Gallien Krueger Fusion 550 Bad Tube? Help!

It’s possible that it’s a tube but there’s a lot going on inside that amp that’s pretty difficult to troubleshoot (even for a qualified tech)

If you can’t return the amp for a refund, I recommend giving GK a call and see if they have anybody in the factory service department that could work in it, or if they know of any of their service centers that are well equipped to work on this model. This is a clever (IMO) design, but with clever and unique comes significant added complexity.

This is not a model that an average tech is likely to be successful with, the chances for creating additional damage is very real ime.

 

There are enough unusual aspects to that amp that experience with that model will be very helpful.

 

Just curious, what amp techs do you know other than Mtronics? Thanks

 

And I only assume you already know Mtronics because all local musicians seem to know them LOL

 

I had a couple of friends who worked there over the years but don't know anything about them now. They appear to be connected to Superstition Mountain Music, but that's questionable.

You really need to give GK a call and ask them who they would recommend for your particular amp and see if perhaps they still repair those at the factory. Of course, these amps are all old enough to be out of warranty and the factory doesn't do much if any out of warranty repairs BUT this is an unusual enough model that there may be an exception.

 

I am sorry to hear that it is not the tube.

 

Ask if it sat for a long time- tube sockets can oxidize over time and bad sound is a good example of what results. If you look around on forums, you'll see recommendations to 'retension and clean the tube terminals'- I have had to do it and it often works but be aware of what you're dealing with (high voltage, if the caps don't discharge when it turns off) and keep your free hand off of the chassis (put it in your pocket). Caig DeOxit is a good choice for this. You can start by gently wiggling the preamp tubes and doing a visual inspection- if they don't glow, you may have a bad tube, one may have become dislodged or the terminals could be oxidized, as I mentioned. OTOH, it could be a dirty switch that has been unused for years- I have a 400RB and needed to clean my switches because a couple of them hadn't moved in a long time before I adjusted all of them when I checked it out.

 

GK was very helpful when I called to get info about my 400RB- sent a schematic and she (IIRC, her name is Carol) sounded like a tech. I asked about the 400GT that I had at the time and she knew that one well, too.

 

It was hard enough for me to get in-warranty help from GK and then the amp died just after an hour or two of playing after being returned that I’ve written off the brand. Good luck! I hope you can get some assistance.

 

IF it's a tube you can still swap it as it's cheap. But as mentioned earlier, a tube is a very little part of an amp.

 

Only the tiniest amount of de-oxit should be used, and caution is absolutely necessary (both for safety reasons as well as not damaging the sockets due to lack of finesse.

 

These were only discontinued in the last couple of years, so your chances of getting help from GK should be high.

 

Older GK amps, while [email protected]$$, can be prone to oxidation in their effects loop.

You might want to try plugging/unplugging a guitar cable into the effects send and effects return jacks SEVERAL times each - basically “sexy time at the effects loop”…

I’ve heard distortion-like problems caused by oxidized connectors.

 

I think he already tried bypassing the loop with a jumper cable.

 

As always, the instructions should be read. I have seen people flood the insides of equipment with 'tuner cleaner' and washed away any evidence of the component numbers on the board. I have also seen people melt plastic, whether cosmetic or in controls, because they used the wrong type of cleaner.

 

Doesn’t GK maintain a “qualified tech” list? I “trained” our local “GK-qualified” tech on this particular amp when I had similar non-tube issues with my MBF500. In my case some connections needed refreshing. It’s been fine since. I’m sure expertise with that amp is out there, and GK does still support it to my knowledge.