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In Reply to: Re: BATTERY for filament heating posted by dave slagle on October 28, 2001 at 15:22:33:
they have the V shaped filament (ok I should call it heater but like I say looks and glows same amount as PX4 V filaments). The cathode is connected at the midpoint and they sound pretty good!!! Whether that cathode connection makes them the same characteristics as a dht but with an equal tap I don't know.
I haven't heard any other idht output valves except the 6EM7 power stage. The 6EM7 is far more clinical, and gets distorted at high output, as a look at the curves would tell (know you don't bother much about curves but they do guide and in practice yes though I prefer 6EM7 to multi grids hooked up as triodes it ain't a dht.) I would like to get hold of some R120's they would be an inetersting listen compared to the 2a3 type and these 6a5g's.
when you say the cathode is connected in the center of the VV it is just a CT DHT filament with the CT labeled cathode... the tube is still directly heated, it just has a cathode tap...or thats how i see it.. the tube drawing shows the filament CT connected to a cathode, but i have yet to see the cathode element in any of the tubes... has anyone else???
for it to be an IDT like most people call it it would need a cathode sleeve... i suspect you could ignore the cathode connection altogether and wire it with a traditional hum-balance or DC and the tube would function the same... but given that the CT is there you would be foolish not to use it!
That makes sense to me, as I said it sure looks like a filament. I see the centre tap as a gain, though an inconvenienceas it means it's not a plug in replacement for 6B4G. Having said that not a problem to guys like us, I very much like the sound of these so I'll use them until destruction.
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