New 5E3 build - great sound; at unamplified guitar level...

[FreddieRay]

Hello all,

Let me first introduce myself. I'm a first time amp builder with little experience in electronics other than soldering jack cables. I have no technical background whatsoever (yes, I have read some articles and some book fragments about valve amps but I do not consider this to be solid technical knowledge). I am from Belgium, so please excuse me if I'm using strange or incorrect language.

Last month I completed a 5E3 kit I bought off of a Dutch website (tonefactory.com). It came with an EHX 12AY7, an EHX 12AX7, two JJ 6V6's and a Sovtek 5Y3 (which is, if I am correct, really a 5AR4?). I constructed this thing with some kind of photo manual, which had poor instructions in very poor English. I built it into an old Peavey cab in which I installed a Jensen C12N, fired it up, and the sound coming out of it was just the kind of sound you would expect from a Tweed Deluxe; only, with the amp on 3, at about the volume of an unamplified electric guitar.

I have since done the following (everything one step at a time, never fixing the problem but also, never making it any worse or different):

- checked all wiring visually and with a multimeter, 6 times, going point to point
- checked the wiring under the board with a multimeter
- checked the tube socket contacts with a multimeter
- checked the resistance values of every resistor
- removed the two "number 2" input jacks (correctly that is, not just cutting the wires)
- removed the extra speaker jack
- plugged in a different speaker
- hardwired the speaker
- removed all cathode bypass caps (assuming one could have been faulty, and being told this wouldn't hurt the circuit)
- replaced the rectifier tube (with a JJ GZ43)
- replaced the preamp tubes (with two JJ 12AT7's; I figured they would do fine for testing purposes, not worrying about sound at this point)
- replaced all coupling caps with new Mallory 150's (assuming one could have been faulty)

I should also mention that my build differs from the original Fender design as follows (referring to right and left while looking at the original Fender layout):

- the rightmost power filter cap is grounded to the middle pot; the middle and leftmost power filter cap are grounded to the leftmost pot, along with the power tube cathode resistor (don't know if that makes any difference)
- the screen grids on the 6V6's get their voltage over 470 ohm resistors (via the unused pins 1)
- the plates on the GZ43 get their voltage over rectifier diodes (Vishay BYV26E)

The voltages read:

- V1 (12AT7)
1: 129,3 VDC
2: 0 V
3: 2 VDC
4: 2,8 VAC
5: 2,8 VAC
6: 120,3 VDC
7: 0 V
8: 2 VDC
9: 2,8 VAC

- V2 (12AT7)
1: 127,1 VDC
2: 0 V
3: 2,1 VDC
4: 2,8 VAC
5: 2,8 VAC
6: 181,6 VDC
7: 5,8 VDC
8: 65,4 VDC
9: 2,8 VAC

- V3 & V4 (6V6)
1: 356 VDC (using pin 1 for connecting the 470 ohm resistor to pin 4, as mentioned earlier)
2: 2,8 VAC
3: 401 VDC
4: 355 VDC
5: 0 V
6: 0 V
7: 0 V
8: 22,1 VDC

- V5 (GZ43)
1: 0 V
2: 414 VDC
3: 334 VAC (using pin 3 for connecting the rectifier diode to pin 4, as mentioned earlier)
4: 334 VAC
5: 334 VAC (using pin 5 for connecting the rectifier diode to pin 6, as mentioned earlier)
6: 334 VAC
7: 0 V
8: 405 VDC

That is about all the significant information I can think of... I'm completely out of ideas on this one, and I would really love to see it working. Any ideas?

Thanks in advance
F

[loudthud]

Greetings FreddieRay,

Your voltages look correct. Normally V2 pin 7 will not measure correctly. But pin 8 shows an acceptable voltage which indicates there is no problem on pin 7. When you touch pin 7 with your meter probe, did you hear a loud click or thump from the speaker? That is normal.

Does the guitar sound distorted when the volume controls are at 12? That could indicate a short or problem at the speaker jacks. If the sound is clean, that could indicate a problem at the input jacks or the volume/tone controls.

You said that you "hardwired the speaker". Did you do this in a way that completely disconnected the speaker and output transformer wires from the speaker jacks?

