Two peavey 6505 heads

[Simpson]

Hello.


A friend of mine brought me two peavey 6505 heads.
They are exactly the same and both had some bad connection issues.

The difference is that one amplifier has more gain and headroom than the other.
I have followed the signal and noticed that it is almost equal until it reaches the power amp board.

I have swapped the tubes and the louder amplifier remains louder.

Could it be related to the fact that the plate voltages have a difference of 35V?

[Pedro Vecino]

The 6505 in Europe have a selector for 220 / 240V. In Spain we have 230V and with the amplifier set to 220V, 500V appears on the 6L6 plates. Set to 240V, 465V appears.
At 500 volts the sound has more tension and greater dynamics. I adjust them depending on the style that is played. I imagine the difference in power is not very relevant, but its musical effect is there.

[Delta362]

Is the signal coming out of the phase inverter about equal between the two amps?

I'd check the component readings on the two power boards with the power tubes pulled and no voltage applied. See if there is any obvious difference, or if one of the power amp boards has been modified.

Has the bias circuit been tweaked for either one? A common mod is to make the bias adjustable.

[Simpson]

The 6505 in Europe have a selector for 220 / 240V. In Spain we have 230V and with the amplifier set to 220V, 500V appears on the 6L6 plates. Set to 240V, 465V appears.
At 500 volts the sound has more tension and greater dynamics. I adjust them depending on the style that is played. I imagine the difference in power is not very relevant, but its musical effect is there.

Here is 230V too. I have checked and both are selected to 220V.

Is the signal coming out of the phase inverter about equal between the two amps?

I'd check the component readings on the two power boards with the power tubes pulled and no voltage applied. See if there is any obvious difference, or if one of the power amp boards has been modified.

Has the bias circuit been tweaked for either one? A common mod is to make the bias adjustable.

The amplifier has no modifications and the signal out of the PI are identical.
I have checked the amp pcb and it has no problems.

[xtian]

Please confirm that the power tubes' screen and grid resistors are in good shape on the amp with lower output. Also make sure the FX loop is not causing a drop in volume (insert a short jumper cable from FX send to FX return).

[Simpson]

Please confirm that the power tubes' screen and grid resistors are in good shape on the amp with lower output. Also make sure the FX loop is not causing a drop in volume (insert a short jumper cable from FX send to FX return).

Everything mentioned above is fine. I double check it.

[Delta362]

For both amps, what are the DC power supply voltages at plate, screen, and V3+, V2+, V1+ as shown on sheet 2 in the power supply section?

[Simpson]

For both amps, what are the DC power supply voltages at plate, screen, and V3+, V2+, V1+ as shown on sheet 2 in the power supply section?

Low power amp:

373AC
Plate: 470V
Screen: 466V
V3: 430V
V2: 306V
V1: 289V

The other has:

377AC
Plate: 505V
Screen: 499V
V3: 461V
V2: 329V
V1: 312V



I have noticed on the scope, that the output of the phase inverter, in the low power amp,
has a lot more gain, 50V rms compared with 30V rms of the other one.

[The Dude]

First, "The amplifier has no modifications and the signal out of the PI are identical."

Then, "I have noticed on the scope, that the output of the phase inverter, in the low power amp,
has a lot more gain, 50V rms compared with 30V rms of the other one"

Which is correct? If the latter, I'd be comparing voltages on the PI tubes. Either that, or I'm not understanding those statements correctly.

[Simpson]

Which is correct? If the latter, I'd be comparing voltages on the PI tubes. Either that, or I'm not understanding those statements correctly.

Both of those statements are correct, only made at different times.

The latter statement was verified yesterday. The volume now is lower and more distorted than before.

[Enzo]

On the weak one, pull the little mute JFET and see if it improves.

[Simpson]

Hello Enzo,


The voltage was falling a lot with the signal.

I have removed the main pcb and I found that track burnt.

It's the track on one filter cap.

It's going to be very hard to remove that completely.

[Delta362]

I would take a dremel to it and carve out all of the carbon impregnated board material. Then use either wire or clipped leads from components to rebuild traces where they need to go.