Mark II 1959 Reissue Hum

[Ray Baker]

I'm looking at all the miles of extra wire on the PPIMV and that's a fine candidate to introduce noise. That run should be super short and make sure that sleeve on the shielded wire is only terminated on one end.

I've had a couple noisy PPIMV's before. Some cases I think the pots themselves were bad, either that or it was getting interference from another part of the circuit.

You might be able to tap and poke on the pot and resistors and manipulate the wires a little to see if that changes things.

I shortened the PPIMV wiring to minimal essential, no change in hum. At this point most everything else from a troubleshooting perspective is outside my skill sets and capability, @Pete Farrington mentioned heaters.... In my engineering world "Heaters" are for raising the temperature of chemicals in a tank or bringing up air temperature, so I have zero clue what he's referring to in an amp. It's time to take to a real amp technician.

 

[Dogs of Doom]

tubes have heater filaments inside. He's talking about the voltage feed to the heaters in the tubes...

I'm not a tech, so, IDK which pin feeds the heaters right off, but, that's what I believe he is referring to...

 

[Ken Underwood]

I shortened the PPIMV wiring to minimal essential, no change in hum. At this point most everything else from a troubleshooting perspective is outside my skill sets and capability, @Pete Farrington mentioned heaters.... In my engineering world "Heaters" are for raising the temperature of chemicals in a tank or bringing up air temperature, so I have zero clue what he's referring to in an amp. It's time to take to a real amp technician.

Oh dear, i totally agree Ray

 

[Ray Baker]

@Pete Farrington @PelliX @Purgasound after my last post I had pretty much accepted that I was going to have to take the amp to a real tech.. After rereading the responses and analyzing the diagram, particularly the components before V3 I tried two last things. I hit the valves with DeOxit to confirm a sound connection to the sockets.... No help... then I hit the EQ pots with DeOxit.... Hum gone!

 

[Tatzmann]

Funny, had an occuring hum in a 1959 of mine too. Already knew that it was coming from somewhere around v1. Just today put in a new valve...hum gone...put in the old valve to check again...hum gone. Guess dirty socket, although i cleaned them at the first checkup as i got the amp in.

Nice that yours is humfree again, so let there be rock!

 

[paul-e-mann]

I have a Mark II 1959 Reissue that has a hum. I originally attributed it to being directly next to a TV, Verizon Gateway router and Netgear Nighthawk Mesh router. History; When I got it the capacitors were in need of replacement. So, I have no playing time with the amp prior to that. Below are the things I did prior to use:

• Replaced capacitors
  • Sourced from Amp Repair Parts, F&T’s
• Added Lar Mar type MV
  • Kit from Granger Amps
  • Installed per D-Lab (You Tube)
• Biased amp
  • After the above I still didn’t have the gain I was looking for. The capacitor replacement fixed the popping and snapping and the Lar Mar did what it was supposed to but I didn’t even play the amp more than ten or fifteen minutes because it wasn’t at the gain level I wanted.
• Purchased a Hot Mod Mr. Scary.
  • At this point I have exactly what I was hoping for, most amazing sounding amp I have now but…. It has a hum. Things I have tried to identify it, in the order I tried it and each one of these steps the was amp powered off then back on:
    • Unplugged all electronics and made the amp the sole user on the power source
    • Removed the Mr. Scary
    • Removed the instrument cord
• Next steps:
  • Remove Power Tubes
    • Question; Should I remove all at once or one at a time, Rule them out in one clean sweep and if that’s it put them back one at a time to identify the offender?
  • Remove pre-amp tubes
    • Same as above?
  • Check soldering on the Lar Mar shielding?
    • The hum is what I would expect if the Lar Mar had been installed in the front panel and without shielding.
  • Other?

Pull out all tubes and see if it hums. Put in all power tubes try again. Put in all preamp tubes try again. When does the hum begin? Once isolated start fooling around with those tubes.

 

[Ray Baker]

Hi @paul-e-mann , Problem solved

 

[Tatzmann]

Aaannnd...it's back....hahahaha.

(It's never just a valve or dirt, atleast not in my case.)

 

[paul-e-mann]

Hi @paul-e-mann , Problem solved

Dirty EQ pots??

 

[Ray Baker]

Dirty EQ pots??

That's what I'm thinking. I did the three pre-amp tubes first to rule that out then did the pots. After that the hum went away, now to see if it stays gone over time. I noticed that the "Middle" was the only one to seemed to "crackle" before clearing up.

