Slow Build...

[lavrgs]

I am trying to determine if my power transformer is ok - fingers crossed. Because I was blowing fuses when I tried to measure voltage I have removed all the tubes. I also found a problem with the heater wiring so I am taking a step back to figure out where I am. I'm
I need some advise for inspecting the pt. I have measure the resistance on all coils and I have no opens. I don't find any specs for the resistance but red to red 167.4 ohms blk to blk/wht 3.6 ohm and grn to grn .5 ohms.
My next step will be to disconnect all wires, add line voltage and check to see what I am getting. As you may recall I was blowing the fuse when checking the red wires - I have tried to find a short but it appears ok
UPDATE I tested the transformer and it works - whew so I'm going to redo the heater wiring and get back

[colossal]

My next step will be to disconnect all wires, add line voltage and check to see what I am getting. As you may recall I was blowing the fuse when checking the red wires - I have tried to find a short but it appears ok

This is what you want to do. Go back to basics. One variable at a time. Test each lead with respect to ground to verify that your PT is in good health.

[lavrgs]

UPDATED Voltage check - I no longer blow fuses when checking the pins on the rectifier. but pin 3 voltage was acting wonky, unstable, on the initial check. I let the amp sit for a while and now it's stable at 373 - it's not shown on the attached chart. I don't have a reading for V3 pin 6 because it's not connected.
After redoing heater wiring and disconnecting and rewiring the PT Still don't have tremolo because it's causing a ruckus... I once again lifted the wire going to V3 pin 6 and it's happier. I do have a lower volume on the tremolo channel vs. the normal channel and the amp does not seem to be as loud, after putting it back together. I haven't done any troubleshooting on that yet. I still haven't re-done my grounds to get them off the pots but I am happy with how quiet the amp is...

[colossal]

Your voltage chart is still confusing to me. Is the second line of measurements the phase inverter and the third your Trem channel? If V2 is your phase inverter, you have a very serious mismatch on Pins 1 and 6. These should be relatively close. My suspicion is that your Pin 6 measurement is erroneous as your Pins 3 & 8 (shared cathode) voltage is reasonable so Pin 6 should in reality be much closer to Pin 1's measurement of about 250V (still high, but due to your high mains voltage). The question of your EZ81 rectifier Pin 3 measurement being 36V is also wrong. 373V is high but reasonable. An unstable B+0 measurement sounds to me like you have an intermittent connection somewhere in your power supply; again, check each solder joint in the amp. The solder on a properly flowed joint should have a nice, shiny "mercurial" droplet look to it. It should not look dull and dark grey and be "collapsed" into the turret (a sign of overheating). JMPGuitars posted examples of properly and improperly soldered joints. Do not apply heat for long, you WILL damage parts. Run the iron hot, get in and get out.

Regardless, if you are getting an improvement in noise at idle, that's a step in the right direction. Sounds like you are making progress. Check out Explorerman's thread, if you haven't already, as he is dealing with similar problems in a Mojotone build.

[lavrgs]

As I wait for a couple parts I will go through the grounding scheme again. First goal is to remove the bus off the back of the pots - the plan is to use a copper buss wire for the preamp side.
Ground Confusion
My problem is that I am getting confused as I check where I have grounds and I am unsure if I should or shouldn't.
Pardon my first elementary knowledge on this but follow me through
Case 1 Input jacks - when I touch pin 2 & 7 on V1 they are grounded - I believe that is that correct - until the jack has a plug when they are infinite.
Case 2 Heater wire Pin 4,5 and 9 are grounded - technically there is 0.7 ohm resistance but I have my meter set to beep and it beeps. When I remove the center tap from ground I don't get a beep (infinite) - so I'm thinking it's ok.
Case 3 Speaker jacks - This one I don't understand...The speaker operates as expected but all 6 points of the connector are grounded until I disconnect the wire to the output connector and not have a plug in- I may be confused but I don't think there's a problem.

I have checked all the tube socket pins to make sure that only the heater pins are grounded.
I have checked the EL84 that I think is bad and the filaments are continuous and no other pins are shorted. I checked the EZ81 and it's the same filament pins are connected - that's all I can do at home.

When I get the new tubes I will do another voltage check to see if anything changes.

[JMPGuitars]

Case 1 Input jacks - when I touch pin 2 & 7 on V1 they are grounded - I believe that is that correct - until the jack has a plug when they are infinite.
Case 2 Heater wire Pin 4,5 and 9 are grounded - technically there is 0.7 ohm resistance but I have my meter set to beep and it beeps. When I remove the center tap from ground I don't get a beep (infinite) - so I'm thinking it's ok.
Case 3 Speaker jacks - This one I don't understand...The speaker operates as expected but all 6 points of the connector are grounded until I disconnect the wire to the output connector and not have a plug in- I may be confused but I don't think there's a problem.

