Need help trouble shooting MOD 102 amp kit.

[smallpoxchampion]

Just finished assembling this project and am experiencing some trouble getting it to fire up. This is my first attempt at anything amp related, i've done about a dozen stompbox projects up to this point and trying to get my feet wet with building amps. I've gone over the layout and double checked my work, I'm a little unsure if i have certain components mounted properly because ive never used strip terminals. As of right now, i'm not getting any sort of signal or sound when its turned on. The red indicator light does turn on though.

Here is a schematic: http://www.modkitsdiy.com/sites/modk...chematic_0.pdf
Here is the layout: http://www.modkitsdiy.com/sites/modk...drawings_0.pdf

Using the troubleshooting guide from the MOD kits website (here: http://www.modkitsdiy.com/sites/modk...supplement.pdf) I took some voltages on the suggested test points and here's what I wound up with.
HV: 286 VDC
B1: 286 VDC
B2: 280 VDC

Power Tube Electrodes
Pin 7 286 VDC
Pin 9 0 VDC
Pin 2 0 VDC
Pin 3 0VDC

Preamp Tube Electrodes:
Pin 1 255 VDC
all other pins measuring 0VDC

Lastly here are some pictures of the inside of the chassis.




Any and all feedback is appreciated, I can post more photos if need be. Thanks!

[52 Bill]

Welcome to the place.

The voltages that you posted shows that there is little or no current flowing through your amp.

A quick look at the photos show that you have the red wire from the output transformer connected to the B2 node of the power supply. It should be connected to the B1 node.

The photos also show that you are using a painted chassis, with ground points connected to the chassis with nuts and bolts. When you tightened up the nuts and bolts did you test them with your meter to see that they were really connected to the chassis ground? Sometimes the paint will keep the terminal strips from making good contact.

I also could not see where the B2 node of the power supply connected to the screen grid resistor (1K) of the power tube. But that could just be your photos.

[smallpoxchampion]

Welcome to the place.

The voltages that you posted shows that there is little or no current flowing through your amp.

A quick look at the photos show that you have the red wire from the output transformer connected to the B2 node of the power supply. It should be connected to the B1 node.

The photos also show that you are using a painted chassis, with ground points connected to the chassis with nuts and bolts. When you tightened up the nuts and bolts did you test them with your meter to see that they were really connected to the chassis ground? Sometimes the paint will keep the terminal strips from making good contact.

I also could not see where the B2 node of the power supply connected to the screen grid resistor (1K) of the power tube. But that could just be your photos.

As I was checking through I noticed I had forgot to run a wire from T6 where that 1k resistor is to T4. I hooked that up and took voltages again and here's what I came up with.

HV- 261 VDC
B1- 258 VDC
B2- 188 VDC

Power Tube Electrodes:
Pin 7 254 VDC
Pin 9 185 VDC
Pin 2 0 VDC
Pin 3 5.1 Vdc

Pre amp:
Pin 1 170 VDC
Pin 2 0 VDC
Pin 3 0 VDC
Pin 6 117 VDC
Pin 7 0
Pin 8 0.94 VDC

Also, just to make sure I'm understanding this correctly. B1 is located on the 3rd pin from the right on T2 and B2 is located on the 2nd pin from the right on T2. If that's correct I do have the red wire from the output transformer in the right spot (3rd pin from the right). Does it make a difference if I connect that wire to the top or bottom of the terminal strip? As of right now it's connected to the top portion of that pin.

I also was sure to file off the paint from the chassis where the terminal strips are mounted. I didn't measure it with my meter but i suppose it wouldnt hurt to go back and test those spots.

Some more pictures.
This is where I forgot to run a wire from T6 to T4

[52 Bill]

Some of those voltage are better. The preamp tube section connected to pins 1-2-3 is still not turned on. Double check the wiring around that section of the circuit.

