MOD 102 Kit not powering on at all. Any suggestions?

[LOUDthud]

The wire going to pin 9 of the 12AX7 is laying right across the wires going to pins 1, 2 and 3 which is the input triode side. I suggest you unsolder the wire from pin 9, untwist about 1 turn from the wire that goes to pins 4 and 5, and re-route that wire along the chassis, as far as possible from the pins 1, 2 and 3 wires, then to pin 9. You can see in the instructions pic how the wire to pin 9 has some distance to the socket as it comes around to pin 9.

[Stephen1966]

I should note, the output is going through an attenuator, so it's not as loud as it would be straight to the speaker.

Just to add my tuppence worth here... Have you tried it without the attenuator?

[vipor3D]

I should note, the output is going through an attenuator, so it's not as loud as it would be straight to the speaker.

Just to add my tuppence worth here... Have you tried it without the attenuator?

Yes, I have. Unfortunately it didn't fix the issue. I wish the fix was that simple, though

[martin manning]

Did you remove the paint from all the ground points that bolt to the chassis?

[vipor3D]

Did you remove the paint from all the ground points that bolt to the chassis?

When I started the project, I followed the instructions that said to file the paint from the inside edge of each chassis hole. It wasn't specific, so I assumed it meant the literal inside edge of the hole (as in the inside ring of the hole that would touch your finger should you put it through the chassis hole). I've seen examples of this build where others filed all the paint away on the inside of the chassis where screws meet the chassis. I went back and did this for many points on the chassis (input and output jacks, all the pots, and under most of the terminal strip connectors (The two that connect to the filter caps, the T3 strip that connects to the pots, and the T4 strip between the pots and V1). Could it be that I just need to go back and do that for the last 2 terminal strip connectors?

Edit: Went back and filed the paint under the last two strips and it didn't fix the problem

[vipor3D]

The wire going to pin 9 of the 12AX7 is laying right across the wires going to pins 1, 2 and 3 which is the input triode side. I suggest you unsolder the wire from pin 9, untwist about 1 turn from the wire that goes to pins 4 and 5, and re-route that wire along the chassis, as far as possible from the pins 1, 2 and 3 wires, then to pin 9. You can see in the instructions pic how the wire to pin 9 has some distance to the socket as it comes around to pin 9.

I rewired the filament wires between V1 and V2 but it still didn't fix the buzz/hum issue

[Phil_S]

Reposition the blue wire so it is away from the green filament wires. Bend towards the middle of the socket and up into the air a little.
On the other socket, reposition the white wires that look to be laying on the green filament wires. Bend them up a bit to get some (more) air between the white and green.
Maybe it won't help, but this is quick and easy. There is a chance it might.

[vipor3D]

Reposition the blue wire so it is away from the green filament wires. Bend towards the middle of the socket and up into the air a little.
On the other socket, reposition the white wires that look to be laying on the green filament wires. Bend them up a bit to get some (more) air between the white and green.
Maybe it won't help, but this is quick and easy. There is a chance it might.

I tried it but unfortunately didn't seem to fix my issue

[martin manning]

Make sure all three of the lugs attaching the terminal strips to the chassis are making good metal-to-metal contact on the flat surfaces. I would also run the red/yellow wire directly to the negative terminal of the 47u reservoir cap, where it says T1. edit: Star washers between the lugs and the chassis would be a good idea too. The green earth ground lead from the power cable should be on its own dedicated ground lug too.

[sluckey]

Unplug the instrument cable from the amp. Does the buzz go away or at least get significantly better?

Do you have any fluorescent lights or light dimmers near the amp?

[Stephen1966]

You know, it's going to be something simple. Don't lose heart.

Can you verify this is how you have your heater wires? It's difficult to make out from the photo.

Untitled-1.jpg

The connection between pins 3 and 4 is there to elevate your heater voltage - in theory, that should eliminate the hum but the artificial centre tap that Martin talked about earlier is another way and there are instructions for the 102+ that show you how to do that with a pair of 100 ohm resistors. The instructions to upgrade your 102 to a 102+ include cutting that connection between pins 3 and 4 on V2.

