Traynor YGM-4 No Output

[The Dude]

If you are saying the capacitor is open because there is 138VDC on one side and OVDC on the other, capacitors do not pass DC voltage and that is not a reason to suspect the cap is bad.

[Sleet]

Okay thanks The Dude. Any clues from my new voltage numbers?

[g1]

The new numbers indicate the power tubes are cathode biased. So either the schematic is not a match, or the unit has been modified.
None of the numbers seem to show any obvious problem, so you will probably have to do some signal tracing through the circuit.

Sounds like the amp was working fine before then one day just quit working? If so, you don't need to worry about the cathode bias of the power tubes as it worked ok before.

[Helmholtz]

I remeasured all of the voltages of the tube pins.

At first glance I don't see anything with preamp voltages that would prevent the tubes from working.

But, as said earlier your output stage doesn't match your schematic.

Acc. to schematic power tube cathodes (pin 3) shouild be grounded and grounded means at 0V.
Also the grids (pin 2) are shown to have a bias voltage of -17V.

Your amp obviously uses cathode bias.
WIth a cathode voltage of around 40V, EL84s are essentially in cutoff.
You need to find and check the cathode resistor (a big power resistor, probably something like 130R/5W or more).
It's either gone high resistance or open.

[Sleet]

I found another "redrawn" schematic for the YGM-3, which is in theory nearly identical to my YGM-4. Not sure if this one makes more sense?

[nosaj]

The one pasted on the lid is the one I would follow.
nosaj

[Chuck H]

The one pasted on the lid is the one I would follow.
nosaj

I've had three Traynor amps. All still with the lid schem. The schematic provided was accurate every time with little exception. Maybe an odd value in a couple of non consequential places was off, but this could be a case of parts on hand when building for an order. I would trust the schem provided with amp first unless it's obviously wrong (which could happen for a few reasons, though I have never seen it.). Also...

We've diagnosed many Traynors here based on photos of the lid schem. And I can't think of a time when it didn't work out.

[g1]

It still shows fixed bias, with power tube cathodes grounded, and negative voltage at grids. Yours seems to have been changed to cathode bias, with zero volts at grids and positive voltage at cathodes.

Follow wires from power tubes pin3's, do they go to a resistor? What is the value of the resistor? Is there a cap in parallel with it?

[Helmholtz]

See e.g. post #10.

[Sleet]

G1, Yes, pin 3 is connected to a resistor that wire connects to pin 3 of V4 and there is a jumper wire to pin 3 of V3. The more I think about it, I remember now having replaced both of the power tube sockets before I put it away. I probably wired the replacements incorrectly. I did take detailed pictures of the original sockets before removing them. If I can find them.....

[g1]

Yes, I would say the socket pins for grids and the cathodes are wired incorrectly. Should be around -15V at the grids and cathodes should go to ground.

[g1]

Your picture with the blue arrow is pointing at pin2, not pin3. That pin is wired correctly and should have around -15VDC on it. The power tube pin3's should be connected together, then to the chassis like that black wire at the other tube socket is doing. Is that black wire connected to pin3?

[Sleet]

So, just as a follow up, I've gotten the amp working again. V3 was incorrectly wired. I had pin 2 grounded instead of pin 3. It's running, not sounding too great, but everything is functioning. I may put a signal through it and see what the output looks like on my scope. Thanks to everyone who replied to this posting!

[g1]

Are both power tube pin 2's connected to the right places? Do you measure around negative 15VDC at both power tube pin 2's ?

[Sleet]

I just checked pin 2 of V3 and V4. They're both reading -19.46 VDC