5150 Combo blew a fuse and now won't work correctly.

[Zabel Zarock]

Hi guys! Apologies in advance for a long-ish post.

Re-tubed my 5150 combo with a kit from eurotubes. 2 matched 6L6's for power and 5 EC35S in the preamp, with 1 balanced for the phase invertor. All went well and the amp was fine for about 3 weeks. Used it for 3 hours in rehearsal and gigged with it no problem. Sounded awesome aswell

Now, halfway through a gig on Sunday night it blew the fuse (halfway through a solo I might add). I changed the fuse out when I got home, but now when playing through it the volume/post gain controls on both channels are screwed. Here's the symptoms:

The volume goes no higher than what it is at 2, even if its turned to 10. Altho when you get to 10, theres a change in the tone. Volume between 0 and say 0.5 is scratchy like a dirty vol pot on a guitar, then its either on or off. No graduation. The tone isn't there either. I had the lead channel with the gain maxed out on 10 and volume upto 3. It sounded like the volume was at 2 and the tone was like the rhythm channel with crunch enabled. Not the face melting metal tone you'd get from the lead with gain around 6.
Also the EQ's dont seem to work.

Also before we went on stage, the amp was sat in stand-by mode and the amp of the band before us fell backwards onto mine. Dunno if this is related but it seems a coincidence.

I've had the head section out and checked over for anything obvious but everything seems to look ok. Tubes looked fine, no scorch marks or anything. No loose connections or burnt PCB's. But like I said before, I'm a total tube amp newb so any help/advice is greatly appreciated.

I've dropped Bob at Euro an email to se what he can suggest, also posted this over at the Megadeth forums where I moderate. Just trying to brainstorm things out before I take it to a shop.

Thanks!

[z1n]

If you have your old tubes you could try putting them back in to eliminate the tubes but I have no idea if they are 6l6's as well or if you took it to get biased or what but other then that, take it to a repair shop. oh and in a middle of a solo! doh! that sucks!

[Shibs]

Hi guys! Apologies in advance for a long-ish post.

Re-tubed my 5150 combo with a kit from eurotubes. 2 matched 6L6's for power and 5 EC35S in the preamp, with 1 balanced for the phase invertor. All went well and the amp was fine for about 3 weeks. Used it for 3 hours in rehearsal and gigged with it no problem. Sounded awesome aswell

Now, halfway through a gig on Sunday night it blew the fuse (halfway through a solo I might add). I changed the fuse out when I got home, but now when playing through it the volume/post gain controls on both channels are screwed. Here's the symptoms:

The volume goes no higher than what it is at 2, even if its turned to 10. Altho when you get to 10, theres a change in the tone. Volume between 0 and say 0.5 is scratchy like a dirty vol pot on a guitar, then its either on or off. No graduation. The tone isn't there either. I had the lead channel with the gain maxed out on 10 and volume upto 3. It sounded like the volume was at 2 and the tone was like the rhythm channel with crunch enabled. Not the face melting metal tone you'd get from the lead with gain around 6.
Also the EQ's dont seem to work.

Also before we went on stage, the amp was sat in stand-by mode and the amp of the band before us fell backwards onto mine. Dunno if this is related but it seems a coincidence.

I've had the head section out and checked over for anything obvious but everything seems to look ok. Tubes looked fine, no scorch marks or anything. No loose connections or burnt PCB's. But like I said before, I'm a total tube amp newb so any help/advice is greatly appreciated.

I've dropped Bob at Euro an email to se what he can suggest, also posted this over at the Megadeth forums where I moderate. Just trying to brainstorm things out before I take it to a shop.

Thanks!

Sounds like it could be the Output Transformers gone, with out having the amp in front of me, it's tough to diagnose, could be a few things or even multiple things.

Shibs

[yard dawg]

I bet something got damaged when that amp fell on it. Id do like the other guy suggested and try the old tubes. If that doesnt work maybe its your speaker bearings????????

[Zabel Zarock]

Unfortunatly I threw the old tubes out. Rookie mistake I guess

Someone else mentioned on the Deth boards that if a preamp tube has gone bad then it can reduce your volume quite alot. I guess it would also explaine the fuse blowing and the crappy overdriven tone and not the usual face melting distortion.

