• 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.

Oh no...not another Baby Huey EL84 build.

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eldarvanyar

eldarvanyar

Member
Joined 2008
Bas Horneman said:
I've ordered local. Not only Dutch but also around 20km from me as the crow flies. The ones on the picture below are single ended ofcourse. But the ones I ordered are based on those cores.

Perhaps interesting. I've asked UL taps to be 25% instead of the ubiquitous 43%.
Click to expand...

Hi Bas,

can you say why you went for 25% instead of 43% for UL Taps.

Thanks again

Lee
 
Bas Horneman

Bas Horneman

Ex-Moderator
Joined 2002
basaudio.wordpress.com/
Hi Lee,

Sure because Dynaco Z565/MagneQuest MQ565 had them. And I thought the 565 sounded better than the other EL84PP transformers I used to have.
Output transformer for EL84 PP

And I read this somewhere on this page Why have I never seen any 6L6GC-based ultralinear amps? | Audiokarma Home Audio Stereo Discussion Forums:
True UltraLinear operation is in fact very specific with regards to the tubes used, optimum screen tap percent, and even the type of bias system used. Unfortunately, many if not most transformer manufacturers today are dumb-stuck on the idea that optimum UL operation is achieved in all tubes with a generalized tap placement at 40% of the winding. Nothing could be further from the truth. Relative to the performance characteristics that true UL operation achieves, use of a less than the optimum tap percent can be quite detrimental to the performance of some tubes, with straight pentode operation producing much better results than a poorly placed UL tap achieves. As stated before, UL operation of the 6L6 family of tubes requires the screen tap being placed at 43% of the winding, with a reflected load impedance of 6600 - 7600Ω depending on the bias scheme used. The 6550 family requires the taps be placed at 40%, with a reflected load in the 4-5KΩ range depending on bias arrangement. EL34s operate best with the taps at 33% using fixed bias, while the EL84 family works best with fixed bias and the taps placed at 25%.
Click to expand...

Doesn't mean he is right though. But Hafler and Keroes also determined 25% (But that was probably for max power)

At the end of the day...I don't think it matters THAT much. Would have been nice to perhaps be able to switch between 25 and 43%. At least then I might have an anecdotal opinion on it.

Here is a thread on diyaudio where I also asked for opinions: UL for EL84. 22-24% is better than the dogma....40% is lowest distortion....
Unfortunately the link I put up in that post does not resolve anymore.

But you can see Eli Duttman also posted an anecdote:
The highly revered "iron" Freed wound for the H/K Cit. 2 is tapped at approx. 20%.
Click to expand...

The Citation 2 uses KT88 though if I'm not mistaken.
 
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T

TG

Member
Joined 2002

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T

TG

Member
Joined 2002
zintolo, all this data is pretty well-know, but, like Bas said, it gives no info on the harmonics spectrum which is also very important - say, 10% of 2nd and 1% of 3rd harmonics is preferrable for PP amp to the 5% of 2nd and 2% of 3rd harmonics.

I actually have both 20% and 43% (or is it 40%?) OPTs somewhere in the drawers, but a) both of them are PP (so some special method of testing is requred, like driving only one tube with the audio signal - not sure if it's gonna be 100% indicative) and b) neither I have EL84s on hand, nor the time and/or personal interest to mess with all this right now.
I might get back to it some time in the future though.
 
Bfpca

Bfpca

Member
Joined 2007
Hi Bas

Your amp looks fantastic, with your usual attention to design and construction details. I have finished my EL84 BH and will be posting a thread on it shortly. I had the same issue with providing bias adjustment in a convenient way and came up with something using available parts that you and others may be able to use. I am truly pleased with the sound of mine. Even driving 4 ohm 90 dB speakers that are a difficult load it sounds great.
 
eldarvanyar

eldarvanyar

Member
Joined 2008
Bas Horneman said:
6n2p-EV and 6p14p-EV
Click to expand...


Hi Bas,
Did you have to wire the differently for the Russian Valves and make any other adjustments regarding resistors etc

I have a stack of 6n1p-EV and 6n2p-EV that I bought last year

According to my notes on my iPhone they have to be at 6.3v

How to use 6N1P and 6N2P Russian tube ― Hi-End vacuum tubes, sockets, capacitors, nixie. Retail and wholesale to worldwide.

I would be happy to be able to use them in the BH - I know on some diy builds I have read people have wired in a switch to enable an easy swap between 12ax7 and 6n1p

Can you say what difference you have found

Thanks again

Lee
 
eldarvanyar

eldarvanyar

Member
Joined 2008
Hi Bas,
Yes I have ordered the boards and waiting for delivery which is delayed due to COVID-19.

Can you post a direct link to the BH EL84 BOM as I cannot seem to find it.

I am thinking through the project at the moment. I sent two emails to the Dutch guy regarding the same output transformers as you but still not had any reply.

I am wondering about Audionote EL84 Output Transformers which are similar in cost and weigh a hefty 4kg. They are used on the OTO PP Amp.

The Toroidy’s look very good as well particularly in their covers. My understanding is that the better the output transformers the better the sound. I don’t want to hijack your thread and can start a new one if that would be better.

Thanks

Lee
 
Bas Horneman

Bas Horneman

Ex-Moderator
Joined 2002
basaudio.wordpress.com/
I don’t want to hijack your thread and can start a new one if that would be better
Click to expand...
No it's fine. I don't see it as my thread. It's all about communicating with each other about this fine hobby of ours. You are welcome to ask.

Here is the BOM I used on mouser. It is not a complete BOM. But contains some parts which are not typically in my house like the semiconductors etc. The rest are easy to get locally for better prices. As mouser is not cheap...

Mouser Electronics Inc. Nederland

And for the rest see the BOM that snapper linked to.
 
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