Valve amp bias

[Mixc]

My guess... would be the brown one.
Its in a very easy to get to position, something a good designer would do.

[karma67]

Second photo shows the sense resistor. It is 1 ohm, Brown, Black, Gold, Gold.

Connect the meter across each of these in turn and adjust the respective trimpot.
For 30mA you will measure 30mV (millivolt) on the most sensitive voltage range on the meter.

Job done

My guess... would be the brown one.
Its in a very easy to get to position, something a good designer would do.

thanks guys oh and obviously dont use a metal screwdriver it actually sounds fine now so it might have been my ears but i will check to be sure.

[AD Audio]

30ma sounds very low for an amp with claimed 100watts per channel. It won't do any harm at that level but I'd expect 60ma to get the claimed output

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[karma67]

I’m only going by what the maker told me, he also confirmed what has already been stated that it is indeed the brown resistor that the bias is measured from.
Could you tell me what doubling the bias would do in terms of what I’d hear, from the little I understand it would shorten the valve life, but if it brings a great improvement I could live with that.

[AD Audio]

The difference you'd hear depends on the amp design, your speakers and other factors. In my own amps I can hear the sound decrease in quality as bias is lowered from the optimum 'hot' spot for example. As for valve life, the Radford STA100 and TT100 run their valves at 60ma and valve life is decent.

But I'd check with John and go with his recommendation and /or ask him what he thinks about backing off the bias a bit. If the setting is in fact 60ma, backing off to 30ma is a huge reduction to around 17 watts dissipation per tube.

[karma67]

It’s the other way round,30 is what he told me to set the bias at. So I guess it would be upping it if anything.at 30 there is absolutely nothing I’m unhappy about, the sound is lovely,as always though there is that “what if” thinking lol

[Bigman80]

Do what JW said. You'll just end up spending large sums on replacement valves more often.

[AD Audio]

It’s the other way round,30 is what he told me to set the bias at. So I guess it would be upping it if anything.at 30 there is absolutely nothing I’m unhappy about, the sound is lovely,as always though there is that “what if” thinking lol

What I'm saying is maybe 30ma bias is wrong and you misunderstood as 30ma bias will not get near the claimed 100watts a channel.

So I'm simply suggesting you double check with John and follow what he says.

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[karma67]

Ah I see.

[Edward]

I'm struggling to understand why a valve amp that is not self biasing has been set up so it is (seemingly) not easy for an owner to bias it.