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Old 26th February 2011, 09:49 PM   #1
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Default Simple SE with EL34 and 600v B+

While my red board is on hold, i did an inventory of what i got. I have 1 extra "ten pounder" power transformer that does 310 or 620ish b+ and some new winged C el34's. Could i make this work with the simpleSE?

The power supply will be external and supply the b+. So would have to change RK to something like 1.2k to match the extra 100 or so volts extra. Im Not sure if i need to increase r14/r22 10k.
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Old 27th February 2011, 01:17 PM   #2
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Could i make this work with the simpleSE?
I doubt it. The 800 volt plate rating on the EL34 might have applied to the original Mullard tubes, but todays tubes would probably explode!

Lets assume for a minute that the tube would withstand 800 volts on the plate. The screen grid can't. It is rated for 500 volts maximum and todays tubes have alignment problems making some glow in an SSE at normal voltage (about 450 volts). This means that triode or UL are not going to work, so you would need to run pentode with the screen at a lower voltage. Pentode would require some negative feedback to lower the output impedance.

Another issue with all of the popular audio tubes is the fact that the plate is on pin 3 and the heater is on pin 2. If the plate voltage is 600 volts the peak of the audio signal will swing up to 1200 volts (higher if the amp is overdriven). An arc can develop in the socket or the base of the tube between these two pins. I have seen it happen, but it is usually in guitar amp applications. When the plate voltage jumps into the heater supply, parts are going to blow!

The most that I have fed my SSE is 525 volts and the only tubes that would work were EH KT88's.
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Old 27th February 2011, 05:53 PM   #3
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Originally Posted by nightanole View Post
I have 1 extra "ten pounder" power transformer that does 310 or 620ish b+ and some new winged C el34's. Could i make this work with the simpleSE?
Is it 620 CT? ie 310-0-310?
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Old 27th February 2011, 06:15 PM   #4
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Originally Posted by boywonder View Post
Is it 620 CT?
There's no center tap on the "Ten Pounder". You either need to build the doubler or use a full wave bridge.

Of course, if you had two extra Ten Pounders around, you could series the HV secondaries together to create a virtual center tap...

Last edited by Ty_Bower; 27th February 2011 at 06:19 PM.
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