Traynor YVC80 Tube Amp (Project)

[TomCarlos]

Bill.... I will replace U6 with an NTE generic from Fry's. I called Yorkville and they are sending a new switch and yellow LED.

For now, I want to remove the physical standby switch from the circuit. I need to know if the amp can pass a signal. Once I reach that milestone, I can then turn my attention back to the Standby (physical) switch.

Does anyone else think the switch diagram on the schematic is confusing? I redrew it. I see how that switch puts 2 volts on U6 Pin 1 or the Switch grounds Pin 1. The thing I don't get is this.... The MOSFET... When that device is "working" does it mean that the amp is Operating or in Standby? I am guessing "Operating." Correct? And for the Mosfet to be working, that requires Pin 1 of U6 to be at 2 volts. That 2 volts turns on the U6 Diode which activates the other side of U6.

For now, I think I want to remove the physical Standby switch, rewire so that R135 connects to Pin 1, Pin 2 to ground, then see what happens with the Mosfet.

(Honestly, I could care less about the entire standby mode.....).

Will pick up parts and report back.

Thanks.

[52 Bill]

I see how that switch puts 2 volts on U6 Pin 1 or the Switch grounds Pin 1. The thing I don't get is this.... The MOSFET... When that device is "working" does it mean that the amp is Operating or in Standby? I am guessing "Operating." Correct? And for the Mosfet to be working, that requires Pin 1 of U6 to be at 2 volts. That 2 volts turns on the U6 Diode which activates the other side of U6.

The 2 volts is the forward voltage of the led inside U6. If the led was open or not there, there would be 15 volts at pin 1 of U6. When the switch is out/up the led is shorted by the switch contact, so it is turned off. When the switch is pushed in, the contact no longer shorts out the led and the led turns on, which then turns on the phototransistor side of U6. This turns on the gate voltage to the mosfet which open the path from S to D.

As I posted before, the switch seems to be bad and is not shorting out the voltage to the led side of U6 (pin1). If the led in U6 does not turn off, then the amp will stay in standby mode. If you remove the switch, ground pin 1 of U6 and see what happens at the gate of the mosfet.

[g1]

The schematic shows the switch in "operate", the upper contacts are shorted together on both sides. So the standby Led is shorted out and the voltage appears across the operate Led. On the other side of the switch, pins 1 and 2 of U6 are shorted together. This turns off the transistor of U6B. This means the Fet is turned on, low resistance from drain to source. So when working properly, in operate mode the voltage at the source should be around 400V or whatever the drain is. The drain to source is acting as a regular standby switch would in a Fender amp, letting the B+ through.
As 52Bill said, when the switch is depressed, voltage appears at pin 1 of U6. This turns on U6B transistor which turns OFF the Fet. So it goes high resistance from source to drain and you do not get B+ at the source. This appears to be what you have, or you are in a limbo state.
You said you have 0V at pin 1 of U6 with switch in either position.
If you really want to check other parts of the amp, you can remove the Fet and install a jumper between the source and drain pads on the circuit board.
As there are no voltages shown on the schematic, here is a link to an older ycv40, voltages shown should be similar.
http://www.toomanyhelicopters.com/sc...al_w_Schem.pdf

the switch seems to be bad and is not shorting out the voltage to the led side of U6 (pin1). If the led in U6 does not turn off, then the amp will stay in standby mode. If you remove the switch, ground pin 1 of U6 and see what happens at the gate of the mosfet.

I'm not sure if the switch is bad or the U6 Led is shorted, but he did measure 0V at pin1 with switch in either position. So this should put the amp in operate mode, yet the Fet is not passing full B+.

[TomCarlos]

Quick update then need to call it a night.

Thanks Bill and G One. I took Pin 1 to ground. Here are the other voltages on U6

Pin 6 Base = 61 Volts
Pin 5 Collector = 72 Volts
Pin 4 Emitter = 70 Volts

Thanks for the tip on removing the Mosfet and shorting out. I will look at the YVC40 circuit as well. Yes, not having voltages is making this tough.

I appreciate the help on this... and will pass the favor along to the next person.

[g1]

You can also try removing U6 to see if the Fet then turns on.

[TomCarlos]

Ok..... U6 out, Drain to Source has jumper... I now have 432 volts at that junction.

The amp is passing a signal very faintly. So I need to start at the beginning. No signal can be heard at the headphone output. So...

