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I'm trying to trouble shoot a problem I'm having with my amp... one day it just shut itself down.

I've debugged my way thru a few things and it seems that the amp wants to trip anytime the power to the tube heaters is on with tubes in.

Pulling out the multi-meter, it seems that the tube heater circuit has continuity with ground. I disconnected the transformer wires from the terminal strip where it was soldered to the tube heater wires and found that the tube heater wires no longer connected to ground, but the transformer wires still show continuity to ground.

Is my xformer borked? or am I missing something?

The 6.3V heater winding has few turns comparatively speaking. Since the CT of the 6.3 winding is grounded you will also measure the two (green) 6.3V wires having continuity to ground.

Still have doubt? Disconnect the CT from ground and measure again.

PTs rarely fail when used within their operating specs.



Pull out all the tubes and turn the amp on, does it still trip?

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Hmmmm... wish I understood transformers better. Once I disconnect the CT, the 6.3V no longer show continuity either...

Without tubes, the amp does power up OK. It's only when the power tubes go in that it shuts down.

If it was working and "one day it just shut itself down" then I suspect tubes.
Inspect the tubes.
Then Start with the rectifier tube and check voltages, then preamp tubes. If its all good until then, try the power tubes but that would be my suspicion.





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

That was my initial suspicion as well. I put in a set of new power tubes when I realized the it shut down once they were installed.... didn't seem to change anything....

I wonder if I can find a tube tester somewhere....

Just to revisit this issue. I let things sit for quite a while; got busy... finally got back at it...

I'm still confused as to what is going on.

I did build a trouble light set up to help things move along...

With no tubes, everything fires up and passes the voltage tests

With all tubes in, fine on standby, trips when taken off standby

With the rectifier in, I'm fine to take it off standby

With the rectifier and a tube in V5, I'm fine to take it off standby

With rectifier and tubes in V4 and V5, it trips..
With rectifier and tube in V4, it trips.... (corrected)

I've checked every resistor, every ground connection...

This is contradictory. First you say Rectifier + V5 is OK. Then you say Rectifier + V4 + V5 trips. Then you say Rectifier + V5 again but this time it trips. Is this correct or did you mean V4 the second time?

Either way, I would suspect grid resistor R23 is bad or possibly screen resistors R30 and/or R31. Check those guys again. If they are bad it's entirely possible you shorted out your sets of power tubes during your testing too.

Your bias resistor, R20, is another suspect. Also make sure all your wiring for biasing the power tubes is good... no cold solder joints, etc.

Also, here is a fantastic amp debugging guide to look through... http://www.geofex.com/ampdbug/ampdebug.htm

Meant V4 the second time.

I've tried what I could make sense out of the geofex site....

Does it happen the same if you swap the power tubes or does the tripping follow the tube?

Check you V4 wiring thoroughly especially the screen resistor.

R23 tests at 99.8 (100)
R30 tests at 8.52K (8K2)
R31 tests at 7.96K (8K2)

R20 tests at 149.3 (150)

I think its safe to say that they seem to be within tolerances...

Also... the trip stays in the socket.. tested it both ways with 3 different tubes....

BTW.. I appreciate all the help....

Check all of your wiring around feeding and leaving V4. Look for loose joints and/or cold solder joints. Check all the way back to the phase inverter and out to the transformer and bias circuit.

All checks out. Checked for continuity all the way thru and the resistance at each point as well. The poke and prod test on the wires show them all firm.

Seems to me you had issues with your vrm in the past.
I had issues with mine made smoke come out of my output transformer ( still works amazingly)

Have You taking the vrm out of the circuit to see if you still have issues ?

The vrm was the first thing to be removed...

Did you ever get this resolved ?

Do have another rectifier tube and power amp tubes?

From the screen resistor to the screen connections on the sockets you do have continuity to both tubes?

A picture of the power half of the amp would be great if this is not already worked out

sorry been

Still trying to sort it out.... retested all the transformer stuff as per the geofx link... checked all the resistors again, tube swaps, etc...

There is continuity from the grid resistors to the grids and the resistance thru the resistors are good.

By shut down does it blow the fuse ?

With Just the rectifier tube in do you have High voltage to both the Plate and screen connection on the power tube sockets.

If yes disconect the first 8.2k dropping resistor (Decouples pre amp from power amp power supply)

You might want to reheat those solder conections for the cathode resistor and cap for the power tubes. and then try to put in your power tubes one at a time


If you look at this picture when the turet gets hot enough it will tend to suck the solder in

I agree with Saz... your solder joints look a little suspect. When they are in balls like that they could possibly not be making good contact with the turret. If you have connections below the board or lower on the terminal they may not be conducting well. Your joints should either suck the solder in like that first turret of his or form a nice shiny dome that covers the top of the turret like in the second one from the right.

What I would do is take your iron, heat up the turret, take some new solder and melt it on top. That will melt the old solder and get it all to nicely flow together and make sure you have good "flow." You should be able to visibly watch the solder actually flow into/over the turret.

This amp was working and then stopped. The problem seems to be related to V4 socket/ wiring. With the tube pulled out, look for a short to ground on all the pins and connections around V4. Look for any signs of sparks between leads. Look for wires that may have the insulation melted off and ar making contact with adjacent wires. Pull all the leads away from each other.

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

The solder bubbles are a recent thing; I touched up all the turrets to make sure, but no big deal; 15 minutes with an iron and they are all gone now. All the resistors test out correctly going turret to turret (learned early on not to test on the leads if what I really want to test is the connections).

By shutting down, I do mean blowing a fuse.

For all my testing right now, I am plugged through a trouble light (i.e. bulb in series) so that I don't keep blowing fuses.. the bulb takes the load. If you think taking the test bulb out is needed, please say so....

All right... Voltages... rectifier tube installed, nothing else......
B+ 425 vDC

V6 (rectifier) -
pins 1 and 7 - 308vAC each
pin3 - 424 vDC

V5 (power)
pins 7 and 9 - 419 vDC
pin 2 - 0

V4 (power)
pins 7 and 9 - 419 vDC
pin 2 - 0

V3, V2, v1 (pre amp)
pins 1 and 6 - 413 vDC on all