6A6 as phase inverter?

[thorpej]

I recently came across a couple of opportunities that, given the sap that I am, I couldn't refuse.

One of these was a bunch of NOS 6A6s in shop-worn boxes. 6A6s are electrically equivalent to 6N7, just in the older ST bottle and UX7 base. Originally intended to be class-B power tubes, they also can be used as driver tubes if you run the two triodes in parallel.

But, it occurred to me that, because the cathodes are electrically connected, they could be used as a phase inverter... specifically, in a long-tailed pair.

Anyone here ever used the 6A6 or 6N7 in this application? (Fender used the 6N7 in a floating paraphase configuration in the Fender Deluxe 26 "Woody", but not as a LTP.)

 

[6l6gmike]

Yes I have used 6N7's as a long tailed pair. I have Russian cold war surplus ones and so far they are working well in my shop amp. I have not had any microphonic issues like I have had with the surplus 6sn7 ones. They have 400ish hours on them now.

I have built this amp with a little spin on of my own. http://www.single-ended.com/Lagarto/shishido/images7/6L6PPSHI.png Schematic is from listed website. I tried to copy and paste the schematic. We will see if it works.

 

[Retrovert]

The 1930s cathedral radios used a 6A6 as both the gain stage and phase splitter to drive a 2A3 or similar. You might try digging out some of those schematics.

These are very old tubes, btw. For a new build you might be happier with something a bit more modern, like a 6SN7.

 

[thorpej]

These are very old tubes, btw. For a new build you might be happier with something a bit more modern, like a 6SN7.

Part of the appeal is using an old tube. I have a stash of 27s that I've thought about using in an amp project, too, although I mostly have those as spares for my radios that use them (or, as is the case with my Sparton Equasonne, can be adapted to use them if necessary).

 

[Retrovert]

Part of the appeal is using an old tube. I have a stash of 27s that I've thought about using in an amp project, too, although I mostly have those as spares for my radios that use them (or, as is the case with my Sparton Equasonne, can be adapted to use them if necessary).

Those 27s would be perfect for the line stage, but I don't know about the output stage, unless you have very efficient speakers. (For those unfamiliar with it, the 27 is the grand-daddy of modern triodes, often using a beautiful mesh grid and punched plates. It is a tube that looks like a tube, and a tube that looks like someone put a lot of care into making it, which was actually the case.)

You picked all of those tubes up NOS from Elmer Cunningham using your time machine?

You could also use that collection to build a Theremin, which used a 27 as the pitch oscillator. Every home needs at least one Theremin. (And, yes, I do own one but mine is the solid state version from PAiA.)

Further reading:

Schematics: rcatheremin.com/manuals.php
Tone Stack with 27 Tubes: rcatheremin.com/tone.php​

 

[thorpej]

Nah, I wouldn't use the 27s for the output... they would be for the first stage, if I used them. For the output, I'd either use for 6L6G (ST bottle, of course!) or 300B (because that seems fun). I obviously would not be using actually-old 300Bs.

Teramin is a cool idea for the 27s, though

 

[Retrovert]

Nah, I wouldn't use the 27s for the output... they would be for the first stage, if I used them. For the output, I'd either use for 6L6G (ST bottle, of course!) or 300B (because that seems fun).

Of course, what else looks like an amplifier tube? Unless it is a 6BG6 with the cap...

I obviously would not be using actually-old 300Bs.

Because you could sell one for a mortgage payment?

Teramin is a cool idea for the 27s, though

Your neighbors will call HomeSec because you've either got Roswell aliens or ghosts living in the basement.

The Theremin is an easy circuit to build. I just had other projects and I never really much used mine.

I've read that the tube versions require a bit of time to stabilize, but I think that with a modern scope it would be possible to identify the sources of unwanted oscillation and instability and remove them with some small capacitors or beads.

 

[arts]

Your neighbors will call HomeSec because you've either got Roswell aliens or ghosts living in the basement.

The Theremin is an easy circuit to build. I just had other projects and I never really much used mine.