Here is a link to a previous post where I describe how to do resistance checks at the speaker jack:

Safety Note: Power should be off, power cord disconnected from mains power, and caps should be discharged.

http://music-electronics-forum.com/t23028/

If the speaker jacks are connected correctly, my next check would be at the input jacks. Here is a link to a thread where I describe resistance checks for the input jacks in post # 14.

http://music-electronics-forum.com/t12667/

To check the volume controls, measure the resistance from V2 pin 2 to ground (chassis). The reading should be 500K ohms. Your meter might not give a stable reading if you move the volume or tone controls but the reading should stablize in a few seconds.

[FreddieRay]

Hello loudthud,

First of all, thank you very much for your reply. I did hear the thump from the speaker you were talking about.
When I hardwired the speaker, I connected OT green to the output jack tip lug and OT black to the output jack sleeve lug. I then connected the red speaker wire to the tip lug and the black speaker wire to the sleeve lug. I assumed that was a direct connection, but as this did not fix my problem, I undid the change and rewired the speaker with a jack plug.

I did the measurements you suggested and here are the results.

Let's first clarify how I wired the jacks in the amp:

- Output
OT green -> Tip
OT black -> Sleeve
Nothing -> Switch
(only one output)

- Normal Input
V1 pin 2 -> 68K resistor -> Tip
Tip -> 1M resistor -> Switch
Switch -> Sleeve
(no #2 input)

- Bright Input
V1 pin 7 -> 68K resistor -> Tip
Tip -> 1M resistor -> Switch
Switch -> Sleeve
(no #2 input)

1) Output section

With the speaker connected: 1.7 ohm between speaker terminals.
With the speaker unplugged: 7.2 ohm between speaker terminals.
As for the resistance OT frame to chassis, I got a little confused - did you mean the actual frame around the OT? That gave me an infinite resistance reading to ground (it is covered in some kind of transparent substance), so I measured this from the leads.
OT black to ground: 1.2 ohm.
OT green to ground: 1.7 ohm.

2) Input section (always referring to the #1 inputs, as I do not have #2 inputs on this amp)

With no cable plugged in:
- Pin 2: 67K to ground
- Pin 7: 77K to ground

With an open ended cable plugged in:
- Pin 2: 1348K to ground
- Pin 7: 1246K to ground

Cable tip to ground: 1286K.

Cable tip to pin 2: 67K.
Cable tip to pin 7: 77K.

The guitar sounds distorted with the volume set to 12. V2 pin 2 gives me 469K to ground.

Does that seem somewhat right or very very off? (as my numbers are not really matching with what you specified...)

[loudthud]

Note that I was editing my post at the time you posted your reply.

On some old versions of the Fender 5E3 the black wire is connected to the frame of the output transformer which is where the ground connection is made by the screws holding down the transformer. Your transformer has a black wire that should be grounded at the speaker jack.

Your resistance readings look good. Normally you can expect a variation of +/- 10% or even higher depending on the accuracy of your meter and the resistors used.

The distorted sound indicates that the input jacks are connected correctly and the guitar signal is being amplified by V1 and probably the first half of V2. Bruce said in a post a short while ago that there is a common build error around the second half of V2. I'll look for that. The 469K reading is in the acceptable range.

I assume that turning down the volume controls quiets the guitar signal. Is that correct?

[FreddieRay]

Turning the volume all the way down does indeed quiet down the amp to silence. Both volume controls equally affect the amp volume, whichever channel I am plugged in to - I could for example plug the guitar in to the normal channel, and get the same volume from one knob on 5 as from the other one on 5. Maybe this is just because everything is a little low on volume and I can't really tell the difference; or is this a problem?

I rechecked for possible build errors around the second half of V2. Pin 6, 7 and 8 are connected to the correct turrets on the board and I get continuity beeps from my meter sticking one probe in the socket holes and touching the leads of the corresponding components with the other. While I was at it, I rechecked all the resistance values on the board, and they were all in the acceptable range. I cannot test the capacitors, but having replaced them all would indicate to me that they are not the problem.

I should mention that the terminals on the preamp tube sockets are really quite loose (I bent them on assembly, maybe a little bit too far?). Could it be that one of the tube pins is not making contact when the tube is plugged in?

[pdf64]

The heater voltages seem lower than expected, below the minimum of 5.7V; could you check that?
Pin 7 of the output tubes isn't showing heater voltage. Probably just a mismeasurement (the tubes must be conducting as proved by the cathode voltage) but it's worth checking.
As you are measuring Vac, what Vac is on the plates as your hit a chord, starting at V1.
Don't measure the output tube plates though, yet, as flyback voltage spikes may damage your meter.
Pete.

