Mojotone Amp Kits Leave A Lot To be Desired........

[JeffBlue]

I am nearly finished with my Mojotone Studio One build, but.....the power transformer is defective. I have over 300 volts DC at the diode rectifier and no power to the pilot lamp or filaments. No filaments, no electron flow. I keep calling and they will not answer.

The Studio One kit arrived with the front and rear face plates on back order, missing two chickenhead knobs, missing a 220k ohm 1/2 watt resistor, missing one 4-40 machine screw for mounting the tag board. Two of the holes in the chassis for mounting the tag board are not in alignment (the tag board is being anchored by only two screws with all four stand-offs installed)

This is my first amp build and it has been made more difficult with having to improvise. Mojotone didn't provide enough color coded wire to match the diagram so I added another color wire to finish. I provided my own Mil spec teflon wire for all of the grounds to the chassis in a dual star ground that I bolted to each side within the chassis. I am very disappointed because the hold-up is Mojotone. I am still waiting for my chassis face plates. This amp will be totally useless without a functioning power transformer.

 

[ranjam]

That seems strange. Not often at all, but a few times I see an extra screw or bolt in the package, just from over zealous packers. Short changing you is not the norm. Also, they should have called or emailed about the face plates, and asked if you wanted the order shipped out 'as is', or wait for the back ordered items. And that's not being nice; it's a PITA to Mojotone to pay for the shipping on back-ordered items. But they'll give you an option to get started while you wait for the face plates, so it's maybe looking at least a little considerate.
Without know what kit you have, 'over 300volts DC' isn't necessarily wrong. If this is a tweed Champ, it may be right. Measure the 'unloaded' AC on the secondary, and get an idea if the transformer is bad.

 

[King Fan]

This isn't my experience with Mojo. Not totally A+, but A- at worst. I just built a biggish Mojo kit, their blackface Princeton Reverb, and I only got 'extra' parts. There were things I supplemented -- they sent only white wire, which is how they illustrate the build. I added bearclaw tube clamps on the big tubes and tube shields on the small ones. The OT flange holes were wider than spec'd, so didn't line up with the correctly-spaced chassis holes. I replaced their orange-drop caps with ones I like better -- but that's on me, not them.

One thing to double-check -- at first I thought the bolts and nuts were counted wrong, but I found that some holes I assumed were for one thing were for another, and then the bolts they sent made more sense. I ended up swapping in a few 'shorter' bolts so they wouldn't have too much shaft sticking through the nut -- but I found my local Ace hardware happens to have a huge aisle of nuts and bolts (theirs are all I guess distributed by an outfit called 'Hillman') and the Ace folks can help you match size and thread pitch.

There are folks on here who may be able to help you troubleshoot the PT. I can't see on the Mojo site what tranny this 1w amp uses -- do you have some ID info?

 

[JeffBlue]

Mojotone emailed me after I emailed them. I am supposedly getting something going about a replacement transformer after sending detailed photos. I wished they would just get busy and send me a new transformer so I can get back to finishing my amp build. I should already be playing through my new amp. There is no reason to troubleshoot the PT........either you have filament voltage or you don't. Something is seriously wrong with the transformer because it runs extremely hot.

 

[screamin eagle]

Bad experience happen. And it sucks when you're the recipient of such things. However it hasn't been my experience with them and they seem to have a decent reputation. Hopefully in just a few short weeks it'll all be forgotten about.

 

[johnnyha]

Your experience with Mojotone is like a refreshing dip in the pool compared to my experience with Triode Electronics which was like drowning in a raging sea of excuses and false promises. I did not get over half my parts and after stalling and stalling, 6 weeks later they mailed me AN EMPTY BOX!??

 

[dankilling]

Mojotone will make it right- I've never had major issues with them.

 

[MilwMark]

I know folks get frustrated but I wish they wouldn't generalize like this. I've never used Mojotone but my local shop has great things to say. Even a title like "My One Mojotone Experience Leaves a Lot to Be Desired" would be more accurate than the current title IMO. A potentially more fair way to approach would be something like "Here's My One Mojotone Experience - Is this Representative?". But I guess folks get frustrated and need to vent sometimes.

 

[JeffBlue]

Steve Snyder sent me an email with a photo that I sent him and he circled where I needed to make a change. He also emailed a manual that I didn't receive with my order. I was working from a diagram that was great for the most part, vague on the building of the switch relay board assembly. I wouldn't have made the mistake with the photos in the manual. The pilot lamp and the filament wires are carrying voltage but the tubes still wont light.? I have no idea how this can be. The plates in the tubes are energized but not the filaments. Trying to get Steve from Mojotone to help give me some idea what is going on with my amp. (Steve is the designer/creator of the Studio One amp)

 

[dan40]

Could you post some clear detailed pics here? We may be able to spot a problem and get you up and going. If you have any doubts about the PT, you should unsolder all secondary and filament leads so that you can test them out of circuit. This will help to narrow down whether the problem is circuit related or a PT issue.

