Is your unobtainium power switch worth $5 and an hour or so of your time?

[neevo]

1. Yes
2. Figure 1W per amp of primary current. So yes, unless you mount the thyristor to something to act as a heat sink, it'll burn up.

Hey EW, I didn't remove the cap on the switch when I did this mod to my KA-7100's power switch. Should I have?

 

[EchoWars]

It can interfere with the operation and possibly cause the device to trip when you don't want it to. Beyond that, with the thyristor in place it serves no useful purpose.

 

[neevo]

It can interfere with the operation and possibly cause the device to trip when you don't want it to. Beyond that, with the thyristor in place it serves no useful purpose.

It will be removed then. Thanks.

 

[steveUK]

I use an aftermarket RF remote controller and socket. So, the receiver's mains switch is never broken or closed under power, and you also now have remote on/off control of the amp or receiver, just sit back in your armchair and switch on! Here's the unit I bought on Ebay, I'm in the UK but I'm sure you can buy similar versions suitable for US sockets too: http://www.ebay.co.uk/itm/321774418712?_trksid=p2057872.m2749.l2649&var=510686522132&ssPageName=STRK:MEBIDX:IT

 

[Hak Foo]

I was thinking for the "just leave it permanently on" approach, a good choice would be those "Power Centres" they used to sell for desktop PCs-- big box of a power strip, typically sized to fit under a CRT monitor, with a bunch of individual switches in front for each outlet. That solves the worry some people had about "I don't want to turn on my sources after my reciever".

The form factor would fit well in a typical equipment stack, and you often see them in thrift shops for next to nothing. (Also, while you're there, get one of those old composite-video-and-RCA-audio video game switch boxes and use it to split a single Aux input into three or four!)

 

[Watthour]

One potential problem with ignoring a failing contact (whether in a switch, relay, line tap, bus bar, etc.) is that when power is turned on elsewhere the inrush current still has to pass through the marginal contact. When the surge current is applied to the poor contact it is likely that arcing will continue every time power is interrupted and applied.

 

[Hak Foo]

I definitely see your point. But from a protective perspective-- if you have something that's in decent shape currently but don't want it to suffer long-term due to mechanical wear and tear as well as arcing-- an external switch is better than nothing and avoids having to touch mains voltage stuff.

 

[Watthour]

For preservation I would agree. As a "band-aid" for an already failing switch it probably is not such a good idea. Ultimately, cleaning the switch and installing a relay, thyristor, and/or current limiter would be the best solution, but the external switch might protect the original for some period of time before the permanent "fix" is applied.

 

[rottalpha]

This thread should be a sticky

 

[CharlieBee]

Right on Watthour, "but the external switch might protect the original for some period of time before the permanent "fix" is applied." A switchable power switch is the savior of the "unobtainable power switches" for those who will accept. See Post #36 on this old thread.

Bill D

 

[Raccoon1400]

This thread should be a sticky

Or added to here:
http://www.audiokarma.org/forums/in...-repair-restoration-reference-threads.426532/

I've got a method for rebuilding a certain problematic alps switch with new contacts there. That method could work well in combination with this one too. I've got a pioneer SX-650 lined up for the mod in this thread and I'll do it may more times if it works well.

 

[Hak Foo]

Okay, stupid question:

Since the current to the switch will now be "about 120ma" according to the original post, can you use relatively thin wire to the switch leads?

Obviously, I'd use the original thick wire for the connection from the mains and transformer to M1 and M2, but I didn't want to chop up too much of that in case I had to ever restore it to stock. I have some thin solid-core aluminium wire handy-- not labelled on the insulation, and the spool is completely wrong. If I had to guess, it's probably ~28AWG... would that be sufficient for the switch? The charts I see suggest even 36AWG would be sufficient to carry 120ma with headroom.

I could scrap an old clock-radio for the mains cord, but that feels inelegant, and I'm thinking it will lead to big huge blobs of heatshrink and solder coming off the triac, trying to contain two big wires

FWIW, The target unit is a JVC JR-S300, with a name-plate rated draw of something like 165 watts, and a fuse that I think is rated at 4A-- I'm suspecting that the currents involved in this unit are fairly non-threatening.

Also, looking at the schematic (for a slightly different related model) and the actual unit, there's just a capacitor for the snubber across the power switch. Typical?

 

[redk9258]

I have some thin solid-core aluminium wire handy--

Throw that stuff away! Or recycle it. Do not put aluminum wire in any electronics equipment.

 

[Mr.White]

A switchable power switch is the savior of the "unobtainable power switches" for those who will accept. See Post #36 on this old thread.

Bill D

I've been using a power strip with my Lafayette LR-9090 for two years with no problems. Probably got the idea from your original post. I keep the receiver in the "headphones" position and switch on and off from the power strip. After it warms up a bit I can switch it back one notch to "Speaker A + C" if I want to listen through speakers. It's worked flawlessly every time.

