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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 14th Sep 2020, 11:12 am   #21
vinrads
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Default Re: An amplifier using EL508's

Some food for thought there, a fourteen valve stereo amp, now that would be something. Mick.
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Old 14th Sep 2020, 11:39 am   #22
Radio Wrangler
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Default Re: An amplifier using EL508's

Some transformerless designs use massive paralleled banks of line output valves in a totem pole push-pull arrangement. Some of these valves can get up to 1 amp peaks of cathode current. So sixteen output valves can give you +/- 8A of output current, though that's being rather hard on the poor bottles. Theoretically this gives 256 watts into 8 Ohms, but speakers have impedance dips and a voltage amplifier is expected to just keep on driving current. I was wanting to create an all-valve equivalent to two solid state amplifiers I was playing with and they were in the 100-200W league depending on load impedance.

About 290W of heater power just in the output stage.

We're all daft once, and access to a punch press with tooling that would cut holes for valve sockets in one pull led me astray? If filing had been involved, I might not have bothered.

David
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Old 14th Sep 2020, 2:28 pm   #23
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Default Re: An amplifier using EL508's

Quote:
Originally Posted by vinrads View Post
... a fourteen valve stereo amp ,now that would be something.
GEC's Application Report No 3 Amplifier Circuits for KT88 (dated 1978) details the design for a 400W amp based on ten KT88s wired in parallel push-pull and driven by three 6SN7s. The power supply contains four GXU1 half-wave xenon rectifiers for the HT and a 6X4 for the bias supply. Eighteen valves in total. And that's just mono. So thirty-six valves for stereo (you might get away with thirty-five if the 6X4 could provide enough current for biasing both channels ).

Cheers,

GJ
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Old 22nd Sep 2020, 1:22 pm   #24
vinrads
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Default Re: An amplifier using EL508's

I wonder what it would cost today . Oh I was forgetting my last amp had twelve valves ,don't you just love it , Mick.
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Old 23rd Sep 2020, 6:29 am   #25
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Default Re: An amplifier using EL508's

Someone on the forum built an amp with 10 EL84's I think, but in his case if my memory banks aren't tricking me it wasn't for power but noise. I've had fantasies about building an amp with dozens of EF80's say or 6N7's or some cheap valve. Heaters supplied from a SMPSU but the hole cutting is a turn off.

Going the other way I've already built a 6 x EL34 amp but it's never been fired up in anger properly, I have neighbors unfortunately, oh for the days when I lived in a wood miles from anywhere, but then I had no lekky : )

Andy.
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