let the trouble shooting begin.

Well, I got everything finished up and installed on my 18 watt project. I double-checked my circuit and all my solder joints, etc. all looked in order. I confess, I wasn't that confident about checking the plate voltages with the amp on, so I just installed the tubes - when I didn't see/smell any smoke or other dubious-ness, at the power on, I buttoned up the back and plugged in my guitar and flipped the stand by.

But... No sound -- none what so ever, not even a hum. Any suggestions/tips of where to even start sorting this out? Is there a logical order of things I should check to begin with?

Damn.

Are the filaments at least getting juice? If nothing is glowing, you can backtrack all the way to your power and standby switches, as well as fuses (which I'm assuming you checked).

The first step for me is to make sure that the amp is getting power. You can check for power to the filaments with the amp on standby. After that I typically check the A.C. voltages going to the rectifier. If they look good, (and you're nervous about measuring your plate voltages), then double check the wiring to the standby switch.

You can also check plate voltages right at the tube sockets w/o them installed (other than the rectifier). You just have to know what each corresponding pin is for, and also consider that the voltages will be higher without any tubes.

If you can get through the process of confirming that you're getting power to everything, you can move onto double checking that all of your wiring is correct. Then triple check it.

And remember to discharge the caps each time. It's easy to forget at the debugging stage, especially if you're going back and forth.

Is the speaker hooked up?

Get a copy of the layout and verify that all of the leads on each component go where they are supposed to. Mark off each component on the layout once verified.

Remove the tubes and check your plate voltages.

Are the heaters glowing?

1. Does the light come on?
2. If not, is the fuse installed?
3. As mentioned, are the speakers plugged in?
4. Also as mentioned, are the tubes lighting up?
5. Are the input jacks wired up correctly?
6. Are the voltages looking normal?

It was mentioned above by I will stress it a little more: Pull the tubes before you do any more troubleshooting. The problem could be with the output transformer/speaker jack/speaker connectors. If this is the case you could blow the OT running the amp without a load.

If there is NOTHING then that is probably where the problem is. If you have the right plate voltages on the output tubes and they are lighting up you should have at least a little hiss if the speaker/jack is connected correctly.

1. Does the light come on?
2. If not, is the fuse installed?
3. As mentioned, are the speakers plugged in?
4. Also as mentioned, are the tubes lighting up?
5. Are the input jacks wired up correctly?
6. Are the voltages looking normal?

1. check
2. check
3. check
4. check
5. As far as I can tell, in any case neither set of inputs gets any sound.
6. I will pull the tubes and check it out.

The speaker jack was the first thing i thought about as well but that seems to check out. anyway maybe tomorrow if I get a bit of time I'll delve into it again.. thanks guys, I'll keep you all posted.

just picked up an epi Casino this week as well, so I'm stoked to get it working.

Ok, so I checked the continuity through all the ground points and that checked out.

I then removed the tubes, and measured high voltage AC which gave a reading of 303

Then I put the rectifier back in and got the following voltages:
B+ was 425 VDC

V6
pin1 301
pin3 435
pin6 303

V5
pin3 .6mV
pin7 423
pin9 423

V4
pin3 .5mV
pin7 422
pin9 422

V3
pin1 416
pin2 .5mV
pin3 .3mV
pin6 418
pin7 .3mV
pin8 .3mV

V2
pin1 416
pin3 .2mV
pin6 422
pin8 ?

V1
pin1 418
pin3 ?
pin6 419
pin8 ?

So they seem a bit whacked. I had trouble getting readings on certain pins because my meter would just fluctuate or it would start around 22 and then gradually taper down to a decimal number.

I wonder if I'm even measuring it the right way? I'm measuring DC correct?
the negative probe of my meter on the chassis and the positive probe touching the pins?

Try again with only the preamp tubes and rectifier in. I dont think that will hurt anything.
You should see the voltages on the Pin 1/6 of the preamp tubes drop to normal voltages. Everything else looks kosher but I dont know the 18watt schematic off by heart.

Do you have an oscilloscope? If so, you could do a bit of signal tracing. Start at the output of the preamp stage and work backwards if there's no activity there. An audio generator would also be an asset so you wouldn't have to keep strumming a guitar to generate a signal.

Hey guys
thanks for the tips; Unfortunately I don't have an oscilloscope or an audio generator (I'm the quintessential amateur) Anyway: I've remeasured the voltages with the all the tubes in and got the following (numbers in brackets are the suggested voltages):

V1 - 12AX7
--------------
Pin Volts
1 142 (154)
3 .96 (1.0)
6 144 (160)
8 .95 (1.0)

V2 - 12AX7
--------------
Pin Volts
1 179 (184)
3 1.48 (1.6)
6 248.5 (278)
8 178.5 (184)

V3 (PI) - 12AX7
--------------
Pin Volts
1 204 (184)
2 48 (55)
3 62.5 (80)
6 199.5 (217)
7 46.5 (54)
8 69 (80)

V4 - EL84
-----------
Pin Volts
3 11.3 (11.7)
7 330 (364)
9 320 (354)

V5 - EL84
-----------
Pin Volts
3 11.26 (11.7)
7 332 (366)
9 292 (354)

As you can see they seem a bit low - but I'm not sure the variance that is allowable for these.

