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In Reply to: Re: 26 instead of 27 driver w/45 posted by mwiebe on January 29, 2007 at 13:41:30:
Base of 27 is:
1 - fil
2 - anode/plate
3 - grid
4 - cathode
5 - filBase of 46 in triode is
1 - fil
2 - anode/plate
3 - grid
4 - grid 2
5 - filSo to switch from 27 to 46 you would presumably disconnect the cathode resistor from pin 4 and connect it up to the centre point of two resistors going to pins 1 and 5. You would then connect pin 4 to pin 2. You would have to work out the new cathode resistor value. Since the mu of this is lower, it would be quieter. Presumably it would work with AC as above, provided your 2.5v filament supply feeds just the one tube and not several.
For 1624 the mu is similar. Pinout is:
Topcap - anode/plate
1 - fil
2 - grid 2
3 - grid 1
4 - NC
5 - fil
So here you need to run the plate lead up to a topcap, connect the cathode as with the 46 and connect pin 2 to the topcap. In this case the filament current is 2.5v at 2amp, so you need to check that your filament supply can deal with this before proceeding.I hope I have all the above correct - if it is then these two tubes may be worth trying, provided you know what you are doing and can do all the calculations for cathode resistor value etc. In neither case is it a plug and play option, but in both cases the tube base and filament voltage is the same. Like I say, you need an independent filament supply to each tube since they are now directly heated.
Follow Ups:
thanks
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Boo!
The 1626 is 12v heaters and octal, but its sound has been likened to the 45 in some postings.
The 47 should be same base as 46, though operating conditions would vary. Again, as with the 27 and 46, flament is 2.5v at 1.75amp.The 49 is yet another UX5 base, 2v filaments with a filament current of 120mA, so you'd need resistors or something to bring the voltage down from 2.5v to 2v. Pinout is as 46 or 47.
The 24a is a theoretical possibility, though I doubt if it would sound good enough to be worth trying. also UX5 base, 2.5v at 1.75A filaments.
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