trinityamps.com

Well, I got everything finished up, installed, double-checked my circuit, 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.

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sounds like a ground connection is missing, check the speaker jack, the pre amp grounds etc. what i do is take a test lead and connect one end to the chassis and go around and touch all the places that should be grounded.

This is normally where we start from with any new amp build - http://paulamps.com/info.html#FirstPowerUp

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Great tones come in small glass jars!

thanks guys
hopefully I'll get some time tomorrow to go back to delve into it further.
cheers for pointers of where to start.

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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?

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Does anyone have any thought on the above voltages? Are the weirdly high or out of whack?

Should I reinstall the preamp and power tubes and measure again? (i.e. is it safe to do this?) I'm wondering what the likely causes of this "no-signal what-so-ever" could be assuming I followed the layout correctly which as far as I can tell I did. I was expecting to be trouble shooting squeals and hums.

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Are you measuring at the tube pins, but without the tubes installed and working? If so, you will get some silly high voltage readings. But at least that shows there aren't any shorts along the way. Now you need to plug the tubes in and carefully measure again.

_________________
Great tones come in small glass jars!

Lots of troubleshooting stuff in the resource section - from the manual viewforum.php?f=12

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hey guys
thanks for the trouble shooting links coco; so I've remeasured the voltages with the all the tubes in and got the following (numbers in brackets are coco's 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?

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Make sure you're measuring for AC (not DC) on the heater pins. Lots of 12ax7 types don't glow as bright when working properly - but, if you're not getting ~6.3vac on the heaters you'll get no sound.

Voltages look close enough. If the heaters check out double and triple check the input jack wiring. Then double and triple check the output jack wiring.

Do you hear hear anything when you touch your meter probe to pin 7 of the EL84's?

Edit: Fixed. Doh!

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Deric®

That's 6.3VAC. touch pin 2 , 7 of V1 with a small screwdriver & see if you get a pop. Make sure the OT is connected properly.

The input jacks can be confusing too so this bypasses them.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Also, when giving the pin voltages it helps if you post the supply (mains or wall outlet) voltage.

If the supply voltage is above or below the design nominal the rest of the amp voltages follow along

Ok,
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.

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 are correct.

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You must have 6.3 VAC across the heaters (from pin 4+5 to 9) on all the tubes. Check that heater wiring first before you pll anything apart.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hi Coco
I rechecked again and still only 3.2 across the heater wiring and even at the terminal strip where the wiring connects to the green 3.15VAC wires from the power transformer.( - which somehow makes sense)

I guess together they add up to 6.3 at the tubes - correct? -- so it seems weird that they don't unless I've done something wrong. By my inspection everything is on the correct pins though and seems properly soldered.

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Heater wiring to these tubes has three wires - Two green on green - yellow.
Grens hould go to terminal strip (be sure one is not attached to a grounded lug on the term strip. And the green-yellow goes to the power ground terminal lugs.

Then there should be 3.2 from each green wire to ground and 6.3 across the two green ones.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hi Coco I'm sorry to be thick but I'm not sure I follow.

I see the two greens to the terminal strip (3.2VAC - check) and the green/yellow to the power ground lug (check). Coming home tonight I thought I figured it out; that I must have made a mistake and that the 2 wires should join at the pins but they don't according drawing. One goes to pin 4 and the other to pin 5 on the el84s (or pins 4 and 5 and the other to pin 9 in the case of the 12 ax7s). So how do the two green wires combine to get the 6.3 V I need on the heaters Or a better question, what would prevent them from combining to get that voltage? Assuming everything is soldered where it should be?

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Check that the two greens are connected to a treminal lug that is not conneted to ground. You should have 3.2 VAC from one green wire to ground and 3.2 from the other green wire to ground so the total across the two greens is 6.3 or so.

If not then pull the green yellow off ground and measure between it and each of the other green and see if you get 6.3 VAC across some combination.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

did this amp ever get fixed?

Hi all,
Actually, I've had little chance to work on it all fall until this week.
Anyway, I found a step by step troubleshooting plan over at 18watt.com that I've been going through and as far as I can tell everything looks kosher until I go to turn it on and there is no sound.

In anycase, 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, it looks like something may be up with my preamp stage. Although I should point out that I'm aware the sIII schematic has a gain pot on the TMB channel that is missing form some other 18 watt schematics and this may be why...

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?[/url]

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