Also I noticed that the preamp tubes don't seem to be glowing like the el84s or the rectifier and when I measured the heater pins got really low numbers, like .2 mV. I wonder if this could be part of my problem? Should I be getting a strong reading off these pins?

Anyway, I appreciate your help. I'm actually quite impressed with myself that I haven't blown anything up of electrocuted myself yet. I'm learning lots.

cheers

Ok... you dont NEED a scope (but it helps).
Do you know how to discharge your filter caps? Basic electronics safety? You are already in the guts of it so I hope so but you want to make sure you dont get yourself killed (yes.. it does happen). You built the amp so I am assuming so (although I dont like to assume anything)

Test the speaker/cable in another amp. Does it work? Yes. Ok, rule that out.
Put the power/rectifier tube back in and power it up (with the speaker). Once it is warmed up take the plate voltages again. The values dont matter, but you should hear a click when you touch the probe to the plate. Do the same thing for the control grid.
If you dont hear any pops turn the amp off immediately.

If you hear pops when you measure the control grid voltage then most likely your power amp is fine and the problem is in your preamp.
If you DONT hear any pops the problem is between the plate and the speaker. That would be the OT or speaker output jack. Triple check the OT leads. Shorts, cold solder joints, make sure you have the transformer wired correctly.

If you DO hear the pops you can trace back by the pop method in the preamp. Work your way back until you dont hear the pops. When that happens you have just passed the problem.

Noise injection...good technique in a pinch!

If you're VERY careful and can hold a small metal screwdriver while touching ONLY pin 2 of V1 and V2 [with the volume set at 3 or so, and keeping your other hand in the back pocket of your pants] and you hear hum through the speaker, you'll know you've got a problem with the input jack wiring.

Disclaimer: Don't do this until after you have followed DH82c's advice above...and don't try it while standing in a half-filled bathtub.

Yeah, I'm being extremely careful here.

So I re-checked the mains and got 303VAC on pins 1 and 7 of V6.
but, only 3.25 VAC across the heaters on all the rest of the tubes (shouldn't it be more like 6.5 ?)

Also no "pop" when I touch pins 2 or 7 at V1.

From what I can tell the output jack and OT to the impedance selector are wired ok (orange (16ohm) to pin3, green (8ohm) to pin 2, yellow 9 (4ohm) to pin1, pinA to output jack).

I'll have to pull the input jacks out of the chassis to be 100% but visually from what I can tell they look correct.

bump

Also no "pop" when I touch pins 2 or 7 at V1.

With the amp turned off you should be able to measure the resistance between the tip of the output jack and ground. What do you get when you do that?

Could you post a copy of the schematic?

I agree the heater voltages on the preamp tubes seems nearly non-existent at .2 mV. What do you measure with the tubes pulled? Do you have pins 4 & 5 tied together and you're measuring AC between that tie point and pin 9?

So...any news?

Hey gionnio and others. I found a great step by step troubleshooting post over at 18watt.com. So I'm planning on working through that hopefully this week. I'm currently a grad student and my amp tinkering has been temporarily pre-empted by mid-term paper writing. (luckily the tdpri is still here for my procrastination needs) Anyway, will keep you all posted as to my progress; cheers again for your help and advice thus far.

Here is the step by step for anyone else that's interested.

-With the Tubes NOT in place, turn the POWER switch ON and having STANDBY on OFF.
- Set your multimeter to VAC and measure across pins 4 and 9 (or 5 and 9 as 4and5 are connected together) on V1, V2 and V3.
-Also check voltage between pin4 and pin5 on V4 and V5. They should all read around 6.5V, maybe a bit more with no tubes in place.
-Then check voltage (AC still) between pin4 and pin5 on V6 (rectifier tube) and it should read around 6.3V.
-Check voltage (AC) between pin7 and pin1 on V6 (rectifier) you should get around 600V.

-Insert ONLY your tube rectifier (V6) and turn ON the Power. Let the tube heat-up for a couple of minutes.
-Check the voltage (DC) on the pin 3 of the V6 (red probe on the pin, black probe on the ground lug - it'd be great if you had a probe with a clamp so you could do the measuring with one hand bahind your back for safety). The multimeter should read 300 and some Volts DC. Check that you get the same voltage on the Standby Switch leg.

