Valve amp auto & manual bias adjustment; pros and cons

Please share this...
Share on FacebookTweet about this on TwitterShare on RedditDigg thisShare on LinkedInEmail this to someone

Ask an expert

I am need of your expertise as I have some questions regarding running a valve amplifier. I interested in changing from my Primare A30.1 to a valve based amplifier. I have listened to a few valve amplifiers and have been impressed with the way they present music but am not sure how much “maintenance” they require.

I have been reading the various articles available about auto & manual bias adjustment and am a bit confused. With manual bias, does this mean every few months I would have to attach a volt meter and readjust the bias setting for the valves or does it only need adjusting when new valves are fitted?

I am also a bit concerned about some reviewers commenting on the sensitivity of the speakers attached. I am using KEF XQ20 stand mounted, which have a claimed 88dB sensitivity. With a valve amplifier with a rating of 35/40 watts per channel would this sufficient to drive my speakers? I don’t/can’t listen too loud – about 30-40 max displayed on my current Primare, but this is 100 Watts per channel! Am I correct in that if a solid state of 30-40 watts can drive my speakers then a valve amplifier should also?

I have looked over many reviews and listened to a few examples and with the sort of money I can stretch to I would be looking at the following models:

Icon Audio Stereo 40 Mk III, the KT88 based integrated or Puresound A30 or ... looking over ebay for a few months I could purchase a previously more expensive type second hand such as the Audio Research VSi55 or similar.

Any answers you can give me would be greatly appreciated and would hopefully help me narrow down my options. Thank you for any help you can give.

What are known as 'fixed bias' amplifiers give a little more power but need regular re-adjustment, every few months. It isn't difficult, but you must have a voltmeter. They also need adjustment when one or both valves are changed.  Auto-bias amplifiers are most popular because they keep the valves balanced both initially, and as they age; no adjustment is needed.

Power valves have a life of a 2-3 thousand hours; small signal valves around 10,000 hours. Power valves like KT88s do a great job and are not overly expensive, hence their popularity. It sounds like the 40 watts or so available would be fine for your purposes. Curiously, valve amps sound more lively and dynamic at low powers than solid-state amps so will suit you in this respect.

Although the Audio Research VS55i is more expensive I would not label it clearly better than the other models you mention. It is tight and punchy, though. I tend to favour good KT88s; WAD or Icon Audio are the ones to audition I feel.

Please share this...
Share on FacebookTweet about this on TwitterShare on RedditDigg thisShare on LinkedInEmail this to someone