Amp build thread #2: Super Reverb

[clintj]

Light bulb moment! The bright cap bypasses the volume knob. Bad ground maybe? I reflowed every solder joint on the pots along with the buss wire I'm grounding with, and voíla! The hum is virtually nonexistent now. Finally, I think we have no more gremlins in the circuit. Whew. Presenting El Diablo.

[moon]

post deleted

[moon]

Oops didn't see your post! Glad to see you've got it fixed.

[jonfields45]

How do Mojotone kit prices compare to buying a Fender PCB based replica? Jon

[clintj]

Actually, the kit was a couple of hundred dollars cheaper than Fender's reissue. Given the future serviceability and upscale components, the kit can be a bargain if you've got the time to build and troubleshoot it properly. If I sat down and added up the build time hours though, I would have probably come out a little ahead buying an original one somewhere. The medium to high power Fenders don't seem to go for what the Princetons and Deluxes do.

[moon]

One of the great things about a hand-wired build is the ability to tweak it. Making the amp a little brighter, or adding a touch more gain, may be as simple as swapping out a cap or two.

[jonfields45]

Weber kits seem to be a bit cheaper. Did you consider them? Thanks, Jon

[clintj]

I've looked at them, and have talked with people that have built them. You still get good results with them. I've also heard the Ceriatone kits compare favorably with ordering the parts piecemeal from small shops and bulk supply houses like Mouser. You will get a working amp at the end either way. Hoffman Amps also is another place I've run across; his chassis boxes look really well done and he does both standard and custom eyelet/turret boards.

I like the upscale parts (Switchcraft jacks, CTS pots, Sprague and Orange Drop caps, original style carbon comp resistors, etc) Mojo uses, and I'm really happy with their cabinetry and covering work. I'd rather build with first rate parts the first time and not be wondering if it could be better.

The next build will probably be built piece by piece; I'm looking to build a Matchless clone and I'm not finding much in the way of upscale kits out there. So far I have a layout diagram, and a source for the transformers, and that's about it.

[clintj]

My, my. This thing is turning out to be a bit cantankerous. Turned it back on to wring it out some before setting up mics for recording last week, and had low volume. Chased that, and got a hum back in the reverb control. Fixed that, and had no Channel 1. Fixed Channel 1, and lost more volume. Chased after that, picked up a wicked hum. Adjusted lead dress some more, now it's amazingly quiet at idle. And when playing, too. Time to order some proper bench equipment so I can really find out what the issue is - gain issues/signal loss, or an oscillation hiding somewhere. Very curious....

El Diablo as a name may have been a little too prophetic. At least my Tweed still runs great.

[moon]

Wish I had a helpful suggestion I could make. Intermittent electrical problems can be a real pain to track down.

At least there's a positive to take away: it's a nice, quiet circuit and it's very close to fully working. Can't wait to hear it

[clintj]

Me too. I'm at the point I'm thinking it's either something in the signal path like a coupling or cathode cap acting up, or I've got a parasitic oscillation sucking up power somewhere I can't hear. Either way, an oscilloscope should shed some light on the problem. There's only so much I can test with a multimeter and a chopstick to poke things around with. She's in the corner taunting me from under her dust cover until then.

[clintj]

We might have a true "light bulb" moment. If my multimeter is right, I might have a bad neon bulb/LDR assembly. That would direct almost all preamp signal direct to ground right before the PI tube, hence extremely low volume on both channels.

[clintj]

Yeah, that was part of it but not all. I also found a resistor on one of the reverb tubes that was reading open intermittently and have a replacement ordered. I do have an ever growing list of things it's not, though.

I'm down to only having the normal channel connected; I lifted a wire out to disable the more complex vibrato channel and pulled its tubes so I can troubleshoot the phase inverter and power section alone. Who knows, maybe I'll find the troublemaker today or tomorrow. If not, my tax refund should show up so I can order some more advanced test gear.

[moon]

"Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.


Winston Churchill

[clintj]

Originally Posted by moon

"Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.


Winston Churchill

Probably more Pogo than Mr. Churchill.
"We have met the enemy, and they are us."