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EL84 Amp - Baby Huey
EL84 Amp - Baby Huey
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Old 8th January 2021, 07:13 PM   #2481
PKI is offline PKI  United States
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EL84 Amp - Baby Huey
Got this guy AS-2T230 - 200VA 230V Tube Transformer - AnTek Products Corp MAybe an overkill, but.. :-)
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Old 8th January 2021, 07:28 PM   #2482
Francois G is offline Francois G  United States
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Good choice in my opinion. I have have bought that one too, but not implemented yet.

I expect the extra current capabilities will prevent excessive voltage sag under load.
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Old 10th January 2021, 06:09 AM   #2483
PKI is offline PKI  United States
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EL84 Amp - Baby Huey
Quote:
Originally Posted by itsikhefez View Post
No worries, I actually went through the same thing a few months ago assembling a BOM for the EL84 PCB.

I started with the values in the BOM file "BOM EL34 and EL84 Baby Huey Dec 23, 2018.pdf" which is somewhere in this thread.
Then I went through the remarks in Bas's Wiki, and lastly with the comments on an annotated schematic by zintolo also somewhere here.

Here is a link to a Dropbox hosted Google Sheet with the selected components. I didn't build it yet though so can't guarantee the correctness.
Hey, thanks for offering, but it doesn't look like I have an access to see it.
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Old 10th January 2021, 09:50 AM   #2484
zintolo is offline zintolo  Italy
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Quote:
Originally Posted by PKI View Post
Got this guy AS-2T230 - 200VA 230V Tube Transformer - AnTek Products Corp MAybe an overkill, but.. :-)
Code:
ELECTRICAL CHARACTERISTICS
Outputs	4x
Power	200VA
Output Voltage  	Current
230V	0.4A
230V	0.4A
6.3V	4A
6.3V	4A
Please note that you need to have another secondary 50 V 100 mA to supply:
- the negative side of the PI
- the negative side of the PowerDrive
- the fixed bias
- the positive side of the PowerDrive

This will give you around -35 Vdc and +35 Vdc, based on it you can look at the table I posted and select the right resistor for the R16 and R17 mod.
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Old 10th January 2021, 01:59 PM   #2485
Francois G is offline Francois G  United States
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Quote:
Originally Posted by zintolo View Post

Please note that you need to have another secondary 50 V 100 mA to supply:
- the negative side of the PI
- the negative side of the PowerDrive
- the fixed bias
- the positive side of the PowerDrive
Very good point! I have small 60V toroids for this purpose.

I thought 100 ma is probably generous. Out of curiosity, what is the required minimum current capability for such transformer shown by your simulations? I know 5VA is about a small as transformers go.

Last edited by Francois G; 10th January 2021 at 02:01 PM.
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Old 10th January 2021, 04:00 PM   #2486
zintolo is offline zintolo  Italy
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I don’t have the laptop with me, but let’s consider 2 mA each of those, for two channels, it will be 16 mA. Then you need to change the caps at startup, etc... let’s consider 50 mA.
50 V x 0.05 A = 2.5 VA.
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Old 10th January 2021, 05:27 PM   #2487
PKI is offline PKI  United States
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EL84 Amp - Baby Huey
I have 60V transformer for this purpose. Ho did you you calculated +/-35V again please?
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Old 10th January 2021, 05:51 PM   #2488
zintolo is offline zintolo  Italy
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50 Vac x 0.707 = 35 Vdc (minus the voltage drop across the diode, omitted as a first approximation)
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Old 10th January 2021, 05:57 PM   #2489
PKI is offline PKI  United States
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Oh I see :-).
So with 60V I will be at 42V so should look at around 20k?
Part of your table:
40 red led 18,3
45 red led 20,8
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Old 10th January 2021, 06:45 PM   #2490
zintolo is offline zintolo  Italy
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I’d go with a standard 18 or 22 kOhm, without complicating things with two 10 kOhm resistors in series.
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