BluesSlider Posted February 22, 2015 Share Posted February 22, 2015 Greetings All, Why would a MkII Bogner with new TungSol 5881's run so hot it is damaging the pc board at the point where the tube sockets are soldered into the board? I just had a MKii fixed up (got it when it was in need of repair, it was making loud bursts of noise) and the amp tech only replaced a resistor and the tubes. It's sounding great with a new pair of 5881's, even though I have to adjust all the channel volumes down to 30% to bring the master volume up to 9 o'clock in order to have a usuable volume.Since I got the amp home I've noticed the odor of melting insulation/components. It's very subtle, but it's there. When I took the head out of the combo I noticed a small whitish residue around the solder pins. It looked like salt water had dried and left a spot of salt residue. Each pin of the tube socket of each of the 5881's had it around the solder point for the tube socket. When I took out the tubes, the odor was much stronger, and the plug end of the tubes smells strongly of burnt plastic. So it seems like the tubes are overheating in the socket. I've played one gig with it and this is the result. It was on for an hour, then off for 45 minutes, then on for a couple hours. The smell is very faint when the amp is all together. I am wondering is it possibly over-biased? The amp tech I had work on it said a lot about how hard it is to get Line6 schematics and parts since they moved to China. Should I take it back or find another tech? Blues Quote Link to comment Share on other sites More sharing options...
spaceatl Posted February 24, 2015 Share Posted February 24, 2015 hmmmm.....I do wonder about the plate voltage rating on the Tung Sols....Those are real 5881s are I recall...Max Plate voltage is 400...You have to be very careful about 5881s...They are not all the same.......you need a tube with a Max Plate rating of 450 volts or higher as I recall... I think the issue is using Tung Sol 5881s in a 400 volt amp with a Solid-State Rectifier....Check your plate voltage...I bet it's ready 420 volts or so....That's past Max on those tubes...You can generally use Russian 5881s...With Tung Sol, I think you have to go 6L6...6L6 of anything will always work...I am using Mesa 5881s....but those are Russian version with higher Plate rating....Your tech should have noticed this... Quote Link to comment Share on other sites More sharing options...
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