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EL84 Amp - Baby Huey
EL84 Amp - Baby Huey
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Old 8th January 2018, 07:44 PM   #1861
pchw is offline pchw  United States
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EL84 Amp - Baby Huey
Quote:
Originally Posted by meanman1964 View Post
Marc , do you need one or two of this power transformer for a stereo amp ?
Not Marc :-)
As long as you don't bias too high (I will say, 85mA per tube), it should be good for a stereo amp, with the assumption that you don't intend to overload the PT continuously :-)
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Old 9th January 2018, 08:26 AM   #1862
bandol83 is offline bandol83  France
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@ meanman1964,

Yes, one transformer will be enough for a stereo amplifier, it is specified for 400 mA ! That is the reason I indicated the price for only one piece, while I put the price of two for the output transformer

Marc
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Old 10th January 2018, 12:20 AM   #1863
meanman1964 is offline meanman1964  Belgium
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Marc ,
Can I take 220µF for C10-11 ?
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Old 10th January 2018, 02:56 PM   #1864
bandol83 is offline bandol83  France
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Yes, it is recommended to use bigger capacitor if you can insert them, if you cannot it is possible to keep the lead long enough to solder them without any problem

In the BOM I even suggested 330 uF 100 V like Nichicon UFW2A331MHD, I used them they are a little squeezed but can fit (see photos)

Cheers,
Marc
Attached Images
File Type: jpg Ampli KT88.JPG (363.9 KB, 454 views)
File Type: jpg Ampli 6CA7 stereo.JPG (513.0 KB, 457 views)
File Type: jpg Montage ampli EL34 fini dessous.JPG (323.1 KB, 445 views)
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Old 12th January 2018, 09:11 AM   #1865
bekim is offline bekim  Albania
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Hi Marc et all,

I am going through the documentation you posted in your GB thread, and I have few questions regarding the amplifier.

1. How much current = mA will be enough per channel? You mention for stereo is sufficient 300 - 400 mA, I might use 2x 6CA7 tubes and I have to order power transformer and provide details.

2. Bias power, again you mention in documentation that, 50VAC and 50 mA will be enough, but is that current enough for two channels or is required more? In other words, will 10VA will be enough for two boards?

3. Feedback connections - what are these for? Negative feedback? Is it required to connect?

4. What will be power output when use 2x EL34 or 6CA7?

5. Output Transformer - Can I use Ra=4k instead 0f 4.3K suggested, and 40W rated power?


Many thanks,
bekim
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Old 12th January 2018, 10:16 AM   #1866
zman01 is offline zman01  Bangladesh
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EL84 Amp - Baby Huey
bekim,

IIRC Marc gave an example of a suitable transformer for bias power:

TST20/014 INDEL - Transformer: toroidal | TME - Electronic components

That one is rated at 20VA.

You will find model number for a suitable power transformer in Marc's following post:

EL84 Amp - Baby Huey

Last edited by zman01; 12th January 2018 at 10:19 AM.
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Old 12th January 2018, 04:58 PM   #1867
SCD is offline SCD  Canada
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Hello all:
I have been following this thread for along time. It is starting to get a little too big and diverse.

Good for Marc for moving ahead with his Group Buy for an octal based project.

I am thinking it is time to break off the discussion around Marc's project from the project and discussion that Gingertube began. By creating a consolidated thread on Marc's project it will make it easier to follow and more sense to those that are heading in that direction.
It will also allow Ian's thread to remain on topic.

Right now it is a bit confusing with both discussions at the same time.
Is this a reasonable idea for others?
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Old 12th January 2018, 10:11 PM   #1868
gideon1990 is offline gideon1990  Netherlands
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I have been passively following this the last few months, especially for a KT88 version, and it all looks awesome but I have to say that it is indeed getting confusing
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Old 12th January 2018, 10:17 PM   #1869
adam1016 is offline adam1016  United States
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Quote:
Originally Posted by SCD View Post
Hello all:
I have been following this thread for along time. It is starting to get a little too big and diverse.

Good for Marc for moving ahead with his Group Buy for an octal based project.

I am thinking it is time to break off the discussion around Marc's project from the project and discussion that Gingertube began.
I completely agree with this. As somebody who just wants to build an EL84 baby huey, I feel that there's so much unrelated material to wade through in this thread. If anybody is looking here, AFAIK the most recent schematics are way back at posts 602-604
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Old 12th January 2018, 10:31 PM   #1870
bandol83 is offline bandol83  France
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Hi bekim,

Several persons already give you good advise about transformers, but I would like to give you more details :

1) The current that you need will in fact be dependent of the output tubes that you are using and of the supply voltage between 350 V and 450 V. By exemple a 6V6 will consume half the current of a 6CA7... With the 6CA7 and the Hammond 4.3k output transformer on my amplifier I use a toroļdal transformer of 250 V AC and 300 mA and it is not very hot

2) The 50 V AC transformer will only supply few mA on the negative side for the input differential amplifier and the output bias as well as few mA too on the positive side for the MOSFET driver. With 50 mA you will have more than enough capability, 10 to 20 VA will be perfect, I suggest a 2 x 24 V AC because they are quite common

3) Feedback connector is, in principle, not needed in a Ultra Linear or triode version, it can be required in pentode version (I haven't tested that !). I know one case where a builder use it for a differential input---

4) The output power will be dependent of the voltage and of the output transformer, I will say between 30 W to 50 W

5) Yes, you can use a 4k transformer and 40 W will be enough if you don't push your amplifier with more than 400 V anode voltage ! I recommended a Toroidy 4k 80 W output transformer : TTG-KT88PP TOROIDY - Transformateur: de haut-parleur | TME - Composants electroniques

Cheers,
Marc
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