 

[Hak Foo]

Throw that stuff away! Or recycle it. Do not put aluminum wire in any electronics equipment.

I ended up scrtapping a PC powersupply modular cable for better-quality wire. The insulation says 18AWG with a 300-volt rating. I figure if the mains voltage hits 300 in an American house, this will just be one line-item on the homeowner's insurance claim.

Just tested so far with headphones, so I'm still worried about heat production when I throw a real load on it. I was able to bolt the triac to a small hole in the metal bottom chassis with some thermal paste., right near the front outer-case bolt. I'm not quite sure about the heatsinking capacity of the chassis. I'm hoping if it overheats, the small gap between the plastic side case and the bolt/chassis/triac will prevent the side case from melting. :/ Part of me is thinking of buying a small TO-220 size heatsink as extra insurance, but the words "comical overkill" keep floating in my head.



Coming from the PC hardware enthusiast sector, "put a heatsink on it" means installing a fan-cooled device the size of a small grapefruit that weighs roughly the same as a Toyota Celica, using a clamping mechanism originally designed to restrain the criminally insane, and capable of keeping a device the size of a half dollar radiating 150 watts at about 30c over ambient. So I'm not sure if "bolting it to the case" is a sufficient way of handling a likely peak of two watts.

 

[EchoWars]

If you have it bolted to the chassis, that's all that is needed.

 

[Hipocrates]

LOL


Like this!!

 

[nj pheonix]

I was going to ask about heatsinking. For my education if you're using a 25A device on an amp with a 3.2A main fuse, do you still need heatsinking?
Glenn i was just looking at post #140.
I'm guessing this applies to me. If that's the case and chassis mounting would be ugly (inconvenient). Would a small bolt-on heat sink be adequate?
something like this?
http://www.mouser.com/Search/Produc...000Gvirtualkey53210000virtualkey532-507302B00

 

[EchoWars]

That's kinda wimpy, but under normal listening conditions would probably be OK. However, something like this is much preferable:

1" tall - http://www.mouser.com/ProductDetail...=sGAEpiMZZMttgyDkZ5Wiuua5pzU5xE5ZX3Yy1QskXag=

 

[K7sparky]

Okay, stupid question:

Since the current to the switch will now be "about 120ma" according to the original post, can you use relatively thin wire to the switch leads? I use AWG 22 or 24 stranded for the physical strength. The short runs could be done with #30 wirewrap wire but why waste your time"

Obviously, I'd use the original thick wire for the connection from the mains and transformer to M1 and M2 That is correct even if it looks wierd.

I have some thin solid-core aluminium wire handy-- not labelled on the insulation, and the spool is completely wrong. DON'T waste your time with Al core wire - toss it in the TRASH and buy stranded or solid if you must hook up wire.

Also, looking at the schematic (for a slightly different related model) and the actual unit, there's just a capacitor for the snubber across the power switch. The AC through the cap is a trigger source hooked the the gate of the TRIAC. You can use a web base calculator (if you don't want to do it yourself) for Xc Capacitive reactance at 60 Hz (Xc= 1/2pie F) SHORT STORY toss the snubber in your junque box.

I realize it feels wrong to hook big wires to an itty bitty TO220 devise. Looking at AWG 12 SIS Vulkene hooked to a TO220 is just freaky. That application is a 220VAC front end regulator of the 3KV plate supply for a 2KW output RF deck. Been running for many years and TRIAC is screwed to the chassis.

Took me years to get used to it. Still feels like doing something wrong.

I think the end of EchoWars signature line by my favorite author “relax and get used to the idea” sums it up best.

My guess is you could hang it in free space and it wouldn’t fail. Try it – The worst is the cost of the TRIAC.

I have always just screwed them to the chassis. The only one I have had fail was in a driver between a PID control and my lead melting pot. That happened by a short on the output and the TRIAC was faster than the fuse which is common of solid-state widgets.

Best way I can think to test in your application is screw it to the chassis run your amp full out and feel the chassis temperature with your finger. Best guess is you will not feel any temperature rise. You could also use a temperature probe. The IR temp guns depend on the emissivity of the object aimed at. Great article on the IR temp guns is in the January 2017 QST page 77 by AG1YK and gives a few of the emissivity ratios.

Stumbled over ST (SGS-Thompson) line of "Snubberless “ TRIACS. BTA20-600 20A 600V insulated / BTB20 noninsulated. The line of BTA / BTB in various currents and voltages are rated for high inductive loads same as the Littlefuse Alternistor line and are CHEAP on the bay mostly free shipping.

Last 2 mods on RS440s were done with the BTA20-600 isolated TRIACS screwed to the chassis with a #6 screw. Used a very light coat of thin silicon grease. Really like the insulated tabs.