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Old 2nd April 2003, 08:28 AM   #11
Jay is offline Jay  Indonesia
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<i>"Well, if we had an idea about this regulators' composition it would be great help to you. Short of that it's rather pointless."</i>

Well, I think you are right. But not 100%

The pre-amp is SE (I havenít had a chance to have a second look on the circuit). Hence there will be an important voltage ripple due to changing current in the load. How much current or voltage maximum required by 12AT7 pre-amps? I donít know. With 300V transformer, I think the output will be around 200V? I noticed a potentiometer in the regulator, so this may be to set the output voltage (so itís quite variable).

If the 12AT7 acted as regulator, the maximum plate current and power dissipation is important thing to notice. I noticed a 300V transformer and 400V capacitor, so the output after the bridge may be 350V. If the potentiometer can adjust the voltage to say 200V as the minimum pre-amp requirement (regardless the current requirement), the voltage drop will be 150V (maximum, because other components are likely to drop the voltage instead of increase the voltage; I didnít see a big cap in the output). With 150V voltage drop, and the ability to dissipate about 2W, the current will be around 2/150, less than 20mA. From the maximum value of 12AT7 plate current itself (15mA), I canít imagine a pre-amp requires such a low current (I donít know about tubes).

Thus, the 12AT7 must not act as a regulator? So what? Error amplifier? For error amplifiers, current and power capability is not important. The important thing is the gain and the ability to handle an expectedly wide range of voltage, right? The 12AT7 and 12AX7 shows equally the same maximum voltage (so I didnít write it on my first post), but different gain. The 12AT7 is 70% (or 60%?) of 12AX7 gain, so why is 12AT7 chosen for this circuit? Is 12AT7 cheaper than 12AX7?

<i>"I think it is posible to design a good stable power supply for vacuum tube amplifiers. The use of choke input filters is a must."</i>

Of course it is possible But choke is a must??
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Old 2nd April 2003, 08:35 AM   #12
Jay is offline Jay  Indonesia
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And <B>valveluver</B>,

The regulator is not supposed to handle voltage ripple due to the load alone, but some variations in the main line.
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Old 2nd April 2003, 11:26 AM   #13
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Default RE:REGULATOR.

Hi,

In your first post you state you are building a preamp using the 12AT7 in the amplifying stages plus an two tubed regulator.
One 12AT7 plus another tube unknown to us.

I assume the 12AT7 is used as an error amplifier, you than ask if you could use a 12AX7 instead of this.

Again assuming the above is correct, my answer would be : yes, you can provided you adjust some values so you can take advantage of the higher mu of the 12AX7 otherwise it is rather pointless.

That is what I meant in post # 6.

Also, you say you have a 300V CT xformer, depending on how you intend to rectify that voltage it could give you a B+ of as much as 800V which is of course way too much for your preamp.

So, for a series regulator using all tubes you would need a series pass device (a trioded EL84/6BQ4 e.g.), a 12AX7 as an error amp and a voltage reference such as an 85A2/5651.

Hope it helps,
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Old 2nd April 2003, 12:17 PM   #14
Jay is offline Jay  Indonesia
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<I>ĒAlso, you say you have a 300V CT xformer, depending on how you intend to rectify that voltage it could give you a B+ of as much as 800V which is of course way too much for your preampĒ</I>

I donít know how tube rectifier works, but it canít be 800V as the rating for the supply caps is 400V

The other tube is something like 12B4A, I donít remember. With solid-state regulator, I know that brutal change of component values may lead to loosing regulation function. Here I donít have oscilloscope to tweak the regulator, so I will do it by ear (quite hard, huh?). But the most important thing I want to know is the riskÖ (like this one below)

I have old caps that Iím using for 70V Bride Of Zen pre-amp. I want to use them for my tube pre-amp (CRC after the rectifier). The voltage rating is OK. If these caps are blown, will the tubes in the pre-amp be damaged? I think it is very unlikely, but Iím not sure (I may use expensive tubes in the pre-amp)

Thaks, Frank!
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Old 2nd April 2003, 12:22 PM   #15
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Default Solid state rectification

If there is a problem with solid state rectifiers, can anyone explain the noise that I am supposed to see or hear?

A 10 henry choke has a reactance of +j. 7500 at 120 hertz. If the noise occurs above 120 hz the reactance is even higher.

A 100 mirofarad capacitor has a reactance of -j. 13.2 at 120 hz. and is even lower above 120 hz.

How could such a noise make it through the filter?
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Old 2nd April 2003, 12:30 PM   #16
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Default SAND RECTUMFRIERS.

Hi,

Quote:
If there is a problem with solid state rectifiers, can anyone explain the noise that I am supposed to see or hear?
If you feel courageous you could take a look here:

HIGH SPEED DIODES.

Cheers,
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Old 2nd April 2003, 12:48 PM   #17
Joel is offline Joel  United States
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Default Re: Solid state rectification

Quote:
Originally posted by valveluver
If there is a problem with solid state rectifiers, can anyone explain the noise that I am supposed to see or hear?
Don't even bother trying - only Frank can hear it. He has a golden ear.
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Old 2nd April 2003, 01:06 PM   #18
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Default ...Bedtime reading...I need to get a life...

Hi Frank,

That's a great thread, I've enjoyed reading and learned a bit.

As someone who has used 1n4007 for a while and had good success applying snubbers to them to quiet them down - I was surprised at the difference BYV26E ultrafast soft recovery diodes made ( Benny Glass recommended and suplied). I actually rate them better than using 5U4 or GZ34... That may just be lucky in that the BYV didn't excite the parasitics but the valve diodes did...

Joel,

It not just Frank there are lots of us who can hear these differences - It's just Frank who has his head above the parapet

ciao

James
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Old 2nd April 2003, 01:53 PM   #19
Jay is offline Jay  Indonesia
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<i>"If there is a problem with solid state rectifiers, can anyone explain the noise that I am supposed to see or hear?
A 10 henry choke has a reactance of +j. 7500 at 120 hertz. If the noise occurs above 120 hz the reactance is even higher.
A 100 mirofarad capacitor has a reactance of -j. 13.2 at 120 hz. and is even lower above 120 hz.
How could such a noise make it through the filter?"</i>

I donít know about this, but I think you should be able to see it in an oscilloscope if the noise does occur. (I have never used oscilloscope in audio, just for other purposes in university). Can we hear it by ear? If the noise does occur, why not?

From my experience with power supply regulator, I prefer to call it ďhumĒ, not ďnoiseĒ. The effect is in the bass performance. It is about 100Hz right? (some countries have 50Hz instead of 60Hz) When the bass had become tighter and clear, I assumed the ďhumĒ had gone.

As for LRC filtering (never used an inductor), calculation on paper had never been accurate. I used that value only as a base value and then tweak it by ear. I couldnít believe that I could hear such thing

I donít really care if SS rectifiers are more noisy than tubes. If I had a chance to have both types of regulators, I will try to hear it and choose the one I prefer. It could be the rectifiers, could be just the ďwrongĒ brand, could be something else, but you cannot blame my ears. They are the only measurement tools I have
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Old 2nd April 2003, 02:05 PM   #20
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Hi,

I always use 10H choke for my power or pre-amp.

But I hadn't hear this problem.

I think the tubes noise may be large than this one & Make more effort to low down the hum is mainly.

thanks

Thomas

www.diyaudiocraft.com.
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