Warning LED when valve stops conducting - a little SS help needed

What people are working on at the moment
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#91 Re: Warning LED when valve stops conducting - a little SS help needed

Post by Nick »

RhythMick wrote: Fri Feb 15, 2019 3:11 pm
Nick wrote: Fri Feb 15, 2019 1:35 pm You could try a LED inside a bridge rectifier.
ok quick bit of googling and ...

Capture.PNG

Is that something like what you had in mind ?
No, literally a LED inside a bridge rectifier. Rectifier with ac terminal one to each resistor cathode, LED with dropper resistor between the bridge + and - terminals.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
RhythMick
Old Hand
Posts: 747
Joined: Fri Jun 23, 2017 12:24 pm

#92 Re: Warning LED when valve stops conducting - a little SS help needed

Post by RhythMick »

Mike H wrote: Fri Feb 15, 2019 3:32 pm Getting very complicated again. Batteries? Nah. :D

I like this:
RhythMick wrote: Thu Feb 14, 2019 10:56 pm
Something like this ?

1550185320490414.jpg
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 :D )
haha, you're right of course

I think I have the following options...

1) Live with it, keep an eye on the heaters especially if it starts buzzing
2) Rewire the heaters in series, so if one fails they both stop
3) Warning LED per valve in heater circuit (comparator, powered from 8v on DC board)
4) Warning LED per valve pair comparing current through valves

Both 3 and 4 are interesting learning exercises for me, even if in the end I go with 1.

I haven't seen any recent opinions on 2.
RhythMick
Old Hand
Posts: 747
Joined: Fri Jun 23, 2017 12:24 pm

#93 Re: Warning LED when valve stops conducting - a little SS help needed

Post by RhythMick »

Nick wrote: Fri Feb 15, 2019 3:39 pm
RhythMick wrote: Fri Feb 15, 2019 3:11 pm
Nick wrote: Fri Feb 15, 2019 1:35 pm You could try a LED inside a bridge rectifier.
ok quick bit of googling and ...

Capture.PNG

Is that something like what you had in mind ?
No, literally a LED inside a bridge rectifier. Rectifier with ac terminal one to each resistor cathode, LED with dropper resistor between the bridge + and - terminals.
+ and - not connected to anything (except the Resistor/LED) ?
RhythMick
Old Hand
Posts: 747
Joined: Fri Jun 23, 2017 12:24 pm

#94 Re: Warning LED when valve stops conducting - a little SS help needed

Post by RhythMick »

Nick wrote: Fri Feb 15, 2019 3:39 pm
No, literally a LED inside a bridge rectifier. Rectifier with ac terminal one to each resistor cathode, LED with dropper resistor between the bridge + and - terminals.
Forgive the hasty sketch, but you mean like this ?
Capture.PNG

No external power, so the led lights IF the difference between the voltages at the ends of the resistors differs by more than 3 diode drops plus the drop over the current limiting resistor.

Interesting, but wouldn't that be directly in the music path ?
RhythMick
Old Hand
Posts: 747
Joined: Fri Jun 23, 2017 12:24 pm

#95 Re: Warning LED when valve stops conducting - a little SS help needed

Post by RhythMick »

RhythMick wrote: Fri Feb 15, 2019 9:22 am Or combine the outputs in a NOR. Single led lights if either of the comparator outputs goes low, but not both.
I meant XOR of course, not NOR
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#96 Re: Warning LED when valve stops conducting - a little SS help needed

Post by Nick »

RhythMick wrote: Fri Feb 15, 2019 4:41 pm
No external power, so the led lights IF the difference between the voltages at the ends of the resistors differs by more than 3 diode drops plus the drop over the current limiting resistor.

Interesting, but wouldn't that be directly in the music path ?
Yep, thats it, throw a cap across it of you like, to stop it lighting on audio. Yes, it would be in the signal path, but if its not conducting would it be there?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
RhythMick
Old Hand
Posts: 747
Joined: Fri Jun 23, 2017 12:24 pm

#97 Re: Warning LED when valve stops conducting - a little SS help needed

Post by RhythMick »

Nick wrote: Fri Feb 15, 2019 5:00 pm
RhythMick wrote: Fri Feb 15, 2019 4:41 pm
No external power, so the led lights IF the difference between the voltages at the ends of the resistors differs by more than 3 diode drops plus the drop over the current limiting resistor.

