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Power Resistors in kits
#1
Hi all Tuberionatians!


I noticed that in the kits there are no Power Resistors anymore for local decoupling.


Or so it seems.
Maybe they are rated 1 Watt and I just don't see it.


In earlier times it was advised to raise them above the PCB or circuit card, but I don't see that notice anymore.
Have the resistors become so much cooler?


Also, it was always advised to make a shape with the legs instead of just keeping them straight.
I always wondered what that is about.
I can think of only one scenario:
The Power Resistor gets very, I mean extremely hot in case of some failure.
It melts, no it boils the solder and threatens to do a "melt down": sink down the solder holes onto the board.
There it could make a short if it touches another component on the way down.
Therefore the legs are bent, so that it can not lower itself onto the board.


Kind regards,

Eric-Jan
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#2
Hi Strelok

In the London Power kits, all power resistors are elevated by 6mm (0.25") and the kit notes show a little drawing and directive for this.

Decoupling resistors in preamp kits are all 600mW and do not get anywhere near to that dissipation during normal use, and therefore do not require elevation, nor do they have to be flame-proof types.

All electronic components use their leads as heat sinking, which is why you see such fat leads on zeners and high-current diodes. In some cases, it is advisable to leave a long lead on these components so their heat can be dissipated properly. In London Power kits, we use large solder pads wherever possible, both for heat dissipation and simply because a large solder connection will long out-live a small one.

Formed leads are usually to protect the point of exit of the lead from the component body. For example, epoxy-dipped capacitors or enamelled resistors have an outer coating that "wets" and flows out over the lead, just like proper solder connections. This flowed covering over the lead wire is fragile. Were you to bend the lead right at the body, the thinner part of this covering would fracture and the moisture seal would be compromised. Forming the lead before installing the part moves the stress point to the point of forming and retains the moisture resistance, and thus preserves the life expectancy of the component.

Have fun
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#3
Hi Kevin!

Yes, I see. The decoupling resistors are not seen as Power Resistos because... they are not.
Aha, that's the reason for not bending too close, you'l break the seal
Thanks for clearing that all up!

What about the special shape for the Poeer Resistors, the legs bending inward toward the body and then out?
Is that to prevent them sinking down into the card?
I guess not.

Someone said that if you bought a home audio amplifier and you let it sit in the closet for 10 years without turning it on ever, you cannot use it anymore.
My first impression would be "filter caps" but that does not seem to be the solution.

Do you have any idea what this is about?
How long does a tiny solder joint last, is that is?

Thanks,

Strelok
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#4
Hi Guys

Additional lead forming makes elevation of the component simpler for installation. Some power resistors are offered with elaborate extra bits to achieve this.

Yes, storing electronic equipment for extended periods kills the electrolytics, as TUTs describe a few times. No good comes from collecting amplifiers that are not powered regularly - guitars? fine - but not amps.

Have fun
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#5
I like that phrase: "elaborate extra bits". Just bend it, man!

So a cap job could fix that?

The guy said the amp would be useless.
To which I can now say "that's just, like, your opinion, man" (I haven't seen that movie, I just know the quote)


Strelok
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#6
(06-03-2021, 09:42 PM)K O\Connor Wrote: Hi Guys

Additional lead forming makes elevation of the component simpler for installation. Some power resistors are offered with elaborate extra bits to achieve this.

Yes, storing electronic equipment for extended periods kills the electrolytics, as TUTs describe a few times. No good comes from collecting amplifiers that are not powered regularly - guitars? fine - but not amps.

Have fun

(06-04-2021, 02:52 PM)Strelok Wrote: I like that phrase: "elaborate extra bits". Just bend it, man!

So a cap job could fix that?

The guy said the amp would be useless.
To which I can now say "that's just, like, your opinion, man" (I haven't seen that movie, I just know the quote)


Strelok
Yes.  I can't tell you how many amps that have been in storage or just not used I've had to re-cap for customers.  They will come right back to life!
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