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

[vipor3D]

I didn't think it was that bad considering this was my first build, and I don't do this kind of thing often.

How/what could I improve for the next build?

I didn't mean to denigrate your workmanship, my comment was just about the use of terminal strips and their somewhat random placement and spacing of components. (Even their effects pedals are built on terminal strips.) If you look at some of the Tweed Champ and Tweed Princeton builds posted here, they look much better with an eyelet board even though the circuit is quite similar. Much easier for the novice builder to spot mistakes and components are not so crammed together.

For your next build, choose a kit that has an eyelet board and practice striping wires to lay neatly. You may need to purchase some extra wire. Be extra careful when you strip the transformer wires, it's kind of messy if you cut them too short.

Note: On a push pull amp, it is sometimes necessary to reverse the wires from the Output Transformer to the Plates of the output tubes. Leave the wires full length until the amp is running properly.

No worries. And regarding your comment about cutting transformer wires too short, I didn't realize when first building the amp that it instructed you to wire in a more old school fashion and not the modern way which wires the fuse and PT to the switch. The instructions said to wire the PT directly to the fuse which is what I did. Now I believe the PT wire might be too short to reach the switch lug if I try to rewire it. Are you saying that having to "extend" the PT wire with new wire would be a bad idea?

[vipor3D]

Update - I reviewed everything again realized both red PT wires were one lug off instead just the one initially noticed here. I made the change and tried the amp again and it came to life!

The only thing that I seemed to notice wrong was a loud hum. The guitar signal came through as expected and sounded pretty good except for the hum. Any suggestions on where to start to eliminate it?

[vipor3D]

Update - I reviewed everything again realized both red PT wires were one lug off instead just the one initially noticed here. I made the change and tried the amp again and it came to life!

[LOUDthud]

Now I believe the PT wire might be too short to reach the switch lug if I try to rewire it. Are you saying that having to "extend" the PT wire with new wire would be a bad idea?

If you must extend a transformer wire, it's best to use Heat-Shrink tubing to insulate the splice. Don't be tempted to use black electrical tape, it will eventually come off. You may have a hard time finding the right size heat shrink that will shrink down tight. Don't give up, keep looking.

Same idea applies if you have unused wires on a transformer. Use heat-shrink, don't use electrical tape. I like to strip a little bit of insulation from the end of the wire and bend the wire back over the insulation so there is a bump for the heat shrink lock on to and not come off.

[Stephen1966]

Update - I reviewed everything again realized both red PT wires were one lug off instead just the one initially noticed here. I made the change and tried the amp again and it came to life!

The only thing that I seemed to notice wrong was a loud hum. The guitar signal came through as expected and sounded pretty good except for the hum. Any suggestions on where to start to eliminate it?

Congrats on getting the amp to start up. Chasing down a hum can be a long process but if you eliminate each of the possible sources as you go along you will get there.

Check:

Heater wires - check they are connecting to the correct pins on the sockets.

Avoid parallel positioning of heater wires with signal wires. If it has to cross a signal wire, it should cross at 90 degrees.

A nice tight twist on the heater wires can help to reduce the emissions/oscillation.

Ensure the polarity of the heater wires is correctly phased across the tubes - not easy to see if you use the same colour for both sides. Looking at the schematic, the wire that goes to pin 4 on V2 should go to pin 9 on V1. There should also be a jumper across pins 4 and 5 on V1.

Solder joints - thoroughly chopstick your wires, connections.

Double check everything is bolted down tight.

Thinking of your tubes, I would suggest before you switch it on again, go through the build with the schematic and check again, every single component connection, marking off each connection as correct as you check them on the schematic.

The hum is usually AC in origin and the heater wires are the most likely source of that but if you can rule out all of these you can start to look at things like possible ground loops and tubes.

Edit: it could be something as simple as the lead dress you have and shifting wires around might be enough to cure the problem. Looking at the transformer though, you have 4A of current available on the heater coil, the EL84 draws 760mA and the ECC803 (12AX7) draws around 300mA so if you wanted to rule out AC hum you could modify and make it 6.3VDC. DC filaments with this tranformer (269EX) would be okay.

[Stevem]

This type of trouble shooting is mainly a process of elimination.

Start with removing the preamp tube, is the hum still there?

