What Differences Between EL84s and 6V6es?

[e-merlin]

I've had several EL84 amps but never one with 6V6es. I'm wondering what the basic differences in tone would be. And any other differences, for that matter...

[Wally]

Depending on the 6V6 you use, there might be very little difference. That is, modern JJ
6v6's are closer to being a 6L6-type of tube in many ways.
If we are talking true 6V6's, the EL-84's might be a bit softer on the break-up...depending on the biasing situation of course. I have often wanted to use some Yellowjackets on a 6V6 amp just to run the experiment you are interested in.
Circuits are big factors in sonics. The El-84 and the 6V6 have similar operating parameters, if I am not mistaken.

[e-merlin]

I would just love to get close to that 6L6 tone in a lower power amp.

[marshman]

Aren't there some tweed circuits with 6L6s that make around 25 watts? Low volts, cathode bias and moderately sized iron should get you pretty close. Probably won't sound very BF, but hey, it's a start.

http://www.ampwares.com/amp.asp?id=137

Don't get me wrong, I'm seriously jonesin' a 6V6GT amp myself, but think I wanna go BF, probably a DR(RI or DIY, not sure yet), though I took pretty well to the 18 watt reverbless thang, so maybe Tweed is the way to go.

[JohnnyCrash]

Yeah, the circuit is the main thing, not the tubes.

A Vox AC15 (EL84's) is more tweed Deluxe (6V6) than a BF Deluxe, but a Peavey Classic 50 (EL84's) is more like a BF Deluxe (6V6) than a Vox AC30 - roughly. In sound, not in circuit.

Fixed bias with solid state rectification and huge filter caps can mean the amp has more bass than one would assume a EL84 amp would have. Compare a cathode biased, basic circuit like the 5E3 tweed Deluxe and your 6V6's sound not so much like a BF Deluxe with the same 6V6's.

Most people instantly say EL84's are "British," but many early '40s and '50s Gibsons used EL84's (known as 6BQ5's in America)... sometimes we over-generalize, so listen to the amp, not what tubes it uses.

Originally Posted by marshman

Aren't there some tweed circuits with 6L6s that make around 25 watts? Low volts, cathode bias and moderately sized iron should get you pretty close. Probably won't sound very BF, but hey, it's a start.

http://www.ampwares.com/amp.asp?id=137

Don't get me wrong, I'm seriously jonesin' a 6V6GT amp myself, but think I wanna go BF, probably a DR(RI or DIY, not sure yet), though I took pretty well to the 18 watt reverbless thang, so maybe Tweed is the way to go.

I've built a few cathode biased tweed style 6L6 amps and I have to say what most folks characterise as a "classic 6L6 sound" is not there so much. Early tweed, low watt 6L6 circuits don't have that really big and tight clear bottom and glassy top - they almost act like louder 6V6's... different than 6V6's, but not like a Mesa or Twin Reverb at all (or other 6L6 amps).

[Scott S]

Going by the RCA data, a pair of 6V6's at 250V into a 10,000Ω load is good for about 10 watts. With fixed bias, a solid-state rectifier, and decent filtration, that should make for a fairly tight amp without getting ridiculously loud. JC, have you built anything like this? In theory, it would fit e-merlin's needs nicely, but it's hard for me to "hear" prospective designs in my head.

I've heard people on the interwebs going nuts over fixed-bias EL84 amps, too...

- Scott

[patrickhowell]

Originally Posted by e-merlin

I would just love to get close to that 6L6 tone in a lower power amp.

A single-ended 6L6 is good for about 12 watts. How's that sound ?

[e-merlin]

Originally Posted by Scott S

Going by the RCA data, a pair of 6V6's at 250V into a 10,000Ω load is good for about 10 watts. With fixed bias, a solid-state rectifier, and decent filtration, that should make for a fairly tight amp without getting ridiculously loud. JC, have you built anything like this? In theory, it would fit e-merlin's needs nicely, but it's hard for me to "hear" prospective designs in my head.

I've heard people on the interwebs going nuts over fixed-bias EL84 amps, too...

- Scott

I know zilch about amp design. I would like to build something, but now that I have a job, time is limited, so I probably won't build anything I can't find in kit form.

[hwestman]

Don't know if this is a valid comparison. Take it for what it is...

In my Superchamp I run Ruby Tone Bones and my impression is that the top end gets a bit silkier, there is more compression and sweeter, less grainy overdrive.