 

[dankilling]

Steve Snyder sent me an email with a photo that I sent him and he circled where I needed to make a change. He also emailed a manual that I didn't receive with my order. I was working from a diagram that was great for the most part, vague on the building of the switch relay board assembly. I wouldn't have made the mistake with the photos in the manual. The pilot lamp and the filament wires are carrying voltage but the tubes still wont light.? I have no idea how this can be. The plates in the tubes are energized but not the filaments. Trying to get Steve from Mojotone to help give me some idea what is going on with my amp. (Steve is the designer/creator of the Studio One amp)

Sometimes it's really hard to see the filaments in a 12axxx tube glowing. Probably the same for the 12bh7 that is in the power section of that amp. Do they warm up to the touch? If current is flowing and the tubes are wired correctly, they should at least warm up to the touch. Post up some pics of the build and hopefully we can help sort things out as well. Mojotone is a respectable company, they won't leave you high and dry.

 

[clintj]

I've had parts issues in two Mojo kits. One was a missing resistor and grommet, and the other was a wrong value resistor and a missing pair of bolts. Both times a quick email got them to drop them in a priority mail envelope and send them. Nobody is perfect, but I get the impression they don't do an independent second check of their packing lists before they go out the door.

Contact them, they should make it right for you.

 

[Wally]

Do you have the tube sockets wired correctly?

 

[ICTRock]

I used to build boothill amp kits for a guy and ended up telling him to quit buying those because of missing parts ... I'm sure I could have contacted the distributor and waited for new stuff but in the end its cheaper and quicker to just replace myself and move on. I get it from the novice standpoint but the more you do this stuff, the more you adapt and overcome the minor setbacks. btw, good luck dealing with anyone and a dead transformer regardless of manufacturer or distributor ... if you value your time, buy a replacement and move on.

 

[Fatknuckle]

Center tap (s) well grounded? I have had positive experience with Mojotone for years. When things get missed, they have been quick to rectify the matter.

 

[robrob]

Disconnect the 6.3v leads and test them for around 6.3 volts wire-to-wire.

 

[JeffBlue]

Steve from Mojotone had me send more photos so he could see what I was doing. I definitely got the filaments working thanks to Steve. My solder joints aren't the best. I had everything working but no sound. I removed the tubes and turned the amp on to test voltage readings. I was reading 344 volts DC on pin 1 and pin 6 on the output tube socket. The readings on all of the rest the sockets on pins 1 and 6 were reading approximately 0.618 volts DC. What? Then something bad happened when I went to test output socket to verify and pins 5 an 6 somehow got too close and I had arcing and plasma. I quickly disconnected the power cord and blew out the flame. So this one is on me. I'm a freakin' rookie. Still trying to figure this thing out. Thanks for your input guys.

 

[Galibier_Un]

Your experience with Mojotone is like a refreshing dip in the pool compared to my experience with Triode Electronics which was like drowning in a raging sea of excuses and false promises. I did not get over half my parts and after stalling and stalling, 6 weeks later they mailed me AN EMPTY BOX!??

Silly me, I didn't realize that Ned Carlson (aka Uncle Ned from rec.audio.tubes) hasn't been associated with Triode Electronics for some 7 years. I bought a 5E3 kit from them last Summer. OK ... a few resistors were missing and they made good on it quickly.

I had a devil of a time with hum and went through four grounding scheme revisions to get the amp down to annoyingly noisy (as opposed to completely unacceptable). Somewhere during the process, I pulled everything out and opened up the input jack holes in order to install isolation washers. The funny thing is that I had all sorts of good documentation on my hard drive from folks like RobRob (Rob Robinette) and for whatever reason, I followed the layout they had on their website (with a couple of cross checks to other layouts).

The problem ended up being a terrible grounding scheme. The preamp buss grounded to the chassis from the filter cap side of the buss instead of from the input jack side! Three of the four layouts (power transformer specific) are still wrong as of this writing: those for the 40-18021, and both versions of the 40-18017 (120V & 240V).

The diagram linked to the 40-18016 is the closest to being correct. It does however, connect the screen supply filter cap ground to the preamp cap's ground instead of to the B+ cap's ground.

I can't be the first person to have this problem, and no doubt, they've fielded tons of questions on this (to the extent they have any sales). I let the project sit for a year.

Three weeks ago, I was inspired to pick it up again based on a thread on the Gear Page, and with a fresh set of eyes, I immediately realized the problem. Sometimes, when you're building a kit, you enter a passive state, and turn off your critical faculties. Mea culpa.

I e-mailed Triode last Monday - pointing them to their error and have received not so much as a 'thank you' from them.

I'm normally not too hard on small businesses, but clearly, this fits into an inexcusable pattern - not worth of my supporting them further.

... Thom

 

[LeftyAl]

I once built one . It was interesting to build, but I would never do it again. It was fun too.But it was expensive . For the amount of money and time I put into it ,I could have bought one

 

[LeftyAl]

Not mention the fact that Two of the tube sockets were actually numbered 180 deg. off.The key in the socket, instead of being between 1 and 2, the key was between 8and 9.And I of course wired using the numbers as my guide.Now tell me that that won't screw things UP. That took a month for me to figure out.