#1
Whats up everyone....

i admit that im not the most knowledgeble with tubes so i was wondering if you guys could help me out..

ive owned a mid 80s jcm800 for the last year and have had the usual troubles of a 20+ year old amp.... recently i noticed my tone sounded a bit muddy and i looked and saw one of my EL-34s wasnt glowing... im still getting sound out of the amp, it just sounds crappy. i was wondering how that is possible and what damage that could be doing? i also blew a fuse in it last week which im attributing to the dead tube. i read a previous thread saying that it could be arcing which would blow the fuse.... ANYWAYS what do you all think? regardless im taking it to my local shop to get a full look over but just wanted to know what everyone thinks about it and to learn a little more about it!

thanks
Josh
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
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Marshall 50w JCM 800 with 1960AX Cab
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#2
take it to a guitar shop and get some new tubes and a complete service. try and get some mesa tubes too.
Quote by Mad Marius
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#3
My guess it it's probably just the tube.

Are you having any other problems with it, except the tone suckage? Blowing frequently, extreme buzzing, burning smell, etc..?
#5
I haven't had the new fuse blow yet.... the fuse that was in it was an old ceramic fuse so that could have been part of the problem.. so the new fuse in it is a slow blow fuse... but its been buzzing/humming a little more than usual but no burning smell. i had the other EL 34 die on me in August... now that puppy smelled like it was burning big time when that blew. ill just end up getting it re-tubed. i have electro harmonix tubes in it right now.. i love the sound but any suggestions on new tubes other than mesas?
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
Gibson Les Paul Special
Amps
Marshall 50w JCM 800 with 1960AX Cab
Fender Deluxe Reverb
Avatar 4x12 w/Celestion V30s
EHX Stereo Pulsar<Dunlop Rotovibe<MXR Flanger<EHX Big Muff
#6
there isnt even any heat coming off that tube btw... that any indicator that its dead? and it has absolutle NO glow at all... before when the one tube died it had some glow to it just not very strong...
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
Gibson Les Paul Special
Amps
Marshall 50w JCM 800 with 1960AX Cab
Fender Deluxe Reverb
Avatar 4x12 w/Celestion V30s
EHX Stereo Pulsar<Dunlop Rotovibe<MXR Flanger<EHX Big Muff
#7
Arcing normally causes a snapping or popping noise. It's doubtful that it's causing an overload condition, which is blowing the fuse. Arcing is normally caused by a bad tube. If your amp has more than 1 power tube and 1 of them is not working, it's still possible for it to work on the other one, or other ones. In an amp with 2 power tubes, each tube is on, or conducts for one half of the cycle. So, when 1 tube is amplfiying, the other one is in cutoff, or is biased out of operation. The tubes trade off amplifying the signal. This reduces their duty cycle, which reduces heat and operating current - since they're not operating single-ended, or Class A. You're hearing the result of 1 tube - if your amp only has 2 tubes. I would definitely have all of the power tubes replaced, if they're more than a couple years old. The fuse blowing is the result of something causing an overload. Without having the amp sitting in front of me, it's real hard to say what could cause it. Could be something in the power supply. Possibly the bias is wrong and it's pulling too much current. Could be any number of things.
#8
Was the old fuse a slow blow? If you've replaced a fast blow type with a slow blow, you could be asking for a larger repair bill. Never, ever, never, ever replace a fast blow with a slow blow and never, ever, never install a fuse with higher current handling than what's specified. You can install a fuse with less current handling, but never go larger. That's when you find that a $25 transistor blows in order to protect the $.25 fuse.
#9
is it a twin channel 800? if so what year?
My band.
www.myspace.com/bransonny

My gear.
Marshall: JCM800 2205, 6100, 1960AV
H&K: Triamp MKII, Duotone
Mesa: Recto recording pre, 212
2 Avatar 412 (v30's)
Gibson: LP std, SG std, SG goth, SG spec
G&L ASAT classic
Martin DC-16GTE
#10
Quote by JoshSGPGH
I haven't had the new fuse blow yet.... the fuse that was in it was an old ceramic fuse so that could have been part of the problem.. so the new fuse in it is a slow blow fuse... but its been buzzing/humming a little more than usual but no burning smell. i had the other EL 34 die on me in August... now that puppy smelled like it was burning big time when that blew. ill just end up getting it re-tubed. i have electro harmonix tubes in it right now.. i love the sound but any suggestions on new tubes other than mesas?

You just replaced one tube before? You're supposed to replace them in matched sets.
#11
Quote by Ddjembe Mutombo
is it a twin channel 800? if so what year?


i have honostly no idea what year it was... this amp was/is sort of a mystery its a twin channel 50 watt jcm800 tho

Quote by KG6_Steven
Was the old fuse a slow blow? If you've replaced a fast blow type with a slow blow, you could be asking for a larger repair bill. Never, ever, never, ever replace a fast blow with a slow blow and never, ever, never install a fuse with higher current handling than what's specified. You can install a fuse with less current handling, but never go larger. That's when you find that a $25 transistor blows in order to protect the $.25 fuse.


All i know is the fuse was ceramic... i dont believe it was a fast blow. i replaced it with the same current handling and everything. btw thanks for all the help steven you are a freakin genius

Quote by forsaknazrael
You just replaced one tube before? You're supposed to replace them in matched sets.