-If you got the voltage to be the same, flick the Standby switch ON (still no tubes in place other than the EZ81 rectifier as V6).
-Check the Voltage (DC from now on) on the first lug of the double 32uf can capacitor where the lead from the standby switch is soldered to. That should read the same voltage as you got on the pin3 and on the Standby switch.
-Check the voltage on the other lug of the can capacitor (after the 2k resistor) the voltage should be slightly lower than before.
-Check the voltage after the 100R/3W resistor - again slightly lower than before it - and also check the voltage on the pin9 of V5 and V6 - that should be exactly the same as the voltage measured after the 100R/3W resistor.
-Check the voltage at the pin1 and pin6 on V2 - that should be lower than the last measured voltage.
- Check the voltages at pins 1 and 6 on both V3 and V1.
You should get lower voltages as you go further on.

The voltages will be higher than the ones you will get with the tubes in place.
-BLEED THE CAPACITORS AFTER YOU HAVE DONE THIS!
- It can be done by connecting the pin1 of V1 to the chassis with a lead with clamps at the end. Leave it for 2 minutes to discharge the capacitors. REMOVE THE LEAD jumepring pin1 with the chassis.


-If everything is correct so far.
Install V1, V2 and V3 and check the voltages again just as you did before.
Voltages will be lower here.
If everything is OK,
Connect the speaker, install the EL84 tubes, turn the power on, leave it for a couple of minutes for the tubes to heat-up and flick the standby on.
Even with the volume completely down and tone to 12o'clock, you should have some hum at the speaker.

the voltages at each pin of each tube and do a chart just as it's done on the sheet here http://www.18watt.com/storage/Voltage-Chart.htm

If everything fits the values OK, you should have some sound - considering that you've done all the wiring properly and all the components are exactly what they should be and where they should be.

Hi all,
Actually, I've had little chance to work on it all fall until this week.
Anyway, I've worked through the step by step troubleshooting plan above as far as I can tell everything looks kosher until I go to turn it on and there is no sound. (but I didn't expect any as that's been the problem)

In any case, I've measured my voltages again with all tubes in, speaker connected and standby off..

Comparing my results to the chart in my manual they don't look too far off but when I compare them to this chart HERE, (http://www.18watt.com/storage/Voltage-Chart.htm) it looks like something may be up with my preamp stage. Although I should point out that I'm aware the trinity kit schematic has a gain pot on the TMB channel that is missing form some other 18 watt schematics and this may be why...

Here is a link to my schematic http://thepopmodule.com/bin/SIII_boost.jpg

Anyway, here is what I measured with the voltages suggested by my manual in brackets:

V1 12AX7
Pin 1: 150 (155)
Pin 2: --
Pin 3: 0.87 (1.0)
pin 4: H
pin 5: H
pin 6: 145.5 (155)
pin 7: --
pin 8: 0.92 (1.0)
pin 9: H

V2 12AX7
Pin 1: 152.3 (180)
Pin 2: 0
Pin 3: 1.18 (1.5)
pin 4: H
pin 5: H
pin 6: 249 (272)
pin 7: 152.2
pin 8: 152.8 (180)
pin 9: H

V3 12AX7
Pin 1: 200 (220)
Pin 2: 46.5 (52)
Pin 3: 70 (75)
pin 4: H
pin 5: H
pin 6: 202.7 (217)
pin 7: 47.7 (62)
pin 8: 70.2 (75)
pin 9: H

V4 EL84
Pin 1: --
Pin 2: --
Pin 3: 11.1 (12)
pin 4: H
pin 5: H
pin 6: --
pin 7: 327.4 (345)
pin 8: --
pin 9: 316.9 (340)

V5 EL84
Pin 1: --
Pin 2: --
Pin 3: 11.2 (12)
pin 4: H
pin 5: H
pin 6: --
pin 7: 327.8 (345)
pin 8: --
pin 9: 318 (340)

V6 EZ81
Pin 1: 287.5AC (292)
Pin 2: --
Pin 3: 337 (350)
pin 4: H
pin 5: H
pin 6: --
pin 7: 287.5AC (292)
pin 8: --
pin 9: --

I do notice that pin 2 of V2 has the shielded wire from the gain pot and I read 0 on that pin - is this normal?

So back to square one, any suggestions of where to go from here?

With the amp turned off you should be able to measure the resistance between the tip of the output jack and ground. What do you get when you do that?

Oh, and If I'm doing it right- i.e., red probe on the "hot" terminal and the black probe on ground. I get nothing, actually on either terminal of the output jack and ground I get no ohm reading or continuity.

