Amp build thread #2: Super Reverb

[redir]

Originally Posted by clintj

It is. I'm building a Mojotone kit. You can go cheaper and get a Ceriatone or Weber, but I liked the quality of the Tweed Deluxe I built so I stuck with them. I personally wouldn't start with one of these, I'd go with a simpler amp design first or even some pedal kits. Pedals are good for learning, without the added bonus of lethal voltages.

No, I don't build these to sell. It's a fun hobby for me though. I fit in build time around my work schedule, so it takes me a little while to get through one. I'll be picking it back up this weekend, and posting more pics as I work.

Cool yeah it seems like a real fun hobby. I've built kit pedals and modded many pedals and have built about ten electric guitars and have been doing guitar repair for 20 years. I've never even thought about building an amp before but I'm sure I'm good enough with a soldering gun but I can't read schematics from Greek either.

I was thinking something simple too like a Fender Champ clone. Cool stuff!

[clintj]

Originally Posted by redir

Cool yeah it seems like a real fun hobby. I've built kit pedals and modded many pedals and have built about ten electric guitars and have been doing guitar repair for 20 years. I've never even thought about building an amp before but I'm sure I'm good enough with a soldering gun but I can't read schematics from Greek either.

I was thinking something simple too like a Fender Champ clone. Cool stuff!

Schematic reading is a big plus when you have a question or are troubleshooting, but many amps can be built using nothing more than a layout diagram. I've seen pics of Fender employees building amps with just that in front of them. Now we have the internet where you can look up various grounding schemes, pics of internals, theories on lead dress, etc.

A 5F1 Champ is a classic amp, and so simple. Three tubes, two knobs, and one speaker. My first was the 5E3 Deluxe, and it even worked on the first power up. We'll find out how well I do on the Super hopefully later this month. Nine tubes, fixed adjustable bias, on board reverb and tremolo, and three circuit boards. My fingers are crossed it works the first time, with no weird issues to trace down.

[clintj]

Quick catchup post for today. I've installed the speakers in the cabinet since last post, and most of the heater wiring. I've got a lengthy dentist appointment later (apparently I cracked a molar and need a root canal - yuck) so we'll get back into it tomorrow depending on how that goes. Here's some more pics.

Front of the cab


Rear. Speakers are Jensen C10Q's


Chassis

[moon]

That's going to be a beauty. What speakers did you choose?

[clintj]

Originally Posted by moon

That's going to be a beauty. What speakers did you choose?

Thanks! Came with four new Jensen C10Q's in the kit. I was really thinking about ordering a set of Webers, but these seem to get good marks from other Super owners. Speakers are an easy swap later if I decide to change them out anyway.

[Neon Soul]

Originally Posted by Tone Gopher

Just add 1 ohm resistors between the output sockets and ground, and put test jacks on the back panel. Set your multi-meter to read voltage and it'll give you a direct read of current (mA).

Details: Tie pins 1+8 together, connect 1 ohm resistor between 1+8 and ground. Run wire from each 1+8 to red panel jack; run wire from ground to black panel jack. Iterate for each output tube or tube pair.

Set DVM to voltage and insert probes to monitor voltage drop across reference resistor. V=RI >> mA across resistor translates directly to mV. Iterate for each tube to read bias current.

For anyone else reading this thread, DON'T ground pin 1 on a vintage Fender style amp.

Tying pin 1 and 8 on a Marshall is common place but vintage Fender circuits pin 1 is a tie point for the grid-stopper resistor and the negative bias voltage will be on this pin.

[Bob Womack]

That's looking great!

Bob

[clintj]

Finished the heater wiring and most of the power tranny wiring this morning. Had a grand time trying to figure out why I was seeing connectivity between the two legs of heater wiring until I realized I had left the pilot light bulb in. Also got the bias supply board built and ready to install. Next is placing the main board in the chassis and connecting the flying leads to various components.

[moon]

Do you know the drill trick for twisting wires? Grab two wire ends in the chuck and pull the other two out tight while you spin the drill. It gives you a much tighter twists than you can do by hand to help avoid hum induced by wires carrying high AC currents such as heater wires.

[clintj]

Originally Posted by moon

Do you know the drill trick for twisting wires? Grab two wire ends in the chuck and pull the other two out tight while you spin the drill. It gives you a much tighter twists than you can do by hand to help avoid hum induced by wires carrying high AC currents such as heater wires.

I do, it was just easier to do each short run of heater wire by hand. Tight quarters in there. The tranny wiring is stranded, and is pretty insistent on trying to unwind itself as soon as I let go.

[clintj]

Dinnertime. Got most of the tube socket wiring done this afternoon, and pulled leads to set the large cap board in place underneath. All that's left is the rest of the sockets, pots, jacks, and other miscellaneous connections. Band practice is tomorrow, so I'll try to get more done Monday. Movie night with the kids after dinner sounds good right now.

[clintj]

I think I might be done with the build. (knock on wood) At least I'm out of parts, anyway.

Went through, checked every solder junction. Found a missed one on the midrange tone pot to ground connection. Went through a second time, looks good. Break for a half hour, traced everything again. Still looks good. Next step is install tubes and power up, seeing if I get warm heaters on all tubes. Then a quick flip of the standby switch and see what happens. If nothing weird happens, set the bias and play some.

[moon]

Good working method you've got there. I'm always worried about creating a problem I don't know how to fix but if you're careful and methodical the chances of that happening should be pretty low.

This'll be like a second Xmas

[clintj]

Switched the power switch on, got a good pilot light and heaters glowing. Cool.

Switched the standby switch to On for a couple of seconds, nothing weird happening (pops, smoke, hums, etc). Cool again. Power down.

Plug in a guitar, power up, switch Standby to On.... Hmm. No pilot light, no sound. Crap. Blew the fuse. Got to pull the chassis, bleed the filter caps down, and have a look around now.

[moon]

Is there a simple way to disconnect the vibrato and reverb parts of the circuit? That might help to isolate the problem.

If you're stuck you can often get some really good technical advice on these forums:

music electronics forum: debugging your build

diy audio

TDPRI