Now I haven't tried different 6V6'es or EL84s and in addition the Tone Bones run the amp in cathode bias mode...

So from a scientific standpoint my observation doesn't really count for much....

[sjhusting]

Originally Posted by Scott S

Going by the RCA data, a pair of 6V6's at 250V into a 10,000Ω load is good for about 10 watts.

Sounds like a pair of 6AQ5s. I've got a bunch of those that I'm trying to decide what to do with.

steven

[Scott S]

Originally Posted by sjhusting

Sounds like a pair of 6AQ5s. I've got a bunch of those that I'm trying to decide what to do with.

steven

Yeah, supposedly they're the electrical equivalent of 6V6's, except with lower max voltages. If you have enough, how about a quad of them for ~28W? With fixed bias and a little negative feedback, it's the CBS Fender answer to the AC30 that never was!

I'm kinda in the same boat. I've amassed lots of tubes, most of them unusable in Fender/Marshall/Vox amps, but would probably sound just fine if I designed something around them. The problem is that I only have one of a lot of them!

- Scott

[marshman]

I've also got a litle stockpile of 6AQ5s...thinking something PR-ish will be the result, but the great thing about not knowing much about how to actually build amps is that it gives me plenty of time to dream.

[ntasher]

I have had a bunch of 6AQ5 laying around for years. My first go at tube amps some 18 years ago was a push pull design around them. I remember watching in awe how one of them started glowing red... then little sparks went off inside... hmmm...
I later built a 4W single ended 4x4" combo with one of the survivors. It was nice but nothing remarkable. Haven't looked at them in years....

[sjhusting]

Gibson did some 6AQ5 amps, like the GA17. The first version of the Musicmaster bass amp used them too.

I've got eight, mostly Phillips, and I'm going to do something with them, I just don't know what. All NIB. Maybe a little DR. Maybe a little Plexi.

The first amp I built was a single-ended 6L6; pretty much a Fender BF preamp in front of the tube. It sounded fine, actually, though looking at pictures of the guts today scares the bejeezus out of me. Made maybe 8-9 watts with ~315 V on the plate.

steven

[skibum1999]

the sound of an amp is 85% in the circuit, 14% in the speaker, and 1% in everything else. and the player, too, of course :). i dont care if its handwired, ptp, pcb, smd, runs 6v6 or 4x4,. it astonishes me that builders arent wise enough to offer mass produced, pcb clones of classic amps (d*mble, train*reck, Match*ess, etc) at low prices. id be all over them!

[Wally]

6AQ5....I have a voice of Music component stereo system that runs 6AQ5's. I also have a Harmon Kardin stereo amp that runs 6BQ5's. These amps get good hifi sonics....firm bass, good highs....
I have one or two GIbson/Epi amps that are running 6AQ5's. My take is that it is the circuit more than it is the tube. One can design around a tube's parameters to achieve the sonics one wants...within certian limits, of course.

[e-merlin]

Originally Posted by skibum1999

the sound of an amp is 85% in the circuit, 14% in the speaker, and 1% in everything else.

I tend to disagree with your proportions. I think it's more like 40-50% speaker, just based on my experience. I don't suppose you'd ever make a Gorilla sound like a Twin just by plugging it into a Twin's speakers, but I bet a quick listen would fool you.

[JohnnyCrash]

I agree that a speaker has a major role as well. IDK about 40%-50% though. While a Vox AC30 aint the same without Celestion Blues, it still sounds very much like a Vox without em.



6AQ5 tubes
Hmm... I think I have a few 6AQ5's laying around. I never got to looking at any spec sheets on them so maybe now is a good time for a "group project" hehehe

We could break-in the new Shock Brothers DIY amp forum section here with a circuit design brainstorming and build. Heck maybe we could design a nice new modern guitar amp from the ground up around these tubes.

Perhaps staying away from borrowing too much from existing 6AQ5 designs.

What do you guys think?

[muchxs]

Within its limits a 6AQ5 is equivalent to a 6V6. Its limits are primarily plate voltage, by the book plate voltage is supposed to be maxed at 275 volts. You can get away with 300 volts on the plates cathode-biased.

It's a handy little audio output. The 7 pin miniature socket doesn't take up much space, it goes in a 5/8" hole.

Reverb driver tube, perhaps?

