[majoconz]

I'm wary of ECL86's. An auction buy of a Blaupunkt "Sultan" sounded pretty good after a bulk replacement of the large C's and 'that' capacitor along with a largish resistor on the output transformer tags, a 1kohm 3 watt job. After 15 minutes or so it started to sound very 'bassy' which got worse and a hot smell - the 1kohm looked a bit toasty. All of the current through the 1k goes into the pentode side of the output ECL86. I attached a voltmeter across the 180ohm cathode resistor to monitor the current. Immediately after warm-up it was passing about 15mA and it stayed there for about ten minutes but then started to climb - when it got to 45mA panic set in. I asked a couple of friends at work and they both said 'that capacitor' which I had already changed but another one made no difference but then someone said 'grid emission' which I had to look up. Apparently ECL86's are renowned for it - I sorted though the spares and found four of them - two Mullards, one unreadable and a Telefunken - only one passed the test and stayed stable at 15 to 18mA - the Telefunken. I wonder if it has a slightly different construction but I couldn't see as it was well 'gettered'. So beware the ECL86! I'm sure that not the same for all circuits, perhaps it's just running near its limits in this one. The data says Va 250v and Ia 36mA so it's running about half the current.