Need Some Assistance Please...JMP

[Cardiac Tom]

Ok, I did not have a lot of time to do anything but buy this at the price that was given...A friend of a friend was in need of cash quick so I walked away with his half stack for what I thought was the deal of the year. Did not have a chance to play it yet (that will change by tonight) but the handle is busted and the pots are dirty (his words) which is simple stuff...Overall it looks great...

Any info would be appreciated...

Front of the head has the small JMP logo

On the back...Master Model 100W Lead...Serial number is 08466K, which I believe is 1978. Has 6550A tubes.

The cabinet is trickier...Don't really see anything on it. It is a straight cab, speaker jack is on the bottom. There is a serial number 04674. Have not cracked it open yet to check out inside. Grill is that salt and pepper looking cover.

 

[charveldan]

If ur cab grill looks like my 78' above thats small Chequerboard not salt n pepper.

There was small check and large check, don't make the small grill anywhere but do the large now.

"K" in Marshall serial is 1978'.

My 78' A & B cabs have G12M 25 watt Blackback speakers.

They made 25 & 30 watt Blackbacks in late 70's only.

 

[sullimd]

Pics??? What did you pay for it, if you don't mind us asking?

 

[Cardiac Tom]

I will post pics when I get a chance...

Looks like the same cabinet...no markings on it at all other then the serial number and the Marshall logo. Do you happen to know what ohm the cab is? Like I said, only one speaker jack at the bottom.

I paid $500.00 total..

 

[charveldan]

I will post pics when I get a chance...

Looks like the same cabinet...no markings on it at all other then the serial number and the Marshall logo. Do you happen to know what ohm the cab is? Like I said, only one speaker jack at the bottom.

I paid $500.00 total..

Use a meter and check the omage on the cab.

Plug a "speaker" cable not instrument cable into the cab, set the meter to Ohms.

Should read about 13.7 thats a 16 ohm cab.

I had one Blackback cab that was wired to 4 Ohms but i was told it was 16.

That could have had a bad outcome.

Standard Marshall wiring on these are four 16 or 15 Ohm speakers wired series parallel = 16 Ohm to head.

These cabs Kick Major ass and the ceramic magnets are superior to anything made today as long as the voice coils & cones are good.

Its good to open the back and check all solder joints. This wiring is soldered to each speaker terminal.

Also make sure the basket screws are tight but don't overtighten.

Loose screws can cause basket rattle when you crank it.

If you have 25 watt speakers with a 100 watt head dont crank the master much more than 1/2 way open.

A 100 watt Marshall can have a peak watts of 175 and waste ur speakers.

Put up pics of the inside ...

 

[Cardiac Tom]

Will do that...since it is unknown at the moment, I was going to test the head with my current cab...thanks for the suggestions!

Another hour to go before I start playing with this amp...Stoked!

 

[charveldan]

Been playing 35 years and with these cabs for 9.

Theyre the best sounding ive had.

I'm 50 and was in high school when these were made.

 

[charveldan]

Lead cones are 1777 code.

Bass cones are 444



Stock wiring harness for 1978' should be red & black wires.

Mine are replaced in this bottom cab.

 

[Cardiac Tom]

Sorry for all the questions, but what model cab is this?

 

[charveldan]

Mine are models "1960 A & B".

Same as today for stock Marshall cabs but they make alotta other model numbers too.

 

[keennay]

The cabs are pretty inconsistent over the years. I wouldn't worry about which speakers should match with your cab type or the serial number of your cab... as long as you know the type of speakers and if they work 100%. It sounds like your amp's headshell could've been swapped at some time, but hey if you love your amp & you're not worried about the resale value then who cares!

That's a great price!... congrats!

 

[Cardiac Tom]

Will have some more pics soon...

I love this amp...And this sucker is loud!!!! Used it at practice last night and it went well...gonna use it at our show tonight, but I am bringing the 900 as a backup just in case...

 

[MarshallDog]

I will post pics when I get a chance...

Looks like the same cabinet...no markings on it at all other then the serial number and the Marshall logo. Do you happen to know what ohm the cab is? Like I said, only one speaker jack at the bottom.

I paid $500.00 total..

Holly shit Bro, you stole that, what a deal, wow!!! That amp alone would go for maybe 1100.00 to 1500.00 on ebay not to mention the speakers are worth probably 150.00 to 200.00 each if in good working order.

 

[lewis_grey]

500 dollars is crazy low, congrats on an amazing deal there and a stellar amp and cab!

 

[charveldan]

Thats a 78 with the 9 inch logo. The small logo is 6 inch
Starting in 79 they went to an even larger 12 inch logo.

 

[Cardiac Tom]

Some of the back side...

Sorry to be an idiot, but what are the jacks to the left of the speaker outputs...not labeled, so I don't know...

 

[charveldan]

Some of the back side...

Sorry to be an idiot, but what are the jacks to the left of the speaker outputs...not labeled, so I don't know...

USA JMP's with 6550's had 4 speaker out as per Underwriters Laboratories spec in the 70's for insurance purposes.

UK models with EL-34's did not.

You can run FOUR 4x12's off ur JMP Homie ...

Id pull the chassis and make sure they're all hooked up first.

 

[Cardiac Tom]

You can run FOUR 4x12's off ur JMP Homie ...

We'll worry about that when I get a fourth cabinet...lol...how would that work impedence wise?

And thanks for all your help!! Will post some cab pics soon...

 

[charveldan]

We'll worry about that when I get a fourth cabinet...lol...how would that work impedence wise?

And thanks for all your help!! Will post some cab pics soon...

16 + 16 ohm cab = 8 ohm to head.

16 + 16 + 16 + 16 ohm cabs = 4 ohm to head.

Two 8 ohms cabs = 4 ohms to head.

One 16 ohm cab = 16 to head.

One 8 ohm cab = 8 ohms to head.

One 4 ohm cab = 4 ohms to head.

Thats it.

 

[Cardiac Tom]

Thank you again!!

I knew the basics, but never thought I would have the opportunity to run 4 cabs...I was happy when I saw there was a 4 Ohm setting with this head...I have played fests before where cabs were provided, but they were 8 Ohm, and the JCM900 does not have the 4 ohm output so no stack (only visually) for those shows...