Valve Testing Parameters

jaymenon

- MHOS
- Gain
- Transconductance

Many sellers provide only the MHOS value.

Is there a practical benefit to knowing the other two (and possibly other further) parameters please?

RiftAmps

Unless you know the operating conditions of the test then those figures are somewhat redundant, so of little use to the purchaser.

The gm (MHOS) result is arguably the most useful indication of the valve's performance, so often is the only result published.

ecc83

I assume we are talking about used valves here? New, unused valves will have the parameters found in any data sheet.

The figures for gm, Ra and mu are related such that mu=Ra.gm but as Mr R says, "depends on conditions". That is why valve data is delivered as curves of Ia v Va for a fixed grid voltage series and the ACTUAL working parameters derived from a 'load line'

I can strongly recommend Merlin Blencowe's "Tube Preamps For guitar amplifiers" The math is '0' level at its worse. (not that I GOT any O levels!)

The amplification factor 'mu' is fixed by the internal geometry of the valve and hardly changes with age and use. MOST of the claims for different valve 'tone' for the same type number are IMHO so much snake oil.

Dave.