DC 5 rhythm channel is down

[Ian.Firmstone]

HI I came to my amp today and found the rhythm channel is down with teh push pull boost the leah channel is working fine and so is the EQ theres no hum no nothing!!

there is only one fuse at the back of the amp - I ve checked round the back and don't seem to have done anything by accident to turn the chanell off - teh foot switch works but seleting teh rhytm channel its still dead.

thinking maybe there is a fuse internally that protects either channel?

Any help much apprectiated thanks Ian

 

[domct203]

Welcome to the forum!

There is only one fuse, the mains fuse on the back.

Is there anything different about how you have the rhythm channel setup? For example, is the EQ only used on the rhythm channel.

This is most likely a preamp tube issue. If the DC-5 has the same preamp tube layout of the DC-3 & DC-10 which I’m sure it does, start with V4, both triodes are used exclusively for the rhythm channel. If that is not the culprit check V1 as one triode is used for the rhythm channel.

To check these tubes, simply swap in a known good tube into the suspect positions one at a time until you locate the problem. Be sure to power down the amp between swaps, and be careful, the tubes can get hot.

Do you have a spare 12AX7?

BTW- if you do not have a copy of the owners manual I suggest you download a copy:

https://mesa-boogie.imgix.net/media/User Manuals/Dual Cal DC-5.pdf

Dom

 

[Ian.Firmstone]

hey thanks so much for the reply! Will get a spare valve and try it out - thanks again!

 

[Ian.Firmstone]

Hey Dom thanks sooooo much you were spot on! V4 swapped and my channel is back! Although I was not skillfull enough to do it without pulling the chassis back out a bit to see the location! I really appraciate your guidance! Ian

 

[domct203]

Always glad to help!

Dom