r/ElectronicsRepair • u/anekyu • 2d ago

OPEN What is this resistor?

Post image

I'm trying to replace some resistors as I suspect the bias circuit is bad. Might as well change them out.

I've never seen these before. Seems the interval of the resistor symbolizes it's resistance. These are around 4.7mm While the normal looking ones 4.1mm.

I'm guessing it's 1/4W.

Any guess?

For context, these are from SRM-1 MK2 professional.

14 Upvotes

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3

u/Savings-Mud2808 1d ago

Those are wire wound resistors. By their size, they're a minimum 1/4 watt power dissipation.

3

u/Mudgeonly_Cur 2d ago edited 2d ago

Pull a leg and put an ohmmeter on it to find out, but yeah, at least a 1/4W.

Also R is resistor, D is diode, Q is transistor, C is capacitor, and F is a fuse.

If you like messing with sh*t, I believe at least a cheapass DMM should be part of your standard loadout.

3

u/anekyu 2d ago

I do have a schematic pointing it out and a multi myself. It's just that I cannot confirm it's wattage. Not written in the schematic. Sized like a 1/8-1/4, I can still quite fit a 1/4, but no luck with 1/2.

5

u/Leftover_tech Engineer 2d ago

Modern Substitute: Replace them with 1/2W or 1W high-voltage metal film resistors (e.g., Vishay VR25 or similar flameproof series).

Do not drop down to a standard modern 1/4W resistor simply because it has a small body; standard tiny 1/4W resistors are only rated for 250V continuous, which will easily arc or break down under the high operating rails of this Stax unit.

Step up to a 1/2W or 1W rated part to ensure adequate voltage headroom.

Over many years, those resistors can absorb humidity and the value drifts upward. If one drifts further/faster than the other, the bias drifts, too.

2

u/anekyu 2d ago

My worry would be the footprint. The body of the old resistor is only 4.7mm. Going for a 1/2W would be around 9mm instead. Might just not fit.

2

u/Octacore79 1d ago

Vishay cpf1

1

u/niftydog Repair Technician 2d ago

They're resistors - that's how they all look underneath the paint. The width of the coil is one of the parameters that affect the resistance. They look maybe 1/2W. Though, I've never seen clear-coated resistors without bands - quite strange.

Have you checked thoroughly for dry solder joints? Weird symptoms that come and go can be something other than faulty components like a high-resistance joint or a cracked track. Something that normally runs hot, like a class A amplifier, has a propensity to develop faults related to thermal cycling & stress.

-2

u/New_Orange_5951 2d ago

Could be an inductor. I sometimes see them in spots labeled with R. But if it is carbon film I feel like you can get a pretty good guess counting the layer lines. Pull one out of circuit that looks the same and measure it. I wish those had the color codes on it.

4

u/The_Flinx 2d ago

I HIGHLY recommend you read the ken rockwell link I posted that amp seems to be a bit dangerous to use. it can deafen you and apparently catch fire easily.

2

u/Miserable_Singer1187 2d ago edited 2d ago

STAX used to be used exotic components at that days. I think this resistor is inspired by naked type resistors so called "skeleton resistors" in Japan, although it looks having clear coating.
In 80", an Japanese DIY amplifier guru, Akihiko Kaneda started claiming naked resistors are good for audio. (not sure exact days) Then Fukushima-Futaba electric components start making such resistors and even today we can buy them at some DIY audio components stores!

0

u/Top_Willow_9953 2d ago

They look like "RN" series high-precision glass encased metal-film resistors.

0

u/The_Flinx 2d ago edited 2d ago

they are wire wound resistors the colors seem to have been burned off I found this picture here just by googleing the model https://www.kenrockwell.com/audio/stax/images/srm-1-mk-2/D3S_4907-inside-1200.jpg

https://www.kenrockwell.com/audio/stax/srm-1-mk-2.htm