Mojotone Fender 5F1 Champ No Output Debugging Help?

[LastLS1]

Hey there everyone!

I was told that this is the 'Best' of the best place to come for DYI's for Amp Kit Builders.

I've put together the Mojotone 5F1 Amp Kit & it does turn on & produce a nice low hum through the speaker but, when I try it with a guitar & cord I get nadda? Absolutely not guitar signal whatsoever.

I'm including some pictures of the build in hopes that perhaps someone here with much more knowledge would be so kind as to help me troubleshoot the issue(s).

Any & all help is greatly appreciated! I followed the Mojotone Schematic that came with their Champ 5F1 Kit.

Many MANY thanks!

[Jazz P Bass]

Champ Build

You must do some voltage measurements.
All the plates & there respective cathodes is a good place to start.

[LastLS1]

I will get the voltages this morning & post 'em up.

Thanks!

Just wondered if anyone could see anything obvious jumping out from the pics.

Appreciate the help.

[tubeman]

For starters, I don't' see that you have your volume pot grounded. The left most lug (from pictures pov) needs to be grounded to the same point as the preamp ground. This is not your issue with no sound at the moment. When you get the amp working again, it would be max volume. Take out your tubes, make sure you have 6.3 volts on the heaters. If you do then put the recto tube back in and measure voltages on the plates.

[LastLS1]

mmmkay

Started probing around with my Voltmeter & when I got to the preamp socket I must have kick started something & beautiful, gorgeous guitar sounds emminated from the amp!

However, even after grounding the Volume POT correctly (thanks tubeman) the volume still does not work.

Also, after the amp has been off for a while I have to once again probe or touch one of the pins on the 12ax7 socket to get it to work again. UGH!

I've ordered a new 9 Pin Socket as I do think my current one, though new is faulty.

In the mean time I'm going to dig around for a fix for the Volume POT to get that working properly.

What an AWESOME FORUM!

People were right! This IS THE PLACE to come for DYI's & Amp builders!

I'm very proud to be a member here.

Thanks everyone. I will report back after I've gotten the socket replacement in.

[JHow]

Before you replace the socket, are you sure all the leads are well-soldered? Could it be bad joint, or even a no-solder joint?

[tubeman]

Started probing around with my Voltmeter & when I got to the preamp socket I must have kick started something

I doubt the socket is bad...Looks like a Belton to me. More likely you have a cold solder joint. I would reheat the connections first. If you reheat, be careful and not use to much solder on the socket.. I have had solder flow into the pins and then you can't seat the tube properly. Also use the Weber layout. It's easier to see than the Fender layout.

https://taweber.powweb.com/store/5f1_layout.jpg

[Jazz P Bass]

5F1 volume pot

How is the volume pot set up.
Fender schematic shows the one leg to ground, the middle leg (the wiper) goes to grid #2 of the 12AX7 & the third leg goes to the previous plate blocking cap.
With the amp off & drained of charge, measure the #2 grid to ground as you rotate the pot.It should vary by the value of the pot (1 meg?)
If it does not. it is hooked up incorrectly or your pot is bad.
Test the pot by first reading the outside legs (overall resistance).
Then measure the outside legs (one at a time) to the middle leg and rotate the pot. You should see the resistance vary up & down the length of the track.

[LastLS1]

Yes.

If you look @ the very last picture I've posted it's the two bottom white clothed wires (one has more of the actual wire showing) that seem to need to be nudged or jumped started? Sorry, just can't think of another way of putting it.

I'm sure I'm jolting the whole amp which can't be good either, though I'm not blowing the fuse.

I do know how to retention a socket though I'm not so sure that will work?

It's very odd that it needs a 'current "jump" of sorts to get it working.

It's a new one on me though as you can see from my post there's a ton of new one's on me! HA!

Thanks for the reply & suggestion JHow

[LastLS1]

Many thanks tubeman & Jazz P Bass for the suggestions.

I will definitely be giving your ideas & help a try this evening & will report back in a bit.

[Wakculloch]

Sounds like lack of ground references, and your meter is providing a ground until the cap charges up again. As you left the one off the pot, have you omitted any more? Maybee.

[LastLS1]

OMG!

Wakculloch I think you just may have absolutely "nailed it"!

Makes perfect sense, in that once the Capacitors get to full charge the amp will work fine as long as it's powered "ON". Even turning it off for a few seconds & she turns right back on!

However, give her about a minute then try to power up & I've got to "jump start" her all over again.

Still have the issue with the Volume POT not functioning but I'm still digging around for a solution on that one. I do believe that the POT & the Socket Grounding issue once fixed will solve both issues at once!

Wow!

What an AWESOME FORUM!

YOU GUYS ROCK!!!!!!