fender deluxe reverb 65 repair

[Helmholtz]

Why do you have a cathode voltage? Did you add cathode resistors?
In post #27 you reported equal grid voltages of -35V. The new OT shouldn't change that.
What are the resistances of the OT primary halves?
Do you have OT specs?

[tepsamps]

Yes i added cathode resistors, 1 ohm. The primary is about just less than 200 ohms per side.
I know that OT does not change grid voltage, but maybe i took the voltage at the wipper of bias pot.
But about G2 voltage? It's strange, no? I'm gonna check the wires...

https://www.hammfg.com/files/parts/pdf/1760H.pdf

[Helmholtz]

Screen voltage at idle often is like a couple of volts higher than plate voltage.
With signal average plate voltage is typically much lower than screen voltage anyway.
Sometimes mains voltage fluctuates by a few percent between measurements making supply voltages change by the same percentage.
Maybe repeat measurements.

[tepsamps]

Thanks Helmholtz.
I changed the 220 K resistors (grid leak) for the bias, and now ir's ok about voltages and i have about 20 mV at both cathode for -40 v of grid voltage (taken at the pin). Quite hot...

But i'm a little concerned about the noise, the static noise i mean. It's quite loud but i'm not used to amps without master volume and it's certainly normal.

When some speak about a re-cap job on old amplifiers, they mean coupling cap and cathode bypass cap? All the caps?

[Helmholtz]

20mA idle current is good. Means around 66% PD - not too hot.

[g1]

When some speak about a re-cap job on old amplifiers, they mean coupling cap and cathode bypass cap? All the caps?

Usually they mean the electrolytics (filter,cathode bypass, bias), not coupling caps unless they are found to be leaky.

[tepsamps]

OK, thanks...

Now i have another issue, the tremolo does not work anymore. It seems that there is no tube inside the socket, almost 0 V at V5a K and 3 V at V5b K. And the voltage does not drop across the plate resistor.

I checked the tube, it's good in another amp. I put another tube, and before i have put contact spray in the noval socket, but it's the same. I have had already this kind of issue in one of my amps, and it was the socket.

I guess it's belton on the DR, and i have already had issues with belton noval sockets, exactly this.

This amp is cursed...

[Tom Phillips]

OK,...Now i have another issue, the tremolo does not work anymore. It seems that there is no tube inside the socket, almost 0 V at V5a K and 3 V at V5b K. And the voltage does not drop across the plate resistor....

I suggest that you investigate the V5A cathode circuit. With the V5 tube removed and the amp off & unplugged, take a resistance reading from V5A pin three probing from the top of the tube socket to chassis ground. Tell us the reading you get. It should be the value of the cathode resistor. If not, then you can start narrowing the test points to determine if it's a bad resistor or a bad connection.

[tepsamps]

I find 2.7 K at pin 3 and 100 k at pin 8, so it's ok. Now from D to pin 1?

I checked also and it's ok, 230 k and 6 M at pin 6.

But this tube is very easy to remove, maybe the contacts are loose. I don't know actually...

[Tom Phillips]

[QUOTE=tepsamps;n1005711.. Now from D to pin 1?...[/QUOTE] I'm not sure what you mean by that.
With the tube installed can you see that both heaters are glowing?
I ask because I have found bad solder contacts at the heater connections to the tube socket that would turn off one heater. Sometimes they are really hard to see until you take a really close look. It is possible for a heater fault to turn off just one of the two triodes inside a 12AX7.

[tepsamps]

I saw a light inside the tube like the other tubes....

Are there one or two heaters, now it's hard to say....

[Tom Phillips]

Are there one or two heaters, now it's hard to say....

It should be easy to see two distinct heaters under low light conditions. See the attached photo which shows two 12AX7 types on the right and in the middle with a 12AT7 on the left. The two independent heaters, one for each triode, are clearly visible.
Since you verified that the tube works in another amp, we are now trying to verify that there is not a wiring problem to either tube pin 4 or to pin 5 which should be connected together. Each of those pins powers one of the two heaters when the tube is wired to operate on 6.3V heater voltage with pin 9 being connected to the other side of the 6.3 V heater supply. We are down to long shots in the troubleshooting process after everything else that you already tried.

[tepsamps]

I have not the good reflexes about this, i admit. But both sides were affected by the problem, as i had almost no voltage at each cathode.
So i changed the socket...
And i have quite normal voltages. At the oscillator, i have 1.9 V for a 2.7 K resistor. But LDR side, i have only 6 volt and no 17 v as on the schematic, but it's better and the tube is held strongly.

But I did not try the tremolo yet ... It's time to eat... I'm back in 4 hours...

[Tom Phillips]

... But LDR side, i have only 6 volt and no 17 v as on the schematic, but it's better and the tube is held strongly. But I did not try the tremolo yet ... It's time to eat... I'm back in 4 hours...

Note that it is normal for that voltage reading to be low when the tremolo oscillator is not turned on via the foot switch.

[tepsamps]

Unfortunatly, it does not work... So now, with the tremolo switched on, i have 4.3 V at the cathode of the oscillator, and 13 V for the LDR.

So when i switch the tremolo on, i hear a poc and the volume is lower when the intensity pot is cranked. More i crank the intensity, lower is the volume.

But no pulsating effect. It has worked when i changed the roach, just before i have the OT issue.

And i did not touch the wires of the trem pots.

Is the optocoupler fragile?