SOLVED::No sound/High Voltages on new JTM45 build

[Tsquared]

Hello,

I'm trying to finish a JTM45 Blues Breaker build using the Ceriatone layout and Classic Components trannies.  So far, I get no output, except for very faint noise when probing the PI grid and cathode pins to get voltage readings.(scratching or hissy sound.)
All voltages are high, but especially the PI voltages.

Filament voltages are all on the money. Triple checking the resistors and caps for value didn't show any problems. Following are the pin voltage readings:
V1
pin 1: 237 vdc
pin 2:--
pin 3: 1.8 vdc
pin 6: 232 vdc
pin 7: ---
pin 8: 1.8 vdc

V2
pin 1: 193vdc
pin 2:---
pin3: 1.26 vdc
pin 6: 344 vdc
pin 7: ---
pin 8: 194 vdc

V3
pin 1:400 vdc
pin 2: 378 vdc
pin 6: 399 vdc
pin 8: 378 vdc

v4 & V5 Valve Art KT66's (both read within a volt for all values between the pair)
pin 3: 450 vdc
pin 4: 449 vdc
pin 5: -52 vdc
pin 6: 450 vdc

Rectifier: (a NOS GE GZ34)
pin 2: 456 vdc
pin 4: 326 AC
pin 6: 326 ac
pin4: 455 vdc/5.16 AC

Any Help would be greatly appreciated. What am I overlooking? What should I try first?

Tod

[sluckey]

V3
pin 1:400 vdc
pin 2: 378 vdc
pin 6: 399 vdc
pin 8: 378 vdc

V3 voltages are all way off. It's as if the cathodes of V3 do not have a path to ground. Pins 3 and 8 should be connected together. Turn power off and check resistance from pins 3/8 to chassis. You should measure approx 15K. If not, look at the attached pic and verify that all components in the cathode circuit are correct value and wired correctly. Just follow the green highlighted path.

PS... When posting tube voltages include grid voltages too, even if they read zero. They are very important.

[Tsquared]

Steve,

Thanks, you were right on the money.  I'll bet my underboard jumper fell out when I soldered the pot lead to the turret (I jumpered it on top after seeing no continuity) and  the voltages are much closer, Although I still don't get any sound from the inputs yet.
Here are the new voltages for v1-v3:
v1
pin 1 224 vdc
pin 2 0 vdc
pin 3 1.7 vdc
pin 6 219 vdc
pin 7 0
pin 8 1.7 vdc

v2
pin 1 180 vdc
pin 2 0
pin 3 1.2 vdc
pin 6 324 vdc
pin 7 180 vdc
pin 8 181 vdc

v3
pin 1 260 vdc
pin 2 25 vdc
pin 3 41.5 vdc
pin 6 207 vdc
pin 7 15 vdc
pin 8 27 vdc

[sluckey]

I don't see any red flags in your new voltage readings. Recheck your wiring, especially input jacks and pot wires. It almost has to be a simple wiring error or incorrect component value.

Exactly which Ceriatone layout did you use? I referenced the JTM45 Blues Breaker but it includes a tremolo circuit, so I wasn't for sure it was the right one. Any of Ceriatone's JTM45 layouts would have worked for the PI voltage problem, but we need the exact layout for the no sound problem.

[Tsquared]

Steve,
I used the Ceriatone JTM 45 Blues breaker layout.  I do have the trem circuit as well, which I did on terminal strips. I was kind of thinking if the pots were all the way down, it would be out of the picture, but I guess I'm wrong.

The voltage readings all seem to modulate, even with the pots all off.  Here are the voltages, as far as I can tell (they modulate pretty quickly.)
pin 1: 200-260 pin 2: -.4 to-.7  pin 3: 2-2.1  pin 6: 457  pin 7: 200-268  pin 8: 200-270

Thanks again Steve! You are amazingly generous.

Tod

[sluckey]

The changing voltages on the tremolo tube indicate the oscillator is working. If you had an analog meter or scope you could see the voltages swinging back and forth at the tremolo speed. That's not the problem with your no sound problem.

Here's a 'divide and conquer' test to determine if the problem is in the preamp or power amp. Turn all the knobs to 10 (max CW position). Straighten out a paper clip to use as a probe. Hold the probe between your fingers and touch the end of it to the center lug of the treble pot. Do you get a buzz sound through the speaker? The buzz should be like touching the tip of a guitar cord that has the other end plugged into an amp, but it will not be as loud. If you have a buzz, the PI and power amp are probably good and you need to look for the problem somewhere between the input jacks and the treble control. If no buzz, you have a problem between the treble control and the speaker jack.

[Tsquared]

Steve,

I get no sound at all when I touch the center tab of the treble pot with a paperclip. The fact that I get noise when I probe the PI pins (except for pin 2, which is dead quiet while pin 7 gets a noise means that nothing may be coming in to the grid via pin 2, right?)   I'll look over the schematic to see what the signal flow should be.  I'm very green on troubleshooting... this is my second scratch build, and the first one worked right out of the gate.

