Loud static-like noise from tube combo

[RobC99]

And no sound from guitar.

Hughes & Kettner Tube 20.

Fuse looks good, next thing to check is tubes?

[onelife]

Does the sound change when you adjust any of the Volume controls? If so, what is the change?

 

Can you see the power tubes? If so, does one of them glow red?

[WRGKMC]

Bad tubes or loose tube sockets - Bad cord - Dirty pots - bad solder joint someplace - or bad cap would be the things I'd check first.

 

If the amp has a preamp out you can also run the preamp out to another amp and see if you get a clean signal up to that point, an you can also try plugging a guitar into the effects return.

 

If the Effects return produces a clean signal and the preamp out produces static, the problem is in your preamp. If the preamp/effects out is clean and the effects return creates static of is dead, the problem is in your power amp section.

 

My first guess would be the tubes however. The amp runs EL84 tubes like a Vox does. They likely have the same high mortality rate so I'd re-tube the amp first. Heat and vibration can cause them to make static noise or they can have elements shorting.

 

If none of that works, you'd need a pro tech to signal trace the problem down to the component(s).

 

These amps are complex then your normal tube amps and they have two inherent design flaws. First they are a hybrid containing solid state and tubes. SS devices need to be kept cool and can fail from the heat from the tubes. The amp also uses recessed pc boards for the tube sockets which is another bad design in my opinion. Heat from the tubes can heat the board and weaken the solder/traces or just cook any components on the boards, including the boards themselves. When you combine heat and vibrations from the speaker it can crack solder joints causing failures.

 

Vintage tube amps use chassis mount tube sockets and the heat from the tubes are kept from the inside of the chassis. The chassis acts like a big heat sink and gives the caps and resistors inside a lower temp. The tubes also create a convection current. As heat rises, it draws in cool air to keep the chassis cool. Problem is this also draws in dust and dirt which clings to electronic components and can eventually short components out. which The recessed PC board mount is an inexpensive way to build an amp, but its an open invitation to allowing the circuits exposure to heat and dirt. Add to that the solid state silicon components and high mortality tubes and you have allot of failure possibilities.

 

[RobC99]

Does the sound change when you adjust any of the Volume controls? If so, what is the change?

 

Can you see the power tubes? If so, does one of them glow red?

Nope no change. Tubes are well hidden and not serviceable by the user which sucks.