New 5e3 build - problem(s)

[atlimar]

Hey guys,

This is a most excellent forum, and I've been following the various builds and debugs for a while now.

I just completed my 5e3 build using the Fender's '57 Deluxe schematic. I got the components/kit locally. (I live in Shanghai, but my Chinese isn't to the level of making much sense when it comes to details of amplifier building, so very little chance for local support ) Hopefully you guys can provide some assistance.

A couple of things that I did different from the schematic. I chose to circumvent the preamp/poweramp heater fuse (as seen in fenders schem) and connect directly to the pilot light and from there onto the tubes. Another thing that I did was to star ground instead of soldering to the chassis.

Anyways, I fired it up without tubes and measured voltages. All looked good.

After installing and measuring with only the rectifier, and later with all tubes installed, it was time to try it out. All things lit up properly, with only a slight hum coming from the speaker. Did more measurements and again, voltages were within acceptable ranges.

With guitar plugged into any of the inputs, the volume output was very low and distorted. Plunking hard on the strings would increase the volume drastically. Definitely not normal.

I shut it off, drained the caps and did some measurements on the resistors. As a side note, I redid the speaker output connections and cleaned up the input and pots a bit. Mostly because it annoyed me how crap things looked.

Anyways, I fired it up again and this time around the hum had increased. After a while the hum was reduced but the volume problem was still present.

While playing single notes there seemed to be slight oscillation / waveform quality to the sound, like it was increasing and decreasing slightly.

I used a chopstick and tapped on some of the solder points. When tapping the ground side of C6 a slight crackling sound could be heard. I tapped it few times and all things went quiet. I shut the amp off, drained the caps and fired it up again. This time, no voltage goes into the caps. The rectifier gets its 341 primary voltage but its heater connections show no voltage.

So... it seems that by trying to solve the volume problem I have introduced another. Any ideas? Could the PT be busted? Its only the yellow (5v) heaters for the rectifier that are not outputting the required voltage. All other PT voltages seem to be proper.

This is a first time build, and I have taken my time figuring things out, reading over this most excellent forum (and learning a lot from Bruce.. wish I could have ordered his kit tbh ), studying the different schematics and layouts out there and whatnot. I am still a novice builder so I will probably ask some stupid questions from time to time.

thanks in advance,
Atli

[loudthud]

It's always a good idea to post a link to the schematic you used so anyone reading this will be on the same page. So when you say C6, everyone knows what you are talking about. Most problems with new builds are wiring errors or bad/damaged components.

You should use your ohm meter to verify some of your wiring. Ohm from the chassis to every point that is supposed to be grounded. Meters vary but readings should generally be below 1 ohm. If there are any wires on the back side of the eyelet board, verify them by ohming between eyelets on the top side of the board. Also, any wires that go to the pots or tube sockets that route under the board to eyelets should be ohmed. Next, record and post the voltage at the tube socket pins (you can skip the 5Y3 socket) and at the plus end of the three big filter caps.

Are your tubes new or from a confirmed working amp? Do you have access to any others you can try?

[atlimar]

Thanks for your reply loudthud.

http://www.fender.com/support/amp_sc...0JUN%2007).pdf

This is the schematic that I used from fender.com.

I went through the board last night and measured both connections and components and double checked my grounding. It does seem to be in order, but its always possible that I missed something.

5y3 socket without rectifier tube
pin 2 5v
pin 8 0V
pin 4 343v
pin 6 343v

As you can see from the schematic, one of the yellow wires connects to the eyelet board to a fuse, and from there to R27 and back to pin 8. It shows 0v. The other yellow wire connects directly to pin 2 and is at 5v's.

When I install the tube the reading looks like this:

5y3 socket with tube

pin 2 0v
pin 8 0V
pin 4 343v
pin 6 343v

This is odd I presume.

The tubes should be new but since the 5y3 doesn't power up the caps I do suspect it to be bad. I will go to the components market later (a very cool place here in Shanghai... a 6 level mall with practically every electronic component manufactured available ) and get another one.

I will get back at this after work, post more detailed readings and attach some pictures.


/Atli

[loudthud]

I'm not sure what's going on with the 5Y3. Did it light up when you installed it? From the data you posted I would say the fuse F2 blew when you installed the 5Y3.

[atlimar]

It worked the first time around, and then it didn't. I measured the fuse, it seemed ok. But I decided to replace it with a new one anyway. Same results, no powerup of the tube.

There is now voltage coming from one of the rectifier heater wires (the one that connects to the eyelet board).

[loudthud]

Don't try to measure across the fuse in-circuit, the transformer winding and the filament of the 5Y3 will look almost like a short. Remove the fuse, then measure it with your ohm-meter.

If there is DC on one heater wire, you should see it on both wires because the transformer winding will have very low resistance.

With the power unplugged, caps discharged and the 5Y3 removed, measure the resistance between the two yellow wires at the 5Y3 socket. It should be less than 1 ohm. If it isn't, you have a bad fuse or bad transformer.

[atlimar]

Thanks for the advice loudthud.

I got the amp to work again by replacing the fuse. So thats good. However, the original problem with low volume and distortion persists. This is getting most annoying.

I haven't had time to look into this properly though, crazy days at work and all that. I will post the pictures this weekend, and do some more measurements.

[atlimar]

Its fixed!

Components were all in order, but after some rewiring and cleanup things are as they should be. (it was a wee bit messy, first time build 'n all) The amp sounds fantastic.