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KT88 Power supply question
KT88 Power supply question
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Old 31st October 2005, 01:01 PM   #1
croccodillo is offline croccodillo  Italy
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Default KT88 Power supply question

Hi all,

a friend of mine just give me a 250VA power transformer, with a 400V AC output.
That means that, once rectified, it should give me something about 565V with no load, and about 510V under full load, a really good voltage.
Of course I can lower it (I will build a SS voltage regulator), and thus I'd like to ask you which is the best voltage to feed a pair of KT88, connected in parallel to form a PSE amplifier (I have 4 mathed KT88, and want to use 2 of them for each channel).
Can I use the voltage as it is or is it better to lower it to, let's say, 450V?

Thanks in advance,
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Old 31st October 2005, 10:06 PM   #2
SHiFTY is offline SHiFTY  New Zealand
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I would use the maximum anode voltage possible, with regulated screen (g2) voltages if it's a pentode amplifier.

500V would be a pretty mild B+ for KT88s I would imagine. At that operating point, and about 75mA each, you will be drawing 300mA on the HT winding, which is quite high. You might want to check it can handle it.

Not usre if you are a newbie, but make sure to read the safety thread. 500V will kill you pretty easy.

I assume you are going to build triode-connected KT88 parallel single-ended? (What a mouthfull!) You will need a pair of SE output transformers that can handle 150mA or more, and you will need to drive the KT88s with somthing like a 6V6, EL84 or similar.

I think i would build a Push-pull amp, you can easily get 100W out of a pair of KT88s, and with a good circuit, better sound quality than pseudo-triodes (in my opinion).

A good link

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