How to fix Fender 5F1 Tube MojoTone Kit amplifier Simple repair Tips 

I feel like I'm back at university...I'm building a Deluxe kit and I'm absolutely positive it would either not work at all or have numerous issues if not for these videos. Latest "lesson" for me is where to land the hot mains wire... I almost feel like I should watch every possible D-Lab video before finishing my kit. THANKS!

I have been playing with electronics for about 70 years and every time I watch one of your videos I learn something new. Thanks, John.

It would be super cool if you could group all the 5f1 related videos into one category so we could easily binge watch all of them

Thanks for the Video of the 5F1 Champ upgrades. Great clear explanations and nice upgrades here. Kudo's to ya!

From your brother in Hawaii. Love your videos , and love you so much .

You have an awesome way of walkng someone through an amp repair I watch these videos sometimes 2 or 3 times watching you work on them It is good I dont live next door, lol, because I would be at your shop daily!!!!

These little amps are incredible!! You’ve got me addicted to these things!! I’m stripping old junk radio cabinets and gaining a huge chassis graveyard!! Thanks for all of this knowledge in easy to consume video format! :-)

I was finising my 5f1 project and I shaw that video a vew month's back .. I remembered the fuse trick descibed at 10:00... I looked for this video four about 3 hours and finally found it 😊

That was a great tip about moving the two input jacks to the outside to wire them before moving them back inside the chassis. I did a 5F1 build this last week and that tip really came in handy. Made it so much easier. I also appreciated the tip about wiring the hot to the tip of the fuse holder.

Great Video. I am getting ready to build a 5F1 and you have a lot of good information on this video. Thank You.

Great video. Clearly explained

Great fuse tip. Never even thought about the hazardous scenario.

When it comes to repairing kit amps it's like "Jacking up the license plate and putting a new car under it."

Beckman?! My dad worked there for like 20 years, I think he'd be thrilled if I picked up some vintage Beckman meters from his era working there, I might go pick some up.

Kit amps can be a ton of fun to assemble, but as you illustrated, not everyone is skilled at it. Your version looks (and works) infinitely better than when you got it, that's for sure!

Thank you for sharing your wisdom with us!!! You always make fantastic educational videos with attention to all safety issues!!!

Hi terry I have 20 chassis I made up from scrap and horded parts for the last 5 years I’m going to start building them this year I can’t wait your videos are great been watching for a long time

Job well done Sir, thanks for all info on rebuilding amps..

Thanks for all the great info! When I do my build, I’ll follow your suggestions.

Great video and tips Terry! Keep em coming! I really enjoy your explanations of WHY you suggest doing things certain ways and how it makes the amps better. Really helpful tips. Thank you!

I love your vids. The safety tips are spot on. Kudos from Ken in NC.

Thanks for that mid thing for making it like a Princeton. I added this to mine with a switch and now I can get 2 different voicing out of the 5f1. ;-) Love your videos, thanks for posting

I bought a variac after watching your videos, it seemed so very important to protect me, mine/and others gear, etc they aren't that much I got my that does 30A for $82 brand new.

Thanks for all the tips Terry. I have my old Beckman digital that still works great and use it on my videos as well.

Really digging those old meters. The corse I took in electronics came with a Beckmann meter their super nice, great video 👌👌👌👌👌

Invaluable information. Thanks for sharing!

I'm loving the 5f1 videos and discussion. I have a boothill kit that has gotten delayed so I'm happy to find all these tips yo add to my notes for when I get time to start my build. I've always planned to go with a 10" speaker and I've also liked the separate power switch as well.

Excellent video! I regret not buying a friend's 1954 Fender Champ back in 1976 as that we would laugh about how long it would take to startup but it had great tone, that along with that I've been thinking about getting a Monotone 5F1 kit I feel much more confident after seeing your video. On the Beckman meters, I too love them. I bought my first one in 1983 a HD110 model and still use it, unfortunately my company mandates yet provides Fluke meters-warning to Fluke users annually Google the Fluke name and model number and the word "recall" as that there have been Flukes that had problems showing false negative readings - meaning it showed the user that there was no voltage yet there was over 400+ volts injuring or killing the users.

Great video Terry!

