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I got my sIII running today and I like the way it sounds. I still have a little idle hum to try to tune out but one other thing is bothering me more.

After playing for a while, I heard a rushing sound start building up in the amp and it was not adjustable with the volume pot. I switched it to standby and back to On and the sound went away for about 15 or 20 minutes. Next, I plugged into the normal channel and the same thing happened.

Where should I start looking for this culprit?

Something that is common to both channels: Power Supply, Phase Invertor or Power Tubes. For it to happen after 20 min, is a long time. I would think most problems would surface much earlier. So, it may have something to do with heat. Maybe one of the tubes is defective when it gets hot. Try a different tube in the PI first.

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

I have had this same issue in one of my early amps, it was a defective 12AX7.
Nigel

Could be a bad 12AX7, I used some old Mesa Chinese tubes for start up. I'll check it out and put in some good RCA's.

Sounds like it could be heat related as well & maybe a cold joint somewhere. See if you can isolate the tube where it happens, and start with those components first. Reheat the solder joints.

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

Great call, Stephen. I resoldered the joints on the power tubes and played it about an hour with no problems. I think that fixed it.

I'm picking up a radio station on the TMB channel when the volume is turned down to zero, so I'm gonna install a cap to see if that filters it out. Regardless, I'll get that sorted out today, I believe.

Here's a problem that has me a little stumped. I have some 5751 tubes and I wanted to try on in V1. The tubes test great and work great in my other amps but it buzzes like an arc welder in the Trinity. What's up with that?

I had to mix and match a bunch of tubes to find a quiet combination and I have one, I just wanted to try the lower gain tube in V1 to see what kind of difference it made.

I cant explain the 5751. It should be fine.

Try this - run a ground from the output jack to the main star ground and see if some of the other problems go away or are reduced.

Is it in a cabinet that is shielded with aluminum foil by any chance?

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

No aluminum foil in the cab, Stephen. I'll try grounding the output jack tomorrow. Thanks.

See if you can locate some with adhesive on the back. Used in HVAC installations. Home Depot?

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

Ok, Stephen. Today I did the following.

1. Resoldered every joint on every socket.
2. Retensioned a couple of pins on V1.
3. Sorted through dozens of tubes to get my absolute quietest and best matched set. I now have 3 RCA 12AX7A's and 2 RCA 6BQ5s that are the best of the bunch.
4. I tried 4 different 5751s and all had a distinct hum like an arc welder. I think it's 60hz. I gave up on them.
5. Soldered a ground wire onto the output jack.
6. Retracted the 16 and 4 ohm OT leads, twisted them together and rolled them up outside the chassis.
7. Double checked all wiring relative to the TMB channel.

Here's where I am. The radio station is almost gone. I taped some foil over the opening and it disappeared. I'll get a piece of aluminum sheet metal to make me a cover. No problem.

The normal channel is very quiet. I can dime the volume knob with no instrument connected and get a slight hiss. Very normal compared to my Fenders.

The TMB channel is another story. It no longer squeals but if I turn the MV to 10 and I start turning up the volume, I get noise that increases from about 5 on up. At 7-10, it's considerable hiss. Is this normal? I realize there's a lot of gain in that channel.

Also, if I cut the power switch off without an instrument plugged in, I get a loud pop. Is this normal? It doesn't seem to do it with an instrument plugged in. I also put a cap across the standby switch, so it no longer pops when I switch it in and out.

I've got a couple of minor buzzes in the chassis and cab to sort out but that's easy. Thanks for your help.

Sometimes a rouge switch will arc slightly as you switch it on and off, I have an amp that pops that I just changed the switch on and fixed it.
Nigel

Good news that the TMB channel no longer squeals and the radio station.

I you turn the MV (= max. gain) to 10 and turn up the volume you are going to get hiss from about midway or so on up due to the carbon comp resistors. Not sure how much you have, but it will be noticeable. The only way to eliminate this would be to replace some of the low voltage resistors with carbon film.

I posted a checklist on tracking down buzzes / rattles in a combo amp.

I have intemittent pops on power switching. If it is bothersome to you, put the same value cap across the switch.

What did you use on the Standby switch? Some Fenders have a 600v capicator on the standby switch to ground. Its to get rid of the pop when the standby is turned on. I have seen .1uf caps there.

.01uF 600V disc across the switch contacts should get rid of that pop. That would bleed any voltage build up. Just be sure the volatge rating is high enough.

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

I put a 400v .047 "death cap" that I took off a Fender across the standby. That should hold up, shouldn't it?

I figured that the hiss was just part of the deal. I just didn't know what the standard was. There's a lot of gain in that channel.

I'm still baffled as to why the 5751s don't work in V1. They sound great in my Fenders but when I crank it up high, instead of the hiss, I get a really annoying sound that I best describe as an arc welder sound. I guess it's 60 hz.

The pop is only present when an instrument isn't plugged in. If it's normal, I'm not concerned because I'll usually have an instrument plugged in.

One of the "buzzes" I have is the end plates of the chassis buzzing against the chassis. I guess I'll use some latex caulk on it. RTV is corrosive and would screw up the chassis.

Where is the checklist for tracking down buzzes and rattles?

viewtopic.php?t=12&highlight=rattle and in the Amp Builders Guide that came with the kit.

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