MagneQuest Forum

RE: here is a great article to read and keep....

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In Reply to: RE: here is a great article to read and keep.... posted by mqracing on March 09, 2008 at 09:52:54

Hey Mike, I cant remember well now but it seems to me you stated somewhere you prefer unshielded trannies even if they can be much more easily offended by hum. Did you or am I wrong?
Good article. I'll save a copy.
My current choice/practice is
HUM
1) Low gain per stage. Yes, and I like two stages amps when gain is not an issue. I use a (single stage) preamp btw.
2) Low grid-to-ground impedance. I am using input trannies and grid choke or direct coupling.
3) Ground bar. No, I return the cathode on the negative lug of the last PSU cap. That lug is my signal ground. I tie only that lug to earth/safety ground and chassis. I never used a ground bus.
4) Triodes. Yes I use triodes but as a matter of facts penthodes just sound good too.
5) Non magnetic chassis. OH! I use iron chassis, not the best choice but the cheapest for the time being...
6 and 7) Power transformers. Mine are not so low flux ... I saved some money here too. Bad decision :-(
8) Low level trannies. Yes I always search for the minimum pick up moving the trannies around.
9) Low resistance paths. I do always check the resistance of cathodes to ground and from ground to chassis and from point to point etc..., I usually want it to be a small fraction (0.1Ohm as a maximum, I use grid bias so cathodes are at 0V). Typically I read 0mV of difference between these points.
15) Heaters. I use DC heaters on my DHTs (LCLC where possible or LC + regulator). AC for PP amps using tranny center taps, I had no need for pots this way.
16) I use metal oxide resistors. Any better choice? Typically I don't use resistor to load cathodes or plates so my resistors are not in sensitive places.

DISTORTION
1) Load. Typically I follow the 5x Rp rules and as I go parafeed I am sure there is plenty of Henries at the primary so the limiting factor is the loading choke. 90H on 1.5k in the current amp. I don't need to squeeze huge watts out of the tubes as I drive 115dB horns.
5) PSu regulation. A test I like to do is injecting a large 50Hz and 100HZ into the amp and look at the B+ modulation. The lower the voltage sag the better.
7) Coupling cap. I like DC coupling now...

Edits: 03/09/08

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RE: here is a great article to read and keep.... - mqracing 18:42:00 03/09/08 (0)

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