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In Reply to: destruction modes of 6C33 posted by fatbottle on September 27, 2002 at 13:55:56:
This sounds like quality issues with the tube. I am thinking 6C33 uses the 7-pin septar socket so you could try triode-connected 829B.
Follow Ups:
...triode connected parallel 829B has no-where like the sub-200 ohm anode resistance of the 6C33 ! I would need an absolutely ridiculous B+ to get any juice out of a stacked 829B SRPP/SEPP output stage and would have to use different output transformers , different parafeed cap and rebias the whole thing which is not an option . Tetrodes strapped as triodes in zero feedback SE designs do not sound particularly good hence my decision to use the triple titty Russian monsters . I was trying to find out if others have had similar problems with their 6C33 designs . I know these tubes can sometimes go > POP < very early on . Oh well , still have a other set of four left !...FB
The number of tubes doing so is extremely low, well under 1% or 2%. Of course the statistics doesn't mean anything for someone building a one-off unit, but there is nothing wrong with that tube, if used properly. Hard to know if you are overstressing it, without looking deeper. In some case the pop will clear the weak spot and you will never see the problem again.
Hi Victor ,
Many thanks . I spent a fair time last night trawling through the archives and found an earlier post where you specified this . The arcing may be as a result of me ramping up the HT slightly (only 15V more) , never had problems before though . The design is SEPP/SRPP with lower 6C33 in fixed bias mode , -50V , 160V , 250mA . Parafeed cap 25uF , currently using a 100VA mains toroid as an output transformer . Top section again is 6C33 with 220 ohm cathode resistor , I fitted a grid stopper of 4.7k between the grid and the bottom of the cathode resistor (could the arcing have been a result of oscillation due to grid stopper too small ?) . It was the top load tube that went pear shaped . Strange thing is that earlier that day the tube in question failed to light up . I keep finding that the pins need an occasional clean on one or two of the tubes . The pins seem a little tarnished on the four I have in the amp at present . I have already had problems with sockets , the Russian ones don't seem to up to the job so I've fitted UK military H.A.T teflons . Maybe the arcing was a result of heat opening up a grid pin connection , I'll have to carefully re-clean the pins and bring the amp up slowly to see what happens . Heat is the enemy with 6C33 if you ask me ....FB
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