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Old 6th September 2011, 02:26 PM   #1
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Default Tubelab simple SE ideas

Hi all,

I have had some simple se boards I have ordered from George sitting in my study for a while and have decided to get motivated and start building.

I need to order everything except for those impossible to get 'transistors' I have successfully built a few pcb based tube amps now and want to go a bit further with this one.

My idea is to use the new kt120 tube driven pretty much to maximum dissipation and I'm hoping to get 20 or more watts in ultralinear mode using diode rectification only.

I would like to use one of the antek toridal power transformers and wanted to get some opinions on what the absolute maximum voltage I could apply to the board would be I'm quiet aware that I would need to series up power supply caps if the rectified voltage gets to be more than 500 but unsure if any resistance values should change for the driver tubes.
Or weather sticking to the max recommended 400-0-400 would be the go

For the outputs triode store has a pretty good looking 30w single ended ultralinear transformer 2.5k or using different tappings 5k I was thinking this would be pretty good configured to use it as 2.5k

Just wanted to throw some ideas around and see what people thought.

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Old 6th September 2011, 04:09 PM   #2
kevinkr is offline kevinkr  United States
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The KT-120 may have linearity issues in SE. I recall the curves and a lot of commentary on their linearity has been posted here so a forum search might be a good idea.
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Old 7th September 2011, 04:18 PM   #3
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Or weather sticking to the max recommended 400-0-400 would be the go
The IXYS 10M45 CCS chip is rated for 450 volts across it. The 10K resistor in series with it drops about 100 volts and the 12AT7 can't pull it's plate down much below 50 volts. The board should go to 600 volts with just the caps in the power supply changed.

I would increase the 10K resistor in series with the CCS to 22K if operation above 500 volts is planned just to lower the dissipation in the CCS.

As stated the KT120 has seen mixed reviews and some users state that the grid circuit resistor must be lowered significantly to avoid runaway especially at higher plate voltages. Lowering the grid circuit resistor will lower the amp gain and possibly increase the distortion. I have not tried the KT120 due to the cost.

I have used an Antek 400 - 0 - 400 volt toroid in my board with EH KT88's. The B+ was well over 500 volts (I don't remember the exact voltage) and the amp cranked out about 20 watts in UL, but I think it sounded better with a 460 volt supply.

I need to order everything except for those impossible to get 'transistors'
You can use the DN2540 (the one in the TO220 package) with a resistor value change but these have a 400 volt maximum rating.
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