trinityamps.com

I have finished my build of the SIII--I finally got some free time.

The voltages in the pre-amp and power tubes look good, but the rectifier is not right.

In my original, no-tubes test, I got appropriate voltages, everything A-Ok within
10% of manual specs.

When I first began the "with-tube" test, I made a mistake.
My damned EZ81 rectifier tube box had an EL 84 power tube in it (my mistake at some point),
so I briefly had the amp on with an EL84 in the rectifier socket.
(Silly, Murphy's-law mistake; the EL84 & EZ81 and tubes are the same shape.)
I noticed voltages were crazy-low, and replaced the tube.

I thus corrected the rectifier tube and took my voltage readings.

The B+, EL 84, and 12AX7 readings are all within 10% of manual spec., most well-within 5%.
Fine and dandy, I thought.

But: Across pins 1 & 7 of the rectifier, in the "all tubes in" test, the meter doesn't say much of anything
(literally nothing or flickering negative readings, just junk);
in the original, no-tubes test, I got 630v at that juncture.

I got 370v at pin 3-ground on the rectifier in the tubes in test

Did I cook something (all or part of the power xformer?!) by installing that EL84 in the rectifier slot?
Nothing smelled hot or amiss. The EL84 was in there for less than 3 minutes.
That same EL84 gives good voltage readings in its normal, power slot, meanwhile

In any case, I get no sound with a speaker and guitar in place (near-dead silence), and these strange (or nada) rectifier readings.
The fuse is intact; nothing ever got very hot.
When the EL84 was in the rectifier slot it glowed normally and wasn't esp. hot.

How could all the tube readings be fine and the rectifier be so odd?
---
The other issue I had so far is that I couldn't tell up from down on the "boost switch"
How critical is the orientation and wiring of that item?

Any advice?
--Johann

Yeh. I think the Power xformer is kaput.

I did the powerless-resistance readings in the power supply end as in the troubleshooting guide
[here: http://www.trinityamps.com/ForumGallery ... pdebug.pdf ]
and I get nothing as resistance from the primary power Xformer winding to the chassis,
and I get about 75ohms for heater-to-chassis resistance (< 100ohms = failure, manual says).

The mystery at this point is how I got reasonable numbers out of all of the
pre-amp and power tube pins when the amp was under the full-power, full load test!
Again, most of them were within 5% of spec--
nothing was odd in that test but the rectifier--maybe I made the rectifier/power Xformer fail while testing
the rectifier? Are there any notoriously boneheaded things one can do to a rectifier while testing it (i.e., with a meter)?
Maybe the power Xformer was gradually failing?
------
Next question: what else could I have cooked?
I assume the power Xformer is cooked--anything else likely?

My education continues,
Johann

Pins 1 and 7 will have AC on them so set your meter accordingly. Check for B+.

Aha. Yes, AC. Thanks for the reminder.
So, let me repeat the tests from the beginning.
All the the initial, tubeless AC tests, all of them, check out within spec.,
including pins 1 & 7 on the rectifier.

However, now the odd symptom is that,
tubeless, I have no B+ VDC--
I just get about 4.0 VDC, which some residual charge
in the cap.

What could have happened to my B+ voltage?
I'll wait for advice (or research) before re-installing the EZ81 rectifier tube.

To get any DC voltage to have to have a rectifier. Pull the rectifier and measure the AC voltages if they are good then your rectifier must be gone.

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

Gad, sorry, you guys will have to put up with my saying some
greenhorn stuff here, I'm afraid.
I know: I have to put the rectifier in to get B+.

Again, the base-line AC voltages with no-tubes test
are all in spec.

I'll report back later.

Ok, after re-starting the test, and realizing I needed to measure
AC (not DC) from pins 1 and 7 of the rectifier,
all of my voltage numbers in the rectifier, pre, and power stages check out
within 5% of the manual spec.

However (unrelatedly?):

1) I got no sound, no white noise, nothin', with or without a guitar.
2) I am not sure I wired the boost switch correctly.

I attach a pic of my wiring of the boost switch; I tried to follow the pattern
on the architectural drawing of the amp layout.

Suggestions for what to check for no sound?
Again, all of the major electrical/ voltage readings are fine throughout all of the tubes.

--Johann

The switch looks fine.
So if the all the voltages check out, and you have the Output transformer and jacks wired correctly, then the most likely culprit is in the coax wires from the input jacks.
Plug in a cable and check continuity from the tip of the plug to the 68K grid resistor. Make sure it is not accidentally grounded.

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

I get continuity from the "tip" of the input jacks, each,
with a cable plugged to the corresponding 68k resistors.
Other ground errors that I could check?
(That is, non-continuity would show "zero" on the meter, right?)

