JCM 900 questions and issues

[Micter]

Wait! Shouldn't a Marshall be running EL34's? I know some of them had 6550's, but most ran EL34 power tubes.

Most are EL34 or EL84 for the lower watt amps.

 

[ido1957]

Most are EL34 or EL84 for the lower watt amps.

Yep - EL34 just replaced in my amp

 

[Lt. Bob]

Yep - EL34 just replaced in my amp

uh-oh .......
I can't believe I missed that.


Seems like it should be EL34's in that amp ..... never mind, I went and looked and it does use EL34's.

iownrocknroll ..... are you sure it was 6L6's he put in that amp?
and if so, did he do any mod to allow it to use 6L6's?
You can't just substitute 6L6's for EL34's.
That's probably your problem ...... not sure if it would damage anything but it sure won't work right.

 

[iownrocknroll]

It depends on the year and the model. They started off at EL 34s then went to 5881's which is a 6l6.

The 800's were all EL34s

I believe some of the older guys had 7027A's

regardless I pulled two tubes and still does the same thing. I'm thinking opamp or transformer.

more leaning towards transformer, but I'm gonna take it to the shop to be safe.

 

[Micter]

It depends on the year and the model. They started off at EL 34s then went to 5881's which is a 6l6.

The 800's were all EL34s

I believe some of the older guys had 7027A's

regardless I pulled two tubes and still does the same thing. I'm thinking opamp or transformer.

more leaning towards transformer, but I'm gonna take it to the shop to be safe.

Did you put the pulled set back in and pull the other set? I would think if it isn't a tube issue it is most likely the output tranny. I have had a very similar issue with a small amp. As it warmed up the volume dropped. I told my amp tech I thought it was the tranny and he begged to differ. I was right!