Case 1- correct, since those are the inputs, and the input is grounded by the jack with no plug inserted, that's exactly as expected.

Case 2- sort of. The center tap connects to ground, which makes the heaters think they're grounded when not on. Do not test resistance or continuity with the amp on. Check the voltages only. Don't think of the heaters as being connected to ground. Essentially, the tap splits the 6.3V line to give you the two 3.15V halves.

Case 3- the speaker output, specifically that part of the OT, doesn't have a ground. It's positive and negative. You're grounding the negative side. Again, don't test continuity to ground or low resistance with the amp on. You and/or (at least) the transformer can get fried.

[lavrgs]

Thanks JMP I did watch a video on a company (in the UK?) that had a JMP faceplate on their UTube vid - any relation?
This Mojotone build has been MUCH better for my education that my Allen build - which was very satisfying. I bought the kits at the same time and three years later the MJT build is teaching me all the things I'll need to start checking on the Allen as it's getting to the point where it's in need of attention...

THX

Bill

[JMPGuitars]

This Mojotone build has been MUCH better for my education that my Allen build - which was very satisfying. I bought the kits at the same time and three years later the MJT build is teaching me all the things I'll need to start checking on the Allen as it's getting to the point where it's in need of attention...

THX

Bill

That's the benefit of a pain in the butt kit. It's tedious in some aspects, but it's the troubleshooting and corrections that become far more educational than a smooth and painless build. I've learned PLENTY this way.

[lavrgs]

I have a problem I will call Mojotonitis... I am considering changing my tremolo layout to TMB, primarily because tremolo is not my thing and that is the part that's not working... As I read the forums there much discussion about the limitations of the Mojotone layout. Before I jump on the grenade, I am reviewing the Valvestorm Tremolo https://valvestorm.c ... Layout.pdf layout for comparison.

Any guidance would be appreciated. Is it easier to stay with the tremolo. I have not fully compared the VS layout to know what rabbit holes I will be going down...like how far do I back up and is it worth the effort to build a new board...that kinda sh*t is what I just don't know...
UPDATE- for 35 bux I could get a bare turret board from Valvestorm and use some components from the MT (empty ) board and buy the extra components I need to finish. I'd guess the cost to be under $100...?

[JMPGuitars]

If you don't care for tremolo, the answer seems obvious.

If you go that route, ignore the points in their layout that tell you to use mounting bolts for grounds. Grounds get their own independent bolts. Otherwise, it looks fairly standard.

Honestly though, looking at that and the other layouts available, I feel like I need to make some more layouts for these. The standard TMB and Tremolo versions I don't bother with, that's why I never made layouts for them...but the ones that are out there might inspire me to do that at some point.

[geoff 1965]

yeah the layouts are a bit dated in the downloads for the TMB's and that latest valvestorm looks good but we've had no feedback from anyone who has built one. i know which layout "not" to use and that's mojotone!

[lavrgs]

that latest valvestorm looks good but we've had no feedback from anyone who has built one. i know which layout "not" to use and that's mojotone!

I bought my Nojotone kit 3 years ago and was never excited about it. I finally decided to get it going and my intial start up when well - except for the tremolo. Trying to fix it caused a lot of trouble that was, unfortunately, operator error.
I decided to get the Valvestorm board and the resistor and cap kit...I expect I should have the parts in a week or so and I will continue posting here.

[geoff 1965]

appreciate the valvestorm feedback and good luck with the build, i like the mojo kits it's just that latest layout has produced a lot of problem's.

[lavrgs]

...it's just that latest layout has produced a lot of problem's.

I would be interested in hearing about the issues you ran into. My experience level is very basic - I have learned about amp circuits from this build - that was the intention, but I have become very frustrated. As stated my intial power on was positive and I was happy with the sound and performance in both channels - but as stated the tremolo was a problem and I still have no idea why. I'm planning on adding shielded cable to that channel. When I get the new parts from Valve storm I may just back up to replace all the sockets...

[geoff 1965]

i have'nt built one and i'm no senior amp tech myself! but go on "forums" then "18W technical discussion" and type mojotone into the search box,you'll see all the issues that layout has caused.

