Troubleshooting my new DIY amp build

[peterc52]

Hi guys,

So I decided to and assemble 2 DIY amp kits from ampmaker.com. I went with the WF-55 4W Tweed style amp and the SE-5a 5W British overdrive amp.

I started out with building the WF-55, and it went very well - no problems at all!

But sadly after assembling the other kit (SE-5a), there were just a bit hum coming out of the speakers. There's nothing happening when I play the guitar og turn the knobs.

I have been troubleshooting this amp for a couple of days, and just can't seem to find the error. And there is a stage of the build where you test the amp for all kinds of things (http://www.ampmaker.com/se-5a-final-testing-970-0.html), and it went through all the tests just fine.

Following were tested:

1 - Total current consumption: 45 mA

2 - EL84 cathode current: 43 mA

3 - EL84 screen current: 4,3 mA

4 - EL84 plate current: 38,7 mA

5 - EL84 plate dissipation: 8,7 mA

DC current on pin 1 on the preamp tube is 144 volt.

And DC current on point A is 240 volt.

I've checked that all wiring is correct, and I can't find any mistake!

The wire between A - B and C - D is under the turrret board.

There is more information on the build at http://www.ampmaker.com/se-5a-construction-manual-948-0.html

Let me know if you need anymore information! I'm hoping someone can help me.

 

[duesentrieb]

check if tonestack's mid pot is grounded,
check if volume pot is grounded.
check if input jack is grounded (start with this, I don't see a ground wire here . . .)

 

[peterc52]

check if tonestack's mid pot is grounded,
check if volume pot is grounded.
check if input jack is grounded (start with this, I don't see a ground wire here . . .)

All the post are grounded, and the inpout jack is grounded on all lugs except lug 1 which goes to pin 2 on the preamp tube.

 

[duesentrieb]

speaker jacks grounded?

 

[duesentrieb]

All the post are grounded,

No. Their chassis are grounded - a "real" ground have mid-pot, volume-pot and gain-pot.

Also how many volts DC do you read between the junction of the 2 100 Ohm symmetrizer resistors and the cathode of the power tube?

And did you check the heater/filament voltage?

 

[peterc52]

speaker jacks grounded?

Yep, on all lugs.

 

[peterc52]

All the post are grounded,

No. Their chassis are grounded - a "real" ground have mid-pot, volume-pot and gain-pot.

Also how many volts DC do you read between the junction of the 2 100 Ohm symmetrizer resistors and the cathode of the power tube?

And did you check the heater/filament voltage?

Ohh, I see!

Lug 3 on mid, gain and volume is grounded.

Could you point in the direction of where i check heater/filament voltage and which places to check how many volts there are between the junction of the 2 100 Ohm symmetrizer resistors and the cathode of the power tube?

I must be the 2 100 ohm resistors that i placed right next to the outer cap isn't it? But where do I measure the cathode of the powertube?

Thanks for helping me out!

 

[duesentrieb]

filaments:
Preamp tube: read volts between PIN 4 or 5 and PIN 9
Power Tube: read between PIN 4 and 5

to read the voltage on the junction you can read either points C or D vs. ground

 

[peterc52]

filaments:
Preamp tube: read volts between PIN 4 or 5 and PIN 9
Power Tube: read between PIN 4 and 5

to read the voltage on the junction you can read either points C or D vs. ground

Preamp tube and power tube is both about 0,005 volt. That is not much, is there something wrong here?

The voltage on the junction is 6,5 volt.

 

[duesentrieb]

Did you read against ground?
Thats wrong for (elevated) filaments - black probe to PIN4, red probe to 9 when reading the preamp tube. Result?

Junction is ok . . .

 

[peterc52]

Did you read against ground?
Thats wrong for (elevated) filaments - black probe to PIN4, red probe to 9 when reading the preamp tube. Result?

Junction is ok . . .

Turn the amp on, set all pots to zero, wait 30 seconds, turn standby off, measure like you say, black probe 4 or 5 and red probe on 9 - it still says just around 0,005 volt.

If I measure the volts between the 2 green wires to the left (which is the heater wires) it also says around 0,005 volt.

What should it say?

 

[duesentrieb]

6.3 Volts - AC, not DC. Set you DMM to read AC.

 

[peterc52]

6.3 Volts - AC, not DC. Set you DMM to read AC.

Ohhh..

Now it reads 6,6 volts.

 

[duesentrieb]

Well, seems that the basics are ok
filaments ok
B+ ok
power tube produces some watts

my guess is still that there is a missing ground somewhere - or the output transformer isn't wired correctly. Check that and make sure the caps are discharged. Follow the instructions on the website of ampmaker, he even provides a full measurement protocol . . .

Good luck, I'm off to a meeting now . . .

 

[peterc52]

Well, seems that the basics are ok
filaments ok
B+ ok
power tube produces some watts

my guess is still that there is a missing ground somewhere - or the output transformer isn't wired correctly. Check that and make sure the caps are discharged. Follow the instructions on the website of ampmaker, he even provides a full measurement protocol . . .

Good luck, I'm off to a meeting now . . .

Thanks for trtying to help me! I'm gonna go through it all again.

 

[roadifier]

Is that an instrument cable out from the speaker out to the cab?

 

[peterc52]

Is that an instrument cable out from the speaker out to the cab?

No, that is a speaker cable.