diytube.com

I would be tempted to get 8 330K 1/4 watt resistors and solder them directly to the lugs of each cap. There should be plenty of space underneath the board.


Just my $.02!

1/4 watt may be a tad small, I like to have about 300% of actual dissipated power for safety margin in resistors. I'd go with no smaller than half-watt, and one watt sould be ideal. Bend the leads around to fit the pads as needed, and keep the resistor bodies off any "metal bits" of the PC board, or at least space them at least 1/8 inch away from etches.

The "stock" 330K SMD resistors supplied on the boards are 1 watt devices, and are a nice clean fit betweem the pads on the solder side of the PCB.

As an example, a 330K resistor connected across 330VDC will consume 1 mA, so the power dissipated through it will be 330 mW or 0.33 W. A 1/4 watt resistor is definitely too small, 1/2 watt is a slim margin, and 1W gives the 300% "safety margin".

In the SDS ST-70 or MKIII or similar boards, on which the caps are in a series / parralell arrangement, the caps (and resistors) will see about 240-250VDC across each, so the power dissipated across each resistor (at 250V) will be 250V X 0.75 mA pr about 0.188 watts, call it 0.2 watts just for round numbers. 1/2 watt resistors would be a bare minimum, but and 1 W would still be the best chooice, for long resistor life.

HTH

/ed B in NH

Ted, Did triode ever get back with you? I've sent 2 emails with no response. I was about to order my dyna transformers from them, but now have second thoughts on this. I may just go with the Dynakit.com iron at this point. They have been very prompt in their communications. Any word on these news tranny's yet?

William,
Yes they sent the parts right away. I put them in last week and powered up with out any smoke leaking out. I would give triode a call and try to resolve it over the phone maybe Matt is just not in this week? As far as the iron goes...all worked out fine. Although I did mention that the plastic grommets mechanically interfere with the transformers, so I found some nice high temp spaghetti to protect the transformer wiring. Rubber grommets would have been a better choice because they would compress when the transformer is bolted down. For now I'm waiting on one of the plastic mounting parts for the speaker binding posts. Soundtastic shorted one of them. When that's done I'll post pics.
Ted

Well it's now June 25 ( almost a month)and still no replacements!!!!!!!!! I called last monday so no priority mail for me! The amp is almost finished and still no PS to install. Thats a little much in my book. I went ahead and removed the the smd resistors. They didn't want to come off. I had to hit them with 2 irons at the same time, while my son flicked them off. I could smell super glue, and it appears as if the were glued on. Ever here of that?
Looking at those tiny things, i'm concerned that the solder will wick under them and bridge the pads. How likely is that?

Wmacky wrote:Looking at those tiny things, i'm concerned that the solder will wick under them and bridge the pads. How likely is that?

Amazingly, it almost never happens. I can't remember seeing a failed DUT at work with a short across the pads. But hand soldering 0402 resistors can cause you problems. :)

Shannon

July 3 and still counting WOW!. Called again early last week and Matt said they had been sent a few day's prior, but still nothing. I've given up, and will order from mouser as I wished I would have done 3 weeks ago. Anyone think radio shack may have the proper through hole resistors that I could modify to work? The amp looks great BTW. I'll post some pics!

Wmacky wrote:Anyone think radio shack may have the proper through hole resistors that I could modify to work?

You could probably use a 5-pack of the 1/2W 470K (Catalog #: 271-1133).

Shannon

I'd like to update that I did recieve a package from Matt today. Looks like I'll have lots of extras now! I'm going to complete this this thing tonight. I'll post some pics if the thing doesn't explode. I'm going to get my evil brother in law to flip the switch, while I take cover!