Looking for Ampeg SVT CL resistor

[MarkusBass]

I'm looking for 10 Ohms 3W resistor used in Ampeg SVT CL on the power amp board. As far as I know it is made by IRC (part of TT Electronics), model AS-2B 3W 1%. On the schematic it's marked as "high surge" - I don't know how important it is. But since these resistors often fail (especially when the user has a failed valve) I think it may be important . It seems that I could by 500 pcs but I need only one, or two.

Mark

[Enzo]

My schematic says 2 watt. So if they installed 3w, that tells us something. If you can't find 2 or 3 watt resistors, use 5w.

The only thing that is going to burn out those resistors is a failed tube, so it isn;t the amp's fault.

[Leo_Gnardo]

If you plan on working on more SVT-CL and similar Ampegs in the future, why not stock up? OK 500 pieces - you won't need - but I always make sure I have 10 or 20 in the parts drawer. The identical resistor is available from Mouser. I also use the 1 ohm version in other amps as a bias current sense resistor. You could just as easily use the 10 ohm.

IIRC Mouser has a European distribution center. Lots of things you'll need for your repair bench. Typically I wait until I need $200 or more in parts then place an order, so I'm not paying more for shipping than the parts cost.

[MarkusBass]

Thanks for replies. Yes, this resistor is marked on the schematic as 2W but 3W symbol is printed directly on the resistor. Also the datasheet say that AS-2B is 3W resistor. I could replace it with any similar resistor but there is not much space to put other types of resistors. The diameter of the resistor is 4 mm. Mouser has IRC resistors but not 10 Ohms value. Yes, I plan on working with Ampeg amps (actually I do it all the time) and I would like to have 10-20 resistors like this one in the drawer. The only problem is where to buy them :-).

Mark

[Enzo]

I do not doubt your amp has 3w resistors, I was inferring that the factory at some point decided 3w was better suited than 2w, so they made the change in production. So moving to even 5w would be OK. But you mention space. The layout drawing has them blocked out looking like large rectangular things. 4mm is about the size of a 1/2 watt resistor. Are they really so close together larger than 4mm won;t fit? You could mount them on end at alternate ends, that will increase the space.

I just looked at 10 ohm 3w resistors at Mouser, and found at least 50 kinds of them in stock, and at least on the first whole page of them, all were available by the each, no 500 piece minimum. The few data sheets I opened showed 6-7mm diameters.

[MarkusBass]

There is size constraint (the resistor looks completly different than on the layout - it has only 4 mm diameter) and precission constraint - it is used for current measurement so it has to be with 1% accuracy. Appart from this, I wanted to find original resistor.

Mark

[Enzo]

That 4mm thing was really hanging me up. The IRC data sheet for the AS-2B says 5.6mm, which is similar to the others I found.

Data sheet:
http://www.irctt.com/pdf/AS.pdf

The RS series from Vishay come in 4.75mm

If you are looking for the original part, I wish you well. It may be stocked somewhere, but it also may have been a special order part for Ampeg.

[Leo_Gnardo]

Dale RS-2B series from Mouser. I measured mine @ 4.5 mm. If necessary ou can "stagger mount" that is, stand one up on its leads. Which may help get a bit of air around it to help cool it. Mouser part # 71-RS2B101%TR $0.75 .

The ones I've found in Ampegs were Dale. No biggie, they need second sources too, in case one manufacturer/supplier is out of stock.

Here's some to select from, hope they have 'em in Europe. They're made in Mexico. Hands across the water!

Rats! Tried to put in a link, it brings you to the top of the selection screen. Here's a photo of the page, hope to save you some time.

71-RS2B10 looks like the identical item, for $1.36, nearly twice the price. Nice! Wonder how that happens...

[MarkusBass]

Thanks guys. This is exactly what I was looking for. It's funny that different manufacturers use the same symbol (as their own symbol) and almost the same specification :-).

Mark

[Leo_Gnardo]

Thanks guys. This is exactly what I was looking for. It's funny that different manufacturers use the same symbol (as their own symbol) and almost the same specification :-). Mark

I don't know what about symbols but I do know a good resistor when I see one.

A couple months ago there was a long-running discussion that started when one of our correspondents bought what he thought were proper 1 Watt 1 ohm resistors for use as current-sensing for output tube cathodes. He bought modern "miniature" resistors. They were going bad one after the other. Early on, I mentioned these 3W resistors as a solution. The thread ran on for about another 100+ entries, sometimes getting a bit heated. I just kept silent & hoped the OP would look back and get some of these. If he did, his problem's solved for good. Cheap too, considering the time & brain power it took to calculate and communicate over the course of weeks.