[martin manning]

The only thing that I seemed to notice wrong was a loud hum. The guitar signal came through as expected and sounded pretty good except for the hum. Any suggestions on where to start to eliminate it?

Another clue is the hum frequency. Is it line frequency (50 or 60Hz) or double that (100 or 120Hz)? Line frequency means the source is un-rectified AC, i.e. heater wiring. Make sure he heater string has a ground reference. I don't see a grounded center tap or other ground reference (100 ohm resistor from each side of the heater string to ground) in the kit instructions or in your photo. I would connect a 100 ohm resistor from each lug on the pilot lamp to the ground lug on the terminal strips holding the filter caps.
Double line frequency means the source is rectified DC, which usually means the ripple voltage just after the rectifier is getting into the signal path.

[Stephen1966]

The only thing that I seemed to notice wrong was a loud hum. The guitar signal came through as expected and sounded pretty good except for the hum. Any suggestions on where to start to eliminate it?

Another clue is the hum frequency. Is it line frequency (50 or 60Hz) or double that (100 or 120Hz)? Line frequency means the source is un-rectified AC, i.e. heater wiring. Make sure he heater string has a ground reference. I don't see a grounded center tap or other ground reference (100 ohm resistor from each side of the heater string to ground) in the kit instructions.
Double line frequency means the source is rectified DC, which usually means the ripple voltage just after the rectifier is getting into the signal path.

Great minds think alike If the hum is somewhere between G# and B on your bottom E string, it's at the higher frequency, so coming from the rectified B+ supply.

[sluckey]

Update - I reviewed everything again realized both red PT wires were one lug off instead just the one initially noticed here. I made the change and tried the amp again and it came to life!

The only thing that I seemed to notice wrong was a loud hum. The guitar signal came through as expected and sounded pretty good except for the hum. Any suggestions on where to start to eliminate it?

See attached pic...

[vipor3D]

Update - I reviewed everything again realized both red PT wires were one lug off instead just the one initially noticed here. I made the change and tried the amp again and it came to life!

The only thing that I seemed to notice wrong was a loud hum. The guitar signal came through as expected and sounded pretty good except for the hum. Any suggestions on where to start to eliminate it?

See attached pic...

I hope the components aren't fried, but I can see how my mistake could've caused that. Any suggestions for parts suppliers with the quickest shipping?

Edit: Just the 3 caps with the 2 diodes would be close to $25 with tax and shipping from mouser. That seems a little steep to me.

Another supplier I've used before has the caps with more reasonable shipping except the 47uf cap only comes in 450v instead of 350v like the cap that came with the kit. Would I be doing harm by replacing the 47uf 350v cap with a 47uf 450v cap?

[martin manning]

Another supplier I've used before has the caps with more reasonable shipping except the 47uf cap only comes in 450v instead of 350v like the cap that came with the kit. Would I be doing harm by replacing the 47uf 350v cap with a 47uf 450v cap?

No worry there, as long as it fits in the space you have.

[sluckey]

I hope the components aren't fried, but I can see how my mistake could've caused that. Any suggestions for parts suppliers with the quickest shipping?

Edit: Just the 3 caps with the 2 diodes would be close to $25 with tax and shipping from mouser. That seems a little steep to me.

You're getting off cheap. That wiring error could have easily killed the power transformer!

[vipor3D]

Another supplier I've used before has the caps with more reasonable shipping except the 47uf cap only comes in 450v instead of 350v like the cap that came with the kit. Would I be doing harm by replacing the 47uf 350v cap with a 47uf 450v cap?

No worry there, as long as it fits in the space you have.

Well I got the parts ordered. Hopefully they'll come soon. In the meantime I guess I'll look over everything and verify the heater wiring is correct

[vipor3D]

I hope the components aren't fried, but I can see how my mistake could've caused that. Any suggestions for parts suppliers with the quickest shipping?

Edit: Just the 3 caps with the 2 diodes would be close to $25 with tax and shipping from mouser. That seems a little steep to me.

You're getting off cheap. That wiring error could have easily killed the power transformer!

I know, I was really lucky there. Not sure I would've even wanted to try to fix it at that point

[martin manning]

I'm not convinced you have blown one of the diodes yet. They are 1kV rated parts and you only put about half of that on it, and maybe the fuse blew quickly enough to save it. I would definitely consider adding an artificial center tap to the filament string. Just need two 100 ohm 1/2W resistors.