I include photos of the Cliff jacks, and of the output jack
wiring. I get continuity signals from the 1,2,3 pins to the center
tap of the impedance pot (I read that post by a guy who said his
pot was set to 4,5,6 but he wired it as 1,2,3--that's not my problem).

There was a slight ground for confusion with the Cliff jacks in a difference between
the color architectural drawing and the B&W manual.

1) I wired both sets of Cliff jacks as "normal," as the color architectural
drawing showed both sets for the sIII wired the same way. (i.e.,
I ignored the TMB scheme (as I am building an sIII) in the manual--should I have?)

2) I did note that the "higher detail" B&W manual image of the Cliff jack wiring showed
a different ground wire scheme than the color drawing.
The color, architectural drawing shows a ground wire apparently
connecting to the top left lug of the high Cliff jack.
The black and white manual image shows the ground wire
skipping the top left lug of the high Cliff jack. (see arrows in images)
I followed the B&W manual for the ground wire path in the Cliff jacks.
-----
Bottom line questions:

1) if all the cliff jacks are "pointing in" the same direction (i.e., their wired sides are facing the right-hand side of the amp),
they can be wired the same in an sIII build? (surely yes, right?)
2) should the Cliff ground wire follow the path shown in the B&W manual drawing?
3) do you see anything obviously wrong in the photos?

cheers,
Johann

The input jacks look OK. I do run the ground wire through all the terminals but you have done it correctly. The OT looks like it's wired in correctly too.
Take a probe, like an unplugged meter lead, and touch the grids of the tubes and see of you get a pop or noise out the speaker. Turn the vol and gain up.
You are going to have to trace the circuit through . I would start with getting the Normal channel to work. See if you can check the phase inverter wiring .

Also, check t hat you have all the jumpers on the board - the jumpers between turrets I am referring to.

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

Some reporting on current re-checkings--
problem being, again: in spite of all my AC and DC voltages being in spec., I got no sound:

--I have tried to check continuity on all of the jumpers--on underside of the board,
to the pots, and to the tubes. I can't find anything wrong.

--I have tried to check all ground points--and they seem fine, too (I still think I must have a short, cold solder, or ground problem somewhere--just haven't found it)

--Thus I have not had any "eureka, that was mis-wired" moments

--The phase inverter wiring seems fine

--The only news to report: a probe check on the grids of the pre-amp tubes, where the input-coax cables come in
gets me modest buzzing in the speaker. It doesn't begin with a "pop" either--it is quiet, but distinct--about as loud as ground noise in a landline handset, but at least it isn't dead silence. A continuous, polite buzz: at about the same level from both the TMB and Normal channels, high or low. The amount of buzz about the same .

In my reading on similar circumstances around amp forums, I note that "voltages all OK" and "no sound"
is an ominous combo for the OPT.

Can someone please walk me through a test to see if somehow I cooked part of the OPT at some point?
I never ran it with tubes with no speaker. Something other than that would've had to hurt the OPT


Any new recommendations?

Quick glance the yellow wire going too the 100r screen resistor is it hooked up to the same turret as the orange wire that goes to the left side of the 8k2 power resistor (hard to see if the yellow makes a quick turn to the left under the board)

working from this picture

Yeh, the yellow wire going to the 100K 2W screen resistor is it hooked up to the same turret as the orange wire that goes to the left side of the 8k2 power resistor. That's as in the plan.

I am going to next try to follow the signal path in this amp
when I get a 'scope in hand. I can't find anything wrong just by re-checking
wire paths against architectural drawings, and I have nearly exhausted multi-meter tests.
I'll report back when I do a scope test. Please feel free to throw suggestions at me, though.

cheers,
Johann

If you're getting some noise out of the speaker, then the OT is good. There must be another issue. Is there anyway you can bypass the input jacks and go direct to the input grid resistors.
Is it possible the coax cables from the jacks are shorting to ground?

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

Good idea. I'll try taking the coax out of the circuit and using a
"generic" input for testing purposes.

Do you have a signal generator and cable?

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

I don't have an electronic signal generator. (Yet--I may be able to get one at Thanksgiving).

I am getting a USB-type oscilloscope soon, though.
Likely prior to any tests with that, I'll take the coax out of the circuit
and see if there is a short in the coax wirings somewhere.
I'll get back to this amp this weekend.
Thanks for all of the good suggestions so far--

I temporarily took the coax out of the circuit and wired a standard 1/4" jack into one of the normal inputs.
I'm still not hearing anything out of the speaker. I couldn't even get modest buzzing out of the speaker this time.
If I probe the 68k resistor points, I get no sound in this test.
Shouldn't I get something by probing those points?

Ok might be a problem at the input side. But try working backwords ( put 1ll controls at high noon) if i rember corectly taking a voltage mesaurment at 2 and 7 of v3 should produce a pop as well as pin 2 of V1> lets see if that gets anything. and Could you post a high res picture of the complete amp