Pignose G40v- maintenance?

[dscid]

Well, like the title says - it's time to replace some things. This is my first tube amp, and I don't really know how to troubleshoot. So, here's the deal:

Power on - idle: sometimes it will make this weird continuous crackling/scratching sound. During this time, if you touch anything on the amp it will respond immediately with a scratch. It's not loud popping/crack, like if you're adjusting knob, and pot needs replaced. It's just this...horrible, shifting scratch...that doesn't go away. Is this a resistor/capacitor problem? I got the amp used, but with new power tubes (put them in myself)...]

Every once in awhile (way less common than the above) I'll get a little whine/noise out of it. It doesn't seem as low as a 60hz hum, but it very well could be - I'm not overly experienced.

Volume knob huge crack/pop every time I adjust it. Simple pot replacement?

That's it for now, I hopefully I can get this thing running like new, or better than (with better electronics)!

Thanks in advance - what should I do =) I will not pay 50 bucks for an analysis at the local shop.

[Don Moose]

Read this first,
then go here for a really good set of debug information.

Be VERY cautious - the voltages inside a tube amp are genuinely lethal!

[Robert M. Martinelli]

Hi,
I don' t know how old the amp is, but most of the problems seem to be related to the pots; not only they can make scratching noise wher turned, but, if they have some open points along the carbon track, when they get there they leave the "door open" to all sort of noises and disturbances ( because of the very high impedance they develop in such conditions ) - so start replacing them all.... another thing I would do is to check for leaky coupling caps, if you got one, DC can pass through, get to the pots and be the reason for the "scratching" noise.

As to the hum - if it really is, it' s always a good idea to check / replace filter capacitors in the PS section.They can leak or develop an ESR ( equivalent series resistor ) which prevents them to properly act like filters.

I' m not familiar with that model, but if it does not have such a thing, you could add a hum balance potentiometer to reduce hum due to heaters' supply. That' s very easy to do, first of all make yourself sure the heaters' secondary winding does not have a center tap, If it has a center tap it' ll be connected to GND - disconnect it and leave it open ( isolate it with tape ). Take a 220 to 500 Ohm potentiometer and connect the center lug of the pot to GND and the external lugs in parallel with the heaters' 6,3 VAC.

Adjust it for minimum hum, you' ll probably find the right position to be somewhere close to the center of the pot' s taper.

A "fixed", non-adjustable version of this hum-balance circuit can be built using two 100 Ohms resistors connected in series, the center to GND and the two sides in parallel with the 6,3VAC.

A word of caution : the voltages inside can kill you with the same ease of a bullet in your head - ensure yourself you have no voltage inside prior to start servicing.

Hope this helps

Best regards

Bob

[dscid]

I wanted to order some paper in oil caps for it, and some resistors.

Anyone know how many caps it will take - and how many/what type of resistors?

Thanks

[Robert M. Martinelli]

I wanted to order some paper in oil caps for it, and some resistors.

Anyone know how many caps it will take - and how many/what type of resistors?

Thanks

Hi,
Before starting to troubleshoot/repair/maintain an amp it is always a good idea to get a schematic of the thing you' re going to service, this way you' ll have an indication about the quantities, values, the ratings and sometimes the type and material of components originally used. If you' re keen enough about electronics, reading the schematic will help you better understand how that particular amp works and it will also make your troubleshooting activities easier.

As a rule of thumb it is always good to replace the original PS filter caps if the amp' s very old, but, as already stated, some of the problems you described could be caused by leaky coupling caps, so check for DC voltage leak across them and replace them if needed. For safety' s sake be sure the new caps voltage rating meets or exceed the original one.

If you still get scratchy noises after replacing the coupling caps, then drop in new pots, If you still get hum after replacing filter caps in the PS section and the amp has no hum balance circuit add one as described in my previous post.If hum cannot be reduced to a reasonable level check the heaters' supply wires layout, the two 6,3 VAC wires should be twisted together all along the way and kept as far as possible from signal paths to keep the amp from picking up hum.

Excuse me if I repeat myself, but ALWAYS be sure to have disconnected mains and fully discharged the caps before servicing the amp, an easy and effective way to do this is to keep playing after disconnecting the mains plug until no sound can be heard. I might seem pedantic, but when it' s about safety it' s better to be clear as possible, the voltages and currents inside a tube amp being potentially lethal.

Hope this helps

Best regards

Bob