.

The plate impedance is such that special output transformers are required. Because of the voltages involved, and the ensuing unusual ratios, this is tricker and more expensive than it otherwise would be for HiFi.

Some have built HiFi amplifiers using high-voltage tubes running at 1,500 VDC or more, with hand-made power supplies and custom output transformers. Such voltages may be lethal, and working on such amplifiers is dangerous. Tubelab at diyAudio has built these, and his recounting of what is required is enough to give any mad scientist a reason to just put down the tubes and walk away.

Hams will pay you good cash money for some of those tubes. So you may be able to not only recoup your investment, but make enough to buy yourself a pair of new manufacture 300B tubes.

 

[trainbuftony]

While i love Retrovert for constantly being the sane voice of reason. Im going to have to dissgree here, or maybe dissgree isnt the right term. The universe is all cold numbers and hard logic, but the universe also gave you these tubes, because clearly your unique path in life requires a pair of 211 SET monoblock amps. There is no explaining away such a thing with reason or logic, its just something a guy has got to rise to. (Im only kidding. Dont do anything which you ard not 112% sure about)

 

[Retrovert]

As the Tao Te Ching teaches, none is so utterly lost as one who seeks a path where no path exists.

In the case of re-deploying high-voltage transmitting tubes for audio, no path exists.

I suggested converting this path into another: "Hams will pay you good cash money for some of those tubes. So you may be able to not only recoup your investment, but make enough to buy yourself a pair of new manufacture 300B tubes."

Because the 300B is one of the true paths to audio nirvana. Many other paths exist, and I do not deprecate them.

But one must find the path permitted by physics and then walk that path. I cannot outrace an Olympic sprinter. Laws of physics, biology, and all that. But I may get into a car and run over that Olympic sprinter, just like a George Miller movie. Physics!

 

[zackthedog]

Well, I see some pretty useful (and potentially valuable) tubes there--the 211's, the 813s (triode-strapped they make a pretty good sub for the 845), and the 811's. Those 2A3's might be worth quite a bit in resale, or use them to drive the 211's or 813's. The 1625's (807's with 12V filaments) would make a nice PP amp. And I wouldn't mind having those 807's! I don't know what you paid, but that's a pretty good haul, with the potential for some nice projects if you're experienced with high voltages.

 

[larryderouin]

Got a use for those 866's. On the WWII Sub I volunteer on, the Internal communications stack (6ft tall RCA stack) has two amps that use 2 or 4(I can't remember which but it's pretty as hell when lit up!) 866's EACH! (You can hear the General Quarters alarm a block and a 1/2 away, and none of the speaker drivers are outside of the Hull.)

I sent our RM/ET an email in case they come up for sale.

 

[Kasanay]

No problem, Larry. In addition to the ones in the photo, I have several more 866 and 866As. Also 872s.
Let me know what you need.

 

[Retrovert]

Got a use for those 866's. On the WWII Sub I volunteer on, the Internal communications stack (6ft tall RCA stack) has two amps that use 2 or 4(I can't remember which but it's pretty as hell when lit up!) 866's EACH!

The generators are AC?

To clarify, I was thinking that the internal submarine distances are not great, so the inefficiency of DC distribution would not be too extreme, and the systems must run with the generators off which would suggest DC power distribution.

It's been decades since I was on the USS Ling, but I remember the massive banks of lead-acid batteries. Much like an electric car in the 1970s, it seemed that the lead-acid batteries filled much of the ship's volume.

 

[maxhifi]

Those little tiny 807's can be the basis of a fantastic sounding amp.

@Retrovert, have you heard a 211 amp before? I heard a Chinese one at a friend's house - it had about 900V of B+, and is single ended. Into Klipsch speakers, it sounded wonderful.. so, at least for some of these, there is not only hope, but a path.

Isn't there a big McIntosh amp which uses the 8005? And there's lots of ways to use the 811. And the 866 is a legendary ham rectifier, I see some pear shaped ones. .

 

[Retrovert]

@Retrovert, have you heard a 211 amp before? I heard a Chinese one at a friend's house - it had about 900V of B+, and is single ended. Into Klipsch speakers, it sounded wonderful.. so, at least for some of these, there is not only hope, but a path.

No, I haven't heard one.

The first problem is that the 211 needs at least 1,000 VDC, which is lethal. I've been hit with a fraction of that and it got my attention, mistakes never repeated.

Some 211 amplifiers go even higher. Twenty years ago John Camille had one running at 1,200 or 1,300 VDC, don't remember which. Impossible to work on without an HV probe, a hot stick (to disconnect the tech from the chassis in the event of shock), and a paramedic with a defibrillator and a hot shot of adrenaline for the heart. I don't even want to touch a knob on that setup. He also had an OTL one which meant even higher current. Enough to kill a handful of platoons, if not an entire division. Ok, one would have to properly wire the division...

