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Old 28th January 2013, 11:02 PM   #1
surfstu is offline surfstu  United Kingdom
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Default heater currents

I've been playing around with a voltage doubler as I have a pair of vu meters that require 12vac or 12vdc ish to drive them. I,m about to build a PP UL amp using 4 ecl86's

My power supply (attached photo) has a couple of thick green heater wires (top right) 6.3Vac

A couple of yellow wires (top left) 6.3Vac

It has a pair of thick red wires (bottom right) 5V for rectifier tube.

The amp I'm building also requires a - 7 V ish rectified DC...

Would really like some suggestions on how to go about supplying all the different voltages without underpowering the ecl86 heaters (which I beleive draw 700-mA) and also without compromising audio.

Is it unrealistic to think that the PSU green heaters wires could power all 4 heaters?

Or could I heat two tubes from the yellow and two from the green and then take a rectified - 7 v from one lot and approx 12vac or 12vdc from the other?

Anyone had any experience with this?
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Last edited by surfstu; 28th January 2013 at 11:04 PM. Reason: made mistake
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Old 28th January 2013, 11:34 PM   #2
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If you're taking somebody else's word for those secondary voltages it wouldn't hurt to check them for yourself; that's not the usual color code. It's more likely to find 6.3 volts on the green pair, 5.0 volts on the yellow pair. Measurements without load can fool ya too.

All good fortune,
Chris
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Old 28th January 2013, 11:50 PM   #3
surfstu is offline surfstu  United Kingdom
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Thanks Chris, I will check the greens! I've been playing with the yellows already tonight and they were approx 7.75 unloaded, I built an amateur (noob) voltage doubler and got 19Vdc from them unloaded...

It still does not answer my question of what topology I may think about for my PSU...

P.s. the thick reds are definatley 5V as they were connected to GZ34 in old amp, the rest of the heaters were split between the greens and the yellows. The greens had an exrtra tube connected to them too...

cheers Stuart
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Old 29th January 2013, 12:07 AM   #4
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Oh, well there you go. Based on the size of that critter you ought to be able to power a half dozen or so of those amplifiers.

All good fortune,
Chris
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Old 29th January 2013, 12:17 AM   #5
surfstu is offline surfstu  United Kingdom
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Do you know how I'd go about utilising the heater supplies for:

.................approx 12Vdc/ac for vu meter driver

.................approx -7 Vdc for ccs

and of course.... 4 ecl86 heaters?

Last edited by surfstu; 29th January 2013 at 12:18 AM. Reason: oooh
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Old 29th January 2013, 12:30 AM   #6
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Without knowing anything about it, I'd keep the 12 volts for the VU meters floating. Maybe make it from the 5 volt winding with a doubler. You have two reasonably heavy duty 6.3 volt windings for the ECL86's, no problemo.

The -7 VDC could be made from the remaining heater winding, or as a "back voltage" by lifting the negative connection from the B+ supply and reconnecting through a 7 volt Zener.
If you have it to spare of course. What are your B+ plans so far?

All good fortune,
Chris
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Old 29th January 2013, 12:46 AM   #7
surfstu is offline surfstu  United Kingdom
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Thanks Chris, food for thought - to be honest, i'm still noobing around.. I'm sure i can build this amp but I'm on a sttep learning curve... My B+ is still unconfigured, spent a night with PSUD2, I want to rectify by tube GZ34 or 5R4

By floating I understand this means a supply from a secondary that is not referenced to ground? I presume if I use a GZ34 in standard full wave rectification then I can no longer use its 5V heater supply to feed into a doubler for 12Vdc?

As far as a 'back voltage' by lifting the negative from the B+ is concerned - I will have to learn how to do this... it sounds complicated right now!

maybe i'm a little out of my depth...

Stuart
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Old 29th January 2013, 02:34 AM   #8
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Quote:
Originally Posted by surfstu View Post
My B+ is still unconfigured, spent a night with PSUD2, I want to rectify by tube GZ34 or 5R4

By floating I understand this means a supply from a secondary that is not referenced to ground? I presume if I use a GZ34 in standard full wave rectification then I can no longer use its 5V heater supply to feed into a doubler for 12Vdc?

As far as a 'back voltage' by lifting the negative from the B+ is concerned - I will have to learn how to do this... it sounds complicated right now!
Yes, the GZ34 will need the 5.0 volt winding all to itself. But you have lots of windings. IIRC one red pair is 6.3 volts? I think the 12 volts needs to be floating because the circuit can accept AC or DC power. This probably means a full wave bridge in line. No biggie for you anyway.

I'm sorry I can't explain the back voltage thing better. Maybe imagine borrowing 7 volts from the *bottom* of the power supply. The remaining B+ stays above ground and the 7 volts goes "below" ground. If your supply was originally 300 volts, you'd have 293 volts B+ left, and the Zener would have to pass all of the current that went through the B+ too.

You'll be great, and have fun,
Chris
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Old 29th January 2013, 03:57 PM   #9
surfstu is offline surfstu  United Kingdom
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hmm, does this mean the whole amps B+ floats 7 V above ground? I'm trying to get my head around this...
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Old 29th January 2013, 06:57 PM   #10
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OK, let's try another way. (I'm sorry I'm not better at this). Imagine the B+ supply to be a 300 Volt battery, so that it's easy to imagine it floating. Now we connect the normal amplifier load and a 7 Volt Zener in series, across the big battery. Doesn't matter where we tie this contraption to chassis, it'll work the same, dividing the 300 Volts between the normal amplifier load and the 7 Volt Zener.

Now lets connect the junction of the NAL and the 7VZ to chassis ground. If we measure with our voltmeter from chassis to top (+) of the battery we measure +293 Volts, and if we measure from chassis to the other end (-) of the battery we measure -7 Volts.

Our rectified AC supply can be just like that battery, with its (-) end "floating" just like its (+) end conventionally does. Make sense? Sorry I'm not clearer.

All good fortune,
Chris
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