Another way, if you have a pot going spare, is to connect one leg of the filament supply to one side, the other leg to the other side of the pot and connect the pot's wiper (centre pin) to ground. Adjusting the pot should allow you to dial out the hum.

Your power transformer's filament coil doesn't have a connection to ground or centre tap of its own so the filament supply needs one of these three methods to minimise the hum.

Other things that can induce hum are dry solder joints - I recommend you reflow any that look suspect. Run a chopstick over them while the amp is on - you will hear it if that's where the problem lies.

[vipor3D]

You know, it's going to be something simple. Don't lose heart.

Can you verify this is how you have your heater wires? It's difficult to make out from the photo.


Untitled-1.jpg


The connection between pins 3 and 4 is there to elevate your heater voltage - in theory, that should eliminate the hum but the artificial centre tap that Martin talked about earlier is another way and there are instructions for the 102+ that show you how to do that with a pair of 100 ohm resistors. The instructions to upgrade your 102 to a 102+ include cutting that connection between pins 3 and 4 on V2.

Another way, if you have a pot going spare, is to connect one leg of the filament supply to one side, the other leg to the other side of the pot and connect the pot's wiper (centre pin) to ground. Adjusting the pot should allow you to dial out the hum.

Your power transformer's filament coil doesn't have a connection to ground or centre tap of its own so the filament supply needs one of these three methods to minimise the hum.

Other things that can induce hum are dry solder joints - I recommend you reflow any that look suspect. Run a chopstick over them while the amp is on - you will hear it if that's where the problem lies.

I haven't given up hope yet, but I'm getting close lol.

I can verify that V2 is wired like the diagram you attached.

I ordered the parts for the MOD 102+ upgrade along with the original kit and was planning to make that upgrade just to get some experience working on the amp, but I was really wanting to get the original build right before making the upgrades.

If I can't figure it out soon, I'm going to just forget it and move on to the upgrades. It'll just bother me to no end to know I wasn't able to figure it out

Edit: I also did a chopstick test. I pushed and tapped on every wire and connection point in the amp and didn't hear anything/any change in the output buzz. However, when I went to turn the amp off, I noticed the buzz reduced significantly when my finger touched the switch. I could be wrong, but that would seem to me to indicate a grounding issue?

[vipor3D]

Unplug the instrument cable from the amp. Does the buzz go away or at least get significantly better?

Do you have any fluorescent lights or light dimmers near the amp?

The buzz is still there with nothing plugged into the amp. I don't have any fluorescent lights or light dimmers nearby, or in my place at all.

[vipor3D]

So I think I may have made a small bit of progress. I tried doing continuity tests for the ground points, resoldered some connections and also filed a little more paint away around some of the ground points. Not sure if it was one or all 3 together, but the buzz seemed to be minimized some in relation to the guitar signal, but I still have the ground issue when I touch the switch or the chassis handles.

I was able to plug in my guitar and could play it without the buzz overriding the guitar signal at lower volumes, but it becomes too much after turning the volume up some. There's also still the issue with the buzz increasing to about 75% on the volume pot then going away when volume is 75%-100%. And I noticed when I turned the treble control all the way up, the buzz got much more noticeable and was overriding the guitar signal.

I also noticed that on certain settings it seemed that the guitar grounding became "backwards" from what I'm used to. By that I mean when I touched the strings or control plate or something, the buzz got louder when normally letting go of the strings or not touching a grounding point on the guitar makes that happen. Would this suggest a grounding issue with a specific point within the amp?

EDIT: Tried playing the guitar through it 15 minutes or so, which is the longest I've let it stay on at once. Everything was going okay then I heard something start physically buzzing in the amp itself. I quickly turned it off and unplugged it.

I have some other things I have to do tonight, but if I have time I plan to open it back up and see if I notice anything

[sluckey]

Remove the input jack and just let it hang by the wires. Scrape the chassis until you see lots of shiny bare metal around the mounting hole for the input jack. Reinstall the input jack using a 3/8" internal tooth lock washer on the inside of the chassis and tighten securely.

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