Having found one making noise I went ahead and hit all of them just to be safe. The "High Treble" "Volume One" I have set to about 6 but I have the PPIMV down around 2. I mention that because when I cycled the High Treble I was concerned that it wasn't "just right"

Are you thinking that it could be something else? Or even come back? I could be wrong and it could have only temporarily went away. I am a little concerned that it's going to return because of how the "High Treble" felt.

 

[paul-e-mann]

That's what I'm thinking. I did the three pre-amp tubes first to rule that out then did the pots. After that the hum went away, now to see if it stays gone over time. I noticed that the "Middle" was the only one to seemed to "crackle" before clearing up.

Having found one making noise I went ahead and hit all of them just to be safe. The "High Treble" "Volume One" I have set to about 6 but I have the PPIMV down around 2. I mention that because when I cycled the High Treble I was concerned that it wasn't "just right"

Are you thinking that it could be something else? Or even come back? I could be wrong and it could have only temporarily went away. I am a little concerned that it's going to return because of how the "High Treble" felt.

Thats great that cleaning a pot got rid of the hum, never heard of a pot causing hum. Just play it and hopefully all will stay good!

 

[Ray Baker]

Thats great that cleaning a pot got rid of the hum, never heard of a pot causing hum. Just play it and hopefully all will stay good!

Over the last two weeks the hum returned, I fully cycled the Presence and Bass pots and it goes away. What's also odd is that if I put in on standby and come back in 15-20 minutes the hum returns, not every time but I have noticed this on more than one occasion. I just cycle the pots and it disappears again. The moment it goes away is when I have either hit 10 or 0, sometimes Presence only gets it and sometimes Bass only get it. It almost seems that when I max out the potentiometer and the pot moves slightly and becomes grounded again.

If I get ambition today, I am going to remove the chassis and check the nuts on the potentiometers.

 

[paul-e-mann]

Over the last two weeks the hum returned, I fully cycled the Presence and Bass pots and it goes away. What's also odd is that if I put in on standby and come back in 15-20 minutes the hum returns, not every time but I have noticed this on more than one occasion. I just cycle the pots and it disappears again. The moment it goes away is when I have either hit 10 or 0, sometimes Presence only gets it and sometimes Bass only get it. It almost seems that when I max out the potentiometer and the pot moves slightly and becomes grounded again.

If I get ambition today, I am going to remove the chassis and check the nuts on the potentiometers.

Does the amp have any mods? Maybe some wires are located in bad spots and moving them away from components will remove noise. Pretty sure the ppimv mod in my 1959 was causing hum and my tech rerouted some wires to fix the problem.

 

[PelliX]

Remove preamp valves starting at V1. When does the hum start? That'll narrow it down. If nothing up to and including the PI does it, you're dealing with some issue in the power stage.

 

[neikeel]

Make sure you lube the pots too - not just clean.
The ppimv pot (if Alpha) can often be quite badly imbalanced (replicates badly out of balanced output valves). Suggest you check.
On modded amps it is always worth checking the grounds (as mentioned). I have found splitting the buss rail on the pots useful to ground each stage to dedicated filter cap ground.
Always have a chopstick hand too.

 

[Matthews Guitars]

If cleaning the tone pots temporarily removed the hum, then it's time for new pots.

 

[Ray Baker]

Does the amp have any mods? Maybe some wires are located in bad spots and moving them away from components will remove noise. Pretty sure the ppimv mod in my 1959 was causing hum and my tech rerouted some wires to fix the problem.

Yes, I installed a PPMIV, Initially the hum was really bad. After suggestions in this thread I reflowed the solder joints and it helped immensely but didn't fully remove it. I shortened the wire length as suggested by @Purgasound in this thread as well.

The hum goes away 100% after cycling the Presence pot and the Bass pot. But it's important to note that when it hums I can cycle the Presence pot and it goes away. The there are times when the Bass pot gets it.

I did remove the valves per @Pete Farrington and the hum went away indicating the EQ section.

I'm going to lube the pots as @neikeel suggests. As I mention in post #24, I cleaned them with DeOit but I have never lubed them.

 

[Pete Farrington]

I suggest to check the resistance between any point in the heater circuit and the chassis metalwork. The balancing / reference resistors may have blown (maybe an output valve shorted sometime?).