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Best way of reducing heater voltage?
Best way of reducing heater voltage?
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Old 20th July 2006, 03:03 AM   #11
agent.5 is offline agent.5  United States
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Quote:


In the primary? Would something from a switched PSU work? I have a couple in the bin, measuring 0.3 ohms each side.
It won't matter if the HT is lowered, it's already 430V (vs. 400V in the schematic).
yes on the primary. Something from a switched PSU should work. Your incoming voltage will drop a bit, consequently your B+ and heater voltages will drop some too.
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Old 20th July 2006, 03:28 AM   #12
Tubelab_com is offline Tubelab_com  United States
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.6 ohms in series with the primary will not drop much voltage unless you have a seriously hungry amplifier.

Look for an "Inrush Current Limiter". Some data can be found in the DigiKey catalog.

http://dkc3.digikey.com/PDF/T062/1405.pdf

If you pick the right size you can get a nice slow turn on (easy on the tubes) and drop 4 or 5 volts in the primary circuit.
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Old 20th July 2006, 06:24 AM   #13
DigitalJunkie is offline DigitalJunkie  United States
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You might be able to find one in an old SMPS also.
I commonly see them in PC PSU's..usually a little green ceramic looking thing,in series with the line input. I've also seen the larger ones in monitors,and whatnot.Ya might get lucky and find one that works nicely.
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Old 20th July 2006, 06:17 PM   #14
showdown is offline showdown  Norway
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Those inrush limiting resistors look promising. I think I've found one, but I have never used them before so please correct me if I'm wrong:

Imax = 1A
R (25C) = 5R
R (Imax) = 0.6R

This could be used, no? Since the amp won't actually get near 1A continuously (more like 0.75A), I'm guessing the resistance will be a little more than 0.6R under load?

OR I could use a 0.47R/25W resistor on each leg of the secondary... but that's the easy way out

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Old 20th July 2006, 08:15 PM   #15
jane is offline jane  Norway
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Quote:
Originally posted by showdown

OR I could use a 0.47R/25W resistor on each leg of the secondary... but that's the easy way out
2 x 0.47R will drop ~1 volt/amp. Not appropriate for the filament secondary, unless the filament current equals 1 x 12AX7 or something like that..
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