Update :73 Silverface Twin

[gtrplayr1976]

In audio, I generally use a scope to look at a Vac signal.
Hook up the two leads to a speaker on any amp & play with the scope knobs.
It's not like you are going to hurt it.
I like the way an actual guitar signal looks.
As opposed to a pure syne wave.

Guitar plugged in , and amp on I'm guessing ,otherwise there wouldn't be a signal ?

[gtrplayr1976]

You can also just connect your scope to the output of your signal generator and experiment with the settings on each to learn what the various controls do.

I was going to do that Tom ,but wasn't sure if I would blow one ,or the other up

[Tom Phillips]

I was going to do that Tom ,but wasn't sure if I would blow one ,or the other up

Now you know it's not a problem.
I'm sure you can find a tutorial to follow along with on YouTube. An important thing is that you do hands on practice with your actual equipment.
There are thousands of hits at How to use an oscilloscope - YouTube . Many of them should be useful.
Even though the equipment being used in the demos is different from your models, the basic controls are still the same.

[gtrplayr1976]

Now you know it's not a problem.
I'm sure you can find a tutorial to follow along with on YouTube. An important thing is that you do hands on practice with your actual equipment.
There are thousands of hits at How to use an oscilloscope - YouTube . Many of them should be useful.
Even though the equipment being used in the demos is different from your models, the basic controls are still the same.

I have found a bunch on youtube. Some very similar to what I have. I'll do what you said ,and just hook it up ,and go.

[gtrplayr1976]

The light dependent resistor (LDR) in the tremolo light bug can fail such that the dark resistance is too low. That loads down the Vibrato channel signal. An easy test for this is to unsolder the wire connected to the middle terminal of the tremolo intensity pot. Try that and tell us if the Vibrato channel comes back to full life. For further information, while you have the wire disconnected, with the amp off, measure the resistance from that wire to chassis ground and report the value. Cover the light bug to keep the light out when you make the measurement.

I tried this when I got home. Removing the wire didn't change anything. I read the resistance with the bug covered ,and it was showing 2.2 meg and climbing. I noticed that the volume on both channels was similar ,but the normal channel just sounds fuller.

[Tom Phillips]

I tried this when I got home. Removing the wire didn't change anything. I read the resistance with the bug covered ,and it was showing 2.2 meg and climbing.

That is normal so one potential problem has been ruled out. Remember to re-connect that wire if you didn't already do so.

I noticed that the volume on both channels was similar ,but the normal channel just sounds fuller.

OK. That's a bit of additional information. Does the whole amp still sound weaker than your 18 W as described in post #1 of this thread?

[gtrplayr1976]

OK. That's a bit of additional information. Does the whole amp still sound weaker than your 18 W as described in post #1 of this thread?

It's probably a lot louder than I realize ,so I would say no at this time. The volume seems to have a peak at about 6-7 ,and after that doesn't seem like it gets much louder. I notice I start with the master at about 7 ,and there is a jump in volume from there to 9. Not a huge jump , but noticeable.

[Tom Phillips]

...I notice I start with the master at about 7 ,and there is a jump in volume from there to 9. Not a huge jump , but noticeable.

To sort things out I suggest that you just set the Master Volume to 10 and leave it there while you do all your testing.

[gtrplayr1976]

To sort things out I suggest that you just set the Master Volume to 10 and leave it there while you do all your testing.

I can do that. When you induce a signal into the amp is the amp on also , or do you just follow the signal with the amp off ?

[Tom Phillips]

I can do that. When you induce a signal into the amp is the amp on also , or do you just follow the signal with the amp off ?

The amp must be on or the signal will not make it past the grid of the first stage preamp.
If you don't have a dummy load or if you just want to troubleshoot the preamps then that is a case where it would be useful to set the master volume to minimum so you don't blast yourself away. In my post #38 I said to leave it on 10 so it didn't affect the evaluation of the overall loudness of the amp.

[gtrplayr1976]

I made a mistake on the type of audio generator I have. It is a Heathkit AG-9A. I found an assembly manual with some user info in it. What should the signal be that I put into the amp to trace ?

[Tom Phillips]

...What should the signal be that I put into the amp to trace ?

I use 50mV.
Note that the amp will be developing full power when the volume control is set around 3 to 5 depending on the settings of the tone controls.

[gtrplayr1976]

I use 50mV.
Note that the amp will be developing full power when the volume control is set around 3 to 5 depending on the settings of the tone controls.

And the signal is input at the input jack ? 3-5 is full power? Sorry for all the questions. Once I learn this there may not be so many ,and thank you.

[Tom Phillips]

And the signal is input at the input jack ?...

Yes

...3-5 is full power?...

Yes again. The numbers are highly variable but by "5" on the volume with the tone pots dimed the output would be starting to clip.Just start with the vol on zero and experiment. I mentioned the numbers originally because, for normal signal tracing, you don't need the amp driving the dummy load with a hard clipped signal.

[gtrplayr1976]

I use 50mV.
Note that the amp will be developing full power when the volume control is set around 3 to 5 depending on the settings of the tone controls.

I tried my generator out. Hooked it to my dmm ,and got it to put out 50mv pretty steady. However if I went too much above that it was very erratic. Maybe caps ,or tubes aging in the unit ?