Thanks Terry! Nice lesson and thanks for the tips. I have no problem with vintage meters. If I could afford to, I would collect them.

Thank yoù for these wonderful vidoes. I replaced the 470 with a 750 ohm cathode bias resistor and was then able to get my 14 watts of plate dissipation. Thanks for the tip!

Thanks for the tips on tweaking the tone. I'll try larger caps as suggested.

Thanks Terry , Great video , Nice tip on the fuse holder .

Great video man I learned a great deal

So many tips and lessons in this single short video that I haven't heard elsewhere. Thanks a bunch. Looking to build a nice little champ, although "v2", by this shop that's improved the old build a bit to meet modern standards (including things like power toggle, but also quality of life like multiple speaker load outputs and tone control :) ), these tips will definitely help judging my work, considering little mods and just safe practice in general.

Great rebuild video!

Nice kit amplifier save and a ton solid of information. Interesting mention the old potentiometer/switch design having a solid metal back to block AF interference.

The only thing you didn't do as a standard practice that i always do it break the hot side of the line in instead of breaking the neutral with the power switch .Great rebuild on the little 5F1

Those green below-board jumpers are terribly hard to see on the pictorial diagram! Why didn't they pick purple, or some other color which doesn't blend into the gray so well? LOVE watching these troubleshooting vids - I learn a lot each time.

Excellent video--thank you!

A question, Terry. Why did you go back to the pot-mounted AC switch, rather than clearing a spot on the front panel for the installation of a toggle switch? Your argument for isolating AC from the audio path was well-reasoned and logical, so I wonder why you left it the way it was?

this is a lot more interesting than the radio videos

Great stuff sir

You're a legend dude.

My last two kit builds, I just followed the layout diagram... patiently, and I got 100% working at first fire-up. If you've NEVER tried one of these kits, I did one on my channel if it helps, but if you can, work under the supervision of someone who's had practice doing this.

Thanks, Terry. I don't know if I will ever build one of these, but I am about to retire, so I will have the time. And I've got no problems with your meters!

Terry, you could open a school to teach 'tronx when you retire! Great tutorial on what to do and what not to do. The 5F1 must be Leo's greatest model! Everyone likes it, me too! Thanxz

Important !Don't forget to connect a speaker cab to not fried the tubes cheers

For Me....the Best!!! channel to present repair Guitar amp ...Greeting From Poland :)

I don’t think that’s a Mojotone kit. Unless they really cheaped out, that looks like a cheap Ebay kit. I always follow the ORIGINAL Fender layout with the brass ground plate under the jacks/pots. Never have an issue with noise/ground loop. The only changes are the modern center tapped 6v heater wires, which some late tweed amps do have. A cathode bypass cap should be on V1. A 1uf to 8uf really bumps up the gain and limits the bass response. The 50/50 on the 6V6 cathode is fine for 6 and 8 inch speakers. If someone wanted, a custom 10” cabinet is available from Mojotone, then you could increase the V1 and 6V6 bypass caps to 25/25 and 100/50. Using those values with a stock speaker size turns a Champ into a fart box. In my opinion of course. Thanks for the Video, Terry. Great work as always!

Yay loved the video. Great job I approve of the Tidiness of the rebuild lol :). You could not publish too many of these id end up watching them all :). Thanks

Your the best Terry

Nice video Terry

D-Lab your No1 in my book from Down under OZ :)

You want that cap on the 12AX7, seems it was on most if not all Fender 5F1s. I added it to my clone, nice improvement.

Another fine job Terry.I have a 5F2 amp,made by Allen amplification.Similar circuits for sure great little amps.In fact when I'm jamming with friends ,they always tell me to turn it down.They are quite loud for only 10 watts.Most of their amps are 50 watts of more,and this thing keeps up with those easily.It's got a 6L6,so I'm thinking this thing has to be at least 15watts or more,plus you can change the tube to a EL34 per specs.What I like is this thing weighs only 20 or so pounds.Easy to haul around,my back sure likes it too. I like these videos, you always show your quick tips on what and not to do.Have a good one.👍🎸🔌

I don't have your level of knowledge Terry, but I believe you might be wrong about those back-up diodes on the rectifier spiking current. Since they are placed in series, not parallel, they still get limited by the voltage drop and internal resistance of the rectifier tube, and would appear to not affect the delayed warm up and current flowing ability of an indirectly heated GZ34.

