Blues Deluxe Reissue-No Sound

[Helmholtz]

With the clips to 1/4" jack you lose some shielding you would have with a real cable, but this is just for testing, not usage.

...and a low impedance source like a signal generator doesn't need much shielding.

[Enzo]

But really, you have the HP unit, why not take a moment and complete the instrument? Make up a cord with 1/4" male on one end and a connector to match the HP on the other. In your case a dual banana plug. You know you are going to need it again and again. I always had a couple such cables on my bench rack.

Got a guitar cord with a bad end? Clip that end off and wire a banana plug there. Two minute job.

I had a few more that were the same but with zip cord for use as speaker cables. Good for connecting amps and cabs to my speaker/load patch panel on my bench.

[Perkinsman]

What ac voltage should I input to the amp?

[Perkinsman]

So what vac do I want to inject to the amp, the schematic only makes reference to 1k kHz

[Perkinsman]

Looking back thru the thread 150-200mv was suggested so I’m going to use 150mv which I’m able to measure directly on the jack input. I ran a line from fx send to another amp input and unfortunately got nothing but hum. I guess I’ll start measuring ac voltages at the TP points & report back.

[Jazz P Bass]

What ac voltage should I input to the amp?

TP1.
4mv @ 1KHz

[Perkinsman]

I went thru the TP ac & dc voltages and about 35% of them are 50% off and 65% were very close to listed value. I'm still not sure 150mV is the correct input voltage. Will doubling or halving the input voltage change values significantly?

[Perkinsman]

TP1.
4mv @ 1KHz

Oh jeez, I went thru almost all the the TP ac & dc voltages earlier with 1k 150mv....about 35% of them were 50% off and 65% were very close to listed value. Will that much input voltage difference change values significantly?

[Perkinsman]

But really, you have the HP unit, why not take a moment and complete the instrument? Make up a cord with 1/4" male on one end and a connector to match the HP on the other. In your case a dual banana plug. You know you are going to need it again and again. I always had a couple such cables on my bench rack.

Got a guitar cord with a bad end? Clip that end off and wire a banana plug there. Two minute job.

I had a few more that were the same but with zip cord for use as speaker cables. Good for connecting amps and cabs to my speaker/load patch panel on my bench.

That's on my add to the bench list this weekend, along with an RCA jax to 1/4"!

[Helmholtz]

Manufacturers often specify very low signal levels, like 4mV or 6mV input signal. Such low levels ensure that each following stage is operated within its linear range and stage gains can be exactly determinated and verified from the ratios of output to input voltages.

With large input signals the gain of a stage typically changes (mostly drops) even without actual clipping. Also DC voltages shift.

[Mick Bailey]

If the amp clips then the AC voltage measurements would be very difficult for a manufacturer to specify. The easier and more consistent way to do this is to ensure that the test voltages are easily reproducible and this means keeping everything clean.

Also, different meters can give wildly different RMS readings for a distorted AC waveform.

[Perkinsman]

If the amp clips then the AC voltage measurements would be very difficult for a manufacturer to specify. The easier and more consistent way to do this is to ensure that the test voltages are easily reproducible and this means keeping everything clean.

Also, different meters can give wildly different RMS readings for a distorted AC waveform.

Not exactly sure what you’re saying here...but without an accurate way to measure my input voltage, I think all my TP measurements may not be accurate either.

I would love to get this amp’s volume to increase today...I have another observation that may or may not help solve this mystery. Neither the “bright” or the “channel select” switches are working. Could this be related to the low volume issue? I’ve cleaned both switches but no improvement. If either switch is broken, would that prevent the volume from increasing?

[Perkinsman]

I’ve been going over power supply voltages. Can someone tell me whether D13 cathode should read .7? It looks like +17 on the schematic. If this diode is bad, would it prevent the volume from this increasing?

[Helmholtz]

I’ve been going over power supply voltages. Can someone tell me whether D13 cathode should read .7? It looks like +17 on the schematic. If this diode is bad, would it prevent the volume from this increasing?

D13 and D14 are 16V zeners. What are DC voltages at TP45/TP46?

[Perkinsman]

D13 and D14 are 16V zeners. What are DC voltages at TP45/TP46?

I’m calling TP 45 the cathode side of D13 & as mentioned, measured.7vdc....TP 46, the cathode of D14 measured-17.3vdc. I see that TP 45 should be +17. Would this cause low volume? Is this part of the grid bias circuit?