My Laney VC30 Guitar valve amps volume keepd fading in

I would check C37 & C38. If one is loose or bad connection, there will be 100/120HZ noise.

First, plug your guitar and cable into a different amp to make sure the problem is the amp. Then check to see if you have output from any headphone jack or effects loop. If so your problem is in the power amp section. If not, it's likely the preamp section. Whichever section it is, it will most likely need to go to the shop.

Bad connection? Loose fittings? I used to get a crackle from my amp when I turned the volume or balance knobs. A quick spray of WD 40 down the shaft after removing the knobs fixed it.

Sounds like output valve, if the amp is more than few hundred hours then suspect this for sure. I don't know much about this amp specifically but does the sound fade/return suddenly or over a few seconds? Try running it with the back off and fan on the valves etc. Then play at loudness where problem occurs and see if any improvement. Remember that at band practice you always play much louder than you think and put a lot of stress on it.

clean all "vr" (variable resistors) like volume bass treb etc, sounds like bad contacts. this happens due time while they oxidating. maybe helps. use "contact" spray for best result

For a test in troubleshooting, see if level from the headphone jack fades or not when this happens and get back to us.

If you play this loud the amplifier MAY be going into a thermal pprotection area. It would be about as loud as a typical boombox when at safe levels.

If you need louder than that, you need a bigger unit.

If the volume always is strong after letting it rest and cool and then fades as you drive it hard, this is the probable cause.

I want you to do a test. while using the amp plug a pair of headphones into the preamp out... note you will only hear stuff on one side if they are stereo phones and the sound may be fairly weak... while the unit is operating correctely then unplug phones and use it. When it fades out plug in phones compare the level when it was OK... If the preamp output fades lower as well, then we know problem is in the preamp section...

We can do a lot of troubleshooting without opening the amp.

I see nothing in the scheamtics that should be an issue causing this...

Since it didn't fail for the tech, think "what was different?". Are you connecting something else? Foot pedal? Temperature? :Loudness of playing?

Now what else is in common to these two units... AHA! The guitar...

If your guitar has a battery in it, the 20 to 30 minutes fading would correspond to a battery failing and then recovering after you unplug the guitar for a while.

IF this is a vacuum tube unit, these symptoms are that of a tube that the heater is intermittent, that is it cools off due to a break and then liights again.

Open the back and observe the heaters in the tubes. DO NOT be fooled by some that have TWO heaters in them. (use a mirror if necessary) A single one that comes and goes can cause the problem and the voiration can make it come and go. This behavior in a tube is NOT somthing readily spotted in a tube checker. The delay in fading and coming back would be the delay in warm up following a heater going out and cooling.

have you got valves fitted to the amp as they can cause fading if old >damaged >not fittted properly also check the speaker connects and try playing half volume the output should be steady.. you say its handmade if you made it pull out the amp board and check your soldering joints look to see fi there is any that need resoldering as they may be getting hot and causing a resistor to fade..