6V6 voltage regulator

[aumamps]

There is another thread elsewhere on the Maas-Rowe Carillon 500 and 500A amplifier for church bell chimes.
However this thread and any other on the net usually end with the "...and a 6V6 voltage regulator on the screens?"

So I was curious if anyone here could dissect this.
Both 500 models (4x6l6 and 2x6550) implement this circuit, though as you'll see in the schematics, they are a bit different.
I can see why 6550 would have an isolated screen supply, but I'm curious as to what the voltage regulation may actually be here. Why not use an OC3?

I own the 4*6l6 model and the PT is 360-0-360.
I was thinking of converting it to a 2*6550 because the OT is around 3.2-3.6k

[LOUDthud]

The 6V6 is dropping almost 300V so you'd need 3 0C3s in series to drop the screens to the 250V ball park and they'd be running near maximum current at full power output. The 6V6 would be running comfortably at about 10W and you can adjust the screen Voltage by changing one resistor. Only bad thing is the 6V6 needs an isolated heater supply.

[aumamps]

Why does one scheme have the 6v6 anode to the O.T. while the other is what looks like biased to ground?

[sluckey]

Why does one scheme have the 6v6 anode to the O.T. while the other is what looks like biased to ground?

Look closely. Both circuits are the same except for the two voltage divider resistor values for the grid. 6V6 plate connects directly to the output of the rectifier tube in both schematics.

[Stevem]

Your going to have a lot of extra voltage raising heater current on your hands with only the load of two 6550s , I would leave two of the 6L6s in just wired up for a heater load.

[R.G.]

The 6V6 is dropping almost 300V so you'd need 3 0C3s in series to drop the screens to the 250V ball park and they'd be running near maximum current at full power output. The 6V6 would be running comfortably at about 10W and you can adjust the screen Voltage by changing one resistor. Only bad thing is the 6V6 needs an isolated heater supply.

Absolutely correct!

This place in the circuit fairly screams for a power MOSFET to replace the 6V6 (with appropriate re-biasing, of course, and heat sinking of some kind) to dissipate 10W, regulate, and not need an isolated heater winding.

[aumamps]

That was my plan. To use a Mosfet Maida regulator.
But considering the layout of the chassis as is, I was just curious.
Of course it came with 4 RCA black plates...and it's so tempting to use them in a confident amp. Or sell them.
I do use one in a single ended two stroke and it has its own sound for sure. Not necessarily better than anything, but it's preferable.

[aumamps]

Your going to have a lot of extra voltage raising heater current on your hands with only the load of two 6550s , I would leave two of the 6L6s in just wired up for a heater load.

Fundamental question here, but doesn't a power supply determine the current available? Basically, a load only pull what current it needs from the supply?.
I don't quite understand what you're implying here.
If you're referring to heater current, 6550s pull more than 6l6s

[sluckey]

Your going to have a lot of extra voltage raising heater current on your hands with only the load of two 6550s , I would leave two of the 6L6s in just wired up for a heater load.

Fundamental question here, but doesn't a power supply determine the current available? Basically, a load only pull what current it needs from the supply?.
I don't quite understand what you're implying here.
If you're referring to heater current, 6550s pull more than 6l6s

4 x 6L6s require 3.6A of filament current.
2 x 6550s require 3.2A of filament current.

Voltage increase won't raise an eyebrow. Might not even show up on a DMM with only one decimal point display.

[aumamps]

Correct, and I will most likely do a 2x6l6 super reverb style output with 40 or so volts in reduction.
But the way I read your post was to utilize 2x6550s and keep an extra 2 6l6s in for a heater load.
That's how I interpreted your written suggestion.

[sluckey]

But the way I read your post was to utilize 2x6550s and keep an extra 2 6l6s in for a heater load.
That's how I interpreted your written suggestion.

Would you prefer to draw 0.4A less current from that PT, or would you prefer to draw 1.8A more current? I know what I'd do.

[aumamps]

Yeah. .4 less.
Which is 2x6550 versus 4 6l6 so I don't quite understand the redundant reply in the first place. Thank You

[sluckey]

Just to be clear, I did not make that suggestion. I was simply refuting it and offering some real numbers to support my thoughts about it. Hope I didn't cause extra confusion.

[aumamps]

I would also be getting rid of half of the valves that are in this amp, leaving leas draw on the heater current

[R.G.]

Fundamental question here, but doesn't a power supply determine the current available? Basically, a load only pull what current it needs from the supply?.

A normal power supply usually supplies a voltage, but has some internal resistance that makes its output voltage sag under load. This is very common to heater supplies because of the resistances involved in the transformer primary and secondary windings and high currents involved. A load does only take what it needs from the supply, but changing loading also has the effect of making the supply voltage sag a little with each added bit of loading.
Transformers have no active regulation, so their outputs sag with load.

I don't quite understand what you're implying here.

The transformer makers design their transformers for a specific loading, and usually make the no-load output voltage a little bit high to make up for sag. When a transformer has a heater winding specified as something like 6.3V at 8A, they mean that their transformer will supply 6.3V only at 8A, leaving out that the output voltage will be higher with less loading. The no-load output voltage on the transformer winding might be somewhat higher.