Traynor YVC80 Tube Amp (Project)

[TomCarlos]

Friends....

I picked up a Traynor YVC80 Tube Amp. This is a PROJECT amp. A previous owner bought this as a non-working amp and then went haywire and started cutting parts to measure them, ran wires where they shouldn't be... you can only imagine. Before I install tubes and attempt to run a signal through this amp, I want to start at ground zero and do some prelim checks.

This amp uses a set of 7815 and 7915 voltage regulators. Those seem to be working ok. I can see the plus and minus 15 volts.

This amp also uses an IRF830 MOSFET High Speed Switch. This was one of the parts where the legs were cut off from the PC board. I installed a new part and measure 432 vdc at the Drain, 250 vdc at the Gate, and 198 vdc at the Source. I am looking at the service manual schematic but do not see any test points to tell me if these voltages are correct. I'm also looking at a datasheet but still lost without voltage test points.

Anyone familiar with this amp or the IRF830?

Thanks, Tom

[Jazz P Bass]

I think the gate voltage is low.

Start by checking the transistor & the diodes.

SM: http://traynoramps.com/downloads/servman/smycv80.pdf

[TomCarlos]

Will do.... and yes, I have the full schematic. I appreciate the lead... will report back in a day or so. Thanks!!

[soundguruman]

the source and drain of the mosf are interchangeable.
It seems that the mosf is a voltage regulator...
but the schematic does not show what it is powering.
the schematic is incomplete and is chopped off.

It is understandable that the Drain = 432 and the source 198 if the load is suitable for 198...
and especially educational if we knew what the source was hooked to.
I don't know if it's right but it has the look of being correct possibly....
there is supposed to be a voltage drop across the mosf, that looks intentional.

[TomCarlos]

Schematic attached. It might be easier to read if from the link shown above (Traynor web site).

As per JPB post, I will check the diode D8 that is connected to the Drain, along with Q22 (NPN) and D7 (Zener).

[g1]

The mosfet is used as a standby switch. They had enough problems with the circuit that they changed it in newer amp models.
U6 connects to the standby switch.
Are you measuring the voltage in stadby mode or "run" ?

[TomCarlos]

G-One.... Thank you.

When I first received this amp, a prior owner cut the leads of the Mosfet so it was out of the circuit. I then found two wires soldered onto the board where you'd see the Gate and Drain. Those wires went to the Standby switch. That just made no sense so I removed the wires and installed a new Mosfet.

Mosfet Voltages with Standby, no power light, Drain=432, Gate=207, Source=204
Mosfet Voltages with Standby, power light off, Drain=432, Gate=199, Source=199

I am going to check the surrounding parts as suggested previously. If Traynor issued a tech bulletin to make this change, I don't have it. Their web site has a service manual and it shows no such mod.

Thanks for the enlightenment... I will continue to dig.

Tom

[g1]

Sorry Tom, I was a bit rushed and left out some info. The YCV40's & 50's had all the mods for that circuit. They still have the fet in them for regulation, but no longer use it for the standby. I think the original idea was to save some hardware cost by using a cheap low current standby switch to trigger the regulator "off". Now in the YCV40's the standby switch turns the standby light on and off and lifts the ground connection of the power tube cathodes.
With the YCV80, either the circuit worked better, or they discontinued the model before it became an issue, I'm not sure how long the 80 was produced.
The website has only the current version schematics, so if what is on your circuit board matches the schematic, you should be good.

[52 Bill]

...so if what is on your circuit board matches the schematic, you should be good.

If the previous owner started making mods or alterations, you will have a very difficult time getting the amp to work properly until you restore the circuit back to the original configuration.

I would suggest that you double check the circuit to the schematic to see if there are any other changes that have been made to the amp.

One of the Operate/Standby leds should always be lit depending upon the mode the amp is in. Has this circuit been changed? You said that there are wires going to the standby switch. Is the switch the original D.P.D.T. pushbutton one or has it been changed?

Posting photos could help us guide you.

[TomCarlos]

Thanks Bill.... Absolutely, I want to make sure the circuit board has the original parts and configuration. I think I'm there.

Around the Mosfet device, I checked Zener D7 (out of circuit) and it produced 9.9 volts. I checked Q22 out of circuit (with my old Heathkit Transistor Checker) and it seems to be ok. I also checked D8 and that seems to be ok.

