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Post by edgebsl on Apr 29, 2007 12:09:19 GMT -5
Ok, so I played a gig fri with one cab for the first time in awhile. I ended up running the master on noon. I thought this should have been unusually loud but it was just enough.
So the next show I hooked up both cabs, turned the speaker selector to 8 ohms and fired it up. I got nothing but hum. I looke din the back and only the right two pwr tubes were lit!!!!
So I turned it off ,rearranged tubes 2 and 4 and turned it on stand by again. This time, all four tubes were lit, a few seconds later the left two died again. So I tried it in half power mode and the amp worked .With all 4 tubes lit up.
I played it on half power and it did not sound very good at all.
Is this a bum tube issue? Or is there something wrong with my amp?
The tubes are only 3 months old. EH 6550's biased at an average of 42 with a bias rite. (39,42,42.5 and 43).
Any suggestions?
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Post by Hacksaw on Apr 29, 2007 12:27:12 GMT -5
I looked in the back and only the [glow=red,2,300]right[/glow] two pwr tubes were lit!!!! So I turned it off ,[glow=red,2,300]rearranged tubes 2 and 4[/glow] and turned it on stand by again. This time, all four tubes were lit, a few seconds later the [glow=red,2,300]left [/glow]two died again. So I tried it in half power mode and the amp worked .With all 4 tubes lit up. Any suggestions? sounds like a bum tube.. since you moved tube 4, to position 2 and the other set was effected, |
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Post by edgebsl on Apr 29, 2007 12:38:55 GMT -5
Would a bad tube light up still?
Oh, and Rik did you get my message...I have that for you
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Post by joshsage on Apr 29, 2007 12:44:14 GMT -5
+1 on the bad tube...
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Post by Hacksaw on Apr 29, 2007 13:57:54 GMT -5
Would a bad tube light up still? Oh, and Rik did you get my message...I have that for you Yeap.. sure will. OH.. I will check.. my phones dead! lol, chargin at the moment. Thanks!! Just curious.. and thinking.. Did you have JJ tubes in the amp before changin? you may need to re-tension your tube sockets. some of the JJ's tubes had bigger socket pins than the spec.. then you change back to other tubes and the new tube makes intermitten contact.. and can cause this issue.. used to be the other way around.. for a while JJ tubes pins where smaller! lol.. now they are too big, from the word on the street.. I havent had a set lately.. |
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Post by edgebsl on Apr 29, 2007 15:14:23 GMT -5
That's just crazy how they light up on standby then shut off when I take it off standby.
And I still say, that the amp didnt sound quite right in half power mode. Kinda bright and not cutting through in the right way.
Is 42ma too hot for 6550?
That's what Josh told me to bias at at the most. So I don't know if that' sthe MAX or just the max that they would recommend. If I had them cooking I could be running through them already. And that could explain why the amp hasnt seemed as loud lately.
Either that or I'm going deaf.
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Post by philm on Apr 29, 2007 19:55:00 GMT -5
I use the info. inthis chart when I bias my Allen amp. It would seem that 42mA is not too high since the range is 40-50. www.ampwares.com/bias.htmlI'd try the retensioning that was mentioned and if that doesn't work, try a new quad and start fresh. |
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Post by jameshealey on May 21, 2007 14:38:41 GMT -5
50ma to about 36ma is the safe range for KT88(6550)'s..
sounds like a tube problem.. I'd quite like to try the KT88's in my competition but replacing the bias resistor seems a bit of a job for someone like me I dont like the inside of amps they scare me stupidly high voltages etc.. I dont mind biasing coz i can do it without touching any components.
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