Blues Deluxe Reissue-No Sound

[Enzo]

How large was the test signal you injected? Guitars do not usually put out a couple volts, while a generator can.

Plug the output of a CD player or a tape deck into the amp input, how's that sound?

[Perkinsman]

Good point but what would putting a CD player into the amp show us? Is it a bit higher voltage than a guitar input but less than the signal I injected?

[DrGonz78]

Did not state what input voltage you used on signal generator. Sure CD player might be similar or stronger than guitar. I would inject signal 1k 100-200mv into the input then I would output the send FX to another amp to see if the signal was strong up to that point.

[Enzo]

Yes. The CD player is a known signal, and not too far off from normal input. You didn't answer what level your generator was set at, but I was concerned you had to turn it up way high to get an output from the amp. That could be all we need to explain why the generator is loud and the guitar is not.

[Mick Bailey]

Modern Fender schematics are usually marked up with test point voltages and I find these useful for troubleshooting. Ovals are AC, boxes are DC. Check all the DC voltages first, then inject a test signal as per the schematic and check them through with your DMM.

[Perkinsman]

Yes. The CD player is a known signal, and not too far off from normal input. You didn't answer what level your generator was set at, but I was concerned you had to turn it up way high to get an output from the amp. That could be all we need to explain why the generator is loud and the guitar is not.

Not sure what the exact level was on my older HP 204b. Amplitude knob says 10mw max & I was probably about half way so I’d take a wild guess approx 5mw. Also, how do I connect the rca Jax from the CD player to a 1/4” jack?

[DrGonz78]

Not sure what the exact level was on my older HP 204b. Amplitude knob says 10mw max & I was probably about half way so I’d take a wild guess approx 5mw. Also, how do I connect the rca Jax from the CD player to a 1/4” jack?

Possibly 5mw is around 500mv RMS? Probably a good strong signal to pump through the amp, but I guess peak value alone might be why it got loud. Inject a known signal read the voltage points with a meter and trace it out as Mick suggested. Here is the schematic and all the test point have been labeled as Mick had pointed out.

Reference to convert mw into related rms mv for test signal. << this is in reference to RF tables but I think it still applies to audio voltages.
https://www.electronics-notes.com/ar...hart-table.php

[Helmholtz]

There is no way to convert output power to output voltage without considering the load impedance.
Accoding to the HP 204B manual its max output is 2.5VRMS into 600 Ohm and 5VRMS open circuit (no load).

[DrGonz78]

There is no way to convert output power to output voltage without considering the load impedance.
Accoding to the HP 204B manual its max output is 2.5VRMS into 600 Ohm and 5VRMS open circuit (no load).

Yes I see now and had just stumbled onto this as well. Can we measure AC mv value using a DMM at the input of the amp to have a reading of the input value?

[Helmholtz]

Can we measure AC mv value using a DMM at the input of the amp to have a reading of the input value?

Sure.
If the level control is linear, the output voltage at 50% setting should be close to 2.5Vrms as the amp's input impedance is large compared to 600 Ohm (being the source impedance of the generator).

[DrGonz78]

Sure.
If the level control is linear, the output voltage at 50% setting should be close to 2.5Vrms as the amp's input impedance is large compared to 600 Ohm (being the source impedance of the generator).

Well that explains why the amp got so loud then hmmm....

[Enzo]

Exactly my point.

And sure, just measure the voltage with a meter. Any good meter will be close enough.

[Perkinsman]

Had to step away from the amp for a couple days but I'll be back at it this week. I love this hobby.

[Perkinsman]

Had to step away from the amp for a couple days but I'll be back at it this week. I love this hobby.

Ok. Back at it today, I’d like to input a signal from my HP 204b oscillator. A couple questions first. My leads from the HP have alligator clips. Can I simply attach them to a 1/4” jack for an input? If so, can I measure the ac signal voltage directly with my dmm leads?

[g1]

Yes and yes. 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.