Preamp tubes - Any coke bottle sized ones ????

[Resonator Guy]

I am currently designing a new build that will have three visible tubes on it, preamp power and rectifier. I have decided on a coke bottle 6V6 and a similar 5R4 and am hoping to find a suitable preamp tube that comes in a similar big glass envelope. No luck so far checking ebay and a few tube suppliers.
Is anyone aware of such a tube or will I have to use a 6SJ7GT, which won't look near as cool? Here is the chassis I will be using. It will have
a big operational tube mounted in the centre of each tier.

[jazbo8]

You could run the 6V6 (or two) as preamp (triode strapped), e.g., see here.

[g1]

You may have more luck searching using the term ST or ST shape, rather than coke bottle.
https://www.google.ca/search?q=ST+sh...BpC3qQGnnIH4CA
Coke Bottle or Big Bottle Preamp Tubes? [Archive] - AudioBanter
http://www.diyaudio.com/forums/tubes...aped-tube.html

[Resonator Guy]

Thanks jazbo8 and g-one. The 6V6 as preamp is interesting and gave me a few more things to think about. ST as the shape designation is a great help and you learn something new every day. Here is a crude mock-up of the look I am after. Pilot light will be behind the dial opening and two knobs - on/off and volume. A 6" speaker at the one end with a switching jack for an external and a little radio chassis inside holding the PT. I have replacement transformers for a champ that should work fine. It will be a winter project but I am mentally designing it now.

[Enzo]

Or consider a smaller tube with a grid cap on top. You won't have three identical looking tubes, but a grid cap is visually interesting in its own right.

6Q7?

[Resonator Guy]

Those 6Q7s are neat looking tubes, Enzo. I have always shied away from anything with grid caps but it may be time for a change. Do they require special sockets and if so, can you still get them?

[eschertron]

I just pulled a couple of grid-cap tubes from an old radio I found. I don't remember off hand what the tubes are, but they had some very odd socket configurations. One was a 6-pin socket, another was a 7-pin (not miniature). I can try to gingerly remove these sockets for you if you'd like. No guarantees as to their visual condition once they're out!

[Enzo]

The "odd" bases are not because of grid caps. (And some caps are plate caps, by the way) There are octal tubes with them. The old 4,5,6,7 pin bases were just earlier tube types. A cap on a tube is not related to its socket, the tube plugs in like any other, you just need a cable coming up from the chassis to the cap connector.

As far as I know the 6Q7 used plain old octal sockets. But if you find an old 5 pin tube you like or something, tubesandmore.com has those various sockets as well as several sizes of cap connector.

[km6xz]

And use the extra diode sections for soft clipper.
You can get old tubes with two plate caps or two grid caps also which would look cool.
If you want cool plus dual triode, try the 6F8G with one grid cap.
The problem with any of these old triodes is that they were somewhat microphonic and not great at rejecting hum from the heater since they were not the double helix style of later hum reduced tubes.
The best small signal tubes from the late 30s and 40s was the Loctal which had the thin miniature tube style pins and a locking metal indexing center locator. They were used a lot in mobile communications and car radios, were low in microphonics, secure in sockets and very rugged, and quiet. They never replaced the octal however which have had the longest continuous production run of any active electronic components. You can find the tubes but sockets are hard to find now.

If you want more power, there are some very nice looking old old triodes that are large, bulbous, with light-bulb bright direct heaters like 304TLs or the even larger 450th or 750th.
I built some prototype amps with wild metal sculpture see-through cases with matching power supplies(4 units, each weighing about 50kgs ea.) using an 833A mounted horizontally without a socket on ceramic standoffs. The manufacturer who order the designs just wanted something so wild that it would cause high end magazines to feature photos on their covers. It worked. It got awards at the international hi-fi show and a price tag of $45k. The next year I build an even more exotic but more practical amp, with all the active circuit including transmitter tubes, were submerged in a clear column filled with transformer oil. Now the company prices them at $100k for a stereo pair.
So if you get wild enough, someone will pay you a lot for its uniqueness.
I am not sure why those who can afford such gear are the most gullible and easily conned into exotic but marginal gear.

[Resonator Guy]

Well, all this gives me plenty to consider for then next little while. I will probably stick with an Octal tube but I don't know what sort yet. It will be fun, though.
My next job, however, has to do with a 1952 Carvin MOT amp I just received today for my birthday. The seller thought the PT might be shot, but I can't remove the chassis from the cabinet yet; it is thoroughly stuck in there. I have it in the driest place in the house, my workshop, to reduce any swelling and I hope it is a cap leaking over the PT.

[Leo_Gnardo]

Some of the tube hi fi crowd swear the # 27 is the bees knees for preamp duty.

And Stan, didn't you sink some of those big output tubes in an oil bath for cooling? I'm imagining a tube "oil-quarium." How's about a photo or two, and while you're at it a photo of the staff of your new tube sales venture.

[km6xz]

Yeah,

That was back in 2002-3 when I designed and built the prototype but this is what the company is selling now for $100,000.00 for two


And the two girls:


We were out for dinner the other night so I had to take a photo or two....

[wyatt]

Well, if you're going for grid cap, there is the 6J7...the same pentode tube as the 6SJ7 but uses a grid cap (octal base).



THen, of course, you can go for a grid capped power tube like the 807, the grid-cap pre-cursor to the 6L6G (not an octal base).

[Enzo]

But on the 807 that is not a grid cap, it is a plate cap, isn't it? So you;d have B+ out there on the cap. If the cap can be pulled off by inquisitive fingers, they can be shocked by it too. Stick with the 6J7.

[km6xz]

The 807 has a plate cap, not a grid cap so the B+ is out in the open which suggests more attention to safety in design of the amp to prevent any access to the top of the tube by curious fingers.
I built a lot of things with 807s when I was a kid because they were so cheap surplus, $0.30-.50. They also were pretty versatile for a wide range of audio and RF circuits. The only precaution if I remember correctly when using it is a relatively fragile screen grid so a separate screen supply was often needed. But on the good side, a pair can run 120 watts output, and require modest drive, are still cheap and tolerate a lot of plate abuse. Surplus houses will still have quality ceramic sockets and the larger than normal ceramic plate caps. You can connect a little heatsink to the plate cap and increase the dissipation allowance. With 600v B+, a pair could run 150 watts out.