updated marshall jcm 800 amp help thread

Messages
260
alright, so im still looking for help on which type of pot to buy for an '83 jcm 800 2204. the presence pot is bad and needs changing.

john philips also recommended to change the caps. if caps are the black things shown below then i think they have already been changed. blue colored ones are standard.

here's the guts
2k4prt.jpg


this is the knob that is making all the trouble. the presence knob.
261kvnd.jpg


here is the black capacitors(i think?) i was talking about
hvszuq.jpg
 

sliberty

Member
Messages
4,104
I strongly recommend that you bring the amp to a tech. It sounds like you don't have any experience working inside of an amp (no offense meant), and that can be dangerous. Some of the components in an amp (filter caps in particular) carry leathal voltages, and you need to be at least somewhat experienced in working safely in that environment.

If you do insist on changing the pot your self, I would recommend that you buy a pot from Metro Amps. Call them up and ask them for a recommendation of a pot that will best match what you are replacing from a size and feel point of view.

As for the caps, don't do it without help. And besides, if the amp sounds great, they may not need it. The idea that the caps "should be replaced" is not wrong for an older amp, but it is also not a universal rule.
 
Messages
260
I strongly recommend that you bring the amp to a tech. It sounds like you don't have any experience working inside of an amp (no offense meant), and that can be dangerous. Some of the components in an amp (filter caps in particular) carry leathal voltages, and you need to be at least somewhat experienced in working safely in that environment.

If you do insist on changing the pot your self, I would recommend that you buy a pot from Metro Amps. Call them up and ask them for a recommendation of a pot that will best match what you are replacing from a size and feel point of view.

As for the caps, don't do it without help. And besides, if the amp sounds great, they may not need it. The idea that the caps "should be replaced" is not wrong for an older amp, but it is also not a universal rule.
well i want to atleast fix the pot myself. the pot is part of the problem because it makes a thunder-like sound every time i turn it. this could be a problem with the high input channel.

the caps are the black things right? i have no idea how to fix those and would probably have to get a tech if those were the problem. it looks like they've already been replaced, so i dont know why they'd need it again
 

phsyconoodler

Member
Messages
4,301
The original amp had blue colored F,& T filter caps and those may indeed have been changed.The presense pot often makes a scratchy sound when turned on those amps and thats not always the sign it need a new pot.It may have too much DC voltage on the pot meaning it may have a bad cap somewhere in the presense circuit,and installing a new pot won't fix the scratchy noise.
Regardless,you need to get a book on how to work safely inside your amp before you even attempt to do any repairs yourself.Better yet,take it to a good tech and at least get him to assess the problem before you make guesses.
 
Messages
260
The original amp had blue colored F,& T filter caps and those may indeed have been changed.The presense pot often makes a scratchy sound when turned on those amps and thats not always the sign it need a new pot.It may have too much DC voltage on the pot meaning it may have a bad cap somewhere in the presense circuit,and installing a new pot won't fix the scratchy noise.
Regardless,you need to get a book on how to work safely inside your amp before you even attempt to do any repairs yourself.Better yet,take it to a good tech and at least get him to assess the problem before you make guesses.

is not like a sounod with the pot, i can hear it through the speakers. a loud thundery sound
 

rockon1

Platinum Supporting Member
Messages
13,703
The original amp had blue colored F,& T filter caps and those may indeed have been changed.The presense pot often makes a scratchy sound when turned on those amps and thats not always the sign it need a new pot.It may have too much DC voltage on the pot meaning it may have a bad cap somewhere in the presense circuit,and installing a new pot won't fix the scratchy noise.
Regardless,you need to get a book on how to work safely inside your amp before you even attempt to do any repairs yourself.Better yet,take it to a good tech and at least get him to assess the problem before you make guesses.

Good advice! You may replace the pot and have the same problem or worse if you dont discharge the caps(black things) you may get the shock of your life! :eek: Bob
 

TheAmpNerd

Member
Messages
1,056
Good advice! You may replace the pot and have the same problem or worse if you dont discharge the caps(black things) you may get the shock of your life! :eek: Bob


You can lead a horse to water...

...sounds like the guy really want to replace the pot.

No harm there. Replace it.

...then let us know if the problem is there or not.


Okay Noodler...how is that verse ?


Bets, the problem is there after pot replacement or not?



For my money I'd clean and lube the pot first.

If still messed up then replace it.

if still messed up then replace the other components.

If still messed up then take it to the tech you should have
done with to begin with only know you will have a much higher
bill because he'll have to fix your unclean mess that you left behind.

Though funny thing, that pic you have already looks like
the pot was fooled around with once already, look at the
melted out plastic from the pot wiring.



 

phsyconoodler

Member
Messages
4,301
This guy was already asking about pots in another post so I know he probably tried to clean the pots already.
And I'm not a 'noodler,I'm a 'phsyconoodler' phsyco for short:crazyguy

someone left the amp out in the rain
I don't think that I can take it,cause it took so long to make it,
and I'll never have those type of Drakes no more,
oh no,oh no........
 
Messages
260
This guy was already asking about pots in another post so I know he probably tried to clean the pots already.
And I'm not a 'noodler,I'm a 'phsyconoodler' phsyco for short:crazyguy

someone left the amp out in the rain
I don't think that I can take it,cause it took so long to make it,
and I'll never have those type of Drakes no more,
oh no,oh no........
whats going on, im confused now
 
Messages
3,127
Yo Yo Homie G

waz up is they be ryme in about your equipment ....player.

so dig this homey

Chill

you straight up asked our man John and you be totally dissing what he represented.

that ain't cool

but you keep asking the same question and someone who knows less then YoYo Mama will tell homie what choo wanna hear

is that enough 411 or you still confused
 

twinrider1

Member
Messages
14,031
I'm thinking YoYo just didn't get Psycho's Beatle reference. I don't know that YoYo was dis'ing anyone.
 
Messages
3,127
YoYo didn't like the answers he got from John Phillips on another thread and started another asking the same question and getting the same advice on this second thread he started. The thing is he particularly asked for John's opinion by name.

Oh and BTW it's Richard Harris "MacArthur's Park" not the Beatles.


Best
Groovey Records
 
Messages
260
YoYo didn't like the answers he got from John Phillips on another thread and started another asking the same question and getting the same advice on this second thread he started. The thing is he particularly asked for John's opinion by name.

Oh and BTW it's Richard Harris "MacArthur's Park" not the Beatles.


Best
Groovey Records

1) i was dissing on anybody, so i dont appreciate you smartassing.

2) i tried to bring me previous thread back by adding pictures, etc, to get more opinions but no body was responding, so i made a new thread.
 

TheAmpNerd

Member
Messages
1,056
This guy was already asking about pots in another post so I know he probably tried to clean the pots already.
And I'm not a 'noodler,I'm a 'phsyconoodler' phsyco for short:crazyguy

someone left the amp out in the rain
I don't think that I can take it,cause it took so long to make it,
and I'll never have those type of Drakes no more,
oh no,oh no........

Psych not there noodler. beueath such amp int he rain
yet there may :rotflmaobe not such payne as w:munch eye, rather dien arsch//1

Meinstensdu, many aschen hat schone gemACHT HAUTE BIE Dem
dinks dort linkkkk.:p
 




Trending Topics

Top Bottom