Author Topic: Query for JCM 800 Experts... (Read 2695 times)

Skybone · « **on:** June 12, 2006, 05:49:58 PM »

The HT fuse just blew on my 4104 (2204 head), does this mean the amp needs servicing or is it just a straight replacement?

Also, something was rattling (audibly) at yesterday's rehearsal, couldn't see anything wrong with the amp. The base for V1 was loose, which I tightened up, but when I tried it out to see if the rattle had gone, the fuse went...

Also, out of curiosity, the current valves are Sovtek 5881's, rated at 42(?). I bought some Saratov 5881's a while back, rated at 24(?), would this make a difference to the tonality/loudness/bias etc?

Ta.

TwilightOdyssey · « **Reply #1 on:** June 12, 2006, 06:09:31 PM »

Blown HT fuse = bad power valve(s).

HTH AMPS · « **Reply #2 on:** June 12, 2006, 10:41:19 PM »

take the output valves out and run the amp - if the fuse doesn't blow then its 99% sure to be a bad output valve. get a new set and have them rebiased.

:twisted:

fps_dean · « **Reply #3 on:** June 16, 2006, 12:12:22 AM »

Quote from: TwilightOdyssey

Blown HT fuse = bad power valve(s).

Not always though....

Skybone · « **Reply #4 on:** June 16, 2006, 10:42:11 AM »

As a bit of an update, I decided to change the fuse and see if that blew. If it did, I was taking the amp in to the shop for a service.

Fitted new fuses to both mains (T2A) & HT (T500A), fired the amp up, and it was fine. The even better thing was that the rattle had disappeared, must have been the valve base after all.

Thanks for the input guys.

fps_dean · « **Reply #5 on:** June 17, 2006, 09:36:45 AM »

Quote from: Skybone

As a bit of an update, I decided to change the fuse and see if that blew. If it did, I was taking the amp in to the shop for a service.

Fitted new fuses to both mains (T2A) & HT (T500A), fired the amp up, and it was fine. The even better thing was that the rattle had disappeared, must have been the valve base after all.

Thanks for the input guys.

You may be good. The fuse could have been old and rusty for all we know. ;)