Pardon my bump of an old thread, but I have the exact same problem with my MOD 102 kit, and i have much less experience/knowledge in this field. Any chance you can create a drawing or take a picture (and list the parts) of how you created the ”humdinger” that resolved the noise issue you were having? I would love to resolve this issue for myself, but I can’t do it based only on the information in the conversation in the thread.

thanks for your consideration,
jeremy

It worked!!!

I went ahead and performed the mod to the filament heater using a virtual center tap. I set up a "hum dinger" by placing a 200 ohm potentiometer across the filaments with the wiper to ground and with a slight adjustment, knocked out most of the noise! Note: ModKits replied to my e-mail and said the noise was "normal".

I also went ahead and repurposed the BASS adjustment knob as a Master Volume control and simply wired up a couple of micro toggles and resistors to modify the tone stack. Pretty much kept the Treble control as is and created a Mid Cut and Bass Cut control. No, it's not a 31-band parametric EQ, but for such a simple amp, it does the job.

So glad I went ahead and made the changes. I figured once I placed it inside a protective cabinet, I'd be less likely to take it out and tinker with it. Plus, I did build the thing to learn and gain experience... which I did.

Now, the only remaining issue is the amp still plays fairly clean, even with the input to the second stage of V1 maxed out. I guess I could get more distortion by turning up V2 all the way, but that's just too loud for most situations. What this little amp needs is the classic response to this classic problem... add an Overdrive pedal! Which is my next project. Stay tuned.

Thanks again everybody for all your help and input. I just may gig with this little amp one day.

Mods Note:
Please don't hijack other member's thread.
This thread was split from:
Reducing noise in MOD102 DIY tube amp project.
https://forum.allaboutcircuits.com/...-in-mod102-diy-tube-amp-project.106432/page-3

 

You cannot place 100uF in parallel, else pre amplifier will blew up! Try to put 22pf between first grid and anode, and Block the output transformer with 4,7nf. Try to make Feedback from secondary of the output transformer and pre amplifiyng stage. I am not sure, if it will turn noise down, but it will sure make the circuit better. Hope, I helped a little bit.

 

@Jonesy845, Did you get it figured out? I'm 1/2 way through my MOD kit build...

 

Just for Posterity: there is a MOD 102+, and the wonderful people at MOD came up with a how-to conversion document. The 100ohm resistor "Virtual center tap" trick here is what they did on the 102plus.

The conversion document can be found here:
https://www.modkitsdiy.com/sites/modkitsdiy.com/files/media_files/mod102_to_mod102_conversion_0.pdf

This lists ALL the differences between the 102 and the 102+ . For now, I will be installing the 2-100 ohm resistors, Input grid stop reisistor mod, and adding a turbo switch.

 

100 years ago they made the amplifier produce no 60Hz hum by powering the filaments with a battery.
The schematic lists AC signal levels with no input signal and maybe they tried to cancel the hum with some filament AC fed to the cathode of the output tube.
Now I see that this thread is over 5 years old.