[Wally]

Originally Posted by muchxs

Within its limits a 6AQ5 is equivalent to a 6V6. Its limits are primarily plate voltage, by the book plate voltage is supposed to be maxed at 275 volts. You can get away with 300 volts on the plates cathode-biased.

It's a handy little audio output. The 7 pin miniature socket doesn't take up much space, it goes in a 5/8" hole.

Reverb driver tube, perhaps?

I would have thought that the 6BQ5 is much closer to the 6V6 in performance specs than the 6AQ5 woudl be?
http://tdsl.duncanamps.com/show.php?des=6AQ5
http://tdsl.duncanamps.com/show.php?des=6BQ5
http://tdsl.duncanamps.com/show.php?des=6V6

[muchxs]

Originally Posted by Wally

I would have thought that the 6BQ5 is much closer to the 6V6 in performance specs than the 6AQ5 would be?.

Tsk, tsk. (Re: 6AQ5) According to RCA,

"Within its ratings this type is equivalent in performance to larger types 6V6 and 6V6GTA."

[Wally]

What's with the 'tsk, tsk' crap???? Share what you have to share without an attitude, muchxs, if you please. That type of 'excess' is something I don't need or care for.
All 3 of those tubes seems to be in the same general range of performance.
I have read...maybe bad info...that the 6BQ5 is a 9-pin equivalent of the 6V6.
Just trying to learn here....if you can teach, please do so. Good teachers don't 'tsk' anyone. Someone stole my RCA manual, so I don't have the benefit of that resource.
What does it say about the 6BQ5? I am not formally trained and don't interpret all of those parameters. I do know that these tubes are soemtimes stressed beyond design in order to do what we ask them in these gutiar amps, right? If that is incorrect, please educate us.

[muchxs]

Originally Posted by Wally

What's with the 'tsk, tsk' crap???? Share what you have to share without an attitude, muchxs, if you please. That type of 'excess' is something I don't need or care for.
All 3 of those tubes seems to be in the same general range of performance.
I have read...maybe bad info...that the 6BQ5 is a 9-pin equivalent of the 6V6.
Just trying to learn here....if you can teach, please do so. Good teachers don't 'tsk' anyone. Someone stole my RCA manual, so I don't have the benefit of that resource.
What does it say about the 6BQ5? I am not formally trained and don't interpret all of those parameters. I do know that these tubes are soemtimes stressed beyond design in order to do what we ask them in these gutiar amps, right? If that is incorrect, please educate us.

Lighten up, bro.

RCA wasn't concerned with comparing the 6BQ5 and the 6V6.

Europeans embraced the 6BQ5 (EL84), we here in North America went for the 6V6. While 6V6s were used as audio outputs for early television sets they were eventually supplanted by 6AQ5s. The 6AQ5 is almost ubiquitous as an audio output in old televisions.

[Wally]

much..xs, I have read your posts since you joined and have found them to be enlightening.
I don't need some 'tsk,tsk'....and I don't need you telling me to lighten up when you are the one with the attitude. Take your own advice. Present your thoughts in a civil manner, if you please. Take your 'tsk,tsk' and use them where they are appropriate.
Re: the question at hand.....I didn't ask you to tell me where these tubes where used.
I asked you to define your thoughts on the performance of the 3 tubes and delineate the difference in the performance parameters. I also don't think that quoting some one liners from the RCA manual is the complete story on these tubes. Looking at the parameters, I am thinking that the 6BQ5 could be used in the same situations that the other two tubes are used. If I am incorrect, please explain. I understand that due to the smaller size of the 6AQ5 compared to the other two that it might have been advantageous in TV sets from that point of view.
'Bros' don't tsk,tsk each other. They share in a civil manner. IF you don't care to be civil; leave the 'bro' at home, too, in your responses to my posts. Condescending attitude...tsk,tsk and bro...same crap in this situation.

[Wayne Alexander]

e-merlin, back to your original question, though it's possible to design amps that sound pretty similar with different output tubes, if you have EL84 amps, I presume they fall in the Marshall 18-watt or Vox AC15 or AC30 category sonically. The amps that are commonly used that have 6V6's in them tend to fall into the Tweed Champ, Tweed Deluxe or Blackface Deluxe Reverb categories sonically (those are VERY different sounds) though there are obviously lots of other possibilities. Have you played those types of amps? If not you should try them to get a sense of what those amps sound like, which are arguably in the "main" camps of commercial amp designs using 6V6's. It's as much circuit design and speaker type as output tube type, but those amps sound very different from Voxes and Marshalls in stock form.

