jeffg
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Posts: 10
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Post by jeffg on Apr 21, 2016 19:29:05 GMT -7
I have a combo Wreck and it certainly heats up the room when I run it. I checked the idling plate dissipation for the two modes and found that the lower voltage setting runs the tubes at about 12.5W each, while the high voltage setting runs them at just north of 16W per tube! I would think this would kill anything not 7189-ish pretty quick.
Mine is loaded with the Russian 6P14P-EB's, but I really don't feel comfortable with dissipating 16W apiece! Especially not when pushing the amp hard, and the higher dissipation rated Russians in short supply. I kind of feel like swapping out the 25W 50 ohm Rk for a modest bump up, like to 75 ohms or so.
Anybody else up the cathode resistance on theirs?
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Post by DRZ on Apr 22, 2016 9:03:17 GMT -7
Jeff I think you need to recheck your measurements @ 16 watts per tube that would equal 64 watts total, which is imposable. Monday I will check a chassis here and get back to you with my findings.
Two things remember these are cathode biased so the cathode is not at ground potential, it is almost 12 volts above ground so you need to subtract that from the plate voltage not measure from ground for your wattage calculation. Second what is your wall voltage, as that will effect the plate voltage if it's higher then the designed 120V AC. That must be retubed or you bought it used as we ONLY load Z Wrecks with 6n14n , no suffix no EB, I much prefer the standard 6n14n. And they do spec to 7189 values much higher plate voltage and plate currant.
We have been selling Z Wrecks for over 7 years, and 550 units sold, and no one has complained about failure or over heat.
Z
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jeffg
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Posts: 10
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Post by jeffg on Apr 22, 2016 10:44:31 GMT -7
Yes, I bought it used. In the higher voltage setting, my pin 7 plate voltage on the 6P14P is 328V, and my cathode voltage is right at 10V. Which gives a plate-cathode voltage drop of 318V. 10V on the 50 ohm cathode, feeding four tubes vields a cathode current of 50mA, less a couple of mA for the screen grid, so about 48mA plate current. 0.048 * 318 = about 15 watts per tube static dissipation. My wall voltage is warmish here at 122V or so.
I've not owned an amp that put off this much heat in operation. But then, I've never owned an AC-30, either. ;^)
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Post by DRZ on Apr 22, 2016 11:25:48 GMT -7
You do realize the 50 mA you calculate across the bias resistor is the cathode current for all four EL 84's right? I measure using the shunt method is 78 mA per pair of EL 84's, which equals 12.48 watts per tube.
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jeffg
New Member
Posts: 10
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Post by jeffg on Apr 22, 2016 12:36:13 GMT -7
Actually, no. All four tubes' cathode current flow through that 50 ohm resistor. I see a 10V drop over the resistor. Dividing 10 volts by 50 ohms gives a combined current of 0.2A which IS for all four tubes. Dividing that by four, gives about 50mA per tube.
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Post by DRZ on Apr 22, 2016 13:47:16 GMT -7
You did state you calculated a cathode currant of 50mA feeding four tubes. That must be the misunderstanding Still I have never used the voltage across the cathode resister to determine the plate dissapation . I use the shunt plate measurement with a currant meter. Also I use medium gain EL 84's with my self biasing circuits, a high gain EL 84 can run much hotter, as I'm sure you know. Oh BTW welcome to the forum.
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jeffg
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Posts: 10
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Post by jeffg on Apr 22, 2016 14:57:42 GMT -7
Thanks! What's the scoop with the 'regular' 6P14P's versus the -EB variant? I thought the -EB suffix ones were the beefier, heavy duty ones--maybe not so much?
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Post by pcns on Apr 22, 2016 20:14:05 GMT -7
What an interesting thread, welcome to the forum!! Not many places you get to talk directly to the owner and designer of the amps. Todd
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Post by DRZ on Apr 23, 2016 6:54:21 GMT -7
Thanks! What's the scoop with the 'regular' 6P14P's versus the -EB variant? I thought the -EB suffix ones were the beefier, heavy duty ones--maybe not so much? The suffix type are either Ruggedized , or Extended life type. I like the standard 6n14n do to there IMHO sound and tone which is to me is MUCH better. The standard 6n14n are rated at 5000 hours, so they ain't no slouch , and they have no rattles that I have observed in a couple of thousand I have used.
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Post by Dan F"i"fe on Apr 23, 2016 7:24:04 GMT -7
What an interesting thread, welcome to the forum!! Not many places you get to talk directly to the owner and designer of the amps. Todd Not many get the pleasure to interact with the good Dr after one post! Welcome Jeffg!
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jeffg
New Member
Posts: 10
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Post by jeffg on Apr 23, 2016 7:56:35 GMT -7
Thanks all for the welcome! I'll have to run down some of those no-suffix 6P14P's and give them a whirl!
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