I really want to learn the right and logical way to troubleshoot.  So if you're still willing to teach, what next?

Tod

[Shrapnel]

Steve,

I get no sound at all when I touch the center tab of the treble pot with a paperclip. The fact that I get noise when I probe the PI pins (except for pin 2, which is dead quiet while pin 7 gets a noise means that nothing may be coming in to the grid via pin 2, right?)   I'll look over the schematic to see what the signal flow should be.  I'm very green on troubleshooting... this is my second scratch build, and the first one worked right out of the gate.

I really want to learn the right and logical way to troubleshoot.  So if you're still willing to teach, what next?

Tod

v3
pin 1 260 vdc
pin 2 25 vdc
pin 3 41.5 vdc
pin 6 207 vdc
pin 7 15 vdc
pin 8 27 vdc

Okay, Lets look at what we got so far.

On your PI tube, pin 7 gives a noise, but pin 2 doesn't. (grids).
You have a voltage on pin 2, which is normal considering it is elevated from ground via the tail resistor.
You do have voltages on all the pertinent pins (Yes, a duh!) which is good.
I presume pin 6 on v4 & v5 is a tie point, as pin 6 is unused in a kt66/6l6/5881 tube/valve


Have you tried substituting tubes in v3? It's possible to have a bad tube, even if it is new. (sometimes it should be the first place we look too.) Swap it, and do the test on pins 2 and 7  and/or the wiper of the treble pot again. If you got noise on both now, that tube is definitely the problem. (if your tremolo tube is the same or similar, type 12a?7, you already know it is good.)

I'm thinking you may have a bad tube in v3 though.

[sluckey]

I get no sound at all when I touch the center tab of the treble pot with a paperclip. The fact that I get noise when I probe the PI pins (except for pin 2, which is dead quiet while pin 7 gets a noise means that nothing may be coming in to the grid via pin 2, right?)   

That's a possibility. The only thing between the treble pot and pin 2 is a .022µF cap and two wires. Verify it's wired correctly. You can use the paper clip probe to touch pin 2 directly, but be very careful and don't touch pin 1! Safer to use an insulated gator clip lead and clip on to pin 2 with the amp in standby then turn the amp to operate and touch the dangling end of the clip lead.

V3 could be bad, but the number 1 problem with a new build is a wiring error. Number 2 would be an incorrect component value. There are not many components between the PI and the speaker jacks but there is a lot of wiring involved. The Ceriatone layout is very clean and neat in the PI and PA area but that's because they don't show a lot of the wire connections which would clutter the layout drawing. This makes it very easy to overlook a connection or make an error. Double check, triple check your wiring. Check everything, even your speaker jack wiring. Post some high rez. pics so we can look at it too.

You forgot to post a very important voltage for your power tubes. What is the voltage on pin 8 of each power tube? It should be very low, something like 30mV to 50mV. And adjusting the bias pot should cause the mV readings to change. What do you measure?

[Tsquared]

Sluckey,

I've gone over the wiring several times, got readings from the electrolytic caps on board, either with my cap wizard (pulling legs if the cap could not be read in circuit) and confirming resistor values (also pulling legs occasionally to get them out of circuit.)   Nothing!

I've confirmed continuity and low ohmage between jumper points and pots.  Still nothing unusual.  I am hesitant to just start replacing coupling caps, etc yet. I've checked every solder joint, and reflowed several.

 I have new voltage readings to give you since you helped me sort out the dropped jumper.  Maybe with these new voltages, you can help me some more. (See corrected pdf)

Thanks again for all your help, too.

[sluckey]

Voltages look fine, except for that 200 - 290v on pin 9 of V6. That's gotta be a mistake.

I don't suspect your choke or OT (answering your PM to me). I'm still betting on a wiring error. Can you post some high res pics?

[Tsquared]

Sluckey,
I took a bunch of pics, but many were so blurry, they were useless.  I'll post them when I get home from work tonight.

And I'll recheck the voltages in question!!!!

Thanks
Tod

[Tsquared]

Sluckey,

Here goes some pics, Part 1:

[Tsquared]

Part 2:

[Tsquared]

Part 3:

[Tsquared]

Sluckey,

I SCREWED UP THE SPREADSHEET SOMEHOW.  I didn't remeasure the filaments, but they have been right on the money all along.

The modulating 200 to 270 is on pin 8.  Is that high or out of range?

Tod

[Willabe]

Your work looks real good to me, but is that a metal fender washer you stuck/glued down with silicone?

If it is and it comes loose you got Big trouble.     

Mouser and Digi-Key both sell metal hole plugs that snap in.


