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Valve Standard - Burnt Cap?


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So. After following discussions here and elsewhere on the internet, I decided to open up my cabinet and take a look at the dreaded Epiphone Valve Standard PCB and build. Photo one is the entire thing pretty much. Second and third photos are of a brown (capacitor?) item lying across some white part. It all looks a bit burnt.

 

I'm just getting introduced to this brave new world, so please be patient. Here's my questions.

 

1. What is the burnt item?

2. What is the white item?

3. How is this affecting the amp.

4. What should I do now.

 

http://i403.photobucket.com/albums/pp120/gldfshkpr/VS_PCB.jpg

http://i403.photobucket.com/albums/pp120/gldfshkpr/burnt.jpg

http://i403.photobucket.com/albums/pp120/gldfshkpr/burnt_side.jpg

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Hi Kirk.

 

The big rectangular white thing with the stains is your 120 ohm, 10watt cathode bias resistor shared by the two el84's. The burned wires on the T6 and T7 connectors are your power transformer's heater filament voltage supply. Not sure what that burned ceramic disc cap is doing in there. It's not on the 22-Oct-2005 schematic as far as I can tell. May just be a factory mod on a later version of the board, or possibly just an attempted repair. Obviously, it didn't help. Your PT's heater winding has probably been toasted, but if you power up the amp and measure ~7v or so between 'em, it's still alive and can be salvaged.

 

If so, you may want to take a peek at this Baby Will or Superlite PCB option.

http://guitaramplifierpcbs.com/default.aspx

 

That PT of yours, if still alive, can survive the load of these boards. Last summer I used my own VStd PT in a Baby Will VJr conversion project for a friend, and it's still alive and sounding awesome with the Heyboer OT that I got from turretboards.com. The tone is every bit as good as my GDS 18watt, except it's a little punchier due to the solid state rectification.

 

I don't know if the existing Valve Standard's socket holes will line up with the Baby Will pcb, but I suspect there's a strong possibility they may. You can confirm this by checking the build guide and drill templates, and comparing them to your chassis. If not, the chassis can be massaged to fit with some creative drilling.

 

Even with a VJr chassis there's a lot of massaging anyway because none of Baby Will's board standoff holes match the existing board standoffs in the chassis. It's actually a lot of work just making it fit! Plenty of elbow room in the Valve Standard chassis, though, so I figure that may help make the whole conversion job just a little easier.

 

Gil...

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I can't see that T6 is connected, though it's gotta be. My guess is that this is a homemade mod of some sort, that nearly caused that poor cap to burst into flames, by the looks of it! I'd be surprised if the PCB is any good at this point, given the amount of heat that it was obviously subjected to. I'm with Gil...time for a new build in there. Baby Will or SL are options, but you could also go with eyelet or turret board and get away from PCB altogether.

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That chassis would need a pretty narrow 1" wide turret board to fit between the sockets and front panel pots. Turret strips would be the better option. I just laid a VJr pcb in a VStd chassis and the sockets don't line up. Too bad, cuz the clearance for the panel pots would be fine. The distance between tube sockets is wider in the VStandard and VSpecials, so the Baby Will board would require a little extra chassis drilling to fit it in there. But there so much room to play around in, the only real downside would be the longer wires required to hook it up.

 

Gil...

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Hi Gil,

Was hoping you'd see this and/or the one on ppwatt.com - What a surprise this was to see something burnt! Actually, thinking back, I do remember smelling a burning scent one night. It was late. I'd had a few. So I guess I let it go. Amp still works, right? ha ha.

 

Your PT's heater winding has probably been toasted, but if you power up the amp and measure ~7v or so between 'em, it's still alive and can be salvaged.

 

I bought a multimeter today. What do I measure? "between 'em"?

 

I'm installing Phat Cats in my Dot tonight along with new wiring from Mojo. I'm taking my time. Haven't held a soldering iron in my hands for years. I had to buy one of those too.

 

I saw the Loaded MARSHALL 18 WATT "TMB" on turretboards.com and wonder if it will fit into the VS.

 

@m-theory,

The blue wire coming from the PT is not actually burnt. It's just looks that way from the photo, sun and what not. It's connected to a terminal. I'll investigate further when I get done working on the Dot. Appreciate the input!

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Set your meter for AC volts. You should measure a bit over 7v to maybe 8v unloaded between the two heater wires. In circuit, 6.3v is optimal, but with high wall voltages (123vAC), 7v on the heaters is typical. For longest tube life, it should be within 10% of 6.3v. Below 5.7v, and the tube's life expectancy curve is steep and rapidly drops off to zero.

 

If you measure the expected voltages between the two heater wires, reattach 'em, and start writing down voltage measurements on the tube pins. Pins 4 & 5 on the el84, and pins 4/5 (bridged) to pin 9 on the 12ax7's are AC volts. All the other pins are DC volts, so set your meter accordingly.

 

Oh, and before you begin, dig up a well insulated alligator clip and clip that to the end of your black meter probe. Rat Shack sells these in large and small versions. Very handy. This clip-on-the-probe trick will allow you to clip the probe onto ground (or wire, as in the case of the heaters), put one hand in your pocket (and make sure you're not grounded), turn on the power, and THEN use your free hand to hold the red probe to poke around for measurements.

 

You don't want an accidental zap traveling up your arm and crossing your heart to exit through the other hand, or foot, or whatever. So don't be nervous or jumpy from the occasional little sparks. And wear sneakers. Don't stand in your beer. Or on concrete (it's conductive so use a bathmat AND wear sneakers). Don't lean on the chassis or anything metal. Don't ground yourself anywhere at any time. And don't let your grounded kids or pets touch you at any time while your probing around. Zaps will take any available easy path to ground, even across kids that may be touching you. And keep one hand in your pocket! Simple! And easy!

 

Be safe.

 

Gil...

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