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Old 14th July 2009, 04:33 PM   #11
w5jag is offline w5jag  United States
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I should have said 360 volts across the tube, rather than on the plates, but the point is the same - use a rectifier with a bigger voltage drop to shed some unneeded voltage.

The genuine Tung Sol 5881 sounds great - it's one of my favorite tubes.

You might even want to take a try at 6V6's with around a 910 to 1K cathode resistor and a 5W4 or 5Y3 rectifier. 6V6's really sound great in the Simple SE.

Enjoy!

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Old 14th July 2009, 05:23 PM   #12
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Originally posted by w5jag
You might even want to take a try at 6V6's with around a 910 to 1K cathode resistor and a 5W4 or 5Y3 rectifier. 6V6's really sound great in the Simple SE.
Neat idea. What kind of power transformer do you have in yours? The GE datasheet says 315 volt DC maximum across the 6V6GT for a triode connected class A amplifier. I've had good success with some other tubes running them past their rated voltages, as long as the overall dissipation is kept in check.
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Old 14th July 2009, 06:24 PM   #13
w5jag is offline w5jag  United States
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It's a 10 or 12 pound horizontal mount Utah that I bought for a buck at a Hamfest. Actually, I bought the whole homebrew power supply for a buck, and then robbed all the parts out of it. I paid another five bucks for the vertical mount Stancor 4.5 Hy, 200 ma choke.

It has two high voltage secondaries. I can get around 360 to 440 volts on the high B+ tap, and around 180 to 230 on the low B+ tap, depending on the rectifier tube.

I can go higher than 450 with a drop in solid state rectifier, but I have 450 volt caps in it right now, and they make a big mess when they let go.

My OPT's (Hammond 125ESE) are my limiting factors right now - they are only rated for 80ma, and I haven't ran them much past 90 ma.

Most of the old 6V6's, including 5992, are perfectly happy with higher voltages across the tube, providing the dissipation is within limits.

By the time you subtract the cathode voltage, the actual overvoltage is slight, if it exists at all.

Win W5JAG

OK, I found where I had taken some measurements, and these are the voltages I measured on my Simple SE:

High voltage tap / 510 ohm cathode resistor

SSD / 465 volts
5AR4 / 440 volts
5V4 / 420 volts
5931 (5U4) / 390 volts
5R4, 6087/5Y3 / 381 volts
5W4 / 367 volts

low B+ tap / 270 ohm cathode resistor

5AR4 / 215
5V4 / 205

I have some more transformers lined up for my next Simple SE build , so this tranny will probably go back into a homebrew power supply.
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Old 14th July 2009, 06:29 PM   #14
rknize is offline rknize  United States
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Some guitar amps were notorious for putting 320-350V across the 6V6GT, which is why most of the then-current-production tubes from about 10 years ago met a quick and painful death. My Thomas amp runs them under fixed bias at a little over 320V at the plates. A quad of Chinese tubes lasted about 2 minutes. After some reading, I picked-up some NOS Philips tubes and they've worked great for the past 10 years. 360 would be pushing it, but you have to subtract the voltage across the new cathode resistor as well....
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Old 14th July 2009, 06:49 PM   #15
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Most of the old 6V6's, including 5992, are perfectly happy with higher voltages across the tube, providing the dissipation is within limits.
cool ! I also just happen to have 2 6V6's (metal cans) hanging around.

I'll have to see what the new rectifier drops B+ too before trying those...
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Old 14th July 2009, 07:07 PM   #16
w5jag is offline w5jag  United States
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Also, anyone wanting to diddle around with rectifier tubes to drag down B+ should be aware that the 5Y3 marketed by Sovtek is NOT a 5Y3.

It has a voltage drop more like a 5V4, although it's current rating is similar to a real 5Y3. It's a nice tube, but it's just not a 5Y3.

NOS U.S. made, or used U.S. made, is the way to be sure.

Win W5JAG
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Old 15th July 2009, 02:21 AM   #17
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Well that was interesting.

The first rectifier, the one that I was really hoping was going to work since it is a globe/bottle Sylvania 5Y4G - has no heaters - and the getter turned white on one side

The second one actually worked for a bit - 5R4GYA - probably about 30 minutes or so before the fireworks started, first there was a pop in the speakers which accompanied the volume decreasing. Quickly following that was a really cool blue glow and sparks coming from 1/2 of the rectifier.

If I was braver I would have left it in to see what the final death throws look like... but I'm short on fuses...

So 5581 sound for a while, until I can find a replacement rectifier.
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