trinityamps.com

I was playing it this afternoon when the volume petered out just like when you shut the amp off while you're playing. The only difference being that the jewel light on the front was still on. So the amp is on but I have nothing coming out of the speaker.

Honestly it could be something as dumb as a bad power tube. I'm off to my local instrument emporium to get a new set.

Any suggestions where to start troubleshooting? I don't look at this problem as a bad thing as fixing it will help my understanding of amps.

Thanks in advance.

Follow the start-up procedure again and that might lead you to some answers. If nothing is burning, re-measure voltages.

New tubes are an option. Keep us posted.

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

Ok, started from the power up stage.

I started with the rectifier tube out and all the voltages tested within range including the recto heater (orange) wires.

Put the recto tube back in and all the voltages checked out across all the tubes but....... the heater voltages for the recto didn't register. Actually they did but the reading would start between 10-14 VAC and then immediately count down to zero.

I immediately powered down and pulled the recto tube to remeasure When I powered up and remeasured the voltage did the same as when the recto tube was in. It would start somewhere between 10-14 VAC and quickly counted down to zero.

Any thoughts or do I have a screwed up power transformer? The plate and heater voltages on there rest of the tubes all read within spec.


*******Update*********

So I let things cool down then yanked the recto tube and started over. With the tube out I registered 5.5 VAC on pin2 and .05VAC and 0VAC depending on when I measured. When I put the tube back in pin2 starts doing the strange stuff I mentioned above. Pin8 goes between 0.5 and 0 VAC intermittently.

Is it normal for the voltage on Pin2 to go down once the tube is inserted?

No, not normal but sound like the recto tube is bad or the socket has. Since it did work, suspect the tube.

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

Threw in a new recto tube but same thing happened. I'm cursed.

I think it's strange that while the recto tube is warming up I get 5.5 VAC on pin2 but as soon as it's warmed up in starts to do the fluctuating thing again. I keep wondering if this isn't just an example of sag.

What should I try next?

Remove all the tubes, check voltages.

Install only the recto, check voltages; if OK

Install the pre amptubes, check voltages; finally if OK

Install the power tubes.

I'm thinking there may be a bad tube that is actually lowering the entire amp B+ . AKA shorted tube syndrome!!

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

I did the first two. That's when I ran into the weird filament voltage on the recto. I installed the rest of the tubes and the voltages are fine. I even changed out all the tubes for a new set and the amp still doesn't work.

Should I start measuring individual component values and checking continuity?

So with the recto in and no other tubes, it's all fine, but when you put in the 12AX7s, the problem surfaces? If you put only power tubes in ( connect OT to load) and no AX7, is it still fine.

If so, I'd try one preamp tube at a time & see when it happens.

Also, measure the B+ and AX7 heater voltages as well. I'm wondering if the whole PT is being sucked down by one bad tube???

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

With all tubes out I get 5.5VAC to pin 2 of the recto and 0VAC to pin 8. When I put the recto in (following the startup instructions) the voltage remains 5.5VAC on pin 2 and 0VAC on pin 8 until the tube heats up. Then the voltage starts to fluctuate on pin 2. I'm not sure if this is normal or not.

When installing the rest of the tubes I get correct voltage across the heaters and plates of the EL84 and AX7 tubes.

Other than the weird voltage fluctuation on pin 2 of the recto I'm not seeing anything else strange with any of the voltages. I'll post a voltage chart later today.

Once the recto heats up, the heater voltage should stay pretty constant unless there is excessive current draw or a fulty tube. As shouldthe rectified output voltage. Specially if there are no other tubes installed.

Puzzling.

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

Somehow I think that we're not getting the whole picture here. As there should be an explanation to this problem.
need pics and more info.
Thanks

I'll take some tomorrow. Keep in mind the amp was working fine prior to going out. This process actually excites me as it will help me increase my knowledge.

Thanks for the help guys.

So I've been fiddling since my last post. Mostly just trying to learn how to troubleshoot these amps better. As I was fiddling I found that my preamp tubes were cold to the touch even when the amp had warmed up. This led me to start looking closer at the heater wiring. I'd measured the voltage before and it came out ok but I started to probe in different places on the pins and found that if I placed the probe in certain areas I wouldn't get voltage. I quickly resoldered all of the preamp tubes heaters and the amp now works. Yeeeeehaw! I'd thought I'd done a good job wiring this sucker but I'm going to go through every solder joint and double check my work.

While I was changing tubes around I noticed that by tapping on the chassis I would get a plinking sound from the speaker. It turns out I had a microphonic preamp tube. I switched out the 1st preamp tube and it mostly cured the problem. However, I found that if I lightly tapped the 1st preamp tube with my chopstick it would always be a bit microphonic. Tubes that were dead silent in the 2nd and 3rd positions and then substituted into postion 1 would still exhibit a bit of microphonics when tapped. Is this typical of tubes in that position or should I check and see if I have something screwed up in wiring of the first tube socket?

Congrats on the troubleshooting. Lesson on soldering! but that's a new one.

The first tube in the 15 is set to very high gain and will amplify even the quietest tap. You havent screwed up anything. But when it starts to squeal, change it!

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