What is a cement resistor?

[George]

Is it a brand or is it actually made out of cement? I need to use it so I can discharge my filter caps and remove the bright cap on my amps volume pot. Will any resistor of the same values work?

[Mike]

It's a big fat high power low ohmage resistor.

You need a resistor that can discharge the voltage sat on the caps without blowing up and killing your face. No you can't use a standard 1 ohm E12 series resistor.

[George]

Cool, so what sort of ohms and wattage am I looking at to do this safely with a cement resistor? Is it the higher the resistance the slower and safer it will discharge?

I've seen people using things like 10W 25K Ohms which I can't find!

[Mike]

There I can't help you I'm afraid, I'm not an Amp guy, I build pedals.

[George]

That's cool. I've found on Farnells the right resistance but only 2W, but apparently that's safe as well.

Cheers

[George]

FUUCK £20 minimum order!!!!

Dunno what else I need. Suggestions anyone?

[NickS]

TBH, to bleed off high voltage I wouldn't use a low-ohm cement resistor. I'd use a high-ish value so you don't discharge it in a flash and potentially blow the resistor too - high dissipation doesn't necessarily mean it will withstand a pulse of high voltage. My Marshall uses 100k resistors to balance the voltage across fliter caps; this also acts as a bleed. I suggest to avoid the £20 minimum order value you pop into one of your many local Maplins and get a 47k 2W metal film resistor D47K. While this doesn't produce the excitmement and fireworks of a screwdriver blade across the filter cap terminals and you'll need to leave it connected for a few seconds, it should do the job perfectly well. Then you can stick a screwriver blade across the terminals check with a meter just to make sure.

[Sloan]

WHAT THE FUCK.
To remove the bright cap on your amp, just fucking clip one of the legs so it doesn't make a connection. You're done. No need to fuck with discharging the filter capacitors.











I typically use a screwdriver if I feel I need to discharge a capacitor. Yes it's not as 'safe' and causes sparks, but I do what I want. It's better than discharging them accidentally with your hand (that really really sucks).

Before you go fucking around inside your amplifier, make sure you look up proper information and read everything twice.

Here is a link I found in the Google search engine.
http://www.electronicrepairguide.com/ca ... harge.html

[Sloan]

[George]

I dunno, I'm really not keen on the screwdriver method. I want to play this safe and by the book, particularly as I don't have the same knowledge or experience as you guys. I don't want my amp to shit the bed accidentally or kill myself. Even though the bright cap just needs a snip I think it's a good habit to get into.

NickS, thanks for the heads up. Glad I don't have to buy a cement resistor. Looks like I'll get the bus in tomorrow.

[SKC Willie]

I do what I want.

[Haze]

If you are just removing a cap then snip the lead - doneskis

[Doog]

With filter caps?? That sounds like a shit idea.

[George]

I just found the little bastard. It was a bit of a song and dance because it's all modern PCB mounted shit and the pots were hard wired in an awkward place. I snipped it and now its taken away all the harsh brittleness and a lot of the buzz has gone. Hooray! The trade off is it's not as chimey but it feels like the amp is less rigid and more open in a plainer sort of way.

I only did it on the clean channel though. OD channel looked like a clusterfuck so that still sounds like spikey shit.

EDIT: Fuck, I can even play my Strat's bridge pickup without the girlfriend crying and cat vomiting.

[Earth]

Rule of thumb for n00bz fucking around inside amps is "keep one hand in your pocket".

[Sloan]

You can also put a cap across the master vol to cut some 'fizz'. cant remember details but i liked the results on my ampeg.

[George]

Cheers, there's no master on this one so I just did the clean channel (one vol knob). I'd like to do it on the gain channel (which has gain and vol) at some point but it looked really complicated. I take it the cap would sit on the volume and not gain knob?

[George]

With filter caps?? That sounds like a shit idea.

Haha, no it's a "bright cap" sort of like a treble bleed in a guitar but on the amp. I wanted to discharge the filter caps before doing it.

Mission successful. Actually I didn't discharge the filter cap in the end. Fuck it.

[Mike]

TBH, to bleed off high voltage I wouldn't use a low-ohm cement resistor. I'd use a high-ish value so you don't discharge it in a flash and potentially blow the resistor too - high dissipation doesn't necessarily mean it will withstand a pulse of high voltage.

See this is why I don't fuck with this stuff, I get even the simplest things wrong if I don't have a pen and paper handy.

[timhulio]

I keep one hand in my pocket when doing pedal work.









But that's another story.