Alternate indicator power supply?

[catears]

Any reason Dr. D used 390R/1n4003 off the heaters for the LED indicator and not the relay/footswitch supply that is normally mounted right next to it?

An LED in theory shouldn't introduce noise, but it's the extra wires running from the filament taps that I have a concern with. The 450ma from the 6-0-6 transformer should have more than enough juice for one more LED in my mind. Not doubting the master, but I was always taught keep the heater taps twisted and as far apart from everything else as possible in order to reduce hum.

I am interested to hear other theories on indicator supplies and hopefully this will spark a great conversation on the topic.

[vibratoking]

I can't say that I know why he chose this method, but there are a lot of ways to skin a cat. If you run the LED indicator off the 7812 regulator, then the indicator is not necessarily indicating that the tubes are powered. There could be a situation where the tubes are powered, the 7812 has failed and there is no indicator, yet the amp is live. Not much of a power indicator at that point. Noise is not an issue.

[catears]

I can't say that I know why he chose this method, but there are a lot of ways to skin a cat. If you run the LED indicator off the 7812 regulator, then the indicator is not necessarily indicating that the tubes are powered. There could be a situation where the tubes are powered, the 7812 has failed and there is no indicator, yet the amp is live. Not much of a power indicator at that point. Noise is not an issue.

The indicator circuit is wired so if it blows the tubes will still run anyway. The amp itself is what you still want to work in the end, all else failed. If the relay supply fails you only lose the relays with no interruption to the amps function itself, keeping the low voltage/high current winding in the main PT dedicated to powering the tubes and that's it.

I still wire it the traditional way, mind you. But I just finished wiring up relay boards and got to thinking.

[ToneMerc]

I done it both ways, with and without a dedicated relay supply transformer. You really don't need two strands for the footswitch in which one can be used for the LED. Most often I have continued to wire it the traditional way. I do like the fact that the LED indicator is closet to the PT winding verses the regulator circuit. I never really gave too much concern about the AC filament runs from pins 2 & 7 to the terminal strip as they are only about 1.5" in length.

TM

[vibratoking]

The indicator circuit is wired so if it blows the tubes will still run anyway.

That is true in every circuit that I am aware of. If the 1N4003, 330 Ohm, or the LED itself fail then then whole indicator circuit is non-functional no matter where you connect it.

The amp itself is what you still want to work in the end, all else failed. If the relay supply fails you only lose the relays with no interruption to the amps function itself, keeping the low voltage/high current winding in the main PT dedicated to powering the tubes and that's it.

Yes, the amp will still work if the 7812 fails and the PT does not. Ideally, I want the power indicator to tell me if the amp actually has power to the full circuit. In this case, the amp should only work properly when the power indicator indicates power. It is always possible for any amp to work with no power indication if the indicator circuit fails. This is obvious. But, this can also happen if the indicator is connected to the 7812 output and the 7812 fails, also a bad scenario. If you wire the indicator to the 7812 output then you have the following situations:

1 - The indicator lights. This indicates that the relay transformer and 7812 are working, but tells you nothing about PT operation. This is just a relay power indicator and not a 'real' power indicator.

2 - The indicator does not light. This indicates one or more of the relay transformer, the fuse, the power switch, the indicator circuit or the 7812 have failed. In some of these cases, the amp will still work even with no indication. This is not good behavior for a power indicator IMO.

[martin manning]

I like running the power indicator LED from the relay supply. They are physically close to each other and it is better for the LM7812 to have some current draw when no relay is energized. You also get to trade all the components required for the filament circuit-supplied version for at most one resistor, and also clean up the area around the power tubes.

If the indicator is on, it tells me that the amp is connected to the mains, it has AC power, the power switch is on, and that the mains fuse is not blown. This is what I want to know first.

If the indicator is on and the amp doesn't play it has a bigger problem, or it soon will have if there is no load connected.

If the indicator is off and the amp plays then I know I might not have relay/footswitch function.

As far as the PT and filament circuit, they have their own direct indicator, which is the filaments themselves ;^)

[vibratoking]

There are certainly alot of ways to view this. It seemed like a simple question, but the devil is in the details.

If the indicator is on and the amp doesn't play it has a bigger problem, or it soon will have if there is no load connected.

So you want to use the indicator to inform you that you have the amp on and no speaker connected? You can't guarantee that will happen if you connect the indicator to a failed relay supply.

They are physically close to each other and it is better for the LM7812 to have some current draw when no relay is energized.

A resistor, to shunt the minimum specified current, in parallel with the output cap solves this problem. It's what I put in my builds even though I think it is not absolutely necessary in this application.

[Structo]

Tell me more about having a load on the regulator.
I had not heard that before.

What happens to the regulator when there is no load?

[martin manning]

There are certainly alot of ways to view this. It seemed like a simple question, but the devil is in the details.

If the indicator is on and the amp doesn't play it has a bigger problem, or it soon will have if there is no load connected.

So you want to use the indicator to inform you that you have the amp on and no speaker connected? You can't guarantee that will happen if you connect the indicator to a failed relay supply.

No, this was just an incidental thought; same difference with the filament supply powered version.

They are physically close to each other and it is better for the LM7812 to have some current draw when no relay is energized.

A resistor, to shunt the minimum specified current, in parallel with the output cap solves this problem. It's what I put in my builds even though I think it is not absolutely necessary in this application.

That's one more part you don't need if you power thr LED from the relay supply :^)

[Luthierwnc]

I don't use the relay circuit for the power indicator just because I usually have an extra relay or two in there and don't want to tax the supply. The downside is you do have longer heater runs but they are usually well away from signal wires. If I don't use a FET, I will hang a standby indicator off the 150k dropping resistor at the end of the string. sh

[heisthl]

Another reason is at power off the heaters bleed off immediately so the LED goes out quickly.

[martin manning]

I don't use the relay circuit for the power indicator just because I usually have an extra relay or two in there and don't want to tax the supply.

The relays only need 150mW, or 12.5 mA @12V, for the coil, plus another 10-20 mA for the footswitch LED. The RS transformer is rated at 400mA (and the regulator at 1A), so there shouldn't be any problem running four relays plus the power indicator LED.

Another reason is at power off the heaters bleed off immediately so the LED goes out quickly.

Is there any advantage to having the power LED extinguish quickly? I like the slow fade myself, and it serves as a kind of timer- Power switch off, wait for LED to dim (~5 sec), standby switch off.

[heisthl]

Is there any advantage to having the power LED extinguish quickly? I like the slow fade myself, and it serves as a kind of timer- Power switch off, wait for LED to dim (~5 sec), standby switch off.

Some relay PS designs (i.e. no regulator) will leave that LED on for a loooong time unless a relay is on.

[martin manning]

A few seconds says "tube" to me, much longer than that and it starts to say the switch is broken...