The amp powers on. The main light is on, I see the small leds over the channel one controls lit up. When I depress the standby switch, the main power light goes off but the small leds remain on.

As for the original DPDT switch, I believe that is original. Again, a previous owner did a hack job on the board and the traces on the Standby switch were damaged. So I used some buss wire and made sure the connections match the traces.

If this all looks light, I will be measuring for voltages on the tube sockets later on.

Thanks, Tom

[g1]

Did you check all the resistors in that circuit? How about U6, does it's transistor (pin 4 to 5) seem to be switching? I suppose you could try shorting from 4 to 5.
When Q19 is properly on, the source voltage should be close to what the drain voltage is (over 400V).

[TomCarlos]

I think there are some issues with the circuit. First off, when the Standby switch is depressed, I do not see the Yellow night. The Red light does shut off.

For U6 -

With Standby Switch Raised
Pin 1 - 0v
Pin 2 = 0v
Pin 3 = 0v
Pin 4 = 134v
Pin 5 = 136v
Pin 6 = 134v

With Standby Switch Engaged

Same readings as above.

[g1]

Those trace repairs are pretty scary looking, have you checked that they are all functional and not touching each other or redone them?
Is R135 good? You should have voltage on pin 1 of U6 with switch pushed. Do resistance checks on the switch, are both sides working?
Is the yellow LED good?
I'm guessing the switch got fried being hooked up directly to the Fet. And I think a bad U6 may be why someone tried to jumper the Fet with the switch, although it may just have been the Fet bad.

[TomCarlos]

I believe you are right about the switch and U6.

I can see that we in essence have a switch that is doing two separate things.

On the LED side of the switch.... (1) When the switch is up, that is the Operate mode. R134 has 15volts on one side. The other side of R134 has 2.0v. That side of the resistor goes through the switch and connects to the Anode side of LD3 (Red)- and it lights up as expected. (2) When the switch is depressed, that is the Standby mode. We get the same 15V at R134 but I also see 15V at the Anode of LD5 (Yellow). So it appears there is an open circuit... either in LED5 or the Switch is bad.

On the U6 side of the Switch, (1) When the switch is up, that is the Operate mode. R135 has 15volts on one side. The other side that connects to the Switch and Pin 1 of U6 has 1.9v. Pin 2 of U6 is 0V. (2) When the switch is depressed, that is the Standby mode, I get the same voltage.

Mosfet Voltages In Operating Mode, Red power light on, Drain=438, Gate=140, Source=137
Mosfet Voltages with Standby, Yellow light not working, Drain=438, Gate=140, Source=137

While I would like the Standby circuit to work, I am mostly interested in the voltages that should appear on U6 when in the Operate mode. I would also like to confirm the voltages that should appear on Q19. I guess it's not clear to me how this circuit works. I need to study that further. If we activate U6 by forward biasing the diode between pins 1 and 2, that allows the internal transistor on pins 4,5,and 6 to work. So it that allows Q19 to work, does that mean this circuit allows the amp to operate or does it put the amp in a standby mode?

I ordered a new Mosfet and it's on the way. I am tempted to just bypass the switch entirely and force this amp in the "Operate" mode. Once I know that it's working, I could then go back and work on the switch and check the Yellow LED.

I know the wiring at the switch looks scary, but there are no shorts and it matches the traces on the circuit board diagram.

[52 Bill]

On the U6 side of the Switch, (1) When the switch is up, that is the Operate mode. R135 has 15volts on one side. The other side that connects to the Switch and Pin 1 of U6 has 1.9v. Pin 2 of U6 is 0V. (2) When the switch is depressed, that is the Standby mode, I get the same voltage.

Test the switch with an ohm meter. The voltage at pin 1 of U6 should toggle from 2 volts to zero volts. The 2 volts is there because the led in U6 is turned on, the switch is supposed to short out the led to turn it off. If the led stays lit, the amp is never coming out of standby mode.

I believe that the mosfet is just like any other fet and it is always turned on until the gate voltage turns it off. Try shorting across pins 1 and 2 of U6 or connecting pin 1 to ground (same thing). What happens to the voltages on the mosfet?