trinityamps.com

So I recently finished a TC15 and finally tested it out. It works, essentially, but there are some things.

I checked the voltages on the PI and here's what I got (compared against suggested voltages from Trinity):

Pin1: 224.5 (256)
Pin 2: 20.25 (47)
Pin 3: 50 (69)
Pin 6: 325 (256)
Pin 7: 44 (47)
Pin 8: 52.7 (69)

Just to clarify, my voltages are first, followed by Trinity's in parentheses. So one triode seems to be way off, and the other gets close except for a crazy high plate voltage off pin 6.

I checked connections and resistors. All seems kosher. What could be happening? Could it just be a tube issue?

Also, pin 6 on my ef86 reads 106v instead of the 131v Trinity is suggesting.

Channel 2 is also totally muffled. I can max the volume on channel 2 and the output is anemic. It sounds as if channel 2 working. The tone controls work and the volume works, but the output is almost non existent.

I appreciate any insight into these issues.

If all your resistors are the right values in the right places, and all your connections are good, and you have no wiring errors, it's probably the tube. Try swapping in a different 12AX7 for the PI. You could take one of the other 12AX7's if you have to and see if the problem changes.

Yes, try swapping the tube, even V2 as a test. PI voltages seem to fluctuate bit pin 6 is a high and should be closer to pin 1.Test the resistors feeding the plate . They should be close.

However, how does channel 1 sound? Both channels use the PI so it's a good indicator if the PI is basically working .

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

The resistors feeding the plates are very close. That is the odd part. Even the voltages just before the resistors feed the plates are near identical.

So, channel 1 does sound. I'm not sure it's as loud as it could be. My 5f1 build sounds about as loud, if not louder. The contour switch works and so do the master and cut controls along with it. Tge distortion is very weird, though. Could this be crossover distortion from the PI? It sounds wooly and lacks definition. Also, when overdriven, channel 1 decays a little funny. There seem to be some minor swells of this wooly distortion.

Channel 2 is worse. The loudest it gets is similar to turning the master volume almost the whole way down on the other channel. I can hear the volume and tone controls doing their job, but it's all faint. I checked all those connections too and couldn't find anything misplaced.

You havent reversed connections to grids on the PI ?
You tried other tubes? power tubes are OK?
It obviously working but there is one or two things wrong. I always suspect tubes first. Get the voltages correct then check wiring if its still not working , then last suspect passive components.

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

Sorry to be getting back to this thread so late. It's that time of year... Wrapped up some shows, recording, work is... well it's work. Anyways...

I swapped V3 and V4. The voltages I got were very similar, just relatively lower by a few volts. There were no significant changes of any kind. The phase inverter is still way off balance. The tube is not the problem. Now new tube, changed my voltages significantly.

So...

Both plates are off: one is way high, one is kinda low. One of the grids is about half as low as is recommended. That triode (pins 1, 2, and 3) with the low grid voltage is low altogether: low grid voltage, lower plate voltage.

Pin1: 224.5 (256)
Pin 2: 20.25 (47)
Pin 3: 50 (69)
Pin 6: 325 (256)
Pin 7: 44 (47)
Pin 8: 52.7 (69)

*I checked voltages coming down the power rail. All is kosher here. For some reason on the tube side of the pin 6 plate resistor the voltage hardly steps down. But the tube side of pin 1 plate resistor drops by about 100 volts. What could be happening here?

*As for the low grid voltage on pin 2, what's that all about. I couldn't find any shorts or resistors with wrong values. I'm running out of ideas (granted I'm still new to this).

* Should I be concerned that my plate voltage on the ef86 is about 30 volts lower than written? I'm getting 105 instead of 137.

I double checked the output section. The tail resistor is right, the two biasing resistors for the cathodes are right, and all the grounds are right. The plate resistors are right too. I might have to double check resistance on these parts and continuity, but I really doubt it's any of those.

I'm getting sound out of channel 1. Actually sounds pretty good. Channel 2 hasn't been checked again with audio, but I'm getting good voltage readings from channel 2's tubes.

Are all the resistors around the PI up to spec? Make sure the ground connection on the board is good.

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

I found two anomalies. I was measuring resistors near the phase inverter and found two that were not what they said they were. R18 and R19 are labeled as 220k resistors where the master volume control is located. I'm guessing these are grid leak resistors? When I measured them, I got 110k instead of 220k. Now, they are labeled as 220k resistors (red, red yellow). Why would they read at half their stated value. I measured these before soldering them in, they were about 220k each.

Could this be causing some of my problems? Do I need to remove these resistors and measure them outside the circuit?

Probably the MV is low and that essentialy puts the two in parallel so that would be 110K.
mesure the network arount he PI. R11-R14 and thr plate resistors

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

All resistors around the PI measured where they were supposed to be, plates and all. Still got this lopsided voltage happening.

Also, I still can barely hear channel 2. Although the voltage readings are all up to spec for channel 2's tubes and connections, I can't seem to get some serious volume. Channel 1 is plenty loud, though.

The MV was low. Those resistors are good too.

Can you post a picture of V2 and the 0.0015uF cap that goes back to the Volume control....

Andrew...

Here ya go, Andrew

It looks good... i thought that i might have seen a short to ground on the 0.0015 uF cap by mistake, i.e. connected to the ground bus...
What do the voltages look like on V2?
Maybe a short at the inputs for channel 2?

Andrew

Ok, so I put this on the shelf for too long. I was just at that point where I had to step away for a while before I lost it. I'm back at it again, though and still not sure what to do.

I've re-flowed my connections to make sure there wasn't a cold joint somewhere. That didn't change anything, but at least we can rule out that possibility.

My voltages for V2 are all "normal." There is no short at the 15mf cap.

pin1 and 6 are 138V

Pin 3 and 8 are 1.5V

as for V3

Pin 6 269V
Pin 1 & 7 162V

Nothing seems out of whack with channel 2, yet I can't get any real volume out of it. It is a faint sound at full volume.

I still have an imbalance at the PI with the plate and grid voltages. Same as recorder before.

Sorry to bring this back up, but I just want to figure this out so I can use this amp already. I've had it sitting around since November.

can you post a good picture of the pi and the board around it?

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

Here are pics of the PI and board around it.

Looks pretty good to me. Nothing obvious there. Puzzling. May be a bad component or a bad coax connection. Easiest way to check the coax is to remove one and and test that the centre conductor is not accidentally grounded. or temp replace the coax with a piece of wire

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

I'll check it out

Good news, I found out what was going on, but first...

Thank you all for bearing with me through this. I was so not prioritizing this troubleshooting. I feel awful for letting it drag on like this. Anyhow.

It was a loose connection on one of the phase inverter's cathode pins. Tube was biased weird. I found it by probing. I thought I poked and prodded everywhere but...

Anyways the short wire running from pin 8 wasn't really connected to pin 3. You couldn't actually see the connection, but you could hear it when the wire was moved.

The amp works perfectly and is way louder than it was before, which is a good thing.

Question: why was it that the grid voltage on pin 2 was more than halved, but the grid voltage on pin 7 was relatively little changed?

I understand how the lack of bias adjustment ran the plate so hot on the pin 8 side, but how does that alter the other triode's grid?

Thanks again. Loving this amp. There's not much headroom, but I feel like changing the gain might be a compromise for the distortion character and feel of the amp. Also, I've only tried it with my Les Paul. Can't wait to hear the Tele through this!

When voltages are off, so are all bets on how a tube performs. It is a mini-system, they all have to work properly. Glad you found the problem. Good work!! See what focus can do!!

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