Matchless filament voodoo

[Randall]

I have what I think is a custom made Matchless 30/15 chassis. Complaint is low level white noise, and no signal passing. Poor fellow shipped it, and it arrived not working. Traced the signal and found it was not getting to the first pre grid since there is a mystery pcb and 12 pole footswitch wired in between the input jack and tube. Turns out it is a Super Hard On boost pedal hardwired inside the chassis with the footswitch siliconed so that it can not be accesed. Well, there is a first for me! Signal gets to the IN connection of the board, but not the OUT, so I reckon there is the problem, fix that board. I suspect the MOSFET.

Anyway, another thing I see that is puzzling is five 44 pilot lamps in various places umder the hood. They aren't there for lighting, so why? It appears they are wired in parallel with the filaments. What would this be for?

[nosaj]

I have what I think is a custom made Matchless 30/15 chassis. Complaint is low level white noise, and no signal passing. Poor fellow shipped it, and it arrived not working. Traced the signal and found it was not getting to the first pre grid since there is a mystery pcb and 12 pole footswitch wired in between the input jack and tube. Turns out it is a Super Hard On boost pedal hardwired inside the chassis with the footswitch siliconed so that it can not be accesed. Well, there is a first for me! Signal gets to the IN connection of the board, but not the OUT, so I reckon there is the problem, fix that board. I suspect the MOSFET.

Anyway, another thing I see that is puzzling is five 44 pilot lamps in various places umder the hood. They aren't there for lighting, so why? It appears they are wired in parallel with the filaments. What would this be for?

Why do you suspect the mosfet?

pilot bulbs (create filament sag? )

nosaj

[The Dude]

Sounds like a bastardized mess. I know that some of the Matchless have 4 or 5 #44 lamps in the light box. Maybe they just got rid of the light box and crammed the lamps in elsewhere? It could be that filament voltage was a bit to high without the lamp load, or it could just be that somebody wasn't sure what to do with them. There are certainly better ways to lower filament voltage if that's the idea. I'm inclined to agree that the first suspect is the FET for the Super Hard On. There isn't much else to them. I'd check supply voltage to that circuit, first. I'd sure like to see some pictures of this thing.

[Randall]

"Why do you suspect the mosfet?"

Because it's a simple circuit, and signal stops at the gate. Haven't pulled it to measure yet. Not sure which version of this circuit I have, there are some different ones, or I would post a schematic. Basically, input passes thru a cap, there is signal on one side, not the side that connects with MOSFET gate. In circuit diode test reads have my meter chirping like a bird.

Mostly interested in the lamps function in life.

[g1]

Agree with The Dude, the bulbs may be to keep the heater voltage down. The PT may be for an amp that has more tubes. (or a design with a light box )
You can check the spec of the PT vs the tube compliment, or measure the heater voltage with and without the bulbs.

[The Dude]

I'd yank the lamps and measure your filament voltage. If it's reasonable, ditch 'em.

[Randall]

Here are pics as requested.

[The Dude]

Wow. Is that board just flopping around in there? It doesn't even look mounted. And, the switch- why wouldn't they just mount it in the hole with a nut and washers instead of splooging it in? Looks pretty cobbled together to me. Where are they deriving the supply for the SHO board?

[Daver]

The bulbs are there only to light up the faceplate. I've owned a Matchless and seen plenty under the hood. The SHO.... That has to be someone's cheesy mod. They even left in the footswitch? Wow.....

[g1]

The bulbs are there only to light up the faceplate. I've owned a Matchless and seen plenty under the hood. The SHO.... That has to be someone's cheesy mod. They even left in the footswitch? Wow.....

Now I see it. They just light up the whole chassis innards and have little cutaways in the front of the chassis where the faceplate mounts. I had thought to light up the faceplate they would have the bulbs at the front panel but that does not appear to be the case.
This one of the pics shows the cutaways:

[Randall]

The lamps are not lighting up the black faceplate, pretty sure this chassis is an all purpose part. Anyway, why would you want to light up random cutouts? Doesn't make sense. There is however a 2 wire harness that lights up something.

Yes the board is not secured , but it was before I cut away the stitching for troubleshooting. The "pedal" was installed by the factory as a custom order. There is a seperate transformer/supply to provide the 9V to the board. I will ask the builder about the lamps the next time I have a exchange with him.

[g1]

None of those cutouts line up with the names of the controls?

[The Dude]

Speculation/SWAG: Maybe, since it's a "custom" amp built on a Matchless chassis, the original faceplate has been replaced rendering many of the cutouts useless?

[Randall]

OK, now I think I see. Previous suggestion does make sense. This amp only has a Vol and Tone controls, but the chassis is cut for several more options, with square cutouts over round control coutouts. This way, change the faceplate for whatever amp you are building and light shines thru the squares you are using for labels. interesting, because the lamps are mostly set back to the middle of the chassis. but maybe that is a way to get more things illuminated with fewer bulbs. At any rate I will ask Phil next time around.

[Tom Phillips]

The original Matchless control panel would have looked like this in the dark.


The extra wire harness would have powered the lights behind the Matchless logo on the front of the cabinet.