[lavrgs]

As I wait for parts I spent some time re-routing the transformer wires and next I will run shielded cable to the tremolo channel inputs.
I am somewhat gunshy about testing voltages at this point because I don't know if it is possible to blow tube by shorting the wrong pin or did I have some other problem.
My problem tubes are a EZ81 rectifier which appears to get the wrong voltage on pin 3. The measurements are low and unstable. The other tube problem is one of the EL84s which presented itself as I re-did the dim bulb test. When I took it from the V5 position to V4 the problem followed the tube. I also had reduced output. New tubes are on the way but I want to be very careful that it's not another problem that caused the previous tube failure . My only check on the was to make sure the heaters were continuous and no pins were shorted. Not sure I can do much more.

[lavrgs]

I was waiting for some parts so I spent the last couple days checking components, solder joints etc. I replaced the socket on V5 because the DBT told me to. Of coarse when I fired up the amp...nothing, well I knew where to look. I found the heater wiring had a bad solder joint. The good news is that I'm back to where I was a week ago. The bad news is that I'm back to where I was a week ago.
My problem is the "motorboating" so I'm off the figure out why - you may recall it starts when I connect to pin 6 on v3...
I have added my latest voltage check

[colossal]

As I said on page 3, there is an obvious problem with your phase inverter . Pin 6 shows 323V. For the amp to be working correctly, Pin 1 and 6 should be closely matched. So that tells me that you have something wrong with how your phase inverter is wired, a bad tube, a bad 100k resistor, a bad solder joint on that resistor, bad wiring, or a combination of these. Carefully trace your amp in that region, check your solder joints, and check your lead connections. Go through the amp with a copy of your layout and a highlighter and mark off each and every lead and solder joint, one at a time, on the layout, as you go through the amp to verify that you have everything correct. You will need to consider under-board connections as well.

The bottom line is your voltages have to look like the references voltages. Anywhere there isn't a match within 10% or so, you have an issue.

[lavrgs]

OK let the fun begin... I have removed the board so I can try and remember what I did three years ago. I am definitely finding issues. I originally started with an early Mojotone layout and recent started using a newer version...I convinced myself I had shifted components over by a turret but the old version had one more turret...
1. I had double wired connection that were supposed to be under the board - I left the ones on the bottom.
2. found a huge solder ball on the connection where I was having motorboat problems when I connected the wire to pin 6 V3 - was probably touching the chassis...I now have made the connection without huge pulsing.
3.MJ provided a 130ohm 3 watt bypass resistor I changed to 150 ohm 5 watt
4. the bypass cap measured at 210uf vs 250 - not sure that matters - ?
I have checked all the other component values and all are within tolerance.
I am investigating the high voltage on the PI load resistors - the voltage across the 100 ohm resistor feeding pin 1 dropped from 328 to 210 and the drop across the resistor feeding pin 6 went from 328 to 323??? the resistor measured ok and I did not find any mis-wiring other than the double wire feeding the 328...

I'm going to put the board back in the chassis after I clean up the socket wiring which seems like it would be easier with the board out.

So progress is being made.

[lavrgs]

there is an obvious problem with your phase inverter . Pin 6 shows 323V. For the amp to be working correctly, Pin 1 and 6 should be closely matched. So that tells me that you have something wrong with how your phase inverter is wired,
a bad tube, I swapped tubes no change
a bad 100k resistor, it measures ok as does the bypass cap
a bad solder joint on that resistor, if the joint is bad then I should just give up - frustration show through
bad wiring, this is where I need help - I feel the socket wiring is good - what else should I check?

Carefully trace your amp in that region, check your solder joints, and check your lead connections. Go through the amp with a copy of your layout and a highlighter and mark off each and every lead and solder joint, one at a time, on the layout, as you go through the amp to verify that you have everything correct.
You will need to consider under-board connections as well. I lifted the board yesterday and found some issues but I am now confident it's correct

The bottom line is your voltages have to look like the references voltages. Anywhere there isn't a match within 10% or so, you have an issue. I understand the concept

I read that leaking caps could let voltage pass so I lifted the cap and it measures 0.01uf the resistor is 100k. I was going to swap resistors but I convinced my self the problem is somewhere else.
Correct me if I am wrong but I believe the voltage supplied to V2 pin 6 comes from the resistor marked 'Hi" (323 measured)in the attached. I am having trouble understanding why the voltage drop across the right resistor is ok (210V measured) and only drops a few volts across the left hand one. Is it getting voltage from somewhere else? I removed the components I expect I should have no continuity and I don't. Please understand that I am new to this electronic stuff. I will highlight the schematic to complete my review. I am just too focused on the voltage problem...