[muchxs]

Originally Posted by Wally

much..xs, I have read your posts since you joined and have found them to be enlightening.
I don't need some 'tsk,tsk'....and I don't need you telling me to lighten up when you are the one with the attitude. Take your own advice. Present your thoughts in a civil manner, if you please. Take your 'tsk,tsk' and use them where they are appropriate.
Re: the question at hand.....I didn't ask you to tell me where these tubes where used.
I asked you to define your thoughts on the performance of the 3 tubes and delineate the difference in the performance parameters. I also don't think that quoting some one liners from the RCA manual is the complete story on these tubes. Looking at the parameters, I am thinking that the 6BQ5 could be used in the same situations that the other two tubes are used. If I am incorrect, please explain. I understand that due to the smaller size of the 6AQ5 compared to the other two that it might have been advantageous in TV sets from that point of view.
'Bros' don't tsk,tsk each other. They share in a civil manner. IF you don't care to be civil; leave the 'bro' at home, too, in your responses to my posts. Condescending attitude...tsk,tsk and bro...same crap in this situation.

Would you like me to leave? Just say so.

I bring what I bring and I bring it my way. If you left your sense of humor at the door I guess this forum isn't for me.

[Wally]

muchxs, I have a great sense of humor. I have also a sense of propriety. tsk, tsk....is not appropriate for sharing ideas, and it is not humorous. I don't care for you to leave. I wouldn't ask you to leave even if it were in my purview. I just don't want to be talked down to, and I will take excepetion to it anytime, anyplace.
Here's some humor for you.....
A little old lady sees a little boy peeing in her flowers....through the lace around her throat she says...'tsk,tsk...' The little boy says: Nah, lady, that ain't no 'tsk'...that's my penis.

[e-merlin]

Originally Posted by Wayne Alexander

e-merlin, back to your original question, though it's possible to design amps that sound pretty similar with different output tubes, if you have EL84 amps, I presume they fall in the Marshall 18-watt or Vox AC15 or AC30 category sonically. The amps that are commonly used that have 6V6's in them tend to fall into the Tweed Champ, Tweed Deluxe or Blackface Deluxe Reverb categories sonically (those are VERY different sounds) though there are obviously lots of other possibilities. Have you played those types of amps? If not you should try them to get a sense of what those amps sound like, which are arguably in the "main" camps of commercial amp designs using 6V6's. It's as much circuit design and speaker type as output tube type, but those amps sound very different from Voxes and Marshalls in stock form.

My EL84 amps are Peavey Bravos I've owned since at least 94. They are 25 watt, Class A/B amps with two EL84s. I really don't know where they fall in the above mentioned design parameters.

I've only played the newer Deluxe reissues, which I liked, but I didn't play one long enough to decide on buying one. I do like the Blues Jr., which is EL84, right?

I'm just exploring different options and even considering DIY, which will probably be something 6V6, just for something different. I'm primarily interested in how different it will be.

[Wally]

Originally Posted by e-merlin

My EL84 amps are Peavey Bravos I've owned since at least 94. They are 25 watt, Class A/B amps with two EL84s. I really don't know where they fall in the above mentioned design parameters.

I've only played the newer Deluxe reissues, which I liked, but I didn't play one long enough to decide on buying one. I do like the Blues Jr., which is EL84, right?

I'm just exploring different options and even considering DIY, which will probably be something 6V6, just for something different. I'm primarily interested in how different it will be.

e-merlin, I don't know the Bravo and SChematic heaven doesn't have the schematic.
Reissue Deluxe?? Which one...the DRRI or the '57 TWeed Deluxe.
The Blues Jr. (with El-84's) has a circuit that is related to the tweed era. IT is cathode biased like the TWeed Deluxe. However, its gain stage is more akin to that of the 5F6A Bassman with two gain stages before the tone controls cut things down. The '57 Deluxe RI has fewer gain stages than does the bBlues Jr. but is cathode biased. The DRRI is a different animal. THE tone controls sit in between the first two gain stages and it is fixed biased.
In a way, the two Deluxes, which both run 6V6's, exhibit the point of view that the circuit is a major player in the sonics.

[Geoff738]

Not to contradict some of the other points here, but I own a THD Univalve which lets you swap the power tube. And it is amazing how different the amp sounds with different tubes in it.

