• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

EL84 Amp - Baby Huey

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 :D (see photos)

Cheers,
Marc
 

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  • Montage ampli EL34 fini dessous.JPG
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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
 
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?
 
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
 
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 toroïdal 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 :eek:

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
 
Hello SCD, hello all,

I already answered the subject of a new thread in my post 1833 to Patrick (reaper996) !

As I explained, the EL34 Baby Huey is 98% schematically compatible with the EL84 version, the only difference is the output tubes and the value of some resistors... In this thread there was already 6V6, 6L6 and others version of EL34 Baby Huey :)

I don't think this approach is bad for the thread, on contrary it has wake up the thread which was a little bit quite for some time :D

However, if Ian (gingertube) think that I must start a new thread only for EL34 and ask me that, I will do it without any problem since he helped me a lot in this project. I am sure that when I started to ask him some recommendations, he did not believe, like me, that more than 200 PCB will be sold for EL 34 Baby Huey :violin:

Cheers,
Marc
 
Alright, I've bought the parts for the preamp that will (eventually) drive my baby hueys, and ordered the transformers from edcor. I got a pair of xpwr064s, and called edcor about adding 6 ohm taps to the cxpp24-8k, which they graciously added at no extra charge :)

However, I'm now faced with a dilemma. My speakers are RATED at 99db/W(not sure how accurate this is, as they're a fairly new DIY design). I have an old receiver I've been using to drive them until now which is rated at 50W, so I keep the volume as low as it can go. My question is:

The EL34 seems to put out about 50W, but seems to have more of the tone I am looking for (warmer mids, better bass). My transformers are only rated for 25W, and my speakers would never use all this power. Is there a way to limit the power put out by these tubes without having to redesign much of the circuit? Are there significant tonal differences between the EL34 and the EL84, or are they just different power ratings?

I guess at the end of the day, I'm leaning hard towards the EL84, but have been hesitant to pull the trigger.
 
Hi,

I fully agree with crispycircuit, the big advantage of this PCB with the octal socket is to accept a large choice of output tubes from the 6V6 (equivalent of the EL84) to the KT88 or even KT120 :)

With different tubes and power supply it is possible to build your amplifier with an output power from 10 to 50 W but with the same Baby Huey shunt feedback design introduced more than 10 years ago by Yves on an ECL86 amplifier and Ian with the original EL84 amplifier :D

I have added two comparisons of several output tubes which can be used with this EL 34 PCB and a new BOM with different capacitors values for those who want to use higher voltage ( I didn't made test at more than 380 V however !).

Rgds,
Marc
 

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  • CHOICE OF POWER TUBES FOR THE EL34.pdf
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  • BOM Ampli EL34 Jan 11, 2018.pdf
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Alright, I've made my decision and begun ordering parts:

I have decided to stick with the 'classic' baby huey as was posted in post 602. I am going to stick with the EL84 for now, and because I am not using a PCB for the entire project (though I may use proto-boards for the bias sections), I can always swap a couple resistors and the sockets/power supply/transformers later if I decide I want to try different tubes (Or just build another amp with octal sockets :) )

Much thanks for all the advice,
Adam