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I was playing with a band & the trinity 18watt sIII starts having the volume go up & down. Next thing the power & pre amp tubes go dark. A spare set of power tubes didn't remedy it and the original tubes test good.

Any thoughts before I start taking voltage readings?

Can you see a lit filament on the recto tube?
STEW

Yes, the filament on the recto is bright orange.

Check filament voltages on power & preamp tubes. Sounds like a break there at the first tube.

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

here's the recto

p1 307
p3 117
p4 6.6
p5 9.26
p7 307

I see p4 & 5 look off should I try a different recto tube?

There's no reading on P3 on the power tubes. the other pins are normal.

hmmmmm any ideas?

Pin 4 & 5 of recto should be filament voltage. 6.3 VAC. There should also be 6.3 VAC on all the filaments of the rest of the tubes.

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

So the heaters are all measuring good. Could the recto tube be dead? I'll grab another after work and give it a try.

Thanks

A quick check of ypur B+ will answer that question.
Stew

the plot thickens....

Just tested the power tubes and the rectifier tube with a tube tester. They test good & didn't have any shorts.
now for the funny voltages (all tubes in, both switches flipped on)
recto p1 313
p3 400
p4 4.9
p5 9
p7 314

Filter cap B+ 406

Power tube closest to recto
p2 400
p3 nothing??
P4&5 measure 6.9 across the heaters (Gulp)
P7 408
P9 408

A new rectifier tube has no change on the readings.

Could the 200uf cap failed? I hope it's not the transformer... I only have about 100 hours on the amp.

Any tips on what to check next?

How about the filter caps? is 400v too high?

Pull out the rectifier and measure all the AC voltages. Pull out the other tubes and measure the heater vltages.

If all is well, repeat the start-up procedure in the manual.

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

Thanks for the guidance.

OK - I took some time away from this to clear my head. I'm ready to tackle this beast & get it back to fighting weight.

I got my manual out & took some measurements.

Without any tubes, all the ac looks OK.
rectifier socket pins 1 & 7 measure just over 304. Pin 3 shouldn't matter at this point as stand by is off. Pin 4 is 5v and p5 is 9.4v

With only a rectifier tube in, stand by is still off pins 1 & 7 measure just over 304. Pin 3 measures 110, Pin 4 is jumping around 9v and p5 is jumping around 10v

flip stand by again no change in pins 1 & 7. Pin 4 is 4.4v and p5 is 8.3v. Pin 3 is now measuring the same thing as the B+ at the filter cap, 393.

Is this all normal?

On the rectifier, between pin 4 & 5 there ahould be 6.3V AC. Is there?

You are saying Pin 4 is 5v and p5 is 9.4v.

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

I was not measuring across 4&5....

With out the tube in it measures 6.8v
tube, it's 6.6v

is this troubling?

& get this, after putting the tube in, the power tubes light up. So I plug in the SG and it works.

I'm going play through it it for a few hours.

6.6V or 6.8V is fine. It just needs to be within +-10% of 6.3V.

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Great tones come in small glass jars!

Thanks zaphod.

I logged 3 hours on the beast running 1/2 way open. So far I'm cautiously optimistic.

It bugs me that I never discovered the issue.