At least with that amp, that circuit, tubes make a substantial contribution to the sound.

But, I'm trying not to get too hung up on what tubes are in an amp. As mentioned above, the tonal signature of different amps that share the same type of power tubes can vary so much that it probably doesn't really tell you all that much about how an amp is going to sound.

Cheers,
Geoff

[zook]

6AQ5. My favorite amp for these is an Epiphone EA50. It is also the same circuit Gibson used in a 60s Skylark

Here's the schem:

http://www.tdpri.com/forum/attachmen...ation-ea50-pdf

Winnie

[dangelico603]

Originally Posted by JohnnyCrash

I agree that a speaker has a major role as well. IDK about 40%-50% though. While a Vox AC30 aint the same without Celestion Blues, it still sounds very much like a Vox without em.



6AQ5 tubes
Hmm... I think I have a few 6AQ5's laying around. I never got to looking at any spec sheets on them so maybe now is a good time for a "group project" hehehe

We could break-in the new Shock Brothers DIY amp forum section here with a circuit design brainstorming and build. Heck maybe we could design a nice new modern guitar amp from the ground up around these tubes.

Perhaps staying away from borrowing too much from existing 6AQ5 designs.

What do you guys think?

Do it. I would be very interested in watching the designing take place. I'm at a point now where I'm really trying to figure the hows and whys of this stuff. Following a design process from the gound up would probably be quite enlightening for me. So please do.
Jason

[JohnnyCrash]

"Tsk, tsk" can come off as condescending (it did a little bit to me too). If it wasn't meant to be, no big deal, we're adults we can apologize for coming off wrong... regardless, we can all get along. It's not that big of a deal, right guys?

6AQ5
As far as the 6AQ5 and whatever RCA claims (coincidentally, Brimar also claims "the characteristics are similar to those of 6V6GT types" as well), this has little to do with actual working conditions. I've had manufacturer manuals and tech data make all kinds of claims that can be viewed as subjective or even mere opinion... comparing datasheets instantly shows this as a subjective statement.

Many compare the 6BQ5 (EL84) to 6V6's as well, and after looking at the data, it may be a closer comparison than the 6AQ5 (specified voltages, output, etc).

In any case, you also claimed the 6AQ5 is a miniature 7 pin, which it is NOT. They are miniature 9 pin and I've actually used them in an old amp I later gutted, they are sorta like smaller 6BQ5's (EL84's) - except they aren't "browner" with lower voltage like an EL84 at the same voltages, their headroom is different for sure though... perhaps it was just the sets I had to compare, IDK.

Ultimately, a EL84 is essentially closer to a 6V6 and the 6AQ5 is more like a lower voltage EL84... then again different manufacturers claimed different operating specs - to further muck up our discussion.

Originally Posted by Geoff738

Not to contradict some of the other points here, but I own a THD Univalve which lets you swap the power tube. And it is amazing how different the amp sounds with different tubes in it.

At least with that amp, that circuit, tubes make a substantial contribution to the sound.

But, I'm trying not to get too hung up on what tubes are in an amp. As mentioned above, the tonal signature of different amps that share the same type of power tubes can vary so much that it probably doesn't really tell you all that much about how an amp is going to sound.

Cheers,
Geoff

In a single ended, cathode biased circuit, like a Univalve the circuit is at the whim of the tubes a bit more. Headroo and impedance variation at the OT is likewise going to differ depending on the tube used.

From experience (I built my own 10watt single ender that takes nearly any Octal tube type): Sure a 6V6 versus a 6L6 will make a difference, but the amp will not be drastically different.

Again the comparisons between the 6V6 powered tweed Deluxe and Deluxe Reverb (and even between BF and SF DR's) show how much of a role the circuit plays. Same tubes in these three 6V6 amps, but entirely different sounds altogether.

[Scott S]

Since the EL84 is a true pentode* with a suppressor grid and all of the fun secondary emissions stuff that happens during clipping, I'd expect them to "respond" differently than a 6AQ5/6V6. They'll start to draw a bunch of screen current when the plate and control grid head toward zero, where the beam power tubes are a little more "controlled."

BTW, JohnnyCrash, my 6AQ5's have 7 pins. It's the EL84/6BQ5's that have 9.