At some point I think tube audio moves into a category where therapy, plus a day program with adequate oversight, is required to keep everyone out of trouble.

The second problem is it needs a custom output transformer with a 20k primary. Hard to get the inductance/capacitance right to maintain flat response at low end and high end.

I'm not afraid of high voltage, BTW, I'm just very cautious. I have a pair of KLH Nines which need power supply rebuilds. Those run at 7,000 VDC, so potted in wax, which must be decanted, to avoid arcing. This spring Ian and I were going to have a group rebuild of those for safety, and I was going to borrow a portable defibrillator from a paramedic friend (this is not a joke, such voltage is lethal), but he died last fall and we never had the chance to rebuild.

And the 866 is a legendary ham rectifier, I see some pear shaped ones. .

You mean legendary for its spectacular RF hash generation? Yeah, it is certainly is legendary.

 

[maxhifi]

No, I haven't heard one.

The first problem is that the 211 needs at least 1,000 VDC, which is lethal. I've been hit with a fraction of that and it got my attention, mistakes never repeated.

Some 211 amplifiers go even higher. Twenty years ago John Camille had one running at 1,200 or 1,300 VDC, don't remember which. Impossible to work on without an HV probe, a hot stick (to disconnect the tech from the chassis in the event of shock), and a paramedic with a defibrillator and a hot shot of adrenaline for the heart. I don't even want to touch a knob on that setup. He also had an OTL one which meant even higher current. Enough to kill a handful of platoons, if not an entire division. Ok, one would have to properly wire the division...

At some point I think tube audio moves into a category where therapy, plus a day program with adequate oversight, is required to keep everyone out of trouble.

The second problem is it needs a custom output transformer with a 20k primary. Hard to get the inductance/capacitance right to maintain flat response at low end and high end.

I'm not afraid of high voltage, BTW, I'm just very cautious. I have a pair of KLH Nines which need power supply rebuilds. Those run at 7,000 VDC, so potted in wax, which must be decanted, to avoid arcing. This spring Ian and I were going to have a group rebuild of those for safety, and I was going to borrow a portable defibrillator from a paramedic friend (this is not a joke, such voltage is lethal), but he died last fall and we never had the chance to rebuild.

You mean legendary for its spectacular RF hash generation? Yeah, it is certainly is legendary.

The 866 looks cool because of the purple glow. It was also a very popular ham tube. No modern use, sure, but I wouldn't mind one for my tube collection.

120V can be lethal. I always cringe when someone who doesn't have any training dives into a tube amp, where DC and AC voltages are well into the hundreds. 1000V is bad, very bad to touch. That said, proper planning prevents poor performance... and if one is inclined towards the needlessly complex and eccentric, its possible to be rewarded with an interesting sonic experience. OR, you could buy somethint you really want for the value of those 211.

Have to say though that Chinese amp I heard really did sound good.

 

[Retrovert]

The 866 looks cool because of the purple glow. It was also a very popular ham tube. No modern use, sure, but I wouldn't mind one for my tube collection.

The purple glow is why it is sought out for HiFi rectification. The fact is that it spews RF hash, and this can destabilize an amplifier. Tubes are happy to amplify up to a hundred MHz, well, without stoppers to ruin the Q.

120V can be lethal.

Too true. Forty years ago I zapped myself by having one hand holding the scope probe and touching a hot-chassis tube amplifier chassis, which of course had the non-polarized plug reversed, while reaching to adjust the metal-chassis Tek 585. 120 VAC right across the chest. I felt my heart constrict, not beat for a few beats, and then restart. It was an interesting experience, but one I decided need not be repeated.

I always cringe when someone who doesn't have any training dives into a tube amp, where DC and AC voltages are well into the hundreds. 1000V is bad, very bad to touch.

At the same time it results in a really sweet pile of tube gear and electronics books left at the curb.

A CRT poses a similar problem. The muscle spasm will knock someone across the room, just like a defibrillator.

That said, proper planning prevents poor performance... and if one is inclined towards the needlessly complex and eccentric, its possible to be rewarded with an interesting sonic experience. OR, you could buy somethint you really want for the value of those 211.

That was my point. The tubes are valuable, best use them as money and purchase something usable and desirable. I'd build an SE with the 2A3s, because it would be possible lay in a stock of replacements. But to mess around with high voltage which requires expensive and deadly power supplies, plus really expensive output transformers? Yeah, not so much. I'm way past the "Death by Misadventure" glory days of electronics.

 

[maxhifi]

The purple glow is why it is sought out for HiFi rectification.

It is? I'm speechless... old radios used to put a shield around mercury vapor rectifiers.. who in their right mind would use one in hifi application? It must be one of those tubes as jewelry type amps.

