VH4 Problem -- Blown Fuses - HELP

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Cro

Cro

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Hey all,

I know there are some very knowledgeable amp-heads on this board, so I'm posting this thread in hopes that I'll get a response in time for my show tomorrow. Here it goes:

I play through a VH4. Today in practice, the amp died. It would not turn on at all. I checked the main fuse -- it was blown. I replaced it and the amp powered up again, but when I flipped it off standby -- it died again. The replacement main fuse blew. The fuse in channel two is also blown. How does one go about troubleshooting this problem? Do I have a bad tube? Do I only need to replace the fuses? What else can cause this sort of problem? Obviously, it's hard to diagnose and solve the problem over the internet, but based on what I have experienced -- can anyone offer some advice?

Any help would be greatly appreciated. I have soundcheck tomorrow at 4PM EST.

Thanks...
 
If your talking about the fuses below the four leds on the back then you have a bad power tube,I own a herbert so I'm not entirely sure what the back of a vh4 looks like but I'm sure its similar, those are for the tubes.
 
...if its only popping the fuse when off standby its because when its on standby the tubes are only on the heaters and not drawing any current when ya flip the switch it will pop. Forgot to add that.
 
Thanks HBWDB. So I guess it's time for me to buy a matched quartet and re-tube the amp. Oh well, no Diezel for tomorrow's show. I thought the amp was supposed to be able to temporarily survive tube problems like this...

Peter, any ideas why the tube failure system didn't work?
 
I think that might be a herbert/einstein only thing cause they have more than one bias pot,I don't know, good question. In most amps if a power tube goes bad it always pops the main fuse unless its like the herberts and einsteins. I thought vh4 were like that too though. You may want to try reseating the tubes and putting another fuse in to see if that works.
 
http://www.rig-talk.com/forum/viewtopic.php?t=3529&highlight=fuse peter suggest in this what I'm talking about with a guy that has a similar problem, his post is a little bit down the page, so apparently it can happen with a vh4. Heater short or whatever.
 
Also I'm pretty positive on it being only the einsteins and herberts being able to run in "limp home mode" because when a fuse blows on them it blows the pair, cause the fuse is for a pair....if you wanted to play the vh4 pull the corresponding tube pair out, so if its tube "2" then pull the inner pair of tubes and it will reduce to 50 watts and double the impedence(Say if your running 16 ohms to the cab reduce it to 8 ohms from the head to the 16ohm input on the cab, reducing it really in this case) and you could use it tomorrow. It also can be a way to see if its really the tubes blowing the main fuse. I however don't know if the tube pairs have to be in the outer sockets or inner sockets to run safely in 50 watt mode(there's a thread on this in this page but it doesn't say if the position matters), or if it matters at all, so wait till someone answers this to find out before doing so. If it matters just move the good pair to the right sockets, hopefully someone chimes in on this.
 
1. Unhook all midi devices/units
2. Pull all power tubes
3. replace fuse
4. switch on

if the fuse stays alive - either midi-problem or tube-problem - if the fuse dies: --> tech.
 
My Marshall power amp used to pop the mains fuse when my tubes were old/shagged. When I retubed it, it used to stop blowing them again for a year or 2, so it sounds likely to be a tube fault. But do what duesentrieb suggested to know for sure...
 
First of all, thanks to everyone who has been trying to help me here. I really appreciate it. :)


>|<>QBB<
duesentrieb":5084c said:
1. Unhook all midi devices/units
2. Pull all power tubes
3. replace fuse
4. switch on

if the fuse stays alive - either midi-problem or tube-problem - if the fuse dies: --> tech.
Click to expand...

OK. I just unhooked everything and took out the tubes. I replaced the fuses. I switched it on and there's no problem. I'm gonna go grab some replacement tubes.

Question: if I have a quartet of the same brand of EL34's, can I use them as replacements without any additional work (re-biasing)?
 
What brand and have they been graded in anyway? Say like groove tubes has ratings of 1-10. Say if you had a rating 6 groove tube you could replace it with another rating 6 and be good to go.
 
Yeah, all tubes vary so, for example, one Ruby EL34 will not necessarily be the same as another Ruby EL34, however, a Ruby EL34 with a "PC" rating of e.g. 45 can be replaced with another Ruby with a "PC" rating of 45. Each manufacturer has a different way of rating tubes so to know for sure you need the same brand, and also the matching figure. Matching figures from different brands are not compatible usually, i.e. Rubys have a "PC" number, Groove tubes a rating, Watford valves 2 figures x.x/xx, etc. hence why you can't have any tube with the same e.g. "PC" number as other manufacturers don't have a "PC" number or a "groove tubes rating"!
 
Thanks fellas...

I have four Svetlana EL34's that I can use as replacements for my previous set of Svetlana EL34's. Do I have to worry about anything? Where do I find rating numbers or other various vital information?
 
Where did you buy them from? Its either on the base of the tube or on the tube boxes, post back with any numbers you have...if you have any for the ones in the head that is, cause you will have to have both obviously.
 
My brother gave me the replacement tubes. He was using them in his VH4-S before he switched back to 6L6's. I don't know about any numbers.
 
They will probably have to be rebiased then, sorry duder, can't really be sure without numbers. Sorry I can't be of any better help.


-Nick
 
I just wanted to thank everyone for the helpful information and suggestions. The gig went very well tonight... Maybe I'll post some pics when people send 'em to me. Anyone whose interested in hearing our tunes can go to: http://www.myspace.com/doyouseethedark

The recording is pre-Diezel (meaning, before I got one). The next CD is going to be blessed by the VH4 (but I have to work out these problems first)...
 
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