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Old 24th February 2006, 03:25 AM   #1
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Default The Edcor meets the 6AV5

There was a thread that introduced the Edcor XSE-15-8-5K transformer to the world.

Cheap SE output transformers I tested these and posted the results.

There was also a thread where the 6AV5's were tested and abused.

Anyone know anything about a 6AV5GA?

This thread is about what happened when the two meet.

I wired a pair of 6AV5's and a regulated power supply into the same TubelabSE that I had been using for these tests before. The first test was ran at the rated 11 watts dissipation, 300 volts and 35 mA. The amp sounded OK but kind of subdued. In my usual style I turned up the power. Much to my surprise they starded to exhibit the death glow at about 15 watts. This is not what I saw before. These were NOS tubes, not dirty old ones. So I found the old tubes that I had used before. OK now I can crank up the power. I was running 350 volts at 60 mA with no glow. They sounded nice, good bass, clear sparkling mids and crystal clear highs. I listened for two hours with a wide variety of music. It sounded good, but not as good as the Edcor with the 300B.
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Old 24th February 2006, 03:30 AM   #2
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In one of the previous threads someone suggested the 6FW5. I put a pair of these into the amp, and cranked it up to 350 volts 65 mA. No deasth glow, and It rocked. This was the best sounding combo yet. Tried triode, UL, and pentode connections. The results were as expected. My next experiment will be to try cathode feedback.
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Old 24th February 2006, 03:54 AM   #3
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Interesting work, for which my thanks. And also thanks for the tip on your website about Harbor Freight voltmeters. I bought ten.

In this and a few other experiments, you've blatantly exceeded the Vg2(max) voltage. Now, I use screen drive in my amp, originally motivated by the low rating of my sweep tube outputs. Any temptation I had to rationalize running the screen higher (i.e., in "normal" triode mode at, say, 400-600V) was quashed by the manufacturer ratings of triode mode, always at voltages well below limits. Thus I have zero experience in that usage and am curious about the experience of others.

So my question is, which sweep tubes have you used long enough to get a rough idea that no harm is occuring by flouting the ratings? Clearly you're stressing these more than I would, so if it's working for you...
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Old 24th February 2006, 08:24 AM   #4
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So 6AV5 canīt stand 15W?
Thatīs bad news, I recently bought a few NOS Sylvania as future replacements for my 6B4G amp.
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Old 24th February 2006, 01:20 PM   #5
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SY:
I have abused the 6AV5's because I have a lot of them, and they are cheap. I just picked up about 15 more at the Orlando Hamfest, for $3 or $4 each. I have not run any of these for more than a few days so I don't know what the long term reliability will be like. I plan to try them long term in a triode or UL amp soon.

I have operated a pair of 6LW6's in triode mode at about 385 volts (400 volt supply 15 lost in OPT) for several months without any issues. These tubes have a 275 volt rating. They still look, and work like new. I have a large (about 75 lbs) box full of assorted sweep tubes to experiment on, so further experiments will happen sooner or later.

6146's really don't like having their screen voltage pushed, neither do 6AQ5's or 6BQ5/EL-84.

Fuling:
I was surprised to see the red glow of death appear in the NOS pair of RCA's at 15 watts. I dug up the pair of tubes that I used for the original test, and re - tried them. They both were able to take about 30 watts with NO glow visible even with the room lights off. One of these was a GE and the other was a Dumont. They were of obviously different internal construction. Upon further investigation I found at least 5 different internal constructions for the 6AV5GA. The NOS RCA's that I tested had large slots in the radiating fins at the point where the fins attach to the plate. This would limit the thermal conductivity. What were they thinking? I also found RCA's without these slots. I have some Sylvanias, and several other flavors, I will stress test them as soon as I get time. I will be out of town for most of this weekend again.

I also want to get amp specs for the above experiments in triode, UL, and pentode modes.
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Old 24th February 2006, 01:54 PM   #6
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Now that's VERY interesting. I'm using 6LF6, which I understand to be the same as/very similar to 6LW6 except for the base. Have you used 6LW6 in push-pull?

Sorry to threadjack- I can split this part out into a separate thread, if you like.
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Old 24th February 2006, 03:29 PM   #7
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There was an article in Glass Audio back in 1999 that demonstrated a 90 WPC P-P amp using 26LW6's. (It seems to have dissapeared from their web site, I am sure that I have a PDF somewhere if you want it.) That got me thinking about "testing" some of these. I performed my usual extreme testing. I can't find my original paperwork yet, but I remember getting 140 Watts RMS at clip at 1KHz. I was limited by the 80 Watt OPT on the low frequency side. I was using a SS bridge rectifier on a 575 volt 500 VA industrial transformer for a B+ of 700 to 750 volts. I was using my Knight regulated supply for the screen and driver voltage, but I don't remember what the actual voltages were. I was using conventional G1 drive and fixed bias.

This was one of my early Tubelab prototyping system experiments which was taken appart rather quickly to do other experiments. I didn't have it together for long, and I was thinking guitar amp when I built it, so it was never optimized for sound quality. I tend to torture these type of things pretty good (full power for an hour straight, play my guitar through it at the severe clipping level) so if it was a weak design it would have blown up.

Most of my recent experiments have been SE. I will get back to P-P some time. 6LW6's seem to be pretty tough, but there again are about 4 different flavors, and they are not all the same.
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Old 24th February 2006, 03:56 PM   #8
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That's no surprise- with screen drive near class B, I have no problem hitting 150W with 6LF6.

Yes, I'd greatly appreciate a copy of that article. Use the "email" button here, my website's email address is down.
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Old 25th February 2006, 12:10 AM   #9
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150 watts from 2 tubes, tell me more. Plate voltage, current, load impedance, G1 voltage? What is the quiescent G2 DC voltage, and required drive level. I have a lot of these tubes to experiment with, and I have limited experience with screen drive, but this sounds like a great place to start.

Maybe I am too blond, but I don't see any way to include a file using the email button. I hesitate to put my email address in a piece of text anywhere, but it can be found on my website (a JPEG). That stops most of the evil spammers. Send me an email, and I will reply with the PDF. It is almost 600K in size.

The article has some history on the tubes, and claims that the 6LW6 is the octal equivalent to the 6LF6.
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Old 25th February 2006, 12:26 AM   #10
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In my amp, Vg1 is zero (tied directly to the cathode), Vg2 is about -10V, zero signal current is 3mA per tube, 1250 ohms plate to plate, 800V B+. It requires a PILE of drive, 150VRMS or so; it's possible I could get more out at the risk of the output tubes, since the driver poops out first. Despite the very low idle current, the output tubes run very linearly at low power, no visible crossover distortion.

I'll pop you an email about the paper, thanks!
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