Epi VJ problem, help wanted

[Thumpalumpacus]

So I'm jamming on my VJ, volume is wide open, when out of nowhere the volume drops more than halfway. Cycle the power, no dice. Try it with another guitar and cable, no change. Change out both tunes, still less than half-power.

Anyone here experience this? Any help is greatly appreciated.

 

[jimmyjames]

My VHT Special 6 did a similar trick once. I reflowed the solder joints to the tube sockets (tried cleaning pins and pin sockets first) and that sorted it. They're made down to a budget, maybe get a techie to go over everything quickly, or drain your caps and have a shot

 

[SWeAT hOg]

Sorry, Thump. That is a fun amp! I hope you find a solution.

 

[Soul Tramp]

Thump, pull and re-seat all the tubes.

 

[SWeAT hOg]

Thump, pull and re-seat all the tubes.

I think he did? Tunes(sp)=tubes?

 

[Soul Tramp]

I think he did? Tunes(sp)=tubes?

Ops. Don't tweet when you're drunk and don't post too early in the morning.

 

[rabidhamster]

Is it a similar tone at half power, I.e. Distorted like full power

Or just like the amp turned up half way at full blast


My initial guess is a bypass cap shit the bed or lost ground, but I'll wait for your response

 

[Marshall & Moonshine]

Could it be a bad triode in the preamp Tube?

 

[Leña_Costoso]

Output transformer

 

[Marshall & Moonshine]

Output transformer

Isn’t a VJ single-ended? I’d think that means a single primary winding and a single secondary winding.
If either opens, that’s it—kaput.
If it’s a turn-to-turn short, I’d think it would have to change the impedance just so to cause the OP’s problem, and if OT’s are like regular transformers elsewhere in the electrical world, those shorts don’t last long.
I can always be wrong, but it sounds more like a resistor or cap, tube socket or tube.

 

[Leña_Costoso]

Yes it is single-ended so you are correct. Whoever I've had three or four Champs brought to me over the years including one I built that had very low output and the fault was always the output Transformer which is why I mentioned it.

 

[Leña_Costoso]

More on that..... I can't remember checking because it's been a while but my memory tells me what we found was shorted secondaries that was shorted unto themselves. So instead of a full winding you got maybe an eighth of a winding and that gave great Havoc to the impedance and output

 

[Marshall & Moonshine]

More on that..... I can't remember checking because it's been a while but my memory tells me what we found was shorted secondaries that was shorted unto themselves. So instead of a full winding you got maybe an eighth of a winding and that gave great Havoc to the impedance and output

That’s the “turn-to-turn short” I mentioned earlier.
I didn’t think it was a common thing. I’m an electrician aboard container ships and usually transformers of any kind tend to fail a bit more dramatically. They’re never “failING”....
They FAIL.
But I know it is “a thing”, just never seen it.
Interesting.

 

[mdubya]

My Champ used to do that. Turned out to be a cracked tube socket.

I've burnt a resistor before, too. But that took out a tube and the amp was dead until the resistor was replaced.

 

[Leña_Costoso]

Back at a keyboard... and I'll add a bit more re the OT. When the one's I had "went", not only loss of volume but heavy distortion at any volume, even the slightest.

 

[THDNUT]

Throw the amp away and get a new one. Those VJs are disposable aren't they?


My VJ most certainly has an OT (and a choke too) because I installed the MM mod kit.

 

[irocdave12]

Most likely a bad solder joint particularly at the tube sockets. But other jr owners have had a problem with corrosion in the fuse holder or poor intermittent contact there so give that a check too

 

[Thumpalumpacus]

Thanks so much for all the input. While replacing the tubes I made sure to spray some electronics cleaner in the sockets and work the tubes. I didn't notice the sockets being cracked.

I'm on my way to pick up a Tweaker 15 as a replacement. The VJ cost me $100 used, so I'll use it to learn a few things.

I sure appreciate everyone's input (har-har), and will post back occasionally as I open this thing up and have questions or whatnot.

Thanks again, y'all.

 

[rabidhamster]

If you don't get to it before then, bring it to GuitArlington, thats a fine afternoon gathering project

 

[Thumpalumpacus]

If you don't get to it before then, bring it to GuitArlington, thats a fine afternoon gathering project

Much as I'd love to go, I won't be able to; I'm taking 6 days off in early October and have to work those two days. But once I get some time I will take this thing apart and fix it myself if I can. I reckon I've got a year's use out of it, and will use it from here on out to start learning amp-tweaking.

Not bad for $100, eh?