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In Reply to: Will a 417A work with a interstage transformer 1:1 10K? posted by Iczerman on March 24, 2007 at 21:01:12:
The load that the 417A sees will depend on what is connected to the secondary of the IT. If, for example, the secondary is terminated by the grid of a 2A3 and nothing else, then the loadline that you would draw for the 417A would be essentially horizontal (infinite resistance.) Of course there are reactive components: the miller capacitance of the 2A3 grid and the primary inductance of the IT...A 10k 'rating' on an interstage transformer is an indication of appropriate application. In simple terms, you want the source impedance (plate resistance) to be less than 10k and the secondary termination to be more than 10k. Loading a 417A is a good application of a 10k IT. On the other hand, a 600 ohm transformer would probably not work well.
I don't have a lot of experience with the 417A in particular, but if it is like other triodes that I've used as input/driver tubes, then a higher resistance load will sound better than the textbook recommended 2 to 4 times plate resistance. In addition, the more horizontal loadline should be better able to handle the inevitable reactive components mentioned in the first paragraph.
Whether or not you need to add any terminating resistance across the secondary depends on the transformer. Even though it damps ringing, some people find that it hurts the sound. I recommend experimentation and listening. Avoid the temptation to settle for what your scope tells you without consulting with your ears.
-- Dave
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Follow Ups
- Re: Will a 417A work with a interstage transformer 1:1 10K? - Dave Cigna 04:46:18 03/25/07 (0)
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