Fender Hot Rod Deluxe repair

[Mathias]

Looking for some advice on a repair. Having a Fender Hot Rod Deluxe 1x12 from '96 on the bench.
From what I was told the amp has been previously modded to run at bedroom level. But it's just too silent and sterile sounding for the owner.

At the moment I just did the usual on these amps, change out the resistors and lift them from the board as this one was slowly burning up.
Replaced filter caps with F+T's. I've undid some hardwiring and made it back to stock (or at least what I think) but it's still running at the same low level...

There is a 12AY7 in V1 and 12AT7 in V3 but that's not gonna be a dramatic shift from +- 50W to maybe now 1W... right?
The channel switching works fine and the volume affects both channels.

I can't seem to find the mod that has been done to run at low level. If anyone has some advice I'd be more than happy to hear your thoughts.

Some gut shots added and schematic.

 

[NoisyIndividual]

You could check the screen grid resistors on the Output PCB are 470 Ohm or not.

 

[Matador]

There is a 12AY7 in V1

12AY7 is 60% less gain overall. In order to go to full volume, the power amp requires that the preamp can push it to full volume.

I would feed a signal into the power amp in, and see if you can push it to full output wattage. I would also check to make sure you have 60mV across the 1 ohm (shared) cathode resistor.

 

[NoisyIndividual]

I don't recognise the big green resistor below the left most jack socket either.
That's a mod/substitution.

 

[NoisyIndividual]

I remember now, the resistor under the jack socket gets a bit hot, it's part of the footswitch circuit, so someone probably put a bigger one in.
Though I don't think thats really necessary.

 

[pucho812]

Might be the long way home but compare the unit to the schematic.
That would tell you exactly what was changed.

 

[CJ]

Luckily they have the AC volts in the little circles on the schematic,

 

[saint gillis]

Luckily they have the AC volts in the little circles on the schematic,

Yes, inject 1KHz sine 4mV rms and check the levels all the way through, I don't remember if the pots should be full CW or mid-position
If you have an 8Ohms load-box or 150W resistor, put it instead of the speaker to avoid listening 1KHz at high volume during an hour

Another thing, not your may concern for now, but in 99% of the cases in western Europe, these amps are running at better voltages when the transformer is wired at 240V

 

[MagnetoSound]

You need to find out which section has been modded first.

Start from the output stage. Inject OdB or so into the PWR AMP IN Jack and test for full output. If that comes out loud and clear (you know how to measure watts?) then the mod is in the preamp. If not, you’re most likely looking for some sort of dropper resistor in series with the speakers.

 

[NoisyIndividual]

There is also a pre-amp out next to the Pwr Amp in - an Insert, in effect. There may have been a simple mod done here.

In fact you can buy these things to add a "Master Volume" to these amps.

https://www.ebay.co.uk/itm/18650886...ozi0AmEA3ePDiZgp1LrZ6aC3dIwOOPtRoCc4gQAvD_BwE

 

[joekool]

Greetings : have you tested all of the plate voltages ? if you would post them I will be happy to help Trouble shoot.

I am a Mesa warranty repair with over 40 years inside tube amps . I have had a bunch of these on my bench over the years .
I would love to help .