Bronal Posted June 27, 2011 Posted June 27, 2011 The output valve in one of my 845 monoblocks has started emitting a noise like a harsh hish. I know it's this valve because I've isolated it through a process of elimination, changing other valves around. It always comes back to this amp. Is this a sign that the valve is on the way out?
Guest Posted June 27, 2011 Posted June 27, 2011 Hi Bronal Sounds like it could be if your tried another tube in its position and it doesn't make a sound .Does the same tube make the hishing sound in the other channel . Also visually do they look the same plate colour filiment glow . Cheers
VanArn Posted June 27, 2011 Posted June 27, 2011 Bronal, when the amplifier has been turned off for a good while,remove the valves and lightly clean the pins on the valve bases and also clean (and tighten, if required) the valve socket pins.Remember,that 845 transmitter valves use B+ voltages around 1kV,so be careful.56oval has rightly queried if you have actually swapped over the o/p tubes as it is not clear from the post if this first step has been tried.There could be other reasons for the noise,such as component breakdown,incorrect bias adjustment,oscillations etc.The expected useful life of O/P valves is around 2000hrs. so it is wise to keep spares on hand.
Graywulf Posted June 27, 2011 Posted June 27, 2011 as above Bronal, and sometimes, why?????? gawd knows, a valve can misbehave in one socket,,, put it in another? it behaves perfectly.
Decky Posted June 27, 2011 Posted June 27, 2011 I would guess that there must be some caps in the circuit that stay charged all the time - especially on HT lines. Do you really think that is the best advice you can think of?
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