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In Reply to: RE: What tubes to use with this Interstage Transformers? posted by megasat16 on August 23, 2016 at 18:06:41
I have recently built a 300b amp with a UTC H series interstage of 1:2.5. It has been very problematic. A low impedance source is necessary, <900 ohms is a must. At that it still quits 2v before 0 bias, ie; it can't handle grid current. I still haven't solved the ringing problem.
Follow Ups:
Paul,I am sure you aware that most Interstages including H series are not rated for DC. Some H series may have DC rated interstage but if DC rating it's not printed in the UTC catalog, it's most likely to be used with parafeed design.
What UTC H series is it? Mine is not made by UTC. I have a few UTC HA series Interstage as well that doesn't measure as linear as the ones in this topics....
Regards,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Edits: 08/28/16
I'm using one of the HA series (I don't remember which one, possibly HA-108). It is being used parafeed to PP grids (1~;1.2+1.2). I've used parafeed before, successfully. The problems I am experiencing, I attribute to the step up design to power grids. Some engineering buddies told me that step ups will be problematic and crap out into grid current, and they were right. Gain is not free.
No such thing as free gain. HA-108 is not designed for IT with high Rp tube. Low Source Z of around 600 requires Rp lower than 600 or so for the ideal condition. What driver tube are you using? You mentioned lower source than 900 ohms? But are you already maxed out on the driver plate current for the current driver tube Rp?
Tube IT are supposed to have higher Primary Z not to load the driver tube or the power is wasted on the primary side.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
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