help with resistor size

[PeanutNore]

PR01 series. I get them from Mouser.

[soundmasterg]

Isn't it interesting that the larger resistors are the noisy ones.?. Intuitively I would have thought the smaller resistors would have been noisier. In fact that's why I didn't use the ones I have, though I admit to not researching the specs. The small size being discordant in appearance on an eyelet board was the deal breaker. But my thinking was that such a small resistor must be capable of more heat within their smaller dissipating surface area, but more heat means more hiss, right? I'm sure the devil is in the details.

I wonder who it is in China that manufacturers Ted Weber's metal film resistors. Hopefully it isn't MultiComp. Weber's resistors are nice in that they have longer leads than many others. I haven't checked to see how noisy they are in particular, though I have used them in repairs and builds and didn't notice a problem. The longer leads make it easy to use them in repairs of vintage amps where lead spacing distances are large. There isn't a hope for NTE or similar metal film resistors fitting in a vintage Sunn across the top of the phase inverter area in between the terminal strips, but the Webers will.

Greg

Greg

[Chuck H]

I've had the short lead problem such that I actually redesigned a board to fit a particular resistor once. I do mostly custom projects and I DO actually trouble with specs when I think it's important. In this case I needed 220k 1W resistors as totem balancers that were up to the voltage I was planning for. It might not have been as critical as all that, but I only found one part that met the spec in the Mouser cat. Fortunately I hadn't made the board yet but the redesign meant redoing layout and spacing for other components and leads. Anyway... That's my sympathetic note on it.

[soundmasterg]

I've had the short lead problem such that I actually redesigned a board to fit a particular resistor once. I do mostly custom projects and I DO actually trouble with specs when I think it's important. In this case I needed 220k 1W resistors as totem balancers that were up to the voltage I was planning for. It might not have been as critical as all that, but I only found one part that met the spec in the Mouser cat. Fortunately I hadn't made the board yet but the redesign meant redoing layout and spacing for other components and leads. Anyway... That's my sympathetic note on it.

I pretty much use the Webers for vintage replacements unless someone requests the original carbon comp. The Webers will fit in most applications due to the long leads. I've had to redesign stuff to fit too, which is annoying!

Greg

[mikepukmel]

Watch out doesn't mean emminent danger. We should always wear a seat belt driving the car, but if you don't, the car won't blow up or refuse to start.

70C is very hot.

If you learn nothing else theoretical in electronics, learn Ohm's Law. it is not complex, the formula is simple, the three variations of that formula derive from one another. it simply states the relationship between voltage, current and resistance in a circuit. it is something you can count on, and something I use every day. It isn't some corny school book thing, it is a real practical useful bit of science. I have been soldering for 60 years plus, and I have a calculator next to me at all times to do the arithmetic, and I use Ohm's Law every single day I am in the shop.

Reviewing the old posts here. Thanks Enzo! Its not that I don't understand Ohm's law, just that i would have to crank up the amp, measure the voltage drop, to do the calculations. What i don't understand (Yet!!) is how to figure out the voltage drops using circuit theory. I got my first circuits I and II books on a PDF. Its huuuuge. like 600 pages. Will take me a year to get through that.

[Enzo]

Ohm's law has three elements: voltage, current, resistance. To find any one of them, you need the other two. You cannot just look at a schematic and determine a voltage drop unless it is either spelled out already, or there is sufficient information to know the current through a resistance.

As an experienced technician, I know the typical current through a 12AX7 is very roughly 1 milliamp. Some cases maybe as much as 2ma, or in others maybe only 0.5ma. But 1ma is a good rule of thumb for estimates. SO if I know there are two 12AX7 dual triodes running off one B+ node, I can start with 4ma total current. If that current is coming through a 10k dropping resistor in the B+ supply, then the voltage drop across that resistor is: V = IxR = 0.004A x 10,000 ohms = 40v.

But that is a case where I have some existing knowledge. Absent that, I have to have two sides of the triangle.

[bob p]

it's handy to keep one of these hanging over the bench until you've memorized it.

[Sarah]

Hi All,
I ordered 1 watt resistors, 220k and 1.5k. They arrived and they are tiny!

0.098" Dia x 0.256" L (2.50mm x 6.50mm)

I checked the order page, and its the part i ordered

Manufacturer
Vishay BC Components
Manufacturer Part Number
PR01000106800JR500
Description RES 680 OHM 1W 5% AXIAL

These are metal film, with a coating.

Are these OK to use in a tube amp where 1 watt resistors are required? All of the other 1 watt resistors Ive seen are huge, 4x larger or more.

Thanks,
MP

I never observed axial resistors smaller than 4 mm dia X 10 mm Len.

[mikepukmel]

I never observed axial resistors smaller than 4 mm dia X 10 mm Len.

Yeah these are way tiny. I was afraid to use these. The gurus (see above) mostly said that they're probably OK in most parts of the amp. since its a fender type clone, the chassis has no holes, its very shallow, and the tubes are upside down putting heat into the chassis, I decided against using them on this build. What kind of stuff you working on?

[Sarah]

Yeah these are way tiny. I was afraid to use these. The gurus (see above) mostly said that they're probably OK in most parts of the amp. since its a fender type clone, the chassis has no holes, its very shallow, and the tubes are upside down putting heat into the chassis, I decided against using them on this build. What kind of stuff you working on?

Work as field Engineer and hobbyist at Electrical Calculator designs.

[mikepukmel]

Cool!

[mikepukmel]

Work as field Engineer and hobbyist at Electrical Calculator designs.

You thinking about building an amp at some point?

[mikepukmel]

Work as field Engineer and hobbyist at Electrical Calculator designs.

You thinking about building an amp at some point?

[SoulFetish]

J
Get yourself some "resistors" instead of "linear copper free iso-carbon sintered non-inductive temperature compensated resistors".

Yeah, but who's gonna' buy my amps if I use "resistors". "Linear copper free iso-carbon sintered non-inductive temperature compensated resistors" are all the rage with the kids these days, and all the guys on The Gear Page swear by 'em.

[SoulFetish]

I honestly don't know why the MultiComp are so bad, but they are. Could it be size? Material? Construction technique? Is there just a teeny little resistor hiding in a great big package? I honestly don't know.

They're an inexpensive Chinese product, cheap in every respect. I was not able to determine why they're so noisy -- I tried looking up their specs and the spec sheet was just horrible. Not much information. I got the impression that they weren't giving out some of their resistor specs because they didn't want people to know how crappy the product really is.

I won't buy MultiComp branded generic passives unless I don't have any other choice. I prefer to stick to the brand name products unless I just can't find what I'm looking for.

Shit, I forgot Bob's on sabbatical.
Has anyone else had bad experiences with multicomp? This makes me nervous because I bought some resistors and multiturn pots and if they are prone to failure or poor performance, it's gonna be a bitch trying to sort it out and find out which passives were made by whom. I think all the Newark orders over the past year have included some of their Multicomp brand!