                                    Brad     

[Tsquared]

Brad,

It is a metal fender washer, but it is epoxied on. I got tired of mig welding stuff on because it always seems to warp things.  The chassis is a cut and rebent and rewelded Stereo Chorus solid state chassis.  If I'd had a big enough brake, I could have done a much better job, but once I started screwing things up, it just snowballed. There's a bit of body putty on top of the chassis, and it looks pretty cool, but this may just be the last build I cobble together from an unrelated chassis.

I got the old non-working 2-12 combo for $50, but I've wasted so much time mickey mousing it together, I'm shooting myself in the foot. Thank God I don't charge myself by the hour!!

Plus I never realised how cheap the lower end Marshall cabs were... Literally paper board.

[Willabe]

It is a metal fender washer, but it is epoxied on.

I should have known by the look of your work that you were good to go.      

Carry on then.      

I got the old non-working 2-12 combo for $50, but I've wasted so much time mickey mousing it together, I'm shooting myself in the foot.

We all can learn and grow by the price of admission. Got to break a few eggs to make an omelet.     

[Tsquared]

Sluckey and anyone else concerned,

I just had a minor breaktrhough... If I feed a sinewave from a signal generator, I get definite sine output to the speaker when I touch either grid of the PI with the signal. I also get a much fainter, but audible sine output if I touch the treble pot side of the 250pf silver mica cap turret... but nothing on the grid side of the cap.  Not positive what that means... is the silver mica bad?
At least I feel like I am getting somewhere, though.  And I probably haven't hosed any iron or anything expensive

Tod

[sluckey]

If I feed a sinewave from a signal generator, I get definite sine output to the speaker when I touch either grid of the PI with the signal.

OK. That's a mo better signal source than my 'finger on a paper clip' quick test. You should be able to connect the sig gen to the center lug of the treble pot and get the exact same results.

I also get a much fainter, but audible sine output if I touch the treble pot side of the 250pf silver mica cap turret... but nothing on the grid side of the cap.

I don't understand this. That 250pf doesn't connect to any grid.

Look between the treble pot and the grid of the PI tube. I'll take a look at your pics in just a minute.

[Tsquared]

oops,

I mean pin 8, so cathode of v2. sorry.

Tod

[Tsquared]

Sluckey,

I do have signal coming through from the center treble pot tab when I connect the signal generator, but it is about half the volume as on the PI.

Tod

[sluckey]

Which sig gen are you using and are you connecting to the amp thru a coupling cap to avoid upsetting bias voltages and to protect your sig gen from any dc voltages in the amp? And do you also have a scope?

[Tsquared]

Sluckey,

It is an older RCA WA-504B/44D audio generator. And I didn't use a coupling cap.... it has a 600 ohm unbalanced out that I just connected from banana plugs to alligator clips on a coax lead.  What value and type of cap should I use?

Hopefully, I didn't do any damage.  It still works.
Tod

[sluckey]

I'd use a .022, .047, or .1 rated for 600v. Does your voltmeter have an AC RMS function? If so, here's a test I'd like you to do. Set your sig gen to about 400Hz. Set your meter to measure AC voltage and connect the leads to the sig gen output. Now adjust the sig gen output level for .5VAC. Now turn the output level down to .1VAC. Does your meter get reliable readings at both settings? If so, we're gonna do some signal tracing.

[Tsquared]

Thanks, Sluckey.

I'll get everything set up as soon as I get home from work tonight.

Tod

[Tsquared]

Sluckey and everybody:

Thanks for all the help.  I fixed it.  AND IT WAS A STUPID WIRING MISTAKE!!!  It was an underboard jumper that ran to the wrong turret underneath. It was a major bitch getting the turret board and pots out to flip it over, but that's what it took.

Thanks again.  As soon as I get the cabinet cleaned up a bit, I'll post some pics.

What a relief!

Tod

[sluckey]

Hoffman's Law is a bitch! 

Glad you got it. How does it sound?

[Tsquared]

Steve,

I'm listening through an old oxford 12 from my pro reverb... face down in a cardboard shipping box and my $90 epiphone LP Junior, so it isn't quite ideal

But everything works, the trem trems and the presence seems to get nice and nasty. It goes from semi clean to dirty pretty quick, if you turn up the guitar and crank it up a smidge.  I've got a pair of Celestions to go in the cab, or I can just plug them into the 2 weber Alnicos in my Pro Reverb if I don't like the Celestions. Still, it's nice to have a couple working amps for when the guys come over. The cab is going to need some more work before I mount the amp in it, though

More to come as soon as I come down off my relief high!!!

Thanks again for all the help.
Tod

[bnwitt]

This is why I stopped using underboard wires on turret boards some time back. On an eyelet board with a backer board (like the old Fenders) it's not a problem but turret boards on stand offs should not have underboard wires unless they come up through a drilled hole next to the turrets and are fished up where you can see them.  I just run them on top of the board now.