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

Snubbers are generally needed for any circuit with a solid-state switch. I think one might be needed here, too. Here is my reasoning.

When the TRIAC switches off at zero current (or close to it) the tiny residual charge in the junction must be dumped. That may stimulate a parasitic oscillator formed from the capacitance and inductance of the wiring and switch, and thereby create ringing. The ringing's peak voltage may exceed the limits for the TRIAC junction and damage it, either one time or over time.

A snubber is inexpensive and easily fabricated. The snubber's capacitance must be greater than the parasitic capacitance, but it can't be too large or it increases power dissipation through the resistor from its own stored charge which has to be dissipated.

There's another issue. Switching an inductive load (power transformer primary) causes the voltage heading back to the mains to spike as the primary field collapses and is converted back into current. Without a flyback diodes to dissipate it, that energy must go somewhere, and the voltage climbs until current may flow. The destination is back into the TRIAC. Again, same problem with high voltage exceeding the junction limits.

Power transformers without snubbers also ring in normal operation, and that ringing can cause high-frequency spikes which may exceed the junction limits.
 
And what will happen in case of a failure of triac, short as we have with transistors sometimes? The snubbers have been at least reliable if not as effective.
I have gone for these, was a little cheap I guess?
https://www.digikey.co.uk/product-detail/en/stmicroelectronics/BTA24-800BWRG/497-2402-5-ND/603427
https://www.digikey.co.uk/product-detail/en/stmicroelectronics/BTA26-800BWRG/497-4172-5-ND/725386
Your equipment will not shut off in case of shorting. Not a tragic scenario. I've done this mod for years and am happy with the results.
 
I had my Yamaha CA-1000 opened today. I couldn't find the arc suppressor/snubber neither at the power switch nor at the back. Couldn't locate on schematics either.
 
I had my Yamaha CA-1000 opened today. I couldn't find the arc suppressor/snubber neither at the power switch nor at the back. Couldn't locate on schematics either.

I looked at the schematics (from Hifiengine.com) and the snubbers are on the power switch circuit board for all models except the European version, it does not have one.
It is a capacitor in series with a resistor.
 
I looked at the schematics (from Hifiengine.com) and the snubbers are on the power switch circuit board for all models except the European version, it does not have one.
It is a capacitor in series with a resistor.
Thx for this. Mine is European model, MKII.
 
This is a pretty bulged snubber I just took out from the back of Sony STR-6065. The power switch uses a microswitch that I happened to have in store so replaced both snubber and the microswitch. I wonder, maybe the snubber was for 125ACV as the Sony was brought from USA but it's a multivoltage unit, I have 240V in mains.

The microswitch is grounded with a 1000k ohm resistor which read 1200k and I guess the blown snubber at the back (not soldered to the switch as usually) was to protect the switch too, it's soldered at the unaltered power outlet at the back.

Also the Sony does not power off completely. Was same before and after replacing the switch. When it's powered off there is still some light and I can hear very weak sound when I crank up the volume to around max. Is it some kind of 1970s stand-up mode? :)

Now strange update. I measured the bulged snubber and it shows about the right capacitance 29nF or so, did they make them like this or what? It has Sony logo at the top a bit disfigured though by the bulging

snubberbeat.jpg snubberbeat2.jpg snubberbeat3.jpg snubberbeat4.jpg
 
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This is a pretty bulged snubber I just took out from the back of Sony STR-6065. The power switch uses a microswitch that I happened to have in store so replaced both snubber and the microswitch. I wonder, maybe the snubber was for 125ACV as the Sony was brought from USA but it's a multivoltage unit, I have 240V in mains.

The microswitch is grounded with a 1000k ohm resistor which read 1200k and I guess the blown snubber at the back (not soldered to the switch as usually) was to protect the switch too, it's soldered at the unaltered power outlet at the back.

Also the Sony does not power off completely. Was same before and after replacing the switch. When it's powered off there is still some light and I can hear very weak sound when I crank up the volume to around max. Is it some kind of 1970s stand-up mode? :)

Now strange update. I measured the bulged snubber and it shows about the right capacitance 29nF or so, did they make them like this or what? It has Sony logo at the top a bit disfigured though by the bulging

View attachment 1069025 View attachment 1069026 View attachment 1069027 View attachment 1069028

That snubber has a 500v rating printed on it. Since this is drifting away from the original subject I suggest you start a new thread to deal with the 'not power off' problem.
 
