thumperbob 2002 Posted February 20, 2008 Posted February 20, 2008 Hi Ive had a marshall vba 400 valve amp for a few weeks- only used this on a couple of practices- the amp is coupled with the vbc 4 X 12 cab it was designed for. After not using this for a week or two I set it up today for a low level practice- with the cab. Played OK but after a while ( 5 minutes ) it started to really distort badly. As the amp is new I thought it might be my bass- swapped bases- still distorting. I thought I might have blown a speaker- swapped cabs- the other cab. a 2X10 was fine so I thought it must be the cab. I swapped to the marshall cab again and it sounded fine. After about 10 mins again it started to distort and then stopped and sounded fine. I then played for an hour and it was fine. I wonder if I started to play the amp when the valves were not hot enough- there might have been some condensation ( amp kept in the house but it has been cold here ) in the amp. Has anyone else experienced this- I remember in the 80s the valve amps I used were always a bit inconsistent in their workings- help much appreciated. Cheers Bob Quote
Raggy Posted February 20, 2008 Posted February 20, 2008 Could it be anything to do with ohms? I think that head is switchable between 2 and 4? Quote
thumperbob 2002 Posted February 20, 2008 Author Posted February 20, 2008 [quote name='Raggy' post='143671' date='Feb 20 2008, 01:40 PM']Could it be anything to do with ohms? I think that head is switchable between 2 and 4?[/quote] Hi The head is on 4 ohms- cab is 4 ohms I played this again fro a hour and it was great!! I am flummoxed!! Cheers Bob Quote
Raggy Posted February 20, 2008 Posted February 20, 2008 Thats wierd! I've really got GAS for one of these. Sorry i cant be of any help Bob, hope it get sorted. Raggy Quote
d-basser Posted February 20, 2008 Posted February 20, 2008 I had trouble with my last setup (old trace AH150 and Peavey BW) the trouble turned out to be dodgey soldering on the cabinet input causing intermitent distorting Quote
gypsymoth Posted February 20, 2008 Posted February 20, 2008 likely something like that - perhaps loose wiring in the cab or jacks. if a vacuum tube has a condensation problem, it would have ceased to be a vacuum tube. condensation is more likely to be a problem for speaker voice coils - which can arc as a result. Quote
Wil Posted February 20, 2008 Posted February 20, 2008 I've heard the VBA400s can get very hot and cause problems with the PCB in the head - is it somewhere where its getting proper cooling? Quote
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