Also, just to make sure I'm understanding this correctly. B1 is located on the 3rd pin from the right on T2 and B2 is located on the 2nd pin from the right on T2. If that's correct I do have the red wire from the output transformer in the right spot (3rd pin from the right). Does it make a difference if I connect that wire to the top or bottom of the terminal strip? As of right now it's connected to the top portion of that pin.

I don't know how you are counting, but in the photo of the power supply terminal strip, B1 is the 3rd from the left, where the positive end of the 47uF cap connects. B2 is two over from B1 or the 3rd from the right.

[smallpoxchampion]

Some of those voltage are better. The preamp tube section connected to pins 1-2-3 is still not turned on. Double check the wiring around that section of the circuit.

Went back over that portion of wiring around the preamp and touched up some connections and I seem to be getting some improved readings.
P1 118VDC
P2 0 VDC
P3 0.8 VDC
P4 5.3 VDC
P5 5.3 VDC
P6 115.5 VDC
P7 0 VDC
P8 0.89 VDC
P9 5.3 VDC

These are all pretty damn close to what the troubleshooting guide has for those voltages:
http://www.modkitsdiy.com/sites/modk...supplement.pdf
Still getting some wild squeals when I plug into the input.

As for the output transformer wire, I moved that to B1 as suggested.

[52 Bill]

Still getting some wild squeals when I plug into the input

Sound is a good thing. The last you noted was no sound at all.

Turn all controls to zero any change in the squealing? The other thing to look at is the lead dress and the grounding. Try and move any signal carrying wires near the input away from the output circuitry.

[danman]

One quick note...when checking your heater voltages (6.3v) on your preamp and power tubes you need to set your meter to AC. I noticed that you posted all readings in DC but this reading must be taken on the AC voltage setting.

[52 Bill]

One quick note...when checking your heater voltages (6.3v) on your preamp and power tubes you need to set your meter to AC. I noticed that you posted all readings in DC but this reading must be taken on the AC voltage setting.

If you look at the schematic, the heater wiring is connected to the output tube cathode circuit, so there will be a dc voltage as well as an ac component to the heater supply voltages.

[smallpoxchampion]

Sound is a good thing. The last you noted was no sound at all.

Turn all controls to zero any change in the squealing? The other thing to look at is the lead dress and the grounding. Try and move any signal carrying wires near the input away from the output circuitry.

Turns out the input jack was not properly grounded, perhaps the only spot on the chassis I didn't scuff down to bare metal. A quick swipe of the sandpaper and bingo, no noise, totally clear signal. It sounds pretty much as I imagined it would sound being a Fender Champ type circuit. Thanks for all the help, certainly appreciated. Any other tips or things to consider before I close it up?

[Mick Bailey]

Any other tips or things to consider before I close it up?

Nice thing getting your newly built amp up and running - it's the closest thing a man get to giving birth.

Anyhow, some of your solder joints look like they could do with flowing a little more smoothly. With tag strip you need a hotter iron than for PCB work. A hot iron applied for a short length of time. Gets the job done before the component has time to get warm.

You also have some angular bends in component leads and unequal leg length where there's a good lead length on one side and very close on the other. Offer each component up before fitting to get the location as good as it can be.

Where bare leads run close I use some thin PTFE sleeving before soldering. It won't melt and is a superb insulator.

Keep a good space between the power tube cathode resistor and its bypass cap to keep the cap cool.

Personal preference, but with the Chinese ceramic 9-pin sockets I gently fan the terminals out slightly to improve spacing and reduce the possibility of shorts.

[52 Bill]

Glad to hear that it is working.

I agree with a lot of what Mick said, but for a first point to point build, it's not all that bad. Neatness is a good thing and as you go along you will learn how to space things and trim things, etc. Leaving wires longer than necessary is one thing to watch out for.

From your posts here, i get the impression that you don't read schematics very well and have built this from a layout drawing. That's fine, but it will help you get much further along in this hobby if you start to relate the physical parts with the schematic drawing. This will give you a much better understanding of how the circuit operates and how to fix it when it doesn't work.

Anyway, congrats on the new amp.