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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: What to do with a VT-205 and a Eimac 4-125A ? posted by drummerwill on September 28, 2006 at 06:27:24:
If you want a real challenge, build a phono preamp using only
photomultiplier tubes and a photodiode that directly converts the
MC signal into photons and sends the "signal" down fiber optics through the pickup arm. Photomultiplier tubes have plenty of gain, so
this shouldnt be a problem. :)You will have to treat this like an 811A or similar class A2 tube.
That means you will have a big ass cathode follower driving the grid,
probably something like a 6L6 or something.The filaments take 4A, just like the 811A. It glows brighter than an 811A and much brighter than an 845. Then there is all that
heat that needs to go somewhere. The 811A has big plates so it can do
a better job at radiating it. The 3C24 is going to sink most of its heat down the filament pins and the grid pin out the side. These will get very very HOT. Far hotter than any other tube you may have dealt with... Ceramic socket is a must. Airflow would help alot. What it
really wants are radiator clips on the anode and grid pins.... In
operation, its designed so the Tantalum anode gets RED HOT. Given that
there is vacuum between anode and glass, you'd get burned even before you skin hit the glass... If you dont run it hot, it might not getter and gas up earlier than intended...Class A2 will sound good, however, I have no idea about whether or not
you can get away with AC filaments... Believe it or not, I can do AC filaments on the 811A with exceptionally little hum on 102dB speakers. However, the 3C24 is a different beast. 4A over a smaller region of space than the 811A. It might require DC filaments... An awefully
expensive experiment. OTOH, 811/572/812/826 amps can be very easily be
built with satisfying results. Life is too short to have not heard
the clarity of constant-grid-current modulation.-- Jim
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Class A2 around 300V or so.... - Jim Doyle 09/28/0615:56:41 09/28/06 (1)
- Re: Class A2 around 300V or so....So you mean... - drummerwill 16:26:56 09/28/06 (0)
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