Quick check of the key voltages.


- The 7815 and 7915 regulators are working at plus and minus 15 volts
- The 6L6 tubes have 6.6 volts on the heater pins 2 and 7
- The 6L6 have 432 on the plate pin 3 sockets

Checking all three 12ax7s... The plate pins 1 and 6 have 287 volts. That seems a bit high. Q20 is another regulator Looking at the PC board, it is different than the schematic and PC board diagram. I do not see Zeners 21 to 24. So I must have a different version of this amp. For Q20, the collector is at 418 volts. the base and emitter are at 290 volts.

The heater pins read as follow... (and I am trying to understand if this is right...).

V1: Pin 4 = -15 (with respect to ground)
V1: Pin 5 = 0 (with respect to ground)
V1: Pin 9 = 0 (with respect to ground)

V2: Pin 4 = 0 (with respect to ground)
V2: Pin 5 = -15 (with respect to ground)
V2: Pin 9 = 0 (with respect to ground)

V3: Pin 4 = +15 (with respect to ground)
V3: Pin 5 = 0 (with respect to ground)
V3: Pin 9 = 0 (with respect to ground)

[g1]

For the preamp heater, measure the DC voltage between pins 4 and 5. Should be around 13VDC each.

[TomCarlos]

For the preamp heater, measure the DC voltage between pins 4 and 5. Should be around 13VDC each.

12ax7 voltages with negative lead of voltmeter on pin 5...

V1 Pin 4 to Pin 5 = -15.16
V2 Pin 4 to Pin 5 = +15.16
V3 Pin 4 to Pin 5 = +15.10

[g1]

As far as the Q20 regulator, have a look at Q10 on the schematic for the older ycv40 I linked.
The old 40 schematic may be closer to what you have, you may have to go back and forth between the 2 schematics.

[g1]

Can you see that the preamp tube heaters are lit up?
What are pin 3 and 8 DC voltages at the preamp tubes?

[TomCarlos]

Preamp voltages with tubes in sockets

V1, Pin 3 = 1.2 vdc
V1, Pin 8 = 1.4 vdc

V2, Pin 3 = 1.3 vdc
V2, Pin 8 = 1.4 vdc

V3, Pin 3 = 34 vdc
V3, Pin 8 = 34 vdc

It's very hard to work on this amp with pc boards in place. So... I took them out and can now access all points more easily. (I sure hope I can put it all back together!!!).

The amp continues to pass a very faint signal...

BTW... the YVC40 circuit also uses the Zeners for Q20. So I must have a very old version of this amp. I will see if I can contract Traynor to dig up an old schematic. Other option is to drill baby drill and retrofit this pc board to match the latest schematic for Q20.

[Jazz P Bass]

V1 & V2 are used for both channels.
They then go to the preamp out/ power amp in jack.

So use the jack & measure the signal amplitude or send it to another amp, to see if it is proper.

Likewise, insert a test signal into the power amp in jack to see if the power amp is o/k.

[TomCarlos]

I tried sending a line level signal to the amp's "Return" jack.... nothing. I also used the "Send" output to drive another amp. Nothing.

I'm going to keep checking the dc voltages. I wonder if there is something going on with the Return/Send loop... something like a bad jack or connection that is open. I want to look and see if there is a way to bypass "stuff" I don't need. I'm going to keep checking the dc voltages. Not sure why I have a discrepancy on Pins 3 and 8 when comparing V1, V2, and V3.

[g1]

V3 is the phase splitter, it should have a higher voltage on the cathodes than V1&2, your cathode voltages for all 3 preamp tubes seem reasonable.
The new 80 schematic shows that you have to turn up return and master pots to use return jack, and you need to turn up send pot to use send.
As you said, the proper schematic would really help.

[TomCarlos]

Ok.... I am going to put this on hold for a few days... until I hear from Traynor in hopes of getting an "old" schematic. Turns out I have a 2001 model. The version after mine has the Zener diodes driving Q20. If I can make the conversion, I will do that.

Follow up on using the Return to drive the amp. That input is a TRS. I have no idea why. You'd think it would be a mono input. In any event, I fed a signal generator into that jack and it's audible- but no where near the volume level you'd expect.

Again, I appreciate everyone's help but do not want to waste more time here. Let me see if I can get an old schematic and play catch up.

Tom