Orange AD30HTC: No sound. (new OT and voltages in spec)

[fiveightandten]

I'm hoping some of you guys can help me figure this one out.

Amp: Orange AD30HTC (4 x EL84, GZ43, 4 x 12AX7)

Condition: No sound. Not even a peep. No hum, no scratchy noises or pops when I touch the leads of the DMM to the EL84 plates. Nothing.

Background: The amp had a low volume condition. Constant low volume, power level equal to say, a 5W amp. The tone and gain level was otherwise fine. The condition persisted through 2 different sets of trusted tubes and all the voltages were spot on, so I ordered an output transformer (even though it tested ok). The amp sat for a few weeks while the transformer came in, and now there's no sound.

Current condition and testing:
I put a new output transformer in it. There's zero sound with that OT, or with the factory OT. All the voltages look spot on. OT CT, primaries, and EL84 plates are all showing proper voltages in the 330-340VDC range. EL84 cathodes in the 11V range, and all voltages including pre-amp seem to be in spec. B+ rail voltage drop resistors measure fine, EL84 cathode resistors measure fine. Nothing in the amp is disconnected, burned, or has any visibly severed connections (that I can see). 6.3VAC heater voltages are also in spec. All the tube heaters are visibly lit.

The only thing odd that I saw was that the OT primary leads were reversed when I went to pull the factory OT. Though the amp is non-negative feedback. The amp is a 2001 model and has been functioning for years like this.

Schematics and test procedure sheet available here:
The Orange Amp Mods page

[loudthud]

In this case the first thing to check is that the speaker is connected. Measure the resistance across the speaker terminals of the speaker, or the cabinet end of the speaker cable. You should see a very low resistance, below one Ohm. If there is some fault, you will see a resistance about 75% of the speakers rated impedance.

[fiveightandten]

In this case the first thing to check is that the speaker is connected. Measure the resistance across the speaker terminals of the speaker, or the cabinet end of the speaker cable. You should see a very low resistance, below one Ohm. If there is some fault, you will see a resistance about 75% of the speakers rated impedance.

Thanks for the reply. The speaker is connected. I know you don't know me from Adam, but believe me it's not a speaker issue.

I tested the amp, got no sound, plugged the same guitar, same guitar cable, and same speaker cable (with the same speaker cab) into another amp and everything was working fine. ...Back into the AD30 and no sound. It's an issue with the amp.

-Nick

[mac dillard]

If you don't have a signal generator to trace the circuits try this little device. Simple Circuit Debugging

I use it kinda backwards in that I plug it into a CD player and use it to inject the signal where I want to in the amp. Should help you locate where the problem is.

[fiveightandten]

If you don't have a signal generator to trace the circuits try this little device. Simple Circuit Debugging

I use it kinda backwards in that I plug it into a CD player and use it to inject the signal where I want to in the amp. Should help you locate where the problem is.

Excellent, thanks, i'll try that out.

What baffles me is that there's not even any hum or white noise. There's nothing. Normally you hear at least *something*. I'm not even getting any of that typical scratchy noise you get when you touch a DMM probe to the power tube plates to check the B+. There's not a peep out of the amp.

[52 Bill]

What baffles me is that there's not even any hum or white noise. There's nothing. Normally you hear at least *something*. I'm not even getting any of that typical scratchy noise you get when you touch a DMM probe to the power tube plates to check the B+. There's not a peep out of the amp.

Which is why Loudthud mentioned the speaker problem. Is it possible that the speaker jack is defective or miswired?

[g1]

Are there FX loop jacks you can use to determine whether the problem is in the preamp or power amp?

[mozwell]

Is it possible the link LK3 to LK4 is not connected ?
Is it possible you swapped the two black wires, there is one black wire for primary & one black wire for secondary

Power off the unit, discharge the power supply, disconnect the output transformer.
Measure ohms between yellow - white & white - black, if these read about the same, then these are the primary wires & can be reconnected. The rest are secondary wires.
With the transformer secondary not connected, and with speaker plugged in, measure ohms between TX12 & TX14 for a 16 ohm speaker, or between TX13 & TX14 for an 8 ohm speaker. If these measure ok, reconnect secondary to TX12, 13 & 14, power up & try again.
With a signal plugged in, do you get AC volts across R26 and across R27, if so what voltage do you get.
Are all the power supplies at their correct DC levels

Do you get the correct voltage at pin 9 of the output tubes

Are R25 & R28 cathode resistors ok at 150 ohms ?

[mozwell]

Do you get the correct voltage at pin 9 of the output tubes (screens, sch says screen is pin 9, but aren't these octal ?)

[g1]

Not octal, EL84/6BQ5 Pin 9 is correct for screens.