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Trying to understand 6BM8 regulator (audio note clone)

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Hi,

I've built the following the regulator for my phono and linestage. They are very similar to (if not the same same as) what AN UK used in their current linestage:

CLC raw B+ of 360VDC into 6bm8 triode-wired pentode section as the series pass

120K anode load for triode error amp feeding off the raw B+

Regulated B+ is taken off a 150 Kohm & 43 Kohm voltage divider, this is connected to grid of triode error amp. 150K top resistor/ feedback resistor is by-passed by small 50pf cap.

The cathode of the triode is connected to anode of OB2 VR tube, running at around 15ma, unbypassed, feeding off the regulated B+ through a 15Kohm wirewound resistor.

Triode anode is direct coupled to grid of pass tube.

Regulated b+ is 250vdc there about. There is a 22uf cap across the ouput.

Pretty basic stuff I think, but there are a couple of unsual things in this regulator: there is a 820k resistor connecting raw b+ and grid of triode, and also a 133Kohm resistor connecting anode of the triode and its grid.

Questions:

Does the 820K resistor serve as some kind of feed forward and cancellation of ripple?

Why is there the 133k resistor?

I would like to increase the regulated B+ to 260v - 270v, but cannot do this by adjusting the value of the lower resistor in the output voltage divider. Can someone please tell me exactly what I need to do?

General comments on this type of regulator? And if you have experience with better sounding regulators using different tubes, im all game to try things out.

Apologies for not being able to draw a schematic.

I realise that I may have asked very stupid questions here (my education on electronics is limited to highschool Ohm laws, and what I have picked up from this forum in a few years). Please pardon me for those questions. Tks a million!
 
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Thanks Kevin, here you go, hand drawn schematic and taken off the mobile phone. Vi
 

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It does look to me like the 820K and 133K are part of a ripple canceling network. I don't use this in my own designs but have seen people who do. You remove these if you wish. I provide heavily filtered voltage to the pass tube screen in my designs which improves ripple rejection substantially and is unfussy, but at the expense of a large and expensive electrolytic capacitor.

If you need more output voltage you will need commensurately more input voltage as well. If you need 270V the raw input will need to be in the vicinity of (or slightly over) 400V. Once you boost the input voltage you will have sufficient voltage compliance that increasing the value of the lower feedback resistor will boost the output voltage.

I've posted a number of high performance regulator circuits in various threads such as the ones relating to the Muscovite and Muscovite Mini phono stages in analogue source. There is another such posting in this forum..
 
That seems complicated circuit without real benefits.

Below is a simple and basic 6BM8/ECL82 voltage regulator.
According to quick simulations it is possible to get min. 60 mA with 100 Vdc accross the pass pentode (360 Vdc in 260 Vdc out).
Ripple rejection is some 46 dB.

R6 at the schematic represents load.

An externally hosted image should be here but it was not working when we last tested it.
 
@artosalo: i've built very similar circuit to the one you posted, it did not sound as nice as the one used by audio note. Before I go built some other circuits (or go back to LCLCRC) you know we just have the urge to understand how things work, hence the questions.

Also, this maybe so stupid but i just have to ask if there is a way to measure the supply ripple without a scope?
 
The 133k gives a negatif feedback,probably to get the loop gain down for stability reasons.And to prevent the B+ to go up to much if OB2 ignite at a very high voltage (in the dark).
Then there is the 820k.Supose the rawB+ goes up ,the penthode needs a greater -Vg1.So the voltage on both sides of the 120k are expanding result the current goes up.That current has to be delivered by the triode.It would do that with less -Vg at the expence of B+.By adding some voltage from the source of the disturbance , B+ doen't have to change.
Mona
 
Here is one that I have been wanting to try, it is very similar to a design I have used many times,using a 6GV8 instead. The 6BM8 should perform much better because of the higher mu of the triode, and the heftier pentode.

You can also regulate at higher voltages simply by changing the Zener.
 

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It's the same basic circuit, but with a Zener reference. A Zener is quieter and more stable than the neon tube reference, but lower voltage zeners mean higher output impedance and higher voltage Zeners are noisy. You can use a string of 5.6V Zeners or LM329s to get a higher voltage, but without the glow. If you're as sick as I am, you'll use a string of LEDs to get the glow back.:D

Typically, the resistor that's R8 here will be connected on the plate side to minimize start-up issues.
 
diyAudio Senior Member
Joined 2002
Hi,

@T.S. Is the circuit you've drawn the latest incarnation of AN's regulator?
Reason I ask is that it looks nowhere as the original one as used in the M2 Line Stage and DAC output stage.

You can use a string of 5.6V Zeners or LM329s to get a higher voltage, but without the glow.

There's no point in having a regulator using valves without using these nice Stabivolts, is there?
Far more reliable than zeners (they go zzzzzzzzzz) and you can just pull one out, put a different one in, adjust the trimmer et voila.:cool:
Love those orange ones a la 85A2, 5651A and such.Can be stacked too.
As for noise, dunno, never noticed nor measured any.Cancels out I suppose.
Mine's aren't even shunted...

The main advantage of the ECL82\6BM8 over the other ECLs is that it can take up to 900V on it's anode should you need it. That plus it's still being produced AFAIK.

@Denny, if you want a 6GV8 reg with a nice glowing voltage reference then I've got a circuit for you.:D

Ciao, ;)
 
Hi,

@T.S. Is the circuit you've drawn the latest incarnation of AN's regulator?
Reason I ask is that it looks nowhere as the original one as used in the M2 Line Stage and DAC output stage.


Ciao, ;)

This is in the factory-built M3-M8 units. I opened a couple...

The circuit in the AN Kits DAC and pre-amp is a more generic type that use zeners as voltage reference.

One sound very lush and clear, the other one sounds hard and mechanical...
 
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