5e8a build questions

Bhabes · Post by **Bhabes** » Wed Apr 03, 2013 12:06 pm

Hi guys,

I'm building a low power tweed twin, mostly from a Mojo kit, with some part swaps. My question is on the inputs. Do I have them wired correctly? Is there any need to run another ground wire from the ground lug to the chassis? I would think the physical connection to the chassis is sufficient and probably how fender did it back in the day. Thanks!

Brian

Structo · Post by **Structo** » Wed Apr 03, 2013 3:14 pm

This is just my perspective but jacks have a way of working loose since they are probably one of the most used components in a guitar amp.

I like to use a ground bus wire that runs along the pots which terminates to chassis ground below the input jacks.

Then I run a short wire from the jack sleeve lug to that same ground point.

Milkmansound · Post by **Milkmansound** » Wed Apr 03, 2013 3:15 pm

fender used the ground on the jack to the chassis - however, it is not a very reliable ground connection. The modern way is to isolate the jacks and run a wire to a ground lug. That way when the jacks loosen over time you don't get noise or lose signal, a common issue on vintage Fender amps

that said, as long as you keep an eye on the jacks (ie, the amp is yours not for sale) you will be fine doing it the Fender way

Bhabes · Post by **Bhabes** » Wed Apr 03, 2013 3:21 pm

Thank you! And is my wiring correct so far?

Again, thank you for the help.

martin manning · Post by **martin manning** » Wed Apr 03, 2013 3:34 pm

IMO you don't need to isolate the jacks if the ground lead is taken to a ground lug that is close by, i.e. directly below them. The ground loop is small and far from any high chassis currents, provided the rest of the ground scheme is good.

Reeltarded · Post by **Reeltarded** » Wed Apr 03, 2013 3:40 pm

Thanks Martin. You just explained how I have been getting away with murder. I wondered.

martin manning · Post by **martin manning** » Wed Apr 03, 2013 4:25 pm

Aren't you greatly relieved to learn that you haven't really killed anyone? Kind of like waking up from a nightmare?

Reeltarded · Post by **Reeltarded** » Wed Apr 03, 2013 4:36 pm

Well.. I'll take the fifth on that!

Bhabes · Post by **Bhabes** » Wed Apr 03, 2013 6:28 pm

Could someone verify my wiring so far, please?

Thank you!

mr_hankey · Post by **mr_hankey** » Wed Apr 03, 2013 7:18 pm

You could insert a patch cable into the jack and measure the resistance from tip to sleeve, which should be 1M. If there's no plug in the jack, the resistance between the ring and the tip-connector should measure 0 ohms. Repeat for the other jack.

They look alright, but I can't see if the shorting lug is connected to the ground lug on the second jack. If you want to be sure, you should be measuring instead of relying on visual inspections, anyway.

Bhabes · Post by **Bhabes** » Wed Apr 03, 2013 7:39 pm

On the leftmost jack, the switch and ground are connected. I'm following this layout here for the inputs: http://taweber.powweb.com/store/5e8a_layout.jpg

I'll try your resistance suggestion!

Bhabes · Post by **Bhabes** » Thu Apr 04, 2013 12:06 am

I measured and it was .5 meg. Maybe because I don't have all the connections on the first jack soldered, they're only physically wrapped on the terminal. Is the Weber inputs' layout here a good visual reference?

http://taweber.powweb.com/store/5e8a_layout.jpg

Thanks!

martin manning · Post by **martin manning** » Thu Apr 04, 2013 1:00 am

The Weber layout matches the Fender wiring. You should see 0.5M to ground at the #1 input and 1M to ground at the #2. The switching is set up so that the #1 input feeds both triodes and the #2 feeds only one. If both inputs are in use each feeds one triode, and both inputs have 1M to ground.

Bhabes · Post by **Bhabes** » Thu Apr 04, 2013 1:04 am

Exactly what I got, thank you. I'll post some pics when I'm done. It's been a fun project. I've only built British amp clones.

Bhabes · Post by **Bhabes** » Sat Apr 06, 2013 8:35 pm

Done except for the cabinet and power tubes. Anyone notice anything glaringly wrong? It's mostly parts from Tubedepot and Mojo + stuff I had in my parts bins, and a proper Heyboer PT. Speakers are Weber 12A150 with repro labels that I'll wire for 4 ohms. Going to use EH rectifier tubes, TAD short bottle 6L6, old stock 12AX7 and 12AY7. I used Ceriatone's bias scheme.

The Mojo layout has 100 ohm resistors coming off the indicator lamp, I suppose to reduce brightness? Anyone have an opinion on that? I didn't install.

Thanks again for everyone's help!

Few pics then a link to some more.

[img

463]http://kurtsequipment.com/twin5e8a/twin0.jpg[/img]
[img

750]http://kurtsequipment.com/twin5e8a/twin5.jpg[/img]
[img

750]http://kurtsequipment.com/twin5e8a/twin6.jpg[/img]
[img

750]http://kurtsequipment.com/twin5e8a/twin7.jpg[/img]
[img

750]http://kurtsequipment.com/twin5e8a/twin9.jpg[/img]

More pics:
http://kurtsequipment.com/twin5e8a/