Vox AD120VT Problem

[The Dude]

The tube glow is from the filaments. The filament supply is a completely different and separate supply. (The green transformer wires.)

Edit: ......or apparently the brown wires. (they are usually green)

[imf]

thanks, ok that makes sense looking at the schematic, those go right in next to the OPTX1 on the actual board.

[imf]

Edit: ......or apparently the brown wires. (they are usually green)

So apparently they ran out of 100mA fuses and green wire at the factory

[nickb]

Is R84 even sized right? I calculate about 32mA is the failure point for this device. Why try to protect it with a 100mA fuse?

P = I2R
I2 = P/R
I = SQRT(P/R)
I = SQRT(1/1000)

Am I off here? What's R84 even doing there?

The current draw on the DC side is about 8mA. The current pulses on the charging side thru the resistor will be much higher, about 30mA. So, the purpose of the resistor is to drop the voltage. Without the resistor, 195VAC from the transformer would produce about 270VDC after rectification and capacitive storage ignoring ripple.

I'd guess the fuse was chosen to be high enough not to have nuisance blows due to the initial turn on current surge of 270mA or so but low enough to open if the resistor was running so hot as be be a fire hazard.

And thanks for doing the calculation. When I did it I plugged a resistance of 1 ohm into the formula instead of 1K ohm and that is why I didn't think the resistor would blow before the fuse. Duh!

[imf]

Cool actually somewhat get it.

Now I just have to sit here and wait. It would be nice to have a place to get these component parts here on Long Island, but I can't find anything. Mouser is taking a week or so. I'm a little reluctant to order on Amazon. Digikey is in MN so that probably would have been the same.

[g1]

I get Digikey orders overnight and I'm not even in the USA. $8 flat rate shipping. However, my understanding is that this may be a Canada only deal? Mouser is the same price, but usually takes at least a week. Otherwise, Mouser does have better pricing and selection.

[imf]

I get Digikey orders overnight and I'm not even in the USA. $8 flat rate shipping. However, my understanding is that this may be a Canada only deal? Mouser is the same price, but usually takes at least a week. Otherwise, Mouser does have better pricing and selection.

That's fast, are you really close to the MN location in Canada? It's right there basically if you're right over the border.

I ordered some stuff from mouser on the 20th and I just checked that order and apparently it was scanned in from UPS over to my local post office in my town today, so that should be here tomorrow. I paid $5 - the cheapest US postal shipping for that order. No mail for thanksgiving today so I didn't get the shipment confirmation for these 1k/1w resistors yet (which I ordered yesterday). I am expecting ETA around next tue/wed. Not too bad I guess. Just would have been nice to drive somewhere and get them or have a supply house close by like Digikey is for you.

[g1]

I am close, however I've talked to folks all over the country, and most get it next day. They use Fedex International Priority which is 1 to 3 day shipping to anywhere in Canada aside from very remote locations.

[Enzo]

Green for heater winding on power transformers is a USA standard, not a world standard.

[imf]

That's pretty good next day is the speed I'm lookin' for

Well with my first order I used the cheapo $5 economy shipping, but with this resistor order, I did the $8 priority so we'll see if that helps it get here any faster. I ordered some other crap too to start a small collection of parts, not just those 1W resistors.

[imf]

Green for heater winding on power transformers is a USA standard, not a world standard.

Ahh interesting. This is the 01/02 Vox Blueface AD120VT, made in Korea. From what I read, which can only be taken with a grain of salt I guess, these are the better models than the ones produced in Vietnam. The only green wire off the PT is ground.

I've read many complaints on the soldering of the valvetronix series, but this one doesn't seem that bad at all. However the effects loop jack soldering doesn't look the greatest, but if it works, it works. I'll take it one step at a time and see if I can even getting working again before I worry about any of that.

[nickb]

You must have a Radioshack nearby 1K 1W BOGO deal.

[imf]

You must have a Radioshack nearby 1K 1W BOGO deal.

Used to be a ton of Radioshacks around here, one was within walking distance, but they all shut down on Long Island as far as I know.

Edit: They filed for Chapter 11 bankruptcy for a second time in 2 years. Closed over 500+ stores nationwide and all of the LI ones are history.

[nickb]

Used to be a ton of Radioshacks around here, one was within walking distance, but they all shut down on Long Island as far as I know.

Edit: They filed for Chapter 11 bankruptcy for a second time in 2 years. Closed over 500+ stores nationwide and all of the LI ones are history.

That's a real shame. Used to be my goto place in an emergency. There were a couple of big stockists in range but it was a 100 mi round trip. OTOH there was a Radioshack in every mall. A sign of the times and the state of home electronics as a hobby, I guess.

[imf]

That's a real shame. Used to be my goto place in an emergency. There were a couple of big stockists in range but it was a 100 mi round trip. OTOH there was a Radioshack in every mall. A sign of the times and the state of home electronics as a hobby, I guess.

Yeah, pretty sad... they have been around forever. It just happened this past year, although they were slowly going down. Within a 10 mile radius I had over 10 of them to go to here.