Volume jump

[Twangthing]

Hi,

My amp is playng up, & I suspect it may just be a valve that needs replacing but I don't know how to check? The volume is cutting out & in again.. I don't think it's the jack socket or my leads, or my guitars. Plus it only seems to happen in the first channel (outermost jack socket) How do you check for a faulty valve? There are 3 pre and 2 power valves I think. Thanks.

 

[MuddyWolf]

You put in a new tube and see if the problem stops. There is really no other easy way to check a tube. The problem could be lots of things like a bad solder joint or old resistor.

 

[Burning Fingers]

Some info on what make and model amp may allow someone to shed some light on the problem

 

[schmee]

WHAT AMP?
Does it have the plastic jacks?
Sounds like the jack to me.

 

[tubedude]

Clean and retention the input jacks.
If it has breakout jacks (effects loop), clean those also.
Info on amp helps make better choices. What model, how old, any mods etc.

 

[Twangthing]

Sirry

Some info on what make and model amp may allow someone to shed some light on the problem

Sorry.. it's a Fender Blues Deluxe, an old one, 90s maybe? I read somewhere that you can tap them with a pencil & if one has gone microphonic, that's the one you replace. But it's not making noises, it's just dropping out.. I will buy a couple of power tubes & start there I guess, as if it's not that, having spares is no harm atall. I'm not very techy, & I know messing with amps untrained can be fatal..

 

[W.L.Weller]

Do you ever use the effects loop? If not, stick a short guitar cord between "preamp out" and "power amp in", see if that helps.

How long have you have the amp? Have you ever changed the tubes?

 

[Burning Fingers]

The Blues Deluxe amp inputs 1 and 2 share the same preamp tube (V1A) so if it only happens on one input then I doubt that the tube is responsible.
The input sockets may need investigating and cleaning...especially the contacts that are closed when no plug is inserted.

 

[Twangthing]

Thanks for the tips guys. I'll try those out, as they don't involve me dicing with death.. Regarding the inputs, I thought the second input was lower gain (which you might choose for humbuckers or whatever) so would be a different, reduced circuit. But if it's the same circuit then maybe it is the jack after all. Thanks again.

 

[W.L.Weller]

The 1 and 2 inputs do differ, but as you can see in the schematic section that @Burning Fingers posted, they both feed your guitar's signal into the grid of the first preamp tube. (The volume difference is mainly in how much of your guitar's signal gets sent to ground, see @robrob 's site for more info: https://robrobinette.com/How_Fender_Input_Jacks_Work.htm )

Replacing a PCB-mounted input jack is a little fiddly, but certainly doable:

 

[Twangthing]

Do you ever use the effects loop? If not, stick a short guitar cord between "preamp out" and "power amp in", see if that helps.

How long have you have the amp? Have you ever changed the tubes?

I've had it a few years now, but it has only seen bedroom action, & not heaps of that.. () But taking it on tour this summer, so need to get it sorted. It is probably owed some new tubes by now, even though they haven't been overworked tbh. I don't use the fx loop, so I'll check that.