Interesting, but wouldn't that be directly in the music path ?
Yep, thats it, throw a cap across it of you like, to stop it lighting on audio. Yes, it would be in the signal path, but if its not conducting would it be there?
Fascinating approach and good learning. Simple to experiment with. I would expect the bridge to impact the sound, but should be easy to prove
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#98 Re: Warning LED when valve stops conducting - a little SS help needed

Post by Nick »

I would expect the bridge to impact the sound, but should be easy to prove
Bet it wont be easy to "prove" given that you expect it will :-)
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
RhythMick
Old Hand
Posts: 747
Joined: Fri Jun 23, 2017 12:24 pm

#99 Re: Warning LED when valve stops conducting - a little SS help needed

Post by RhythMick »

Nick wrote: Fri Feb 15, 2019 5:18 pm
I would expect the bridge to impact the sound, but should be easy to prove
Bet it wont be easy to "prove" given that you expect it will :-)
Expectation bias? Moi? How very dare you.
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#100 Re: Warning LED when valve stops conducting - a little SS help needed

Post by Mike H »

RhythMick wrote: Fri Feb 15, 2019 4:18 pm I haven't seen any recent opinions on 2.
OK, yeah! Filament goes t!ts up, other valve is saved. Hoorah! All gorn quiet, = alerts user that summat's up. Nowt ambiguous about that. :D
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
RhythMick
Old Hand
Posts: 747
Joined: Fri Jun 23, 2017 12:24 pm

#101 Re: Warning LED when valve stops conducting - a little SS help needed

Post by RhythMick »

Mike H wrote: Fri Feb 15, 2019 8:31 pm
RhythMick wrote: Fri Feb 15, 2019 4:18 pm I haven't seen any recent opinions on 2.
OK, yeah! Filament goes t!ts up, other valve is saved. Hoorah! All gorn quiet, = alerts user that summat's up. Nowt ambiguous about that. :D
Ha indeed.

It would mean losing the virtual cathodes and of course if there are minor differences in the filaments in the two valves then the voltages may not be identical.

What I'm most interested in is views as to the impact on the music.
RhythMick
Old Hand
Posts: 747
Joined: Fri Jun 23, 2017 12:24 pm

#102 Re: Warning LED when valve stops conducting - a little SS help needed

Post by RhythMick »

RhythMick wrote: Fri Feb 15, 2019 5:10 pm
Fascinating approach and good learning. Simple to experiment with. I would expect the bridge to impact the sound, but should be easy to prove
Actually the 10R resistors wouldn't drop enough voltage for the 45s let alone the 26s. When the heater failed I measured 50mA across one resistor and obviously 0 across the other, so across the 2 would give 500mV ish. Not enough to exceed the forward voltage of the 2 diodes and the LED. I could try it if I changed resistors.
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#103 Re: Warning LED when valve stops conducting - a little SS help needed

Post by Nick »

And used Schottky diodes.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Andrew
Eternally single
Posts: 4206
Joined: Thu May 24, 2007 2:18 pm

#104 Re: Warning LED when valve stops conducting - a little SS help needed

Post by Andrew »

Can we please revisit the virtual cathodes?

I see the sense and purpose of these in a AC heated circuit, turns single ended noise into common mode noise etc, but I'm not seeing the value here.

The DHT heaters contribute very liitle to the noise in an amp, so there's no noise rejection benefit; there must be another reason you have them, Mick?

I could very well be missing something, however? I'd need to be reminded of the full circuit....
Analogue, the lost world that lies between 0 and 1.
RhythMick
Old Hand
Posts: 747
Joined: Fri Jun 23, 2017 12:24 pm

#105 Re: Warning LED when valve stops conducting - a little SS help needed

Post by RhythMick »

Andrew wrote: Sat Feb 16, 2019 10:23 am Can we please revisit the virtual cathodes?

I see the sense and purpose of these in a AC heated circuit, turns single ended noise into common mode noise etc, but I'm not seeing the value here.

The DHT heaters contribute very liitle to the noise in an amp, so there's no noise rejection benefit; there must be another reason you have them, Mick?

I could very well be missing something, however? I'd need to be reminded of the full circuit....
Being brutally honest I didn't understand enough to go against the advice given when I raised the question, also that from Jac Van Der Walle. However it's entirely possible that I misunderstood the advice. I agree it's worth reopening the discussion ...

1) with a DC heated DHT using Andrews DC board, is there a benefit to using virtual cathode resistors


Once that's resolved, the 2nd question...

2) with a pair of DHT with a shared cathode, is there any reason not to wire the heaters in series
Post Reply