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Old 13th July 2009, 04:31 PM   #1
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Default 5881 in a Simple SE

I have two vintage 5881's, one made by CBS, the other by Raytheon.

I'm considering putting them in my simple SE for a spin, but when I checked the voltage specs it seems that the 5881 is only rated for a plate voltage of 400v - and my SE is in the 450v ball park.

The only reason I'm considering it is that I know the cathode bias is 36v or so - so it's really only 14v over spec... and these things are guidelines right?
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Old 13th July 2009, 05:05 PM   #2
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How are you running it, triode, UL, or pentode? I'd say go ahead and try it if the screen is below 400V (not if triode strapped), especially since the tubes are not matched so are not high value (except maybe to you ).

It's also not that hard to get some voltage drop with a power resistor or swapping in a different rectifier.
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Old 13th July 2009, 05:37 PM   #3
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I can run it in UL or triode mode via a toggle switch. Also with or without cathode feedback on yet another switch.

At the moment these tubes really do have no value... they came from a friends father's basement and are not known to work. The getters look good, no rattles... they are very likely going to be just fine.

So I'll set it for UL mode and see what they sound like...
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Old 13th July 2009, 10:46 PM   #4
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Hey, it doesn't sound too bad at all !

I think they may have a little bit more bass than the 6L6CGC's... and one tube is definitely working harder than the other. The heater is glowing brighter and the plate is glowing along the fin in the back - but nowhere else. It's also not as bad as the 6L6GC's.

Since they are old tubes I'm still waiting for something to happen...
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Old 13th July 2009, 10:52 PM   #5
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yikes - spoke too soon!

The Raytheon tube - which is the one that I thought was running cooler - just started glowing... and glowing... brighter and brighter while I was watching it.

Turned it off before any melting began - although I was temped to leave it on and see what would happen
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Old 13th July 2009, 11:18 PM   #6
bigwill is offline bigwill  United Kingdom
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Needs less bias current
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Old 13th July 2009, 11:42 PM   #7
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Quote:
Needs less bias current
I checked a data sheet, it should have been within 1-2ma... I'm thinking the plate voltage is too high.

So nice dec-trode, is there a part number for that monster? Perhaps I can bounce electrons all over the glass for that nice blue glow effect
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Old 14th July 2009, 04:42 AM   #8
rknize is offline rknize  United States
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Yeah, sounds like too much voltage caused a run-away.
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Old 14th July 2009, 02:25 PM   #9
w5jag is offline w5jag  United States
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Use a 5Y3 or 5W4 rectifier to drop the voltage down.

I run 5881's often in my Simple SE.

A 5Y3 puts about 360 volts on the plate in my setup.


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Old 14th July 2009, 02:47 PM   #10
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Quote:
Originally posted by w5jag
Use a 5Y3 or 5W4 rectifier to drop the voltage down.

I run 5881's often in my Simple SE.

A 5Y3 puts about 360 volts on the plate in my setup.


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Hmm, I just happen to have a 5Y4G here - looks like that will work great...
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