Another great video with a bunch of quality advice and tips! I'm still in the early stages of learning so tips on when and when not to make changes to existing components is something I usually don't consider, those decisions only come through experience. Thank you for sharing yours with us. Question, when you rewired the board, did you use solid core wire? If so, what gauge and voltage rating? Does the gauge depend on whether it's a filament wire or for plate wiring?

Thank you for posting this video. I was going to start this kit this week. Now I have a shopping list to make the "improvements".

Great vid Terry. I admire the effort you put in. It looked hard to work on such a small chassis and that board. I don’t know why the kit doesn’t use a turret board with stand-offs, which would have been nicer. I have a British made kit which uses a nice turret board.

I don't like the newer auto-ranging meters. Give me the vintage stuff although I do like the newer capacitance meters. I like to run my main power to my switch and then to the fuse. It's just one more assurance the power is isolated when I'm checking a fuse. Great video Terry. Lot's of good tips in this one.

Thank you for the bias calculator page. Is it me, or have modern kit designers never built a kit? I have seen SOME modern instruction sheets that are so atrocious, failure is guaranteed. It almost seems intentional. Not that you find many people younger than 50 building kits these days. Who can afford them?

Nice work as usual. Is it relatively safe to exceed the maximum capacitance rating of the 5y3 rectum frier? You're only exceeding it by 1uF. But I'd assume it's okay. Probably wouldn't stick a 47uF in there as the first cap though. Good tip for wiring the fuse holder. My scope recently blew a fuse from a recent thunder storm. Upon pulling it out, it gave me a little kiss. I opened the scope and wired it the other way around. Lastly, regarding that cathode bias resistor, I see so many of these clones come to me over biased due to using the stock values, and it seems some amp builders who make these clones think I'm talking rubbish. So, they ignore me by the time I explain that voltages from our mains is higher than it was when these were designed. Plus, they're charging boutique amp prices for these builds. Measure the bias and fit the correct value bias resistor. Somehow, I'm the crazy one.

Hi Terry My 5F1 amp was buzzing like crazy when I had the black AC wire going to the switch. I re-wired the switch by sending the white AC wire to the switch and the buzzing was gone! It seems that the black wire on the switch must have been inducing a hum into the volume pot. Not sure why Mojotone says it doesn't matter which wire goes to the switch...clearly the white wire is the better choice.

I like how you approached this and the thought put into the work done to get some electrical safety into it, and that fuse wiring I hope the ket seller updates that PDQ. Would you consider fitting a class X or above across the line cap to an amp like this? or do you not think there is any benefit? I am very slowly working on an electrical restoration of a Czech built 1950's radio and it has a non safety across the line cap in it so I am trying to decide on if I will go for ceramic or ploly across the line (caps made for the job mind) I think / feel my application needs one as RF is there.

If you can find it -- the indirectly heated 6106 is a great sub for a 5Y3 -- the 5V4 as well

Great Video Terry! Does anyone make a better quality Volume pot with the power switch mounted on the back?

Dlab rocks if you want it done right be like dlab and uncle doug.you are the gold standard

Vintage test gear rocks! It does just as good a job (sometimes better) as the modern shiny units, at a fraction of the cost. In addition, most of the older test gear can be repaired fairly easily - not so with the modern stuff!

Built the Hoffman amps 5F2A and had no serious issues building it. Loved the turret board that was supplied, it looks better and seems like it will be easier to fix than an eyelet board. One question, would the cap mods for the PS section and the audio section work for the 5F2A?

Back of the fuse holder and power should/could have some sleeving to prevent accidental electric shock while working on the amp. The rest of the circuit is isolated by the transformer from direct connection to mains supply.

Nice!! Great video!!.... :-)

one smart fella

The under board jumpers get all first time amp builders.thats why i like to just make turret boards. Don,t need backer board. It is elevated above the chassis and i like to drill a little hole next to jumper lands. Route the wire up through the hole and you csn verify the jumper is in and soldered to the turret.

