what he said.
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)
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)
rcavictim said:
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
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.
humm
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
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
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!
Thanks!
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.
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.
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.
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.
If you are getting a custom transformer from edcor for this for cathode feedback anyway, ask for a separate UL winding, that way you can run the screen at ~200V and the plate much higher. But also, if you run enough cathode feedback, you will get a UL effect anyway with a safe fixed low screen voltage.
For new designs from Edcor, there usually a $20 one-time fee, split between two $20 trannies ain't too too bad. But, they may also have already made something like that, in which case they waive the fee...might wanna just ask what they have that is 'close,' and design around that. They're nice people to talk to on the phone, and usually willing to help out. You can also email them but sometimes it takes a while for them to get back to you.
Hi Soren, ... How about running the UL tap to a pentode driver stage's plate resistor, a la E-linear? My mental calculations suggest that this is the same as adding a *boatload* of CFB, without having to couple it through the secondary -- it might even be "too much", in which case you can reduce the feedback with a voltage divider.
You could probably pick a textbook 6AU6 operating point to get plenty of gain and voltage swing to drive the tube to clipping. Check out the Ebb=300V operating points in the data sheet: 6AU6A
60Vrms with a gain ~160 given a 300V supply.
You could probably pick a textbook 6AU6 operating point to get plenty of gain and voltage swing to drive the tube to clipping. Check out the Ebb=300V operating points in the data sheet: 6AU6A
60Vrms with a gain ~160 given a 300V supply.
sorenj07 said:Umm, wow.What kind of output impedance would this 6AU6 have? I can imagine this driving a bigger tube, or maybe in push pull...
Pretty high! ~100k -- but I think it should be sufficient for good bandwidth. "Rs" in the data sheet is less than your likely grid leak resistor value, so that's in the right ballpark. But I have no idea what the input impedance of a 6AV5GA in UL is (probably benign, but someone may correct me).
Consider that the Quad II amplifier uses a pair of EF86s with 180k plate loads to drive 6L6s in CFB-UL, and then puts a global loop around that, and has usable bandwidth to 40kHz IIRC. The 6AU6 should be in a similar or better position.
If there's any doubt of bandwidth, you can go completely nuts and run a 12HL7 driver tube instead. But I'd regard that as extreme overkill, easily capable of driving a very big triode (or serving as a nice little SEP power amp).
BTW, another possibility is to reduce the plate resistor on the 6AU6 and pick a new operating point -- trade some gain for lower output impedance. Lots of ways to run a pentode, but it can take a bit of work to find 'em.
Another BTW: You'd also probably get enough feedback this way to run the 6AV5 as a "real" pentode, with no screen connection. Then just use the UL for "EL" plate feedback, maybe even jack the plate up to 400V, and run low/safe screen voltage from a separate supply. You have a lot of control over the circuit that way, and don't need to watch out for glowing screens. It's also trivial to drive that way!
Did some experiments the other day and decided to do triode curves of a 6AV5, and now to share it with you all I may regret this later when these tubes all go for mad $.
Pardon the slight sloppyness...I don't own a curve tracer beyond that of a few meters and power supplies.
I may regret this later when these tubes all go for mad $.Pardon the slight sloppyness...I don't own a curve tracer beyond that of a few meters and power supplies.
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