Below is the line filter of an Ampex tuner I'm working through:
During recap I'll be replacing the two .005uf caps between the line and ground with type Y .0047uf safety caps. Can I clip out the 1meg resistor or should I leave it? Why is it there to begin with? Thanks
During recap I'll be replacing the two .005uf caps between the line and ground with type Y .0047uf safety caps. Can I clip out the 1meg resistor or should I leave it? Why is it there to begin with? Thanks
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It looks to be a safety feature to discharge the caps and stop the user getting a little shock from the mains plug... which is very common actually. Those caps are tiddlers, its more of a problem with 0.22uF or 0.47uF caps which have been used in the past in some equipment. Those can give a nip to the unwary.
In the UK those two caps have to be small otherwise leakage to earth breaks EMC regs.
They do. I'm thinking back to the days of Mitzi's (Mitsubishi) CTV's and the like which often had 0.47uF caps across L and N before the switch. Ouch 😉
I was beginning to think that was the case. Looks like it wouldn't discharge if the tuner was plugged in backwards though. My concern is that the resistor is going to put some potential on the chassis, and while I know it's not lethal I just don't want it if I can avoid it. The tuner is part of a console system and will always be plugged in through a preamp/control center so I'm inclined to remove it.
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As shown I see the resistor as a safety issue. I assume the unit has a 2 wire plug here and no Earth.
If the mains 'Live' is connected to the conductor going to F1, then when the unit is switched off, the 1 meg resistor connects the mains live to the un-earthed chassis...
Surely better to remove the resistor and move the cap C59 from the 'plug' side of the switch to point B on the diagram. Then the caps are only used when power is on (not all the time the unit is plugged in) and there is no need to bleed them via a resistor, as the transformer will do that.
Maybe a 3 pin plug with earth to the chassis would be a good idea?
If the mains 'Live' is connected to the conductor going to F1, then when the unit is switched off, the 1 meg resistor connects the mains live to the un-earthed chassis...
Surely better to remove the resistor and move the cap C59 from the 'plug' side of the switch to point B on the diagram. Then the caps are only used when power is on (not all the time the unit is plugged in) and there is no need to bleed them via a resistor, as the transformer will do that.
Maybe a 3 pin plug with earth to the chassis would be a good idea?
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Don't bother installing the death-caps, and do remove the 1Meg too.Below is the line filter of an Ampex tuner I'm working through:
During recap I'll be replacing the two .005uf caps between the line and ground with type Y .0047uf safety caps. Can I clip out the 1meg resistor or should I leave it? Why is it there to begin with? Thanks
Yes I was planning on also moving the cap to the other side of the switch. Having components in front of the switch (or fuse especially) gives me the heebie jeebies.
The console's preamp/control center only has provisions for 2 pronged plugs but I will look into other ways to earth the system as a whole. I will be putting a grounded plug on the control center for sure.
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On one of Dysons early Hoovers users complained if they touched the mains plug after unplugging it they got a shock. Turned out some had forgot the 1 meg resistor across the mains.
Dunmo, dubwoofer. Your question sounds like, “Hey there, can I clip out this resistor whose purpose I don't know?”, which begs the best barbed response: “what do you hope to achieve by removing a part whose function you haven't a clue?”
That's the point.
My take is “its there, it was designed to be there, and it should remain there.”. Unlike some of the parts in a mature design that a consumer/enthusiast is looking to 'upgrade' by tube rolling, capacitor swapping, connector gold plating and so on, a resistor on the front end of a power supply has no capacity to affect the 'sonic signature' of the amp, working or not.
So… as others have said.
Leave it alone.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
That's the point.
My take is “its there, it was designed to be there, and it should remain there.”. Unlike some of the parts in a mature design that a consumer/enthusiast is looking to 'upgrade' by tube rolling, capacitor swapping, connector gold plating and so on, a resistor on the front end of a power supply has no capacity to affect the 'sonic signature' of the amp, working or not.
So… as others have said.
