Slow Build...

[lavrgs]

Latest Voltage check

[JMPGuitars]

Your B+ is okay at 350, but your cathode voltage should be 12V. What's your cathode resistor value?

[lavrgs]

I'm using a 150 ohm resistor

[JMPGuitars]

I'm using a 150 ohm resistor

Try a 180 ohm and see where that puts you.

[lavrgs]

Parts received and installed. I have a question about the voltages on V3 (trem) they change with volume and intensity pot. I took the V3 voltages with full on and off of intensity - is on or off the default place to test or does it matter?
The voltages of V4 and V5 are significantly different when calculating the dissipation do you use the V5 voltages or both...?

[JMPGuitars]

Parts received and installed. I have a question about the voltages on V3 (trem) they change with volume and intensity pot. I took the V3 voltages with full on and off of intensity - is on or off the default place to test or does it matter?
The voltages of V4 and V5 are significantly different when calculating the dissipation do you use the V5 voltages or both...?

The cathode cap/resistor is shared between your power tubes. That means the voltage should be exactly the same, or there's something wrong. Could be a wire/soldering issue, could be a tube.

Swap the tubes and see if the voltage stays on the same socket, or follows the tube.

Also measure your B+.

[lavrgs]

I will update voltages later - the glass broke on V4 so I swapped out that tube and will redo voltages with the different tubes. I no longer have a matched pair so I will order a set and update. I'm guessing that a voltage check in the current condition would give an idea of the tube mis=match...?
I still need to get V2 voltages straitened out...

[JMPGuitars]

You need to drop your B+ now, but overall I think it's looking better.

What's your cathode resistor value with those voltage readings?

Thanks,
Josh

[lavrgs]

You need to drop your B+ now, but overall I think it's looking better.

What's your cathode resistor value with those voltage readings?

Thanks,
Josh

I bumped it to 180 based on your recommendation - Based on a wall voltage of 124.5 that brings my B+ (by math) close to 300, so 307 measured aligns

[JMPGuitars]

I bumped it to 180 based on your recommendation - Based on a wall voltage of 124.5 that brings my B+ (by math) close to 300, so 307 measured aligns

That's not your B+. Your B+ is the voltage coming off of pin 3 on the rectifier. You're at 370 with a goal of around 345 (+/- 5V). If you like the tone, cool. If you want more breakup faster, along the lines of the characteristics of the 18 watt, then you want to drop the B+ a little. It's up to you, it probably sounds great either way.

[lavrgs]

I'm waiting for some pre amp tubes to see the effect on V3 . Is there a BKM for reducing B+ voltage for these 18 watt clones?
BKM - Best Known Method

[JMPGuitars]

You can use either high wattage resistors, or the zener diode method. Do a search and you should find some info on here.

[lavrgs]

As a point of reference my amp sounds NOTHING like this...
https://www.youtube.com/watch?v=of_xEvs6bKM

I guess mine sounds more like the modern version in this video - which sounds a bit ice pick-ey to me
https://www.youtube.com/watch?v=ZaUA_mqViGU

[roadshow]

One more thing... I found a thread that showed a mojotone error on the schematic but I am unable to decipher if it's causing the issues I see - I don't understand the error.. I see two foot switches - what is the error in the red line?

Been away so long I have so much catching up to do.

Sorry, that was this post: viewtopic.php?f=4&t=25335&p=242393&hili ... ic#p242393

I meant to include this in that post:

• I have noted the layout vs. schematic error in the attached pdf file. Note that the schematic shows the foot control jack going to the tremolo speed control and V3-2, yet the layout shows tremolo speed control and V3-1.

I made the change to the layout as the schematic looked correct. It probably doesn't help too much at this point, but I did spend time debugging a few things with the MT kit.

Here's a surprise. I sent email to MT on 1/3/2019 and it only took them until 3/4/2020 to make the change and post it after that.

[lavrgs]

I thought I would add a "final" post about the build of a Mojotone Trem kit. After all is said and done I find the sound to be very good.
Lately I have been playing the Mojotone alot - being isolated and all. I have found that it really likes a Les Paul, although many guitars sound good through it.
I have it configured as a head and am using a Port City cabinet. I also have the Mojotone 1x12 cabinet that I bought as part of the kit but it sounds too bright...I never went through speaker changes and I don't know what Mojotone puts in there - it's unmarked.
The building process gave me a good introduction to learning how amps work - I still have a long way to go.
I must Thank all the folks on this site that got me past the hurdles encountered during the build. JMPGuitars Colossal Geoff 1965
I have since built a %E# (fender circuit) and haven't bonded with it...
I will start a new thread for the "Next Build" as I am in the early planning stage...

Thanks

Bill

[Bieworm]

It puzzles me that after all the feedback from customers Mojotone still puts out incorrect documents. They obviously don't bother to do some fieldwork or benchmarking. Imagine the size of the ego that company suffers from... sad situation though...

[lavrgs]

I'm still not waiting for them to return my call from last January....

[Bieworm]

I'm still not waiting for them to return my call from last January....

Jeez!!!