Tube Amps / Music Electronics
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|3/25/2005 1:38 AM|
||Pseudo Triode Mode - Sovtek 5881's - Any Issues?|
I would like to be able to run a quad of Sovtek 5881's in pseudo triode mode with the "half-power" option. I will be running in AB1 in an SLO100 circuit with around 500v B+ and 470 ohm screen resistors. I expect to bias at around 35 mA. My OPT is a New Sensor MOP100 and my power supply is quite solid, typical SLO100/Dual Recto style with a 10H choke.
Are there any issues that I should know about from any of you who have experience of this.
Any advice appreciated.
|3/29/2005 10:05 AM|
those tubes are tough. i threw off 45w each while torturing them @ >600v, plate and screen. just barely got red.
cheap too... can't beat that!
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|3/29/2005 12:06 PM|
A recent Music Man had 720V B+ on a quad of these, with about half that on the screens.
This was toughter on them than if they were in a Twin Reverb but they were working beautifully.
|4/3/2005 1:22 AM|
Thanks for your replies.
How about the option of being able to switch the screens to run them in triode mode for reduced power and earlier breakup, say, for practice use and being able to switch the screens to pentode mode for full power in a gig scenario.
The running conditions would be those mentioned earlier and using all four tubes in triode or pentode mode according to power requirements.
I know this has been done before, in fact KOC has a section on it in TUT1, but is it as simple as it seems? i.e. For instance, would one bias setting be okay for both modes, or in actual practice, would I need more than a simple screen changeover switch?
|4/3/2005 11:16 AM|
Just worked on a JCM 900 head that had the half power triode mode switch.
Just a screen disconnect and no attempt to change the bias voltage - if it's good enough for Marshall...
|4/3/2005 4:51 PM|
Thanks Bill. If EL34's in a Marshall can take it, I should have no problem with a Sovtek 5881
|4/3/2005 5:51 PM|
Actually, this model was shipped with 5881's. Still, you get the point.
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