S.E.X. > 2A3 Monoblock OPT

[Ken]

There's a Canadian Tire just up the road from me  and I did see that meter.  I thought that it only being able to read down to 400R could be a problem.

[Paul Birkeland]

Those are ranges on the meter.  The 400 ohm setting will have three leading digits, a decimal point, then one more digit.  If you're trying to measure a 0.01 ohm resistor (which is extremely difficult to measure anyway), then you'll get a 000.0 on the meter, but it can certainly measure below 400 ohms.

[Paul Joppa]

For the parts order, add four small resistors for grid stoppers; we've often used 220 ohms but anything from 100 to 500 ohms is good. Carbon or metal film are acceptable; carbon composition is better in theory but tends to be fragile unless you get a premium part.

Also don't forget the 3K power resistors should be rated 20 watts, not 10 as in the parts list. Inexpensive metal-oxide ones are fine, but seem to be out of stock in many places; Ohmite wirewound are good, available, and not too costly:

https://www.mouser.com/ProductDetail/Ohmite/B20J3K0E?qs=%2F%252B4YgdRx4NhlrL7xcy2z3g%3D%3D

[Paul Birkeland]

I would add to PJ's recommendation not to use the chassis mount type resistors (with the gold heatsinks).  They will only dissipate their rated power if they are mounted to the side of a battleship, and derating them can be tricky.

[Ken]

@PaulJ:  I will order the grid stoppers as you said.  I did already find the Ohmite 3K 20W resistor at Mouser.

@PaulB:  that meter I linked at Mouser is less expensive and since they're both likely made in China anyway, would it do the job?  I'm already ordering from Mouser anyway.

[Ken]

@PaulJ:  what W rating for the grid stopper resistors?

[Paul Birkeland]

Grid stoppers handle no current (well, nearly no current), but it's nice to have a reasonably stout part with long leads, so a 1/4W part is a nice idea.

[Ken]

There are these three resistors on the original parts list.  What voltage rating should I order?  Mouser offers Vishay/Dale in 200, 250, 300, 350 V

249K 1/4W metal film
681 1/4W metal film
182 1/4W metal film

[Paul Birkeland]

Those all need to be rated for at least 10V.

[Ken]

Paul, they're rated between 200-350V

[Paul Birkeland]

That is 20 to 35 times more than they need to be rated for; it's a non-issue for these parts.

Pretty much none of the resistors in the original afterglow circuit gets worked particularly hard in terms of voltage.  The power supply bleeder is going to see close to 500V on start-up, so that's a consideration. 

[Ken]

I understand but at 1/4W for the R values listed on the parts sheet, 200V is the lowest that I can see on the Mouser site.  Obviously, they do have some with lower V rating but not corresponding to the other specs we need.

[Paul Birkeland]

You do not need to hunt for a low voltage rating, as any voltage rating is more than enough for these parts. This is a maximum voltage, nothing bad happens if you run a 500V rated resistor at 1V.

[Ken]

I understand; just trying to keep the cost down by not over-spec'ing what I really need.

[Ken]

Paul B:  Here are the 270Kohm bleeder resistors that Mouser is showing in carbon film 1/2W.  The max voltage rating offered at these specs is 400V.  I don't understand the difference between the two items listed: one is almost twice the price of the other, at what appears to be the same specs.

https://www.mouser.ca/c/passive-components/resistors/film-resistors/carbon-film-resistors-through-hole/?power%20rating=500%20mW%20%281%2F2%20W%29&resistance=270%20kOhms&voltage%20rating=400%20V