Too true. Forty years ago I zapped myself by having one hand holding the scope probe and touching a hot-chassis tube amplifier chassis, which of course had the non-polarized plug reversed, while reaching to adjust the metal-chassis Tek 585. 120 VAC right across the chest. I felt my heart constrict, not beat for a few beats, and then restart. It was an interesting experience, but one I decided need not be repeated.

I got bit by the B+ of a tandberg 64x.. that was enough high voltage for me, I had to lay down for half an hour before my heart stopped racing.

That was my point. The tubes are valuable, best use them as money and purchase something usable and desirable. I'd build an SE with the 2A3s, because it would be possible lay in a stock of replacements. But to mess around with high voltage which requires expensive and deadly power supplies, plus really expensive output transformers? Yeah, not so much. I'm way past the "Death by Misadventure" glory days of electronics.

True enough.. been there done the though, the 2A3 is a sweet sounding amp, but the output power is quite a limitation.

Regardless of if the OP is into dangerous esoteric amps or not, it's a super find. All I ever find is old TV tubes

 

[Retrovert]

It is? I'm speechless... old radios used to put a shield around mercury vapor rectifiers.. who in their right mind would use one in hifi application? It must be one of those tubes as jewelry type amps.

Yeah, it's a thing. Look at all the builds where the designers says, "I'm using mercury rectifiers!" Only because the only noisier rectifier is a noise diode and those don't carry any current.

True enough.. been there done the though, the 2A3 is a sweet sounding amp, but the output power is quite a limitation.

Sure, but headphones are great, and so are very efficient full-range drivers. No way to run an AR-3 off a 2A3.

Regardless of if the OP is into dangerous esoteric amps or not, it's a super find. All I ever find is old TV tubes

And I bet not even the good ones like an 807. Weirdo tubes like remote cutoffs for AGC and pentagrids for mixers. Ok, one can make guitar effects out of the remote cutoffs and theremins out of the pentagrids, but yeah, useless weirdo TV tubes is all I ever find, too. Boxes used as snacks and toilets by mice, half of them gone to air, priced like they're all NOS 300B's, NIB, too. "You can't fool me, sonny, I know these tubes are valuable!"

 

[Kasanay]

Those little tiny 807's can be the basis of a fantastic sounding amp.

@Retrovert, it sounded wonderful.. so, at least for some of these, there is not only hope, but a path.

Isn't there a big McIntosh amp which uses the 8005? And there's lots of ways to use the 811 .

The McIntosh MI200 uses a pair of 8005 tubes to produce 200 Watts.
The 809, 801, TZ-40, 1625, 813, 830, 807, 211 have all been used by amp builders using near 1KV. The 826, 3C24 and 1646 have been built into amps with much lower voltage.

 

[arts]

I'd call dibs on the 811's. My Altec 1570B's could use some new friends

 

[kirk57]

At some point I think tube audio moves into a category where therapy, plus a day program with adequate oversight, is required to keep everyone out of trouble.

Now that's just funny.

 

[W9TR]

I think everyone is setting their sights too low.

Consider the Eimac 4CX35000C
10V 300A filament
15kV @ 20A on the plates

A pair running push pull AB would make a nice Monoblock.

 

[Retrovert]

I think everyone is setting their sights too low.

Consider the Eimac 4CX35000C
10V 300A filament
15kV @ 20A on the plates

A pair running push pull AB would make a nice Monoblock.

THAT'S not an amplifier; THIS is an amplifier!

We are all humbled by your proposed quarter mega-watt single-ended amplifier with a transformer the size of a suburban home. The push-pull version would generate more eddy currents than one of US Steel's legendary arc furnaces and would require restricted airspace zones for hundreds of miles around it, lest the induced currents melt low-flying planes. The DC filament supply alone would require an entire month's copper output from Bolivia. Pacemakers on the other side of the planet would fail when it played Kenny G., while Motörhead at low volumes would cause entire nations to spontaneously combust. This would be the only amplifier worthy of Disaster Area, which would commission a few gross, merely on general principles.

Disaster Area was a plutonium rock band from the Gagrakacka Mind Zones and was generally regarded as not only the loudest rock band in the Galaxy, but also as being the loudest noise of any kind at all. Regular concert goers judged that the best sound balance was usually to be heard from within large concrete bunkers some thirty-seven miles away from the stage, whilst the musicians themselves played their instruments by remote control from within a heavily insulated spaceship which stayed in orbit around the planet—or more frequently around a completely different planet.

Their songs are on the whole very simple and mostly follow the familiar theme of boy-being meets girl-being beneath silvery moon, which then explodes for no adequately explored reason.

Many worlds have now banned their act altogether, sometimes for artistic reasons, but most commonly because the band's public address system contravenes local strategic arms limitations treaties.

The Restaurant at the End of the Universe by Douglas Adams​