Spidervalve 212 blows 500ma HT fuse

[bnwitt]

I've got a line6/Bogner spidervalve 212 in for repair and am having some HT fuse problems. First of all, the amp came in with a shorted power tube and a blown HT fuse. I replaced the fuse and put in a set of known good pulls first and then a set of good tubes provided by the owner. All was good under test. I ran the amp for an hour with the ma running at 54 on the signal injector and a 4 ohm dummy load. Put it all back together and played it for about ten minutes and no problem. Customer takes the amp home and within 10 minutes it goes dead. Shorts the replacement used power tube in the original bad tube socket

Tore it apart and found cracked solder joints on pin 2 and pin 3 of the power tube socket that had the shorted power tube originally and the second time. Resoldered those two and all other tube socket pins power and preamp. Put in a set of known good pulls and then a set of matched Winged C's. Does fine under test. Owner takes it home and 10 minutes it pops the fuse again. Both Winged C's are good though.

I take a closer look at the Radio Shack 500ma fuses he supplied and they are fast acting. Amp calls for slow blo. Customer also says he keeps noticing the speaker plug keeps coming out of the jack about a 1/4" on the back of the amp. I pull the jack pcb and find that when the plug is perfectly aligned on the 8 ohm jack contacts it is not pushed all the way in and has a tendancy to back out about 3/16" and find it's proper center. So the partially out plug is a good thing not a problem.

I Put in a new fast acting fuse and run it at 54ma for 20 minutes and no problem. So now I'm perplexed. Could it be that his guitar has such hot pickups (my strat full up will only drive the amp to 54ma on typical volume settings (12 oclock channel volume and 9 oclock master) and he's playing so loud that he's pushing the amp hard enough to blow the fast acting fuse? Is there some inherent problem with this model amp ( I see complaints of this fuse blowing all over the internet but with no explaination of a fix) that causes this issue? I mean, there are only 2@ 12AX7s and 2@ 6L6s so you would think 500ma on th HT supply would be ok fast or slow.

Does anyone have experience with this amp and HT fuse problems?

[Jag]

You said the amp calls for slow blo so why are you troubling over this? If the amp calls for slow blo that's what you should be using. Does that solve the issue?

[bnwitt]

Jag,
The issue is even with a fast acting fuse I cannot get it to blow the fuse. It has only blown the fuse when in possesion of the owner but at two different locations so I've ruled out dirty power. I have pushed the amp hard with both guitar and signal injector and it runs fine. The reason I am troubling with this is because this amp does not have enough power consumption with the 4 tubes it has to be blowing a 500ma fuse. With two 6L6s and two 12AX7's running at the plate voltages this amp provides, we are talking about 120ma at full power. That coupled with the fact that incidents of this particular fuse blowing (even with a slo blow from the factory ) seem to be a commonly reported issue with this amp makes me want to get to the heart of the issue before I send the amp back to it's owner yet again. There has to be something to this and I'd like to find out what it is. Having the schematic would be a real leg up on analyzing the issue. I mean, maybe it's in rush current due to the filter cap locations around the standby switch. I sure don't want to pull the board again and spend time following traces. Gosh I had PCB.

[Jag]

Sorry, I must have misunderstood what you meant. So when you sent it back to the owner it had the correct slow blo fuse installed you were just teting on your bench with the fast acting fuse?

Did the owner have everything connected properly. Is he using phones or line out and not plugging in a speaker?

[bnwitt]

Hmm. I posted a reply some time ago and it didn't show up. So here it is again.

No, it had a fast acting fuse both times it went back to the owner as that is what he supplied. This last time the owner took it back home after playing it here and turned it on to no output. I think the amp is afraid of my shop and behaves here. I have every value of slo blo in AGC size, but this one is a GDC and I don't have very many of those. I understand that a slo blo probably would fare better, but the fact that a fast acting fuse won't blow on me is strange. Also it really shouldn't blow unless there is a lot of in rush current. I wish a line 6 service guy would chime in here and tell me if all of the filter caps are post standby switch. There are too many complaints about this amp blowing this fuse to think it is a fluke. Either design or workmanship is at fault me thinks.

[J M Fahey]

Just as an extra check play it full blast , balls to the wall, in your shop.
You are treating it reasonably/mildly and obviously he is not.
Point the speaker towards a an open door clothes closet to absorb some of the sound and blast it *at least* for half an hour, a full hour will be better.
If tired, AC DC on 10 works well.