Just wondering if a Russian near equivalent of the Ac701 tube exsists , Identical characteristics wouldnt be required , grid exiting the top of the valve would be great . 5840 /EF732 is a superb tube for cathode follower mics ,as used by Bruel & Kjaer , and Ive had success building mics with them ,but the top cap grid would be really sweet as it should have very low capacitance and fit perfectly into a pencil mic, solder directly to 7 pin xlr , only the grid going up to the capsule with no wires crossing over , of course the 5840 can be placed inverted and the leads appart from grid bent back around the tube and down to the connector ,but you probably need to screen the tube in that case .I have seen Russian sub mini's with plate top cap connection ,but havent been able to find grid top cap connection .
Sub mini tubes for microphones
- Thread starter Tubetec
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In my data book, the Hiller MCS-2 and the AC701 are the only standard ones with grid at top.
But I think there were once speciality tubes for electrometer inputs that were also made this way, even with specially coated clean-glass to keep grid currents down in the nanos...
Jakob E.
But I think there were once speciality tubes for electrometer inputs that were also made this way, even with specially coated clean-glass to keep grid currents down in the nanos...
Jakob E.
Thanks for the tip Jakob ,
Its all do able with great quality Raetheon JAN 5840 in any case ,and their cheap too , I was thinking flat ptfe gasket/washers could be drilled to allow the valve legs to pass through and provide insulation and support for the sheild which hooks into cathode , then all legs appart from grid soldered to Xlr 7 pin male . A mic could be retrofitted for cathode follower output very quickly and simply , of course you still need a power supply ,but that could be universal to any mic fitted with the cathode follower 5840 circuit , maybe slight variations in polarising voltage/series resistors would be all thats required for proper opperation .
Its all do able with great quality Raetheon JAN 5840 in any case ,and their cheap too , I was thinking flat ptfe gasket/washers could be drilled to allow the valve legs to pass through and provide insulation and support for the sheild which hooks into cathode , then all legs appart from grid soldered to Xlr 7 pin male . A mic could be retrofitted for cathode follower output very quickly and simply , of course you still need a power supply ,but that could be universal to any mic fitted with the cathode follower 5840 circuit , maybe slight variations in polarising voltage/series resistors would be all thats required for proper opperation .