I have no idea i had my local shop do it... im pretty sure they are matched but when i get it re-tubes i will defnetly make sure that it is a matched set.... i will be sure to bring this all up when i get it repaired
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
Gibson Les Paul Special
Amps
Marshall 50w JCM 800 with 1960AX Cab
Fender Deluxe Reverb
Avatar 4x12 w/Celestion V30s
EHX Stereo Pulsar<Dunlop Rotovibe<MXR Flanger<EHX Big Muff
#12
what is the serial number?
My band.
www.myspace.com/bransonny

My gear.
Marshall: JCM800 2205, 6100, 1960AV
H&K: Triamp MKII, Duotone
Mesa: Recto recording pre, 212
2 Avatar 412 (v30's)
Gibson: LP std, SG std, SG goth, SG spec
G&L ASAT classic
Martin DC-16GTE
#14
its a JCM800 2204 model btw
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
Gibson Les Paul Special
Amps
Marshall 50w JCM 800 with 1960AX Cab
Fender Deluxe Reverb
Avatar 4x12 w/Celestion V30s
EHX Stereo Pulsar<Dunlop Rotovibe<MXR Flanger<EHX Big Muff
#16
Generally the main power fuse is a slow blow and the HT rail fuse is a fast blow.

If a tube arcs out and takes out a fuse it'll take out the HT fuse. The HT NEEDS to be a fast blow.
#17
The HT Fuse is the 500mA one correct? if so that wasnt the one to blow... it was the 3 Amp fuse.
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
Gibson Les Paul Special
Amps
Marshall 50w JCM 800 with 1960AX Cab
Fender Deluxe Reverb
Avatar 4x12 w/Celestion V30s
EHX Stereo Pulsar<Dunlop Rotovibe<MXR Flanger<EHX Big Muff
#18
Quote by forsaknazrael
As far as new tubes go...I'd go for JJ. Safe bet.

+1.

Unless you have about 200 dollars lying around. In that case, check out some Mullards or NOS tubes, maybe even some Golden Lions
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#19
haha ya i dont have an extra 200 bucks sadly.... should i look at replacing the preamp tubes as well? i havnt had any problems with them and really dont want to mess with them...
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
Gibson Les Paul Special
Amps
Marshall 50w JCM 800 with 1960AX Cab
Fender Deluxe Reverb
Avatar 4x12 w/Celestion V30s
EHX Stereo Pulsar<Dunlop Rotovibe<MXR Flanger<EHX Big Muff
#20
Quote by JoshSGPGH
haha ya i dont have an extra 200 bucks sadly.... should i look at replacing the preamp tubes as well? i havnt had any problems with them and really dont want to mess with them...

If they don't seem to be causing any trouble, then I'd personally leave them alone.
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How do you say "I'm okay" to an answering machine?

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#21
Quote by stratman_13
If they don't seem to be causing any trouble, then I'd personally leave them alone.


okay sweet.. thats what i like to hear :P
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
Gibson Les Paul Special
Amps
Marshall 50w JCM 800 with 1960AX Cab
Fender Deluxe Reverb
Avatar 4x12 w/Celestion V30s
EHX Stereo Pulsar<Dunlop Rotovibe<MXR Flanger<EHX Big Muff
#22
Quote by al112987
Generally the main power fuse is a slow blow and the HT rail fuse is a fast blow.

If a tube arcs out and takes out a fuse it'll take out the HT fuse. The HT NEEDS to be a fast blow.


sorta a stupid question but can someone explain to me what and HT fuse is in the first place compared to the main fuse?
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
Gibson Les Paul Special
Amps
Marshall 50w JCM 800 with 1960AX Cab
Fender Deluxe Reverb
Avatar 4x12 w/Celestion V30s
EHX Stereo Pulsar<Dunlop Rotovibe<MXR Flanger<EHX Big Muff
#23
Quote by JoshSGPGH
The HT Fuse is the 500mA one correct? if so that wasnt the one to blow... it was the 3 Amp fuse.


Yes, the 500mA is the HT fuse. However if the 3A fuse blows the amp would not be turning on.

Quote by JoshSGPGH
sorta a stupid question but can someone explain to me what and HT fuse is in the first place compared to the main fuse?


So if you follow the power starting from the wall the first thing that the power hits is a 3A mains fuse and it acts as the primary protection from say... a power surge. This fuse comes before everything, so when this is blown, the pilot light won't turn on and no power can go to the amp. The HT fuse serves as protection from power tube failure basically and is in the high tension power rail, basically when a power tube arcs out you need a fast blow fuse that will go out as soon as a high voltage surge hits it from an arc.
#24
Quote by al112987
Yes, the 500mA is the HT fuse. However if the 3A fuse blows the amp would not be turning on.


So if you follow the power starting from the wall the first thing that the power hits is a 3A mains fuse and it acts as the primary protection from say... a power surge. This fuse comes before everything, so when this is blown, the pilot light won't turn on and no power can go to the amp. The HT fuse serves as protection from power tube failure basically and is in the high tension power rail, basically when a power tube arcs out you need a fast blow fuse that will go out as soon as a high voltage surge hits it from an arc.


ya when the fuse blew a week or 2 ago it was definitely the main fuse the amp wouldn't turn on or anything and i just replaced the fuse... no big deal. and from what you are describing i dont think it arced at all... seems like i just need my power tubes replaced!

thanks a ton everyone for the info i learned alot tonight! i dont feel so ignorant about my amp now! great to have so many knowledgeable people on the forums!
Guitars
White Gibson 61' SG Reissue
Sunburst Airline 3PDLX
Gibson Les Paul Special
Amps
Marshall 50w JCM 800 with 1960AX Cab
Fender Deluxe Reverb
Avatar 4x12 w/Celestion V30s
EHX Stereo Pulsar<Dunlop Rotovibe<MXR Flanger<EHX Big Muff