I noticed a 1Megaohm 1/2W resistor from power circuit to ground, same in my Yamaha CR-1000 and Sony STR-6065, in the latter it measured 1.2M (it is +/-5% resistor, does it mean it's used up, should I replace it, maybe with 1W?).

Does this resistor relate to the arc protection and should it be left as it is when installing Triac?
 
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I noticed a 1Megaohm 1/2W resistor from power circuit to ground, same in my Yamaha CR-1000 and Sony STR-6065, in the latter it measured 1.2M (it is +/-5% resistor, does it mean it's used up, should I replace it, maybe with 1W?).

Does this resistor relate to the arc protection and should it be left as it is when installing Triac?

It is not related to the snubber arc protection, its purpose is to bleed off any possible charge that might accumulate on the chassis. I would leave it there if it were mine.
 
I finally got around to trying a Triac to turn on and off an amp and it was a success. I am still looking for the down side of this mod.

This mod should work on any amp and the power switch load will be reduced to around 120 ma and no arcing. The power switch will now last longer that you will.

The test bed is a Lafayette LR9090 (Setton RS) series known for lunching on power switches. This switch had the NO contact for power "on" inside the switch gone, just smoky residue left. This special case required a relay NC contact for the PA Mute / protective relay dump on power "off". I moved the switch NC contact to NO position for the power on function.

Triac used was a Littlefuse Q4025L6 (Mouser 576-Q4025L6) Rated 400VAC 25A RMS for highly inductive loads and tab isolated. Way over rated. Yea olde Fluke gives around 7A AC peak on the 100 ms scale at power "on" and idle current of 0.6A AC at low volume. The Triac data sheet is on Mouser: http://www.mouser.com/Search/Refine.aspx?Keyword=q4025

Note: Triac suffix L6 is a TO220 case isolated tab, if you prefer solder loops for a buck or so more the J6 suffix is a TO218X with loop leads and isolated tab.

For me, the isolated tab and not having to bother with mica and screw isolator is worth a buck or 2. You?

This is a difficult mod with an extensive parts list:
1 ea Triac
1 ea 100 ohm 1/2 watt resistor

Remove the AC line power and transformer lead (and maybe switched rear outlet) from the power switch. Remove the RC snubber across the switch contacts.

Mount the Triac in any handy location.
AC power lead goes to M1
Transformer lead (and maybe switched rear outlet) goes to M2
Power switch:
lead 1 100 Ohm resistor and goes to gate G
lead 2 goes to M2

triacmod_zpsdaf49925.jpg


OK!, so I lied about being difficult

I found a place on the chassis for the Triac that the leads would fit, drilled a mounting hole, soldered directly to the TO220 leads and used heat shrink over joint and lead.

Initial testing was done by removing the transformer primary fuse and hooking up a 100W bulb for a load. After a bunch of switching the bulb on and off, I put the transformer fuse back in and tested and tested...... The amp has been switched on & off left on for days and no problems.

On state voltage drop is 0.8 to 0.9 VAC which agrees with the data sheet curve

Other benefits / thoughts:
1. Littlefuse calls these Triacs: Alternistor Triacs and they are designed for high inductive loads so no RC snubber is required.
2. Power "off" is always at a zero crossing so there is no arcing thus no voltage transients inside the amp to worry the power supply components.
3. Power "on" has no contact bounce arcing. It did not seem useful to add the extra parts for zero crossing turn on.
4. A 200V rated Triac would work, but why save a few pennies and give Murhpy a chance?
5. Lower current rating would work. 3000W @ 125 VAC switching capability is not needed, but see above
6. Triac off state leakage is 50 micro amps which is lower than the original RC filter across the power switch.
7. A MOV and / or RC filter on the incoming power is still necessary to protect the amp from the rest of the world.

After more testing this mod will be refined with pictures and added to the LR9090 repair / upgrade thread.

I hope to get some feed back about possible problems I have missed.
 
Hello K7Sparky or whomever can help. I think I maybe retarded( Mentally handicapped) I have the Kenwood KR-5030, switch is working fine but wanted to add the Triac Alternistor fix.
Anyone help on the connection points for the AC? If I connect it one way, it has a 10volt drop. Triac works.. but not right.
I did keep the snubber circuit on my Triac setup. ( I'll post picture )
1. Should I take the Snubber off my Triac setup?
2. AC connection points?
3. How I connected it the last time; Pictures with snubber and without same- dim bulb goes bright when turning Variac up to 40 volts.
This should be simple. Original switch used to trigger the Alternistor and it is the new switch? Correct or not. ( AC connections )?? Anyone post any pictures? I didn't see any.
I finally got around to trying a Triac to turn on and off an amp and it was a success. I am still looking for the down side of this mod.

