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Help with my JCM800 please!

guitarzdude

Member
Messages
164
This is my JCM800 and i always wanted to know what these on its back do! Is it some kind of attenuator or something? Thanks!



 

mesa/kramer

Member
Messages
3,054
The speaker output jacks?

One is powering the speakers in your cab and one is for running an extension cab.

Or your talking about the ohm selector for matching the correct load for different cabinets (4 ohm, 8 ohm, 16 ohm)?
 

B Money

Member
Messages
5,918
Not sure what you are referring to? Looks normal to me, 2 speaker outs and an ohm selector.
 

Buckeyedog

Silver Supporting Member
Messages
2,457
The ohm selector just allows you to match the speaker load. And just like the above guy said, the other speaker out just allows you to run another speaker cab. If you do run another cab, you will have to adjust the ohm selector to match the load.
 

Frank Speak

Member
Messages
1,356
Your ohm selector appears to be set on 8 ohms. You should check the speaker to make sure it's an 8 ohm speaker. I thought they put 16 ohm speakers in those amps.
 

Tuberattler

Member
Messages
2,411
Also I've always had better luck running the speaker plug from the jack closest to the ohm selector. I was present one time when a friend plugged into the one you're in and it started to smoke the tranny after about 5 min... I'm still not sure why that happened that day but I switched it back into the other jack and he's still using it to this day... 1987 head RI that this happened to.
 

Buckeyedog

Silver Supporting Member
Messages
2,457
There should be a sticker on the back of your speaker. If not, then if you have a multi meter, you can check it by setting to ohm, then pulling that speaker plug out and touching the tip and sleeve. It won't be exact but will tell you if it's around 8 or around 16.

Also just a guess here. At the top it says minimum of 4 ohm's. When you have two speaker jacks, seems likely that the internal speaker might be 8 and when run with another 8, you'd have a 4 ohm load. But definitely check it out so you can make sure it matches.
 

guitarzdude

Member
Messages
164
Your ohm selector appears to be set on 8 ohms. You should check the speaker to make sure it's an 8 ohm speaker. I thought they put 16 ohm speakers in those amps.

There should be a sticker on the back of your speaker. If not, then if you have a multi meter, you can check it by setting to ohm, then pulling that speaker plug out and touching the tip and sleeve. It won't be exact but will tell you if it's around 8 or around 16.

Also just a guess here. At the top it says minimum of 4 ohm's. When you have two speaker jacks, seems likely that the internal speaker might be 8 and when run with another 8, you'd have a 4 ohm load. But definitely check it out so you can make sure it matches.
Took some photos today and it really looks like the sticker on the back of each speaker says 15 or 16 ohmns! Can i then change it to 16 ohms??? couldnt they be in parallel? will that screw anything up?? and what will that do then? louder? better sound quality?? thanks!

Here are the photos i just took:




 
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Buckeyedog

Silver Supporting Member
Messages
2,457
Ah, didn't see that it was a 212. I thought it was a 112. Anyway, stump is right, you have 2 16 ohm speakers wired in parallel which is a total 8 ohm load. It is set correctly as is so rock on!!!
 

guitarzdude

Member
Messages
164
How do you guys find the sweet spot on these amps?? I use the low input, preamp half way and i change the presence based on the guitars pickus!

Am i missing on something here??
 

696

Member
Messages
846
redslim, im not trying to be disrespectful but did you care to read the manual which you can download? it will take you some 5-10 minutes to read. as it seems you dont have a clue how to use such an old amp and things can be very dangerous to your own health, besides killing tha amp by abusing it.

and maybe youll spend 15-30 to google some settings for your amp which are already plentyful in the internets... or maybe just try and find out? we even dont know what kind of music youre playing! should i suggest eric clapton or zakkkk wylde?

just some suggestions...
 

Buckeyedog

Silver Supporting Member
Messages
2,457
Problem with these old Marshalls.......or most Marshalls is that they sound terrific.......when LOUD!! Gotta crank up that master/volume knob to get the best of these. Have you changed the tubes lately? Is it biased correctly?? There are many things you can do to tweak these beasts.
 

guitarzdude

Member
Messages
164
redslim, im not trying to be disrespectful but did you care to read the manual which you can download? it will take you some 5-10 minutes to read. as it seems you dont have a clue how to use such an old amp and things can be very dangerous to your own health, besides killing tha amp by abusing it.

and maybe youll spend 15-30 to google some settings for your amp which are already plentyful in the internets... or maybe just try and find out? we even dont know what kind of music youre playing! should i suggest eric clapton or zakkkk wylde?

just some suggestions...
Ok, i dont mean to be disrespectful either but i'm asking what setting the other TPG fellows are using and not how i should be using it! Also i never said i would be changing the settings on the back! I usually ask these to my amp tech and i just thought someone could answer it here, isnt it what forums are for??! A lot good info, tricks, and how to get away with issues specially on 30 year old amps ARE NOT ON THEIR MANUALS!!

SO WHATS THE PROBLEM WITH ASKING FOR SOMEONE ELSES ADVICE?? WHAT ARE FORUMS FOR???
 
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