The Edcor meets the 6AV5

[kegger]

Going along with Tubelab here, running any of those tubes you mention, including
the 6AV5 in push pull triode should be just fine with your output trannie, doing that
will get yu say 12-20 watts and probably be right where yu want to be power wise.

The 6AV5 at 300v triode works well , I suspect like Tubelab the 6DQ6 probably would as well.

If it were me and having the parts I'd try building a pushpull triode sweep tube amp. (Oh wait I already did, he he he)

[kegger]

Originally posted by rcavictim
kegger,

Nice project! Are you using the low power, hi-mu stage of the 6FM7 compactron as the line input stage on each side? I assume this is a dual triode vertical sweep osc and output tube. Too lazy to look it up.

Thanks, No just the low mu section is being used.

If you wanted to use the other as a preamp, so basicaly building an integrated, should do well.

Or as a buffer from the input I would assume should be fine as well, but I like less stages though.

I've been building with low mu driver tubes latley and have been really happy with the results gotten.
(So I really wanted to try the low mu section of these tubes)

The interesting/wacky/cool thing that happened to me was I built this amp with knowing the tubes I'd
be using for the driver "6FM7/6FJ7/6FY7" all had the same pinout that would let me roll different ones
without having to change anything, but when I first fired up the amp I was getting a way different plate
voltage on the driver then I expected. So I did the math and said this tube is not acting like it's got the
mu of 6 and plate resistance of 1K but more like plate of 2k and mu of 15 or so. I go triple check TDSL
and sure enough it says 1k and 6, so I go get the PDF on each one, Low and behold the 6FJ7's specs
are "more like 2k and mu of 15 or so" Wow darn TDSL, teaches me not to look at the PDF! But this is
actually good thing, I think, as it gives me different gain tubes to roll for the driver plus the 2 lower gain
ones, so plenty of roll/tweak ability, so far I like the tube the circuit was NOT designed for (6FJ7) best.

Keg

[tubelab.com]

I have been experimenting with 6EM7 as a driver. I use fixed bias and a CCS load in an attempt to extract the highest amplitude drive voltage possible with miniscule distortion. I have rolled about 20 tubes through the circuit. All give low distortion, but the bias voltage needed and the tube voltage gain varies a lot. I would have to go back to my amp to see what the exact voltages are but I have tubes that fall outside the adjustment range on both ends of the bias pot. I know that the adjustment range is at least 50 volts or so. The gain varies by a 2 to 1 ratio also.

[kegger]

Interesting results to say the Least!

I haven't tried any 6EM7's as of yet, have a bunch gathered up though.

I'm running the low mu section of the "6FM7/6FJ7/6FY7" with a 5k ohmite brown devil resistive plate load on
a 300v supply and I believe around 820ohm cathode resistor if I recall correctly with a decent amount of current.
(May make some changes with the 6FJ7 in mind)

Tried both with and without cathode bipass cap, not much if any sound difference, just the gain change is all.

Later,
Keg

[John L]

Great thread! Let's move it back up again.

[sorenj07]

Hi, quick question. I've got my hands on some of the older GE type 6AV5's and am considering a Mikael style SET/UL amp, but was wondering if a 6N1P with a gain of 30 could drive the 6AV5 to full power. I'd like to use fixed bias. What kind of range should I have for bias adjustment? Up to -40V or so? This would be using an XSE15-16-5K with 8 ohm speakers.

Thanks!

[kegger]

No and no, Sorry!

But you need a bias range of about 50-60 volts, you could do a slight
cathode bias and the rest with adjustable, leaving the cathode resistor
unbypassed for a bit of cathode feedback, mine worked out nice with a
bit of CFB on the outputs.

You'll either need 2 stages, a larger single stage or using less on the amp
side if you have a pre with a good bit of gain will work as well.

You'd want to get upto 12AT7 range or a 6BK7 might get yu closer for a
single stage and moderate preamplifier gain.

[sorenj07]

No problem! This is all strictly theoretical anyway. I'm thinking about using a simple 6SN7 direct-coupled with B+ at 315V. TubeCad gives me a very clean +-57V of swing with ~5K Zout. That plus cathode feedback for the 6AV5 ought to result in some low distortion.

[sorenj07]

Another question: Has anybody found a general safe maximum voltage for the 6AV5's? Is 320-350V likely to be OK (with fixed bias)? It'd be nice to have a bit more headroom with the drivers..

[tubelab.com]

It has been too long since I did all of the 6AV5 experiments, and I wasn't smart enough to write everything down. I wired the 6AV5 into a TubelabSE which uses a single 5842 for a driver. I had no problem driving the 6AV5 to clipping. The 5842 has a Mu of 40 or 44 depending on whose data sheet you read. I am also using a CCS load so the stage gain is about 40. I think that the 6N1P with a resistor load may be a bit low on gain. As mentioned, the 12AT7 should be OK.

When I tested the 6AV5's I found that some could handle 350 volts, but most could not. 300 volts is safe for most of them. The plate voltage is not the issue, the screen voltage is. Check carefully for any signs of glowing grid wires. If the screen grid wires are glowing the tube will not live long.

I don't have the exact bias readings written down, but my guess is that you will need more than -40 volts. My amp goes from -10 to -60 volts.