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Discussion Starter · #1 ·
Over at the VHTusers site the man himself (Steve Fryette) chimed in to answer a question I had been wondering about for a while now. How is it that my 60 watt can keep up to some 100+ watt amps.

Check it out:
For a good margin of safety, peak power can be considered 2 times RMS. That's a very crude generalization, but accepted as typical by the industry.

Speaker peak handling capacity must also be generalized at 2 times RMS because of the many factors used to determine hard figures.

The typically accepted rule of thumb for safety is 2 X Speaker RMS to 1 X amp RMS, or in this case, 120 speaker watts to 60 amp watts.

VHT amplifier and speaker power ratings are conservative (what we publish is equal to or greater than actual based on generally accepted test parameters - see below).

So normally you'll be OK with a 2X12 P50 cab and a D60. However, speaker rating goes down in an open back cab. But as long as you are not slamming the amp, you should be OK.

Using the amplifiers published model power category as a power rating can be misleading. Same goes for speakers.

Many amp companies do not rate their amps based on actual power performance. Instead they just let the consumer assume that 2 tubes = 50W, 4 = 100W, etc. If pressed some would have to admit their power ratings are based on distortion figures as high as 20% or more, which would translate to ratings that are 20 - 40% greater than RMS at onset of clipping. Hey, you want distortion anyway, right?

Some examples:

Published - 60 Watts
Actual - 62 Watts RMS

Published - 120 Watts
Actual - 118 Watts RMS

Published - 50 Watts
Actual - 50 Watts RMS

Published - 90 Watts/Channel
Actual - 105 Watts RMS/Channel

Published - 50 Watts/Channel
Actual - 62 Watts RMS/Channel

Published - 120 Watts
Actual - 72 Watts RMS ----------->:eek:

Dual Rec
Published - 100 Watts
Actual - 72 Watts RMS

Triple Rec
Published - 150 Watts
Actual - 108 Watts RMS

Published - 90 Watts/Channel
Actual - 65 Watts RMS/Channel

Published - 100 Watts
Actual - 78 Watts RMS

P50 - 50 Watts RMS in a sealed enclosure. Closer to 35 open back.
V30 - 75 Watts in a sealed enclosure. Closer to 50 watts open back.
G25M 50 Watts RMS in a sealed enclosure. Closer to 35 open back.

All amplifier power figures above are based on identical test procedures:
AC Output RMS at onset of clipping (assumes amp under test will actually produce a symetrical wave form at clipping. If not, we use whichever half-cycle clips first).
8 ohm/200W non-inductive test load.
Regulated 120V AC source.
Bias set to manufacturers spec and stock tubes.
Signal input directly to power amp stage for accuracy.
All power amp controls set for maximum clean power (typically Presence - 0, Depth -0, SS Rect Mode, Class AB, etc).
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