Anyone know anything about a 6AV5GA?

[amperex]

If one has the time & parts on hand to play, it would be an interesting experiment. If not having the parts on hand, it may be an expensive experiment with a less than great result.

Radio Daze in NY (585) 742-2020 will sell NOS 6A5G for $33.80 each that are a real triode tube with a cathode type heater.

[tubelab.com]

I remember seing the story about 6AV5's being sold as 6B4's a while back. I never saw a multi grid 6B4, but in this world anything is possible.

I have a few 6AV5's, so I will connect them into one of my Tubelab SE amps and see what happens (I have collected a few strange tubes to try). Since I don't quite remember where I put the 6AV5's, and I have a warehouse with about 100,000 tubes in it, it might take a few days to find them.

[tubelab.com]

I have gathered up 2X 6L6 GC and 2x6L6GB, and 6X 6V6, 4X6K6, 4X 6W6, 2X6AS7, 4X6Y6, 3X6EZ5, 1X 6AV5GA, 5X6B4, 2X811A, 4X6Y6, 3XMETAL 6N7, 2X6LW6, 2X6BL7, 2X6BX7, 5X6AQ5, 5X6BQ5, 4X6CW5, 4XKT88 and I haven't been to the warehouse yet.

[amperex]

I missed a warehouse of tubes for sale by 6 months in Lousiana a few years ago. It was reported to have been closed in the 1970s, but was one of the largest distributors in the south at one time. I always wondered what I missed.

I find small 'pockets' of tubes time to time. A lot of a few 1000 NOS audio tubes came up two months ago. About 1/3 were audio types (surprising) and many were made in Europe in the 50s & 60s..

[tubelab.com]

These tubes were actually given to me in exchange for a few days work. The 2 lots had both already been picked clean of the popular audio tubes. There are mountains of old radio and TV tubes. That is why I know that there is some 6AV5's in there and there are some 6AU5's also along with a few hundred other sweep tubes. I intend to try the sweep tubes for SE amp use in the next few weeks. My favorite is the 6LW6. I have seen a pair (push - pull) of these put out 150 watts RMS for over an hour with no signs of distress. Just look at the guts of those, they make a 6550 look like a wimp.

[quayhog]

Look for a schematic of the Bogen DB-130. It uses 6AV5 tubes and it sounds surprisinly good. I use one for my worksop radio with a matching Bogen tuner. It has in interesting screen voltage regulator circuit using a 6CG7.

respect the screen limits though. I've also tried the 6AU5, it sounds OK and has a higher screen voltage limit.

[tubelab.com]

Hurricane Rita gave us the day off of work yesterday. Nothing to do except listen to different tubes. I Hooked up an old prototype Tubelab SE board to a couple of external power supplies, to allow for continuously variable B+ and filament voltage. Then I attached octal sockets in parallel with the 4 - pin sockets that are on the board, to allow for testing the 6AV5's, 6B4's and other octal tubes. Output transformers were One Electron UBT3's (3000 ohm).

First I tested the setup with 300B's, which provided the expected 9 watts at 5% distortion (my common comparison point) with the power supply set at 400 volts. Listening tests proved that this setup sounded the same as an unmodified amp.

Next test was a pair of NOS Sylvania 6B4's. Max voltage spec is 325 Volts, so that is where I set the power supply. Power (at 5%) was just over 3 watts. They sounded like 2A3's, no surprise here. The bass was not as strong as the 300B's and some of the clarity seemed to be missing.

Now for the 6AV5's. (NOS GE's) I wired them up in triode connection, flipped the B+ switch, the current meter slammed to the right, and interference showed up on a nearby TV set. These puppies like to oscillate. I re did all of the wiring, added stoppers right at the socket for G1, and G2. The oscillation was gone. I started at 250 volts. The tube worked, and biased up similar to the 6B4. It didn't sound half bad, in fact I think that it sounded better than the 6B4, but not as good as the 300B.

I have never been one to follow specs (or rules) so I decided to turn up the voltage. 300 volts (plate and screen), no problem, no death glow, I had the bias set at 60 mA, which is 18 watts disipation. Now these were starting to sound pretty good. Bass was far better than the 6B4's and at least on par with the 300B's, it sounded louder than the 300B's, but I made no power measurements yet.

Time for more voltage, 325. These things ROCK. I am now running 325 volts at 75mA which is over 24 watts dissipation. I ran it this way for an hour. There is no death glow even with the room lights off, the screen wires are not glowing. This is over twice the recommended daily allowance of power flowing through this little guy, and it is still smiling. I made a power measurement and I am getting 12 watts at 5%. Distortion at 5 watts is under 1%. The sound is pretty good. Loud, dynamic, but not as detailed as a real triode. I tried putting the 8 ohm load on the 16 ohm tap to present a 1.5 K ohm load to the tube. Power rose to 15 watts, distortion went up at 5 watts to over 2%, and it didn't sound as good.

OK, I still haven't killed it yet, so I turn the power supply up to 380 volts. Current is now 105 mA. (bias was never readjusted from the initial settings). This is almost 40 watts dissipation (some voltage is dropped in the OPT) the red glow is beginning to appear on the plate, however the screen grid wires are NOT glowing. Power output is 17 Watts RMS at 5%. This amp noe sounds loud, and dynamic, but at this level there is some oscillation seen on the TV on loud bass, which shows up in the sound.

Conclusion:
These tubes can take far more abuse than the typical audio tube. This is common with sweep tubes.
Care must be taken to avoid oscillation.
A good sounding low cost amp could be built with these.
I would use 300 to 325 volts as a suggested maximum, although they can take much more.

I will post pictures and some data later tonight when I get home. I plan to try other sweep tubes, and audio pentodes (triode mode) before taking the setup down. The results will be on the web site when finished. (a couple of weeks)

[Tom Bavis]

If you find any 6FW5s, plug 'em in - uprated 6AV5 (18W vs 11). On second though - send 'em to me!

[tubelab.com]

Picture of the test setup, with 300B's. As you can see, there are many different types of tubes waiting to be tested. A chart with comparison data will be posted on the web site when I have finished them all.

[tubelab.com]

A picture of the setup with the 6AV5's, operating with 300 volts at 60 mA.