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Lordathestrings
Gear Guru
Joined: 01/18/01
Posts: 6,242
Lordathestrings
Gear Guru
Joined: 01/18/01
Posts: 6,242
09/19/2001 2:44 pm
The voltage from the power supply can be reduced by applying a lower voltage to the power cord. An adjustable transformer called a variac can do this. This trick has a well-deserved reputation for destroying tubes, though. The bias [u]must[/u] be adjusted to match the tube operation to the reduced plate voltage.

Adjustable amps have some provision for tweaking these settings. That's why they're intended for use by engineers. Most of us don't know how to set up power tube bias, and the warrantee costs could get out of hand if that was left up to the users.

One issue that I haven't seen mentioned a lot is the speaker. A heavy-duty 50 Watt speaker is not going to sound good if you only feed it 5 Watts. A speaker that sounds good at 5 Watts is not going to last very long when driven by 50 Watts. I keep using the 5 and 50 examples because the 5 Watt output will produce half of the sound pressure level of the 50 Watt output, into the same speaker. A speaker chosen specifically for the 5 Watt amp is likely to be more efficient, so that combination might actually be equally loud as a 50 Watt setup.

On the amptone site, there's a page about the Zeeta amp... http://www.amptone.com/mavenpealzeeta.htm ...which takes the high-quality approach to extreme levels. This helps to mask the fact that a plain 5 Watt amp costs about the same to build as a 50 Watt amp.
Lordathestrings
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