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A simple PushPull balance LED indicator?
A simple PushPull balance LED indicator?
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Old 7th May 2012, 02:18 PM   #31
Elvee is offline Elvee  Belgium
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Originally Posted by nazaroo View Post
Well, I should be okay then, even with the cheap-version transistors.

I did a hand-feel of all the parts, to check for heat,
it seems the hottest part of the circuit is the LEDs?
It should be the transistor, when a LED is half-lit

I went in to one place and asked for "general purpose High Gain PNP" and he gave me a dirty look and said,

"A high-gain is not a general-purpose. Check the internet."

So much for customer service...

what's a common non-general-purpose High Gain PNP, in case I have to go back and buy PNPs from the same idiot?
You don't need a high gain transistor; something with a Hfe of 100 is more than enough

Also, you substituted 68k / 1k2 for the lower resistors, 120k / 680R.
No, I used 68K, but I didn't install the 1K2: it is required if a sharp extinction of the green LED is desired.
Can I do that too? Will that make the circuit / display more stable?

Also what changes would tighten up the on/off of the diodes,
and narrow the Green-light signal to +- 0.1v instead of +- 0.2v like I have now?
Removing the emitter resistors will sharpen the transitions.
Using a smaller size schottky will narrow the green band, but if it is too small, the current will also decrease.

In this example, I removed the resistors and placed two BAT's in parallel.
With a single BAT, it is even narrower, but we loose some mA current.

You can try to play with various resistors and diodes, but if you want something narrower and sharper than that, the sensible option is to use an IC.
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Last edited by Elvee; 7th May 2012 at 02:42 PM.
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Old 6th July 2012, 05:52 PM   #32
CrazzyAbtTubes is offline CrazzyAbtTubes  Canada
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Location: Nova Scotia
This circuit looks great! Pretty simple looks quite reliable, just the thing I was looking for to add to Heathkit mono tube amps I have. The heathkit amps are the W5M model.

I see a couple possible improvements that could be made, one being why not make a DC supply from the 6.3 volts for the tubes and use the to power circuit instead of the HV supply?

Not to make the circuit more complicated than it all ready is for others to build, but could more LED arrays be made for more precise measurement? Also what about the use of a pair of FET's to isolate each side of the circuit from the tubes, they have a high input impedance and are quiet and quite reliable.

just a couple of thoughts that my or may not improve the circuit, but I must say it came a long way from what the circuit originated from.
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