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line-stage preamp tubes? which ones to use...
line-stage preamp tubes? which ones to use...
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Old 17th March 2005, 02:39 PM   #11
richwalters is offline richwalters
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Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
Originally posted by mark_titano

because the lower heaters current it is useful in order to avoid humm problems, large loop areas and and electromagnetic connections.
It is cheaper too...

What is your opinion?

Hi there........arguement not valid if DC heater supply is used...as for electromagnetic connections....that's a new one on me.....I'd always thought the mains tranny was the culprit....perhaps I've misunderstood the 50 Hz wavelength.....

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Old 17th March 2005, 09:55 PM   #12
RockysDad is offline RockysDad  United States
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Location: Bay Area, CA
6BM8 in STC mode sounds to SS-like, huh?....
My guess to why it sounded SS is maybe because I used a discrete transistor? Didnt have a 6AK5 on hand at the time, which is what the original circuit had, so went with it the transistor instead.


Maybe I should try to find a tube to use as a driver instead. Eli had a good thought, though. But, whats with the 6V battery?
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Old 18th March 2005, 12:10 AM   #13
Eli Duttman is offline Eli Duttman  United States
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Location: Monroe Township, NJ
But, whats with the 6V battery?

The battery is for grid bias. You cap. couple at the I/P, use a 1 MOhm grid resistor, connect the "bottom" of the grid resistor to the - side of the battery, and connect the + side of the battery to the triode's cathode. Connect the small load resistor between the cathode and ground. By using battery bias, you avoid calculations and get good bass. 6 V. of bias cleanly handles a 2 VRMS I/P signal, as produced by a CDP.

A final point, connect the O/P of the source selector switch to the "top" of the volume control and ground the "bottom" of the volume control. The wiper of the volume control connects to the CF I/P cap. Use any volume pot. you like that's 100 KOhms or less.
Eli D.
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