Laney VC30-112 Combo - hum problem

[nickb]

Dear all,
I need to say sorry to everybody for fulling You around (unintentionally).
I just check pin output and find that they are not same at 7915 and 7815. I just measure wrong without knowing that its a wrong pin out.
Stupid me. Sorry to all a tousand times.
Now I need to go further. Hope You will help me with it.

OK, but still it should be negative. I have to ask: When you measure the voltage is the black lead of your meter always connected to 0v while you probe with the red one?

[g1]

I just check pin output and find that they are not same at 7915 and 7815. I just measure wrong without knowing that its a wrong pin out.

I wondered if that might be the issue, sorry I should have said something.
As nickb mentioned, measure your voltages with the black probe connected to ground, list what you get on the 3 pins of the 7915.

[Neshco]

Well, yes, I measure it always with black on ground.
Now on pin 3 is a clean -15V.
What I (mis)measure first time is voltage between IN and OUT pin. That was a problem. I just accept that ground on 7915 is in the midle (pin 2) like on 7815, not on the pin 1 as it is.
I just made a problem without a problem.
Conclusion: I have stable +15V on 7815 output and stable -15V on 7915 output.
I stucked on very begining now need to go further and find real problem.

[nickb]

Well, yes, I measure it always with black on ground.
Now on pin 3 is a clean -15V.
What I (mis)measure first time is voltage between IN and OUT pin. That was a problem. I just accept that ground on 7915 is in the midle (pin 2) like on 7815, not on the pin 1 as it is.
I just made a problem without a problem.
Conclusion: I have stable +15V on 7815 output and stable -15V on 7915 output.
I stucked on very begining now need to go further and find real problem.

Try to keep your black on 0V. Clip it and leave it.

OK, you have hum. Any signal at all? Do the controls have any effect?

[Neshco]

Yes, everything is just as should be. Respond to controls, play well, but there is hum that is quite annoying after some time. Its not too loud, but certainly louder than regular "noise" that usualy is present.
Its more distinct with electric guitar. I try it on both (acoustic) electric and classic el. guitar. I can compensate with controls, and "mask" it a little, but thats not it. On drive its even worse.
Again, its not such a big hum, but he is, no doubt, there.
Should I try to replace tubes? Its a quite new amp with very low "mileage" so i droped idea that tubes can be a problem, because they are almost new, but maybe Im again wrong?!

[g1]

Turn the guitar's volume control off. Is the hum still there?
Plug your guitar into the FX return jack, how is the hum level?

[J M Fahey]

Conclusion: I have stable +15V on 7815 output and stable -15V on 7915 output.
... now need to go further and find real problem.

[oc disorder]

Hold the mail... firstly if that amp is two years old .. and never been opened there is a strong chance the output tubes need replacing.
Borrow another 4 and check. At a pinch they could be checked in pairs.
Need to check things like reverb return turned down and HUM BALANCE CONTROL !

Also they have quite a collection of smd components on the reverse side of the pre-amp board.

The previously posted schematic was for the English production.

The new manufacturing team may have made some improvements to the old spitfire post 2008 !

LANEY VC30-212-8 Service Manual free download, schematics, eeprom, repair info for electronics

[Neshco]

Ill let You know as soon as aproach it again Im not at the place today.
PS (offtopic)
Djokovic is again No1 world tenis player!! )

[Neshco]

Hi friends,
just to inform public that I change tubes and hum is gone. Strange, because its almost new amp.
However, there is another problem I didnt notice before (maybe he wasnt there):
Reverb effect while You play just suddenly come and gone. Im not sure that there is some time pattern how long is present or not, just randomly is present and not present.
Any idea except potentiometer which is OK?

[Mick Bailey]

Tubes can drift from their original matching and the imbalance between each pair causes the hum. Sometimes you can rearrange the tubes to improve matters by swapping them around individually from one side of the primary to the other.

Reverbs often go open circuit - either the connectors need re-seating (I give them a squirt of contact cleaner and rotate them slightly) or possibly one of the leads to the transducers has come adrift inside the tray. I'd check the mechanical connections first before looking elsewhere.

[barfoden]

Oh nooooo...

Laney has dumped their old VC30 construction...

Use to a be a combined PCB and chassis mounted tubes..
Now they went full retard,, sorry i mean full PCB...
THe amp is hot cathode biased (95% dissipation at idle) and with the tube hanging upside down the heat of the tubes will gradually warm up the PCB board and dry out components near the tube sockets...

I bought a dirt cheap Laney LC50 with warranty.. This is also a full PCB construction but it is fixed bias with EL34,, so I can bias it cool (55% dissipation at idle) and have less heat problems...
Though the amp has some hiss and the first filter capacitor has a working voltage of 410VDC and is rated at 450VDC. Not super good and if I take out the tubes, the voltage will probably go above 450V unloaded...
Also when I turned a hum adjust pot (AC filament circuit) with a screw driver to find where the noise is lowest, the component had a short at one end of the range .. Fortunately it did not seem to affect the amp... Also bias is limtied to -36V so only EL34 apply,, not 6l6 or 5881 in this amp like in the old amp....

Tired of so many modern PCB amps.. Just see the amount of repair stories for the Fender hot rod deluxes...