Hoping it's a tube issue as thats relatively cheap. Transformers sound expensive!

z1n, it was kind of a Spinal Tap moment. Took center stage, started playing and.......................... WTF??? Lol

[sm5150]

It seems like everyones having this problem.
The same thing happened to me last week with my JCM900 4100 head.
Blew fuse, got new one, but volume wouldnt get louder. Thought it was the tubes, and ordered a new set of 7, but didnt fix the problem. It probably is the transformer, or could be the resistor also...

Im bringing it in to the techs tomorrow.

[JACKSONFREAK]

If its the fuse that blew thats for the output. ( in know marshalls have 2 fuses one for power and one for output) I dont remember if the 5150 does. But i do believe the fuse is designed to blow in the even of a bad output tube. To prevent damaging the transformer.
You could have a cracked tube socket. A cracker or damaged tube from the impact. or the board could have cracked depending on how it was hit or a bad pot shorting out. Like said before it could be anything. or many things. If the amp wasnt biased when you did the tube change it couold have blown the out put tranny. Whish is expensive. But take it too a tech for the proper diagnosis. It could be anything. Including a bad preamp or phase inverter tube.
Gil

[sm5150]

If its the fuse that blew thats for the output. ( in know marshalls have 2 fuses one for power and one for output) I dont remember if the 5150 does. But i do believe the fuse is designed to blow in the even of a bad output tube. To prevent damaging the transformer.
You could have a cracked tube socket. A cracker or damaged tube from the impact. or the board could have cracked depending on how it was hit or a bad pot shorting out. Like said before it could be anything. or many things. If the amp wasnt biased when you did the tube change it couold have blown the out put tranny. Whish is expensive. But take it too a tech for the proper diagnosis. It could be anything. Including a bad preamp or phase inverter tube.
Gil

Yeah After I was done freaking out, I thought to myself, it could be anything, and if i touch it more, i could potentially make it worse. So i just decided to pay some green, and get this amp fixed

[phill_up]

The same thing happened to me. I didn't know if it was my guitar amp or what. I also talked to Bob and he steered me in the right direction
1. buy some contact cleaner and work the tubes in and out a couple of times really cleaning the socket.
2. Take the pins on the tube and VERY gently push the metal pins toward the center of the tube while rotating the tubes in your hand.
This worked for me, maybe you will get lucky as well. Combo amps are hell on tubes

[Firebird V]

I had a friend who had the same problem with a Crate Red Voo doo doo amp. It ended up being a bad tube socket but in any case it was about $150 to fix at a reputable amp repair shop. It was right after he changed the tubes though. When he changed them back the problem did not fix itself. The shop told him that the old tubes were making a connection and when they were removed it was bound to go. Bring it in somewhere reputable and have it diagnosed. Even if it was the output tranny it would probably be worth fixing as these still bring in a good buck used...

[Zabel Zarock]

Thanks guys.

Bob thinks it's likely a tube has shorted due to the knock it took whilst in stand by. Also called a locoal music place that I know is good and their guy said tube aswell. Unfortunatly I totalled my car last Friday so I'm stuck to get the amp over but at least I've got a starting point to start trouble shooting from.

I definatly want the amp repaired. Just recently found every guitarists holy grail of ULTIMATE TONE by using a re-issued tube screamer (ts808) in front of the 5150 and it spanked our lead guitarists Marsahll halfstack during the gig.

I love the 5150 lol.

[Robert Burns]

With my VHT..(blew the B' fuse") Steve is sending me a matched set
of KT-88's...so i should be back up, by the middle of next week. He said
its been a bad batch of 6550's for the last year or so? Maybe this is
a common problem in 07'?

[Retaliator]

I definatly want the amp repaired. Just recently found every guitarists holy grail of ULTIMATE TONE by using a re-issued tube screamer (ts808) in front of the 5150 and it spanked our lead guitarists Marsahll halfstack during the gig.

I love the 5150 lol.

I know what you mean! I use a Seymour Duncan Pickup Booster on my 5150 Combo and it gets a great high gain sound out of it.

[JerryP]

Shorted power tube more than likely, absolutely not a bad output transformer. New power tubes and a new fuse and you'll be back in business.
Jerry

[krimson]

Wow, I'm kinda surprised that your 5150 getting bumped would cause that. One day my 3 year old son was trying help and he moved my 5150 halfstack causing it to tip over. The head fell and landed on a patch of mud. I cleaned it up and it fired up just fine with no issues. I think the mud really helped absorb some of the impact.