[Jazz P Bass]

.
Don't measure the output tube plates though, yet, as flyback voltage spikes may damage your meter.
Pete.

Good call.
Been there.
Done that!

[FreddieRay]

The voltages on V3 & V4 pin 7 were indeed mismeasured; I read 2,8 VAC now - the same voltage I get on all the heater terminals after rechecking. Is that really too low? My heater wires are wired as follows: the two greens from the PT each to one contact on the lamp socket, then from there twisted pairs running to V4 pin 2 & 7 then on to V3 pin 2 & 7 etc.

Now this is very strange and confusing. If I am correct, the plates on V1 and V2 are pins 1 and 6, right? I started measuring at V1, which gave me a steady 279 VAC on pin 1 and 259 VAC on pin 6. It didn't matter if I played the guitar during measurement or not. Touching the pins gave me a loud thud through the speaker, and a great increase in blue light in V3. Is this wrong?

[big_teee]

With that low of Heater voltage, what is you AC Voltage in your country and what power supply are you running?
Also is it possible you could show us some Gut Shot Pictures.
Sometimes a Picture is Like they say a Thousand words.
Thanks,
B_T

[FreddieRay]

AC voltage in my country is 230V. I was unable to find any data regarding my PT.. I checked the website were I bought it, but the transformers that came with my kit are just stupidly listed as 'Custom Made', without any technical data supplied.

Could it be that I miswired the pilot light, losing some voltage to ground there?

Anyway, here are some pictures of the insides, focusing on the power/output section. I know the soldering is really sloppy here and there, but hey, still learning I'm leaving on holiday tomorrow, returning July 25. Thanks to everyone for the helping me so far!

[loudthud]

The fact that you get a loud noise when you touch the meter probe to pin 1 or 6 of V1 would indicate that there is no problem with V2, V3 and V4, the output transformer or speaker connections. The problem has to be between the input jacks and V1. But, the resistance checks from the input jacks to V1 looked good if I understand your explanation of how you hooked them up. V1 could be bad but it's voltages looked good. Does V1 get hot? Re-check the connections to pins 4, 5 and 9.

Blue light from V3 is not good. That tube may have been damaged. Unless you have a spare, leave it in until the problem is found. It could only cause the volume to drop by half, not as much as you report.

Post some pictures of V1, V2 and the input jacks.

[FreddieRay]

V1 does get warm, but not really hot; I can comfortably touch it - as is the case with V2. The larger tubes do get really hot (just to give you a reference as to what I call really hot; assuming that they are operating correctly). I visually and electrically (continuity) rechecked the heater wiring on all the tubes. It's all correct, except from the fact that each wire still gives me only 2,8 V.

I took some pictures of the input section and the tubes, showing the blue light in both power tubes (this was the intensity right after I switched off the standby, it decreased a little after that, while not playing), and the rather faint lights in V1 and V2 (is this normal?).

[Intergalactic Tourister]

I'm not familiar with every input jack but it would appear to be wired incorrectly. Its difficult to see the angle in the picture.

It appears on the input jack the black jumper wire connects from ground (or sleeve) directly to positive (tip).

Remove the black jumper wire were it connects with the resistor at the same junction.
Then disconnect the resistor (from the same junction above) and put it to the ground (sleeve) junction.

From what I can see that seems to be the problem.

[FreddieRay]

Hello Intergalactic Tourister,

Hmm I don't see how you'd get that info from the picture.. I think it's quite clear, and as mentioned earlier in this thread, input jacks are wired as follows:

- Normal Input
V1 pin 2 -> 68K resistor -> Tip
Tip -> 1M resistor -> Switch
Switch -> Sleeve
(no #2 input)

- Bright Input
V1 pin 7 -> 68K resistor -> Tip
Tip -> 1M resistor -> Switch
Switch -> Sleeve
(no #2 input)

Connecting the resistor over Tip/Sleeve instead of Tip/Switch wouldn't make a difference in my opinion, as Sleeve and Switch are jumpered together and thus both at ground potential. Or am I very very wrong here?

[big_teee]

Try wiring like this.
http://site.triodestore.com/5E3Delux...-18017240V.pdf
http://mirror.stones-amp-inn.de/fend..._5e3_schem.pdf
By not wiring both jacks and both 68k resistors.
You are losing out on some of the signal.
I recommend You wire both Jacks and both 68k resistors like the layout.
Then if it doesn't work go from there.
Terry