I've read that the tube versions require a bit of time to stabilize, but I think that with a modern scope it would be possible to identify the sources of unwanted oscillation and instability and remove them with some small capacitors or beads.

Retro-If you are a Theremin fan,I'm sure you are familiar with the most famous of them all,the Hoffman Theremin.

Many years ago,Peter Pringle (who is the present owner of this amazing device) tasked me with repairing it.I had him drop it off at my home,as there was no way in hell I would let this thing out of my sight.Even after the repair was completed (one capacitor,not bad for a machine built in 1929 ) he let me keep it to ''play'' with for a few weeks.

Quite frankly,to have been entrusted with the care and repair of such a famous and valuable piece of music history was overwhelming to say the least,and is the high point of a long career,and also one of my fondest memories.That,and having Pete serenade me with his vast repertoire in my very own living room for a couple of hours

Needless to say,I could never rival his abilities.Not if I had a hundred years.....Check this out,and you'll see what I mean

 

[Pio1980]

6A6/ 6N7 draw 0.8A heater current, about same as power output tubes.

 

[Retrovert]

Retro-If you are a Theremin fan,I'm sure you are familiar with the most famous of them all,the Hoffman Theremin.

Mos def.

I also like Clara Rockmore, who plays a more contemporary style of Theremin music as well as the classical:

Summertime

Liebesleid

Tchaikovsky "Berceuse"

Some of the modern players do amazing things. Check out how Pamelia Kurstin gets bass here:

Theremin Walking Bass

Burrow In Furness

Many years ago,Peter Pringle (who is the present owner of this amazing device) tasked me with repairing it.I had him drop it off at my home,as there was no way in hell I would let this thing out of my sight.Even after the repair was completed (one capacitor,not bad for a machine built in 1929 ) he let me keep it to ''play'' with for a few weeks.

That's an amazing story! Do you have any recordings of your playing? I am a poor Theremin player. But, then again, I'd probably get better if I practiced, which I don't...

Quite frankly,to have been entrusted with the care and repair of such a famous and valuable piece of music history was overwhelming to say the least,and is the high point of a long career,and also one of my fondest memories.That,and having Pete serenade me with his vast repertoire in my very own living room for a couple of hours

Wow, that is a lot of responsibility.

How did that discussion go: Here is something made by the legendary Theremin himself, with his own hands, now go fix it and don't break anything. Oh, and it needs to sound exactly as it did before and behave exactly as it did before. Let me know when it's done and I'll come check it out. If it's different everyone will know you did that.

Reminds me of Tony Platt's story about Lemmy's bass:

He went on to explain how Lemmy's Marshall amp blew up during one of the recording sessions. It was Friday and the boys needed the machine back on Monday. Seemingly lucky, the guitar tech managed to find someone who can get the job done in super-short notice.

"So off he went and we came in on the Monday and I said, 'Did you get the amp fixed?', and he said, 'Yes, absolutely no problem.' I said, 'What was wrong?' and he said, 'Oh, it was just a couple of things that had burnt out. But while he was in there, this guy had all the original circuits and there were a few bits in there that were strange so he's kind of put those right.'

"I said, 'He's done what?!' The guitar tech said, 'Yeah, there were bits of the circuit that weren't the way they should be and he's put them back to where they should be.' I said, 'No, no, no, no. Lemmy's amp has been modified by a series of guitar techs over the years to sound like Lemmy's amp. You don't put it back to a normal Marshall. You leave all this stuff in there.'"

He continued, "Of course we plugged it in and it sounded limp and it just wasn't the right thing. Fortunately this guy could remember what it was he changed to get it sound like it did. It was one of those moments of, 'Oh, my god. No. This is terrible.'"
www.ultimate-guitar.com/news/general_music_news/motorhead_producer_the_secret_behind_lemmys_bass_sound.html​

Needless to say,I could never rival his abilities.Not if I had a hundred years.....Check this out,and you'll see what I mean

That's pretty amazing.