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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 17 Mar 2017, 08:13 
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Joined: 22 Feb 2017, 07:55
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Hi,

I'm building two versions of this preamp - tube and SS supply. Some basic questions:

Can I use a 47uF cap just after the 6CA4 rectifier ? Matt's original design has 33uF as the value ?
In the SS power supply will 2200uF before the 7812 regulator be ok ?

Thanks


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PostPosted: 17 Mar 2017, 17:03 
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jocelys1 wrote:
Can I use a 47uF cap just after the 6CA4 rectifier ?
Short answer is yes. Just be aware that if you are using the Hammond power transformer, it will increase core heating. But that transformer gets pretty hot anyway.
jocelys1 wrote:
In the SS power supply will 2200uF before the 7812 regulator be ok ?
Yes. The 7812 will still handle the ripple without a problem.

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PostPosted: 17 Mar 2017, 22:06 
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Thanks Matt, I'm using the same Hammond in your original design. So, is the heating due to this cap or just the way it is.


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PostPosted: 18 Mar 2017, 08:24 
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jocelys1 wrote:
So, is the heating due to this cap or just the way it is.
It's a little bit of both. First, Hammond power transformers run HOT! It's just the way they are designed. You should never use a hammond power transformer without lots of ventilation.

But the other part of this is about conduction angle. This is the portion of the AC waveform during which the diodes conduct current. The smaller this angle, the more core heating you'll experience. This is a very low current power supply so conduction angle is already small. By increasing the first filter cap, the conduction angle just gets smaller. In reality, at these current levels a 22µf capacitor would probably work just fine. With the 33µf capacitor, the ripple into the first filter is already -68dBv. With the 2H/100µf LC pair, the overall ripple is -112dBv. So there's about 30dB of margin from what I generally require in my designs.

You will probably be just fine with the 47µf cap. But I would not go any bigger than that.

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It's all about the Glass!
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PostPosted: 18 Mar 2017, 13:08 
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Matt, thanks for the 'perfect' reply. I'm going to try and source the 33uF if I can.


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PostPosted: 18 Mar 2017, 13:14 
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I've found Vishay 30uF MKP caps. They're good upto 600v. Can I use them here ?


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PostPosted: 18 Mar 2017, 13:32 
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jocelys1 wrote:
I've found Vishay 30uF MKP caps. They're good upto 600v. Can I use them here ?
Yup. They should work well.

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


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PostPosted: 11 May 2018, 13:01 
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Hello!
Is it possible to make this preamp performing at 0db till 20Khz ?
mabe with changing the output capacitor?


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PostPosted: 12 May 2018, 16:54 
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xrhsto33 wrote:
Is it possible to make this preamp performing at 0db till 20Khz ?
That depends. How close to "0dB" at 20 kHz do you want to be? And with which tube?

The detailed answer is "essentially, yes". You just need to increase the coupling capacitor. How much to increase it depends on the answers to the questions asked in the paragraph above.

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http://www.CascadeTubes.com
Cascade Tubes Blog


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PostPosted: 22 May 2018, 12:32 
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Joined: 31 Jan 2015, 17:59
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Hi, the preamp sounds good, but I have a high hum without source input. Why? :confused:


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