Fender Test Points Question - 5E3

[BlueJim]

I have a newly built 5E3 from a Weber kit. The output level is very low.

I found the Fender site's 57 Deluxe schematic with test points and started measuring. The DC voltages are all pretty close to the values they show.

They also have AC test points, but I'm not certain how to use them. Do you hook up a signal source generating the 100mVAC they show at the input jack and go from there?

Unfortunately I don't have a nice tone generator. Is there a poor man's way to do this?

[BlueJim]

Problem solved. Details follow for the curious.

First it looks like yes you do check the Fender indicated test points using a tone generator. But how to get one cheaply? I found a software solution at NCH Software. Fortunately I had cables with the necessary connections to go from my PC's headphone output to the amp input. I started up the software to generate a 1 kHz sine wave and adjusted the output level to get 100mVAC on a meter. Then I plugged it in to the "bright" input.

I had previously transferred the AC test points from the Fender schematic to a printout of the Weber layout. I set the amp volume about halfway then started carefully checking the voltages. The output of V2A (the tone stack recovery stage) seemed good but the two inputs to the power tubes were far too low; about 5.5 volts instead of the indicated 16.7 and 18.7. A little probing and I found that I had completely omitted a jumper from c6 to r15 and pin 7 of V2!

To be honest, I'm not quite sure why it made any sound at all.

After adding the jumper the amp cranked up nice and loud. Too loud for my apartment I would say although that was expected. Still it's a very pretty sounding amp even the volume is quite low. The Youtube clips I've heard don't do it justice.

If you are considering a first build, the 5E3's are complicated enough to prove a challenge without overwhelming you, assuming you have some grasp of schematics and are moderately handy with a screwdriver and a soldering iron. Expect to hit some bumps and to do some debugging. It's all part of the fun.

[limbe]

I totally agree with you BlueJim.A basic Deluxetype amp or a Champtype amp are good projects if you are a firsttime tube amp builder.You can even build them in sections:Power Supply,Output Stage and Preamp Stage checking each stage before you build the next one.In my experience I find it is very important that you build something that A:Works first time you switch it on or B:You can troubleshoot yourself.I´ve seen guys who have failed to get their first project working get discouraged and just put it away,sometimes for good.Luckily there are forums like this where you can get help.Limbe

[Thin69]

Sorry I am late here but here is a very cheap one that you can build. I built one and the adjustable amplitude lets you dial in the signal strength. This one will produce 1KHz or 2KHz.

http://www.diyguitarist.com/

Click on the Test Equipment tab, then the Two Tone Audio Oscillator

[muchxs]

Originally Posted by BlueJim

I had previously transferred the AC test points from the to a printout. I set the amp volume about halfway then started carefully checking the voltages. The output of V2A (the tone stack recovery stage) seemed good but the two inputs to the power tubes were far too low; about 5.5 volts instead of the indicated 16.7 and 18.7. A little probing and I found that I had completely omitted a jumper from c6 to r15 and pin 7 of V2!

To be honest, I'm not quite sure why it made any sound at all.

I must have two dozen or more signal generators in my back room including everything you could want for NTSC video (tube test pattern generator, anyone? ) all the way back to a Navy surplus tube tone generator the size of a small refigerator. It's a rare occaison indeed when I fire one up to troublehoot an amp build. Usually if I stare intently at the amp's innards ("Men Who Stare At Goats ) the problem eventually reveals itself. There's a funny little thing about wiring errors, if you or I missed it to begin with we can generally stare at the problem and still not see it. As mentioned above that's why it's good to start with a circuit and layout that everyone is familiar with (because we can still screw it up anyway! ) and not make dozens of changes right from the get-go.