My Blues Deluxe is broken, but I think it sounds better-WHY?

[maccampbells]

I may have asked this question in the wrong forum section so I'll try it again here.

So my circa '95 USA Blues Deluxe is broken. The "drive" channel light is on all the time and the footswitch does nothing, other that the light will come on (on the footswitch) when you click the footswitch.

I still have sound and both of the channels volume knobs have an effect, as well as the "drive" knob. I was a little worried at first, but now I think I like it.

It sounds good to me, but what do you think is going on here? How much to fix? Should I even bother until it actually stops working all together? AM I damaging it by continuing to use it?

[CharlyG]

What happens without the footswitch connected?

[maccampbells]

Without the footswitch connected the "drive" light stays on even if I toggle the drive channel button on and off.

[CharlyG]

Does it toggle the drive channel in and out, but it's just the light staying on?

[maccampbells]

Originally Posted by CharlyG

Does it toggle the drive channel in and out, but it's just the light staying on?

I don't hear a difference at all when I switch channels, but all three gain knobs work at once.

[CharlyG]

Sounds like it might be the relays or the 16 volt supply. I would swap V2 and V1 if you don't have any spare for V2 just to eliminate.

[maccampbells]

Is this because "half" of V2 is for switching?

[CharlyG]

The A side of V2 is for the gain channel and the B side is unused (which is kinda sad, they coulda drove the reverb with it). The gain knob just varies the grid bias of V2A. The switching is done by two relays.

[stratman_el84]

By ignoring the problem you risk further damage. The failure could be causing excessive current draw and eventually damage surrounding components or even cause a power transformer failure.

There are a good number of possibilities as to the cause. These are the most likely causes, but not the only possibilities.

The first is that one or both the +16VDC and/or -16VDC supplies have failed. They supply the switching voltage for the relays and the op-amps that do the channel/signal switching. Usually it's one of the zener voltage regulator diodes at fault, but not always. I see this occur with these amps fairly often.

The second is one or both the two switching relays have failed.

The third is the switching circuit op-amps (U3 and/or U4) have failed.

The fourth is the footswitch jack itself has failed and/or one or more of the solder joints connecting it to the PCB have failed. This is not unusual, as PCB-mounted jacks have their leads stressed whenever something is plugged in/out or sideways pressure applied. This is another fairly-common failure with these amps.

Here's a factory schematic drawing: http://www.blueguitar.org/new/schem/...ues_deluxe.gif

Good luck!


Strat

[maccampbells]

I knew this would happen shortly after I got rid of the MusicMan!

:rant:

[CharlyG]

Thanks Strat, looks like I was on the right track, except for changing the tube first. Ima lazy tech always looking for the quick fix.....

[maccampbells]

Thanks I'll guess I'll start by switching v2 then? I have one laying around.

Thanks for the suggestions.

[CharlyG]

I wouldn't since Strat didn't recommend it. Prolly just a waste of time.

[stratman_el84]

Thanks Charly, and no harm, no foul.

Mac, if you're comfortable inside amp guts where there's lethal high voltage, the first thing to do with any troubleshooting is a careful visual inspection with the amp off & unplugged. The next thing is to verify all the supply voltages are present & correct according to the schematic I posted the link to.

If you aren't comfortable poking around inside an amp with lethal voltages and don't have a thorough understanding of how to be safe while doing it, DO NOT open the amp!!! Take it to someone who knows what they're doing and can be safe working on it.

It can take just ONE slip or mistake to end up pushing up daisies from the wrong side! That's guaranteed to seriously cut into playing time!

That being said, the reason I stated that you're risking further damage is that one of the most likely causes of your problem, one or both of the +16VDC/-16VDC supplies having a shorted zener voltage regulator diode, will cause excessive current draw.

This can cause the power transformer to overheat and eventually fail. Overheating is one of the most frequent causes of power transformer failures. It may take some time for the overheating damage to eventually break down the internal insulation between windings and/or the iron core, but the damage is cumulative, and at the very least will shorten transformer life.

On the bright side, if the amp cooks past saving, it makes a decent platform to strip out and build a more conventional tube amp in.


Strat

[maccampbells]

Thanks Strat. I have an electronics background, but that was a long time ago. I'll have to find someone if it's not just changing tubes. It sounds good though!

:-(