Tweed Champ kit not firing, low voltage from PT...

[jdw3]

I built a Mojotone tweed champ and for whatever reason, the first PT didn't work. So they sent me a new one. They were nice about it.

I installed the new one and I have proper voltage on the red wires to rectifier, 330V.

Green heater wires are about half what they should be; I have 3.3V per wire. Spec sheet says 6.3V.

The yellow wire on the rectifier, I have proper 5V on one wire, and nothing on the other.

The amp lights up, tubes glowing and a faint 60 cycle hum through the speaker. Plugging a guitar in, I get nothing at all, not even a faint static. Sounds like nothing is plugged in.

I am not sure what to check next. I'm sure I should've checked each wire before I installed the PT.

Any ideas?

[Blackburn]

About the green filament wires, you SHOULD only see half on each side, that's fine. The rectumfrier sounds like it's your culprit. Do you have the yellow 5vac wires connected pins 2 and 8 of the socket of the 5y3 and do you read any DC coming off them at all? It's very doubtful that you will have gotten two bad PTs.

David

[M Fowler]

Yes you didn't wire the amp correctly is my assessment.

EDITED: PT doesn't have a center tap wire for the filament supply requires you to use a pair of 100 ohm resistor to ground off the pilot light. You will get 3.1v per side or 6.3v with DMM across both wires.

Need some clear photos so we can help.

Mark

[xtian]

Does not sound like the PT is the problem. First, you'll measure 6.6 volts from green to green wire across the heater pair, but only 3.3v if you measure each leg to ground.

Again, if you measure across the two yellow wires for the rectifier heater, you'll see 5vac. Again, don't measure one leg to ground.

If you've got hum in the speaker, you're half way there; at least the power tube is working! To confirm, carefully touch your voltmeter probe to the grid of the power tube (pin 5 if it's a 6V6) you should hear a pop from the speaker.

The issue is possibly with your preamp stage or your input jack wiring.

[Blackburn]

I missed the part where he said he heard hum in the speaker... Guess the rect is not the issue. Probably is in the pre.

Pics!

[jdw3]

[img[IMG764]http://i1243.photobucket.com/albums/gg5 ... G_0613.jpg[/img]
[IMG764]http://i1243.photobucket.com/albums/gg5 ... G_0612.jpg[/img]
[IMG764]http://i1243.photobucket.com/albums/gg5 ... G_0611.jpg[/img]
[IMG764]http://i1243.photobucket.com/albums/gg5 ... G_0609.jpg[/img]
[IMG764]http://i1243.photobucket.com/albums/gg5 ... G_0608.jpg[/img]
[IMG764]http://i1243.photobucket.com/albums/gg5 ... G_0607.jpg[/img][/img]

[jdw3]

I'm thinking it does have a center tap. It has the red/yellow wire which is attached to ground. It also has the 2- 100 ohm resistors, which are attached to ground.

Measuring across the wires, instead of to ground, I got the full 6.3V and 5.4V.

So the problem must be the builder!

Not sure what I did wrong in the input. I touched pin 5 of the 6v6; I didn't get any sound.

[Blackburn]

All seems right with your PT wiring. I'd say it's time to start checking continuity and find your mistake. 99.9% of the time it's a simple wiring error by the builder... I should know.

[JazzGuitarGimp]

I think the next step would be to take some voltage measurements. Check the DC voltages at:

Plate, Cathode & Control Grid of V1 and V2.
Plate, Screen Grid, Control Grid and Cathode of V3 and V4.

Remember, the high voltage inside the amp can be lethal, so work with caution.

[M Fowler]

Does your AC switch work I don't see a wire going from the switch back to the white neutral AC line.

[sepulchre]

Are the heaters working - do the tubes have an orange glowing part in them. It may not be easy to see directly but you should be able to see the glow from it in all tubes.

[jdw3]

Yes, the switch is connected and the tubes appear to be glowing normally. I will check the voltages of each tube.