Where to start troubleshooting - Dead Epi Valve Junior Head

[TyRip]

I have an Epiphone Valve Junior head that I added a Bitmo spanky brat kit to (tone knob, pull top boost) and after trying it out the first time I fried a resistor because the friction connectors to the transformer came loose. I replaced that and the amp worked great for a couple months. Then, I took it apart again, was playing with tubes and forgot about it. When I put it back together, I may have put the preamp tube in the power socket and vice versa. Since then I haven't been able to get even a hiss or any noise out of the amp.

I have swapped tubes (and positions), tried the different impedance outputs, but that's about it. What should I do to try to get this thing working again?

Thanks!

 

[ghostwolf]

does it have a fuse that may have blown?

 

[TyRip]

Forgive my ignorance on the subject, but how would I test the fuses other than just seeing that there is still filament there?

There are three fuses contained in plastic holders in the wires going to the larger transformer, and I opened them up and I still see the small connecting wire going from end to end. Is that it, just that those filaments are still in place, or what should I do to test them?

 

[CIM]

Forgive my ignorance on the subject, but how would I test the fuses other than just seeing that there is still filament there?

There are three fuses contained in plastic holders in the wires going to the larger transformer, and I opened them up and I still see the small connecting wire going from end to end. Is that it, just that those filaments are still in place, or what should I do to test them?

It sounds like the fuses are not blown but you could double check them with a multimeter set on ohms.

I don't mean to cause offence but IMHO if you can't answer such a basic question yourself, you really should ask yourself if you are the right person to be working on a tube amp. There are lethal voltages in there...

 

[TyRip]

It sounds like the fuses are not blown but you could double check them with a multimeter set on ohms.

I don't mean to cause offence but IMHO if you can't answer such a basic question yourself, you really should ask yourself if you are the right person to be working on a tube amp. There are lethal voltages in there...

No offense taken, I understand and appreciate the concern.

I need to be reminded of safety issues sometimes, it never hurts to take the safer road.

I am handy enough with a soldering iron and can read a multimeter, but I certainly don't have a lot of experience, that is why I asked the questions I have. If this is something most would say I shouldn't touch or mess with, that's fine, but I thought if there was a safe way to check these things out, I am not afraid of getting into the amp and trying to work things out if I have directions to go off of.

 

[milocj]

I can't help you out too much, but I would suggest that you double check the fuses for continuity with your meter first even though the filament looks good inside of them. Pull them out of their holders if you have to because I have run across fuses before that looked good but broke the wire right at the cap, and even had the caps pull off with the wire attached to one end.

As long as you know the safety precautions and how to use your meter my next step would be to check the voltages at all of the tube sockets and compare them to a schematic. This has to be done with the amp turned on and plugged in so make sure you know what you're doing if you want to do it yourself. Sorry for the redundant safety warning.

I don't know how the pin outs of EL84s match up to a preamp tube but you may have smoked something if you had the power and preamp tubes swapped and powered the amp up. I know that you can accidentally mix up a 6V6 and a 5AR4 and not damage but I'm not sure if your combination can damage the amp or tubes. Hopefully somebody else can help with that and would know the likely component to get damaged if this could cause a problem.

 

[Post Toastie]

Instead of spending so much time checking out the fuses, just put 3 new in and see if it works. Fuses are dirt cheap.

 

[CIM]

Instead of spending so much time checking out the fuses, just put 3 new in and see if it works. Fuses are dirt cheap.

I'd rather know if a fuse has blown and if so, investigate the cause.

Anyway, how much time does it take to meter a fuse as opposed to go find some new ones?

 

[teleamp]

Are you getting filament voltage?

 

[TyRip]

All of my fuses tested to have no/low resistance, so they appear to be fine.

I have no idea what filament voltage is or how to test, so all I have so far is that the fuses are alright.

Thanks for the help/suggestions, I appreciate it.

 

[teleamp]

... I have no idea what filament voltage is or how to test, ...

Do the tubes light up?

 

[TyRip]

Do the tubes light up?

yes, both tubes light up just fine. Thanks for dumbing it down for me, haha.

 

[teleamp]

OK, with the amp unplugged and the tubes removed, check for voltage on both sides of R12 (measure from the resistor to ground... if voltage is on one side and not the other... the resistor is bad), if present, let the meter drain it down, if no voltage is present on either side (measured to ground) then unsolder one side of R12 and check that it measures 4700 ohms, if zero, or open lead, replace that resistor.... that's my guess.

 

[backline]

What you see or don't see in a tube can be inconsequential. They can appear to be lit, but not work properly. If you are sure your fuse is working, you need to check/replace tubes. I assume you have spares. If that stuff is OK I would start looking at the heater, plate and cathode voltages. Make sure the tubes are drawing current and functioning. Don't these heads have DC heaters? Maybe check right at the heater supply, see if you are even rectifying the 6.3VDC.
Stuff like that, the easy stuff. if you really did have the tubes in the wrong sockets, you may have damaged the tube and/or some of the components. Anyway, poke around with your meter and right down the heater, cat, and plate voltages. Let's see what you get.....
Good Luck

And, you are absolutely sure you have a speaker cable and speaker properly connected????

 

[mcoreltt]

Help with EVJ?

Are you getting filament voltage?

I have a problem: was installing BITMO voicing mod which required soldering to 2 pins on volume and across R1 on V3 circuit board. I wasn't getting any volume, so I desoldered. Then it worked again. I resoldered, again no volume, desoldered, now nothing...

The tubes are not lighting up. I live in a fairly remote area... and have no access to an amp tech. In the short... could this be a fried R1? or is it more likely a fuse?

Thanks!

Matt

 

[jefrs]

R1 is 1Meg input resistor? - very unlikely to fry
Though I'm not sure what "across R1" means, to me that means shorting it which will silence the input.

Not lighting up? - either heater are fried or no volts on heaters.

ECC83 takes heaters on pins 4, 5, 9
EL84 takes heaters on pins 4 & 5 but G2 on 9

There you have it G2 takes B2, high voltage - probably blown the heater on the ECC83, may have blow the EL84 too. The HT and the heater volts have a common ground. Hopefully that acted as a fuse and protected the heater circuit.

Test continuity of heaters and check for volts on heater circuit.