Leave it alone.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
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I figured the resistor was either a bleeder or perhaps in some weird way part of the i/f suppression... What I hope to achieve is better safety and longevity for my equipment, and in a lot of cases what was originally designed to "be there" isn't always safe, or ideal conditions for tubes in a given circuit. Moving the capacitor leg to the other side of the switch and fuse seems like a worthwhile modification and eliminates the need for the resistor as long as the tuner is switched off before moving. Besides, who doesn't switch their gear off before unplugging it? There was a 50% chance of the plug becomming a shock hazard anyway unless the polarity was marked, which I have.
Why the snarky/******* response?
Dubwoofer *expects* nothing, he´s asking about something that intrigues him. Period
Learn to read.
It was designed to be there ... LONG ago, same as DEATH caps.
We are in 2020 brother.
Besides, SAFETY RULES changed.
Has ANYBODY asked about "sound improvements" of ANY kind?
Again, learn to read.
Wrong advice.
I suggest "upgrade to current safety recommendations" instead.
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Great advice, Fahey.
Wait… what advice?
Nothing concrete there, old buddy.
Thinking about judicious addition of surge-and-spike protectors?
How about hi-pot testing for ground leak issues?
Or changing out the EIA cord/sockets, if there are none!
________________________________________
Or one could leave the 1 MΩ resistor as perfectly innocuous. Maybe just 'test it' with an Ω meter, to ensure its still more-or-less a 1 MΩ resistor, but apart from that, it is a sleeping dog. Don't bother sleeping dogs.
Lastly, Fahey, if my comment was a bit snarky, yours was downright ill-tempered. Swearing •••• ••• •••• on DIYAudio is forbidden, friend. Maybe your COVID–19 experiences this week have been deeply irritating, but even so … its Saturday, dude! Pop a cold one and enjoy the Spring/Fall weather!!!
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
The author is asking about a feature that has no purpose and that are a fire hazard.
Better remove it completly.
Better remove it completly.
HAHAHA Have you EVER started a fire with a resistor? I've had some glow orange hot but no flames and that was a 47R resistor with 150VDC across it! Mains voltage on a 1M resistor has no possibility of a flame out.
I say leave well enough alone.
I say leave well enough alone.
A few hours back, when I saw the snort-worthy rejoinder to prevent forest fires, I wrote a reply … then tossed it.
Its comments like 'that' that makes me wonder … just exactly how cognizant of E=IR and P=IE are the denizens who nominally lurk here? and, not to be overly dramatic, but how many of them do we avidly read, consider, test, and sometimes come to accept for their generally good advice?
Maybe it is the jaw-dropping-ly incredible "America Shuts Down as a Nation of Consumer Commerce" business which has all of us questioning whether the status quo opinion-of-the-majority is worth salted beans.
It does.
Just musing…
GoatGuy
The only thing I would do is move the components across the AC line to the transformer side of the fuse...if one of those caps shorts out, the most damage will be a blown fuse. Unfused components across the wall plug should be a matter of concern....
A lot of not very helpful responses to a reasonable question.
The resistor is likely not a UL recognized component and if it fails mains AC could appear on the chassis, not a very desirable state of affairs. (UL would fail such a design today if there was any conductive external surface connected to it.)
I would also ask where the 120uA of current injected into the chassis is actually going, I have had old tuners using this scheme that injected hum and noise into an audio system, sometimes even when tuner was not selected.
If it were me I would remove it, and install a polarized AC cord set and determine the connection that resulted in minimum leakage current, fuse and switch on the hot side of mains. Two Y cap in series from neutral to chassis.
The resistor is likely not a UL recognized component and if it fails mains AC could appear on the chassis, not a very desirable state of affairs. (UL would fail such a design today if there was any conductive external surface connected to it.)
I would also ask where the 120uA of current injected into the chassis is actually going, I have had old tuners using this scheme that injected hum and noise into an audio system, sometimes even when tuner was not selected.
If it were me I would remove it, and install a polarized AC cord set and determine the connection that resulted in minimum leakage current, fuse and switch on the hot side of mains. Two Y cap in series from neutral to chassis.
Resistors may be too hot - but not this one. The fire hazard comes from replacing
the caps, if they are counterfeit, if they are faulty fire might occur.
Better leave them out .