Nicely documented and very educational. One thing I noticed was that your current when you first powered it up after rebuilding it was a bit higher than the current you showed on the Weber site. Is there a certain tolerance that you or in general is expected or allowed?

I'm building a scratch 5F1 and put in an on/OFF switch too.

Can someone help answer this question of mine? I am changing the caps in my old amplifier and i was wondering if i van replace ceramics for film caps? Does the type of cap hava an influemce kn the sound??

Hi Terry really enjoy the vids. Ive been working on a 5f1 and there are a lot of different versions of this amp. Grounding is shown as one way in some versions and as another in other versions. So, what I'm hearing is that the filter cap grounds should be separated from the "signal" grounds? Is there a book that you could recommend to a new amp builder? Thanks!!

I hope this makes sense, I’m very new to this. Do the resistors between the first, second and third capacitors need to bumped up in size since the caps were increased?

Oh yeah, even if someone doesn't have a variac, or a variable isolation transformer like I have, they can still put a series test light across the fuse holder to limit the current. There is really no excuse for plugging in a device and crossing your fingers...

Thanks again ;-)

Boeing should consult Terry to sort out their problems. :-)

Would the caps still be underpowered for a diode rectified power supply? I followed uncle Doug’s p2p build and he upped the first cap from 16 to 20uf and left the other two at 8uf. I just ordered all the parts for it some I’m wondering if I should go ahead and put another order in with the higher value caps. Edit for clarification: I’m using diodes because I’m doing a conversation of a champ 600 reissue. The transformer doesn’t have the necessary winding tap for a tube rectifier.

Great video! Terry, you should learn to play some easy electric guitar riffs.

Thanks for Meters

@13:33, you mention about using 5y3 rectifier only. If the power xformer did not have a 5v winding, can the 5y3gt be substituted for a 6x5gt?

Terry, what value NI resistor you use for your "dummy load" ?

Can anyone help ,I am confused by the input jacks i have the pin connections withe the tip being the middle pin ,ground obviously to the part connecting to ground . I have however seen that the outer pin is the tip and the switch is the middle position as is shown in the diagram on this video. Are there differing connection protocols for these switched mono jack sockets .

What about diodes and a series resistor to emulate the characteristics of the 5Y3 rectifier tube?

Hi Terry, why don't you buy a little looper guitar pedal, this thing keep in memory what you record so you will be able to ask a friend to play something cool and then you keep it and use it as soon as you need to test a guitar amp! You will be in the exact condition where a guitar player would be playing...

Rectifier tubes don't have sag in a single ended class A set-up. Diodes for rectification would not only make little to no difference, present day tubes like the JJ's you have there are robust enough that having a 400v "shock" as you say isn't going to hurt them. Even if you think it will, a stand-by switch would make more sense than using a rectifier tube instead of diodes.

I think a 1uf bypass cap on that preamp would give you more middy sound. 25uf is pretty much a full range boost on that circuit. 1uf should roll off some bass and tighten it up a bit

Hi Terry, question for you on the power-up test with the 1k ohm 6V6 cathode resistor. On the power-up test, was it connected, or was it still a floating lead? You said afterward to solder it in. I am just curious, as I am still learning. Cheers!

I'm in the early stages of building one of the Mojo 5F1 kits. Having an electrical background, I do not like the way that they are breaking the neutral with the power switch. Instead, I am connecting the white neutral from the power cord directly to the white on the power transformer. The black hot lead on the power cord is wired through the fuse, then the side tap of the fuse feeds to one side of the switch. The black power transformer lead is wired to the other side of the switch. Modern wiring codes specify that you should always break your hot wire with a switch, not the neutral.

And the supply wire to the power switch is sitting on top of the ground connection of the main filter cap.....

In this video, you stated not to change the rectifier tube. what would happen if I were to change the preamp tube(s) to lower the voltage going into the output amp?

Nice hakko

hi id like to know how much voltage on the plate of 6v6 thanks

What are your thoughts on modifying the negative feedback loop, such as a trimmer pot or some way to dial in the resistance for a particular tone? Thanks!

But Terry, I saw an old datasheet on the interwebs stating max 32 mf of filtering for the 5y3. Can I damage my rectifier by increasing the filtering like you did?