Warning LED when valve stops conducting - a little SS help needed
#76 Re: Warning LED when valve stops conducting - a little SS help needed
Mike's comments about low voltage supply set me thinking. The datasheet for the LM293P indicates only 0.4mA per comparator. So, how about a battery based circuit. A pair of rechargeable AA batteries should give 2.4v ish and last forever (4000 mAh, around 5000 hours at 0.8mA) if there are no valve failures. Even if 1 valve fails it would only draw 20.8mA, 190 hours and change. Could also easily build in a test switch (add a resistor in parallel to drop the IN-).
The following could be easily constructed and hooked up to a valve pair as a test. The advantage of monitoring the 10R is that I catch any scenario which stops the valve conducting. Battery -ve would connect to the top of the cathode resistor and both comparators in a single LM293P could be used.
To implement it in the amp would need space for 6 sets of battery pairs which would be an issue. Still I think this is worth building a test unit, even as a learning exercise.
As always, all input and comment welcomed and appreciated.
The following could be easily constructed and hooked up to a valve pair as a test. The advantage of monitoring the 10R is that I catch any scenario which stops the valve conducting. Battery -ve would connect to the top of the cathode resistor and both comparators in a single LM293P could be used.
To implement it in the amp would need space for 6 sets of battery pairs which would be an issue. Still I think this is worth building a test unit, even as a learning exercise.
As always, all input and comment welcomed and appreciated.
#77 Re: Warning LED when valve stops conducting - a little SS help needed
It would light the LED's when you turn the amp off.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#79 Re: Warning LED when valve stops conducting - a little SS help needed
Or combine the outputs in a NOR. Single led lights if either of the comparator outputs goes low, but not both.
#80 Re: Warning LED when valve stops conducting - a little SS help needed
In that case you may as well just compare the voltages on the top of the to sense resistors. What is unknown is will it trigger with a audio signal.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#81 Re: Warning LED when valve stops conducting - a little SS help needed
hmmm ... a hysteresis resistor should avoid triggering during signal fluctuations, but does that then introduce something into the signal path ? Will ponder.
your other point is interesting. Right now the objective (of this proposal) is to alert if either valve stops conducting. I'm not sure that's met by comparing the tops of the 10Rs. I'll need to think about that a bit.
The circuit can be simplified by having one reference voltage to both IN-, which could be adjustable using a pot. Also using a CR2032 battery gives 3v, with 220mAh lasting 275 hours or so. Plenty, though not rechargeable.
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#82 Re: Warning LED when valve stops conducting - a little SS help needed
Been following this with interest.
There are isolated integrated current monitors that are not hall effect and thus good for low currents.
With an isolated monitor, one PSU is enough and even its isolation is not critical as the monitors are typically good for 1kv or so.
I'll look for suitable candidates...
There are isolated integrated current monitors that are not hall effect and thus good for low currents.
With an isolated monitor, one PSU is enough and even its isolation is not critical as the monitors are typically good for 1kv or so.
I'll look for suitable candidates...
Vivitur ingenio, caetera mortis erunt
#83 Re: Warning LED when valve stops conducting - a little SS help needed
#84 Re: Warning LED when valve stops conducting - a little SS help needed
Thanks Jack, will look into your suggested candidate.jack wrote: ↑Fri Feb 15, 2019 11:30 am Been following this with interest.
There are isolated integrated current monitors that are not hall effect and thus good for low currents.
With an isolated monitor, one PSU is enough and even its isolation is not critical as the monitors are typically good for 1kv or so.
I'll look for suitable candidates...
#85 Re: Warning LED when valve stops conducting - a little SS help needed
Yes, you are trying to detect when the two currents are different, you have two equal resistors, one in each current with a common tail, if the currents are different, the voltage at the top of each resistor will be different.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#86 Re: Warning LED when valve stops conducting - a little SS help needed
Will need to use the two comparators, to catch either condition (A higher than B or B higher than A) and use hysteresis to smooth out the fluctuations caused by the signal. I think.
#87 Re: Warning LED when valve stops conducting - a little SS help needed
You could try a LED inside a bridge rectifier.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#89 Re: Warning LED when valve stops conducting - a little SS help needed
Getting very complicated again. Batteries? Nah.
I like this:
KISS (Keep It Simple Sweetums )
I like this:
Comparator circuit current is VERY small so I can't see a problem with supply "loading". The biggest current will be the LED, and only when it's on.
KISS (Keep It Simple Sweetums )
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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#90 Re: Warning LED when valve stops conducting - a little SS help needed
So if supply is 8V, then in my last diagram:
R4 = 680R
R2 = 7.5k
Proper job.
R4 = 680R
R2 = 7.5k
Proper job.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."