Biasing Valves question - advice appreciated

[larkrise]

In the interests of getting some varied and helpful information into the forum! Help appreciated.

Please make replies as non-technical as possible.

OK. I have a fantastic integrated Tube Technology Synergy amp. It has 12 x EL34's - new Electro Harmonix that came with the amp - 6 per channel, that are biased via an on board in built biasing meter. The meter shows an LCD reading and the bias is tweaked via some little pots. The manual advises setting the bias for 35. A couple of the tubes can't seem to reach 35 - more like 30 - I was told this is ok providing above reading is above 25. I also notice that the reading fluctuates slightly - gather this is normal.

My questions are - does biasing need to be rechecked every so often. Are the tubes not giving 35 problem tubes or is it the amp? I am told that with a service the tubes should be rebiased by an external professional meter and would be better - is this bull?

I am thinking of getting a full set of Svetlana Winged C, matched - told would make a significant improvement. Any views?

Thanks guys.

 

[LiloLee]

I would suggest changing the valves asap. The el34's will be in pairs and since you can't rebias one to 35 then there is a problem with the pair which may lead to anode thermal runaway. BTW the flucuation is normal.

The winged C are very good so the right choice IMHO, but unless the matched ones are no more expensive than unmatched don't bother. Matched are really for those that can't bias their valves and since you can why pay more?

Once you have them just check every month or so. For the first couple of years this should be easy with little change but as they are used more do keep an eye out for a mismatched pair and replace accordingly. Do not be afraid of buying 2 here and 2 there instead of 12 at the same time.

Finally if you have the amp serviced the engineer would rebias the tubes automatically for you as part of the service.

 

[larkrise]

Lee - many thanks for that. Is an engineer's biasing better than using the on board - or just the same? An engineer suggested to me that his equipment would be more accurate - as said above is this bull?

Anyhow - If i understand you correctly the lower reading on a couple of valves is going to be a valve problem not the amp?

This advice is much appreciated - thanks!

 

[LiloLee]

The engineers kit will be more acturate but don't lose sleep about it, as there is no absolute 'best' value for bias. 35 is just the manufacturers suggestion and you may prefer it at 32 or 38. Have look here for a not too serious explanation http://www.tubedepot.com/whisbipo.html

BTW your dog has good take in liquid refreshment.