- Scott

* That is, if it is one of the ones that is a pentode. Some 6BQ5's (perhaps the American-manufactured ones?) were actually built as beam power tubes so you have to check to see what it is that you have on hand. Talk about muddying the waters!

[Scott S]

Originally Posted by JohnnyCrash

We could break-in the new Shock Brothers DIY amp forum section here with a circuit design brainstorming and build. Heck maybe we could design a nice new modern guitar amp from the ground up around these tubes.

Perhaps staying away from borrowing too much from existing 6AQ5 designs.

I like that idea. Right now, I'm cooking up something using push-pull 6AU6's -- since they were almost never used as output tubes, it's taking a little more scratch work than, say, slapping together the output section from a Musicmaster Bass with a Vox EF86-type preamp. I should have a schemo ready to post in a couple days, and I'm assembling the parts right now. It'll probably sound like crap, but nothing ventured, nothing gained.

- Scott

[JohnnyCrash]

Here's the problem then Scott...

What the heck was I talking about?!

HAHA

I thought I was looking as several 6AQ5 datasheets in a few places (tubedata.itchurch.org, etc). Apparently I was not. I was stone sober, it was a Monday, my shoes were on, all was normal. I think I'm losing my mind. Seriously.

The 6AQ5's I must've been talking about are probably actually 6BQ5's. I got an old Knight PA amp that had an old set in them and somehow must've confused them for 6AQ5's... the plate voltage was way low (in the 200 range) and I remember asking someone on 18watt.com about what to do with such a low voltage PT - they mentioned 6AQ5's - maybe this is where I got things confused... I'm too young to be losing my mind - it's been way too long of a year - anyway apologies for the terribly incorrect info :(

Anyway, let's resume the already scheduled programing (minus the perceived hostility)...

[Scott S]

Hey, no worries, these tubes are so close electrically and visually, they're easy to mix up. I make dumb mistakes all the time, and I honestly fear for how bad I'll be when I'm actually old!

- Scott

[sjhusting]

According to the 6V6 data sheets I've seen, if you want to run a 6V6 at 250 volts or less, you look at a 6AQ5 data sheet - same response curve. The 6AQ5 was designed for use in car radios (yes, car radios used to have tubes in them) and there was a device that converted the 12V from the car battery to something that looked sort of like highish-voltage AC. A device that apparently wasn't very reliable and broke down a lot from making/breaking 12V contact 60 times a second.

The EL84 and the 6V6 occupy very similar spaces in the output tube world. Just as the EL34 and the 6L6 do. The corresponding Euro-tube for the 6AQ5 would be the EL95; which I also have a bunch of. Dirt cheap.

Anyway.

I'm all for the idea of a TDPRI amp. If my opinion is worth anything, I'd be happy to participate. Push-pull 6AQ5 would also give it something different than the usual projects.

steven

[JohnnyCrash]

Originally Posted by Scott S

Hey, no worries, these tubes are so close electrically and visually, they're easy to mix up. I make dumb mistakes all the time, and I honestly fear for how bad I'll be when I'm actually old!

- Scott

I blame the voltage that finds it's happy home to ground through my body. It could be the loud decibels, fast women, and wet fuel - but I need all of those things to survive :)

I am your age, so I'm already scared for my sanity. When we're old... isn't there a Who song about what to do when we're old? I hope I something 'fore I... d@mn, my mind is so gone I can't remember how it ends :)

[Scott S]

Originally Posted by sjhusting

According to the 6V6 data sheets I've seen, if you want to run a 6V6 at 250 volts or less, you look at a 6AQ5 data sheet - same response curve. The 6AQ5 was designed for use in car radios (yes, car radios used to have tubes in them) and there was a device that converted the 12V from the car battery to something that looked sort of like highish-voltage AC. A device that apparently wasn't very reliable and broke down a lot from making/breaking 12V contact 60 times a second.

I'm all for the idea of a TDPRI amp. If my opinion is worth anything, I'd be happy to participate. Push-pull 6AQ5 would also give it something different than the usual projects.

steven

You know what else has been bonking around in my head? At some point in the 1950's, they came up with those space-charge tubes (like the 12U7 and 12K5) designed to run on just 12 plate volts from the car's electrical system with no transformers. How cool would it be to power your tube practice amp from a wall wart or battery pack?

- Scott

P.S. I'm sorry, e-merlin, for continuing to hijack your thread! All this mad-science really belongs in the new forum.