Hi jiteshna,

I think gionnio hit it on the head. If you're reading an open circuit at your output jack there are two problems:

1) Your output transformer is not connected to the jack or is blown open

Check the wiring of that impedance switch. Try measuring the resistance of the output transformer taps directly at transformer wires. You should see some low values in the 2 - 20 ohm range. If you see hundreds or see an open circuit, the transformer is toast. If it's OK, you must look at that switch and determine why it isn't passing the signal to the output jack.



2) Your speaker is not connected to the jack or is blown open

If you disconnect the speaker and put your ohm meter across the speaker terminals, it should read around 3 - 5 ohms. You might hear a little clicking in the cone as you touch the probes to the terminals. If you don't get these responses, and the speaker reads over 20 ohms, (like maybe infinity) the voice coil is open and you will never hear a squeak outta that dude with a million watts on it. Check the continuity of the tip and ring of plug of the speaker wire, too. You should see the same resistance as you do directly across the speaker. If you don't, rewire the speaker and jack so you do.


If you can't figure out the impedance switch, wire the speaker directly to the transformer taps temporarily and I'll bet you'll hear noise - if everything is still operable.

Buena suerte, amigo...


Bob

Ok just to confirm... when I touch the "ground", I've been sticking the probe on the chassis -- correct yeah? and you guys are saying I should have continuity (a closed circuit) between the ground and the "hot" lug of the output jack? with the jack unplugged? or plugged? I've checked and rechecked the impedance switch but will check it again. I apologize again if my questions are maybe obvious to some. But I really appreciate everyone's help.

I'm away for the holidays for a week or so now but when I get back I'll try hooking the OT directly to the jack and see.

cheers
Happy Holidays

Howdy jitensha,

'Hope your Christmas holiday was good. In answer to your question about the output jack:

Measure the speaker at its terminals and at the plug with the speaker disconnected from the amp. You should read 2 - 5 ohms in both places. If you don't, fix the plug or replace the speaker to get the correct reading.

The output jack of the amp will doubtless be a shorting jack, so you'll have to unsolder the "hot" lead from it (the one not connected to the chassis). If you can't tell which one is hot, unsolder both. Measure the resistance across the output jack wires (now floating) to see that they have a 2-5 ohm resistance. If they don't, there is a problem with the impedance selector switch or the output transformer secondary winding. If this is the case, and you don't know what to do with the switch, unsolder the output transformer leads from the switch and measuring the resistance on the OT secondary. If the secondary reads OK (again 2 to maybe 10 ohms depending on the winding tap), connect a couple of the output leads directly to the speaker with jumpers and fire up the amp. You should hear something then.

Lemme know what happens...

Bob

Well, I got everything finished up and installed on my 18 watt project. I double-checked my circuit and all my solder joints, etc. all looked in order. I confess, I wasn't that confident about checking the plate voltages with the amp on, so I just installed the tubes - when I didn't see/smell any smoke or other dubious-ness, at the power on, I buttoned up the back and plugged in my guitar and flipped the stand by.

But... No sound -- none what so ever, not even a hum. Any suggestions/tips of where to even start sorting this out? Is there a logical order of things I should check to begin with?

Damn.

----------------

Hi. My problem is similar to this, but it's a 5 watt Champ clone (with a Tubedepot PCB) and I DO hear hum/static. I have power, lights, lit tubes, and the volume increases as I turn it up. But there is no guitar sound at all. It's as if the amp has nothing plugged into it.

I've double and triple checked my wiring, the input and speaker jacks, and I can't find what's wrong.

What should I check next? Does it sound like an OT issue?

Thanks!

mjtrip001 I'd bet it's not the OT. Just go ahead and start a new thread. If you know how to check voltages WITHOUT killing yourself do that while listening for pops out of the speaker. Start at the rectifier then power tube then preamp tube.
Most times you pass apoint were you get no pops. Thats where your problem (maybe) is.( I say maybe cause it might take awhile to find even when your close.)

Hey guys...if you're going to be messing with electronics in any way, an oscilloscope is an absolute must. I found a Hitachi 30Mhz solid state scope for less than $50 on eBay. It has saved me so much pain and grief.

Thanks for the reply's guys. I was out of the loop for a few days for Christmas. I'll start a new thread with the details/pics/etc..

When I first told TubeDepot about my probs, the tech told me I was using a push-pull OT when a Champ is a Single Ended amp, so that's why I suspected the OT. It's a Hammond 125C.

This is my 2nd attempt at building it. It went OK the first time with an eye-fiber board (it was a kit from Torres engineering), but I suspected a faulty solder joint because I started getting really bad feedback after about a month. I took it apart and now I'm trying to rebuild with the tubedepot PCB. The instructions are so simple its as if someone were holding your hand. That's what's frustrating now. I followed the directions and I'm getting no sound.

Thanks and Happy Holidays. Look for new thread soon..

Mick