700/1 “Tim” WOPL driver board

[AngrySailor]

We were thinking of recycling some sand but you’d need a sifter and moisture is an issue. This small blaster (it a pressure pot machine) tends to ice up or clog the feed with the slightest bit of debris. One bag at least had fuckin road salt in it... that slowed progress a good bit clearing the feed line of rock salt every few minutes... I’ll double check the grade and size soon when I get home.

 

[laatsch55]

Yep, lots of coal slag blastingmedia here. 5.00 a sack.

 

[George S.]

Yeah, I use a Harbour Freight(cheap China tool chain store in the States) pressure pot. The damn thing clogs so easy even after making the mods to open up the passages and upgrading the ball valves. Sifting all material is a must, and dealing with the moisture a hassle. Moisture is the biggest issue, so I put my moisture separater up high hanging in a tree trying to trap the water before the pot. Kind of works.

 

[laatsch55]

We sandblast treaters and tanks EVERYDAY. I think our pot holds 5 bags..

 

[AngrySailor]

It’s 40 grit sand we’re using. I think buddy’s industrial sand uses a different scale as this is comparable to his “00”. His “0” is quite coarse. Heading in to recheck bias. Seems I was using wrong test points...

 

[George S.]

I can get about 3/4 bag in mine before I worry about having enough space left for some compressed air volume. Only have a 60 gal 220v compressor. To small. Need to upgrade wiring and go bigger.

 

[AngrySailor]

Ok just rechecked bias at different test points. Same results. 220mV minimum left channel, it reacts to the bias pot. 20.9v right channel. Just looked over the board again looking at diode orientation and it’s the same left to right, looking for solder bridges but not seeing anything, double checked the board connections and they check out. Already double checked the bias transistor pin outs and BCE is correct. Any ideas to shake down this right channel?

 

[AngrySailor]

I can get about 3/4 bag in mine before I worry about having enough space left for some compressed air volume. Only have a 60 gal 220v compressor. To small. Need to upgrade wiring and go bigger.

This will barely hold 100lbs. I lucked into a pretty mean compressor so airs not been an issue thankfully.

I’m not sure what I’ve done but the right bias is down to 13v now. I’m looking on the back plane rn, looking for shorted components, had a good look at the driver board again and looks good. Should I pull the Q11&12 and check them on the right channel? They were working when this amp came apart. Amp worked fine just has slightly high DC offset.

 

[AngrySailor]

HUH! 220mV right channel!!! I wiggled the Q11&12 sockets, the bais resistor? Is that the right term? Was close but not shorted to anything else but thinking back those two main drivers slid in real easy, would them not making contact cause this issue?

 

[George S.]

See what Lee thinks. I've read those old back plane bias resistors crack or blow out on the back side. Have seen photos where the socket contacts were bad so someone actually soldered the outputs to the sockets. Be care with those charged caps. Here's a photo of my discharge tool.

 

[AngrySailor]

I’ve been checking the voltage at the caps and it bleeds off quickly... it’s sitting at 120V on the variac rn and a 100w bulb is dark. 255mV both channels.

 

[AngrySailor]

What value resistor are you using?

 

[laatsch55]

Not critical Andrew, anything from 50 ohms to 200, just needs to be 5or 10 watt, bigger as you go down in value..

 

[AngrySailor]

Not critical Andrew, anything from 50 ohms to 200, just needs to be 5or 10 watt, bigger as you go down in value..

Yeah figured the 5 ohm 10w wire wounds I got kicking around would go BOOM without even breaking out ohms law...

 

[laatsch55]

They work.....once.
I once left my cap discharges on ( 100 ohm, 10 wstt),. And hit the power switch...before I could turn it off, it was melted.

 

[laatsch55]

You could series 4 of them..

 

[AngrySailor]

You could series 4 of them..

If I had 4 lol

 

[AngrySailor]

The caps don’t seem to stay charged long though. Something drawing them down? They were 3v not a minute after I shut the power off?

 

[laatsch55]

If the dbt was dim, nope...

 

[AngrySailor]

First row of outputs in. All good so far. Tightened up the driver sockets too. Almost had a brain fart and put XPL909’s in. Forgot I had a new set of 2SD555’s kicking around.