Tube Stompbox Help

[t7mackie]

Hi all,

1st post, so I apologize in advance for anything and everything.

I've built a few boxes so far. A couple from kits and a couple from scratch and I do have a bit of past electrical and electronical experience. But I basically know nothing about tubes so...

I scored a bunch of vacuum tubes from my landlord's junk pile out back and I would like to use them for some kind of pedal project.

I've seen the schematics for the Valvecaster and it looks intriguing. From what I can gather the 6EU7 can be used instead of the 12AU7 with a couple changes / pinout differences. I'd like to try to use one or more of the tubes I scored. They appear to all be Magnavox branded Groove Tubes (?).

This is what I have:

3x 6V6
2x 6EU7
2x 6BA6
1x 6BE6
1x 6AL5

Any ideas, schematics, info, etc?

Thanx,

-mac

[davent]

Hi Mac, The 6eu7 is equivalent to a 12ax7 so way more gain than a 12au7. Could make a variety of different amps with 6v6's for power tubes and the 6eu7's up front.

dave

[GGBB]

They appear to all be Magnavox branded Groove Tubes (?).

Can you post pics of the tubes?

[Marcos - Munky]

I'd use those 6EU7s and 6V6s for a tube amp. AX84 Hi Octane and Fender Champ with solid state rectification are good starts, but you can use two 6V6 in push pull configuration for a 15W-ish amp.

[davent]

I'd use those 6EU7s and 6V6s for a tube amp. AX84 Hi Octane and Fender Champ with solid state rectification are good starts, but you can use two 6V6 in push pull configuration for a 15W-ish amp.

My last amp i built i paralleled sockets for 6eu7's & 12ax7's. Had a few 6eu7's and nowhere to use them, won't be cheap to replace when they die but have loads of 12ax7's and won't be any shortage of those out in the world. Using a mix of the two in the amp at present.

dave

[ThermionicScott]

The 6AL5 is a small-signal diode (actually two of them in one envelope.). Bet you could find something cool to do with that in a pedal. 

[t7mackie]

They appear to all be Magnavox branded Groove Tubes (?).

Can you post pics of the tubes?

Yes I can - will do tomorrow.

Thanks all for the suggestions.

[t7mackie]

As requested...

[willienillie]

FWIW, Magnavox didn't make tubes, but Sylvania (or whoever) would brand them for Magnavox.  Pretty common practice back then.  Silvertone, HH Scott, many others did the same thing.  Then there were companies that DID make tubes, but still bought from other manufacturers, rebranded.  The gray-plate RCA 6L6GCs were made by Sylvania IIRC.  I had a GE-branded Mullard-made GZ34 once.

Groove Tubes never made tubes, until the 6L6GE in about 2003.  The earliest of those were made in USA, not sure why (environmental regulations?) but production soon moved to China.  The US-made version was impressive, noticeably thicker glass, and even the spot welds looked extra-heavy duty.  The Chinese version sounds pretty good, but is much lighter overall, and I've had stupid failures from them.

[PRR]

I think he has confused "GT" (glass tubular) for Groove Tube.

98% of all 6V6 ever made are GT bottle. They buy long glass tubing, slice it, slide guts in, with minimal glass-blowing. Alternates are G/GA (semi-Coke) and the metal 6V6.
https://upload.wikimedia.org/wikipedia/commons/thumb/5/5d/6V6_tube_bulbs.png/1280px-6V6_tube_bulbs.png

[amptramp]

The 6AL5 is a small-signal diode (actually two of them in one envelope.). Bet you could find something cool to do with that in a pedal. 

Onwe of those got used in a Tube Screamer version called "Spark Gap".  The semiconductir diodes were replaced by a 6AL5.

[antonis]

Nothing to add except a Welcome..

[willienillie]

I think he has confused "GT" (glass tubular) for Groove Tube.

I think you're right, mostly.  G stands for glass, but T is a designator for the specific envelope shape, doesn't stand for a word.  I think.

[PRR]

I think you're right, mostly.

https://www.tubemuseum.org/SearchResults.asp?Cat=30
"Additional letters:
A Controlled heater warmup time, although can also be used to denote increased ratings ...
B Improved ratings/performance.
C Ditto.
G Glass bulb.
GT Glass tubular.
W Ruggedised version.... "

Also:
"Sometimes a string of up to three Roman letters can be suffixed to the overall number; these generally distinguish various revisions and improvements to the original model or different bulb shapes; use is unsystematic, except that for octal tubes G often indicated a shouldered glass envelope, GT a tubular glass envelope, and neither of these often a metal envelope."  https://www.microfarads.com/audio/226

Post-WWII RCA manuals "Outlines" section show metal tubes as a "MT" type, echoing "GT" for glass tubular.

I've always seen it listed as "tubular". If you visited a factory making GT tubes the "tubular" was overwhelming (at Blackburn the attic was full of glass tubing let-down as needed).

If you have a different reference I would like to see it.

[willienillie]

Actually I think you were right, my RCA tube manual lists "T9 outline" for 6V6-GT, but MTx for metal tubes, and STx (shouldered tubular?) for coke bottle types.  It doesn't say what the letters stand for, but it seems I misremembered what I had misinterpreted, 20 years ago or whenever I last looked at that part of the manual.  Sorry, my bad.

Edit:  My GE manual is the same as the RCA.  Somewhere in the dark, crusty recesses of my memory, I feel like I must have seen a description of "T shape" or "T outline" somewhere in reference to the 6V6, and I guess that was meant for people who would know it referred to "tubular," but I took it to mean "Shape T" or "Outline T."  Many, many dead brain cells ago.

Also, I like how you edited your post (and I responded to it) BEFORE you posted it!

[antonis]

I like how you edited your post (and I responded to it) BEFORE you posted it!

Mojo keyboard..

[ThermionicScott]

"ST" is the one that always trips me up. It didn't officially stand for "shouldered tube" but it's natural to think so!