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View Full Version : Sequel to pin clean: am I biassed against duff valves?



Mike Reed
05-01-2010, 10:39
Well, having gingerly removed all 10 valves in my E.A.R. monos and cleaned the pins with IPA (can't get to the shops for aught else; snowed in!), I reinserted a few times.

Initial sonic results seem to be promising, BUT getting a stable biassing LED showing of the two output valves each side is not as easy as it was. In fact, one biassing screw is at the end of its travel, and I cannot get it to balance properly.

Does this mean that this valve is on its way out? In which case, is it better to change the lot, as I have a new spare set, or just the potentially offending one?

Although fully serviced by T. de P. nearly a year ago, I'm pretty sure he didn't change any of the valves, and I gather that they'd had about eighteen months' use before that

Learning curves at my senile citizen age are problematic, so thank heavens for the helpful bottle-nosed dolphins of this forum in giving me the porpoise to take the tube, as it were!

Spectral Morn
05-01-2010, 11:00
Did you replace/reset all the valves into the same positions that you removed them from ? The bias settings are based on that. It is possible that a few are through age/use worn out, but if they read okay before removal, then I suspect you may not have replaced them as they had been...thus upsetting the readings.


Regards D S D L

Mike Reed
05-01-2010, 16:01
Thanks, NEIL,

Not sure what you mean by 'read okay'. I don't have a meter and probably wouldn't know how to use it to test valves anyway.

I was having a bit of unbalance on one of the 509 output valves beforehand, which is partly why I decided to investigate/clean, and YES, I was very careful to make sure all valves came out and went into the same holders and that the pins were aligned beforehand to avoid damage.

Really, I need to know if:

It's best to change the lot (as they were put in by the previous owner as a
set), or
Change just the potentially offending one, or
Soldier on until erratic biassing shows that the game is up (assuming it will).

I understand that sound quality goes off with valve aging (true or false?) and I'm only interested in top performance. Having extensive new carpeting has clouded the issue a bit.

I supppose logic tells me to start with a clean sheet and replace all, but despite having a number of stereo, integrated and monoblock valve amps. from '64 to the early eighties I never even changed a valve; or anything!

The only bias I knew was the Joan type (sorry, wrong spelling!)

hifi_dave
05-01-2010, 16:30
I think you should e-mail EAR and seek higher authority about what to do.

Thing is, you don't know the 'real' life history of any of those tubes and some might have had a lot more use than others and I would suspect far more than 18 months. You could just replace the pair which are giving the uneven readings and re-bias and all will be well or replace all four o/p tubes, it depends on how you feel about it.

In my experience of using and selling 509's, the tubes will often go on for ten fifteen or more years. The first pair I sold over 25 years ago are still going strong with the original tubes. Tim's usual comment goes something like 'is it still working, does it hum - then leave it alone'.

Not one for messing about is our Tim...:goodluck:

DSJR
05-01-2010, 16:58
509 TV Line-Out valves used to be very cheap as well as I recall.

Tim hated the bull around "boutique" valves as I remember from the 509's launch thirty odd years ago and told us that as 509's used to be thrashed flat out on the TV line output frequency, then they'd be lightly used in an audio application. Remember the old valve TV's where some needed constant attention and others of the same model lasted years with utter reliability

Mike Reed
05-01-2010, 21:01
Thank you, DAVE and DAVE (double act?) for those nuggets. Despite my paucity of valve knowledge, I'd got the impression that these 509s are not your average valve amp. Hence my solicitations.

Yep, 'tis a good idea to email him (hadn't thought of that as previous communication had been by letter and 'phone).

I do know the history of the valves, though, having trusted the previous owner's info.