This mod should work on any amp and the power switch load will be reduced to around 120 ma and no arcing. The power switch will now last longer that you will.

The test bed is a Lafayette LR9090 (Setton RS) series known for lunching on power switches. This switch had the NO contact for power "on" inside the switch gone, just smoky residue left. This special case required a relay NC contact for the PA Mute / protective relay dump on power "off". I moved the switch NC contact to NO position for the power on function.

Triac used was a Littlefuse Q4025L6 (Mouser 576-Q4025L6) Rated 400VAC 25A RMS for highly inductive loads and tab isolated. Way over rated. Yea olde Fluke gives around 7A AC peak on the 100 ms scale at power "on" and idle current of 0.6A AC at low volume. The Triac data sheet is on Mouser: http://www.mouser.com/Search/Refine.aspx?Keyword=q4025

Note: Triac suffix L6 is a TO220 case isolated tab, if you prefer solder loops for a buck or so more the J6 suffix is a TO218X with loop leads and isolated tab.

For me, the isolated tab and not having to bother with mica and screw isolator is worth a buck or 2. You?

This is a difficult mod with an extensive parts list:
1 ea Triac
1 ea 100 ohm 1/2 watt resistor

Remove the AC line power and transformer lead (and maybe switched rear outlet) from the power switch. Remove the RC snubber across the switch contacts.

Mount the Triac in any handy location.
AC power lead goes to M1
Transformer lead (and maybe switched rear outlet) goes to M2
Power switch:
lead 1 100 Ohm resistor and goes to gate G
lead 2 goes to M2

triacmod_zpsdaf49925.jpg


OK!, so I lied about being difficult

I found a place on the chassis for the Triac that the leads would fit, drilled a mounting hole, soldered directly to the TO220 leads and used heat shrink over joint and lead.

Initial testing was done by removing the transformer primary fuse and hooking up a 100W bulb for a load. After a bunch of switching the bulb on and off, I put the transformer fuse back in and tested and tested...... The amp has been switched on & off left on for days and no problems.

On state voltage drop is 0.8 to 0.9 VAC which agrees with the data sheet curve

Other benefits / thoughts:
1. Littlefuse calls these Triacs: Alternistor Triacs and they are designed for high inductive loads so no RC snubber is required.
2. Power "off" is always at a zero crossing so there is no arcing thus no voltage transients inside the amp to worry the power supply components.
3. Power "on" has no contact bounce arcing. It did not seem useful to add the extra parts for zero crossing turn on.
4. A 200V rated Triac would work, but why save a few pennies and give Murhpy a chance?
5. Lower current rating would work. 3000W @ 125 VAC switching capability is not needed, but see above
6. Triac off state leakage is 50 micro amps which is lower than the original RC filter across the power switch.
7. A MOV and / or RC filter on the incoming power is still necessary to protect the amp from the rest of the world.

After more testing this mod will be refined with pictures and added to the LR9090 repair / upgrade thread.

I hope to get some feed back about possible problems I have missed.
 
Hello K7Sparky or whomever can help. I think I maybe retarded( Mentally handicapped) I have the Kenwood KR-5030, switch is working fine but wanted to add the Triac Alternistor fix.
Anyone help on the connection points for the AC? If I connect it one way, it has a 10volt drop. Triac works.. but not right.
I did keep the snubber circuit on my Triac setup. ( I'll post picture )
1. Should I take the Snubber off my Triac setup?
2. AC connection points?
3. How I connected it the last time; Pictures with snubber and without same- dim bulb goes bright when turning Variac up to 40 volts.
This should be simple. Original switch used to trigger the Alternistor and it is the new switch? Correct or not. ( AC connections )?? Anyone post any pictures? I didn't see any.
Pictures didn't work so here's another try.
 
Trying to get the pictures attached failed the first time:
Not sure if they can point out what I'm doing wrong but I'll give it a shot.
 
You don't need a snubber with an alternistor triac. It's designed for inductive loads. As far as connecting the AC, does this help?

PHOTO_20181208_094922.jpg
 
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