[malcolm.mcintyre]

I would, but don’t know how to post pictures here. I don’t have a photo website.
Perhaps this will work?

You can Google “Brimar Footscray UK, and the BVA” to get the history.
Might take a wander around the old factory site in case someone left a chest of tubes around

 

[malcolm.mcintyre]

 

[Blackmore]

I see, good one, but you may already saw the differences, where Tung Sol has SU and yours, just like the majority of the same type of tubes, SL between 6 & 7: 6SU7 vs 6SL7.

Enjoy and thanks for sharing!

 

[Nik74]

@treebug Have you received your HP4 yet? How does it sound?

 

[mr. Vagabond]

I really want to hear my Beyerdynamic DT-990 with this amplifier but unfortunately the price is too high for me. I have experience with electronics and I could do it myself, but the input and output transformers are particularly critical components and largely determine the sound. I will ask those of you who own this amplifier to share more information about the transformers.
For example, if the input transformer is a standard one that is manufactured by another company and can be purchased?
The output transformer I guess is made by EAR? But anyway, if anyone has this capability, he could measure some key parameters of the original transformer, such as inductance, active resistance, winding ratio, dimensions and so on.
The idea is to have as much information as possible to make the transformer with parameters as close as possible to the original one.
I know very well that this in a very difficult task and the amplifier will sound different from the original, but this is still better than nothing. I wish I could give $ 5,000 for a real EAR HP-4, but at least for now that's impossible for me. I will be glad if someone gives more information about this amplifier.

 

[zodiac1234]

I really want to hear my Beyerdynamic DT-990 with this amplifier but unfortunately the price is too high for me. I have experience with electronics and I could do it myself, but the input and output transformers are particularly critical components and largely determine the sound. I will ask those of you who own this amplifier to share more information about the transformers.
For example, if the input transformer is a standard one that is manufactured by another company and can be purchased?
The output transformer I guess is made by EAR? But anyway, if anyone has this capability, he could measure some key parameters of the original transformer, such as inductance, active resistance, winding ratio, dimensions and so on.
The idea is to have as much information as possible to make the transformer with parameters as close as possible to the original one.
I know very well that this in a very difficult task and the amplifier will sound different from the original, but this is still better than nothing. I wish I could give $ 5,000 for a real EAR HP-4, but at least for now that's impossible for me. I will be glad if someone gives more information about this amplifier.

Hi.
This is not a recommended way of going about it.
I'll promise you'll end up spending much more money AND time building your clone - and it will not sound the same as the original.
Measuring transformer parameters is not difficult but neither trivial.

Try to find one 2nd hand - that's the best alternative. I found this: https://elettronica.aaannunci.it/ear-hp-4-e-uno-dei-migliori-e-iconici-amplificatori-2364419c5.aspx
Or try to find fairly generic type of transformers and build your clone around them. Remember: good ones (20 - 20 kHz) are expensive!
You can also try to salvage old radio equipment and hope to get lucky and find a good tranny you can use.
If you wanna reach for the stars, it will not be cheap, and you'll be forced to spend countless hours of measuring and testing instead of enjoying music.

A colleague of mine laughed hard when he saw the prices of some high end amps on the marked.
He decided to build one himself (electronics designer). Needless to say: it took 11 years to finish the product, and he spent 230 grand! Because he wanted to build something that could match the sound quality of his favorite amps.

if you have Sennheisers (HD800), Hifimans, it will sound heavenly. Not recommended with Audezes, but that's just me.
Good luck

 

[mr. Vagabond]

Hi Zodiac1234,
I totally agree with everything you said. I know very well that no matter how much I try to repeat this amplifier, there will always be a difference in sound. That's not my intention. I just have some experience with electronics, I have free time and I like to do things with my hands. Tubes and other components are not expensive, and if I have more information about transformers, I could make them on my own or buy suitable from a reputable manufacturer. In both cases, the sound will be different but I may like it. The AER HP-4, even a second-hand, keeps cost almost as good as new. The probability of finding it at a price that I can afford is close to zero.
So if anyone can give me directions about transformers, no matter whether theoretical calculations or real measured parameters I will be very grateful.

 

[zodiac1234]

......The AER HP-4, even a second-hand, keeps cost almost as good as new. The probability of finding it at a price that I can afford is close to zero....

Did you see the link I sent you? It is selling one for 1300 Euros!
That is almost 1/5 th of the price! Very good deal!

But if you really wanna build something and you are not picky about the sound, you can get just about any off-the-shelf output tranny that fits your output valve/load impedance calculations. I'd recommend hificollective in UK.

Measuring the transformer parameters accurately takes some serious effort.
Im not sure if anyone here would be willing to open up their beautiful and shiny HP4's, get the soldering iron, disconnect components, spend a few hours measuring the trannies, and then put everthing back together again.

You can contact the manufacturer and ask them to give you transformer data. Or you can ask them to sell to you spare parts (the trannies).
Then you can perform measurements on them and get the nesessary data.

 

[zodiac1234]

.

 

[zodiac1234]

I was just informed that the link I posted earlier might be dead....probably sold already.

There is another amplifier that I use, that is just as crazy good, and some believe it is even better.
It is absolutely reference-class amp, But it is monoblock, big and unattainable.

Good luck.

 

[mr. Vagabond]

zodiac1234, thanks for the quick and comprehensive answer. Of course, you are right about everything. It's always better to buy something complete instead of trying to invent hot water. Maybe I'll try to buy a cheaper second hand amp.
But in the meantime nothing prevents me from assembling a circuit and seeing what is going to happen. I have all the necessary parts. The only problem is the transformers and especially the output transformers. Since the amplifier is covered by feedback via the output transformer, which reduces the output impedance of the lamps, it is very difficult to calculate the optimum load for the lamps. Accordingly, I can not calculate this depth of feedback as well. In short, I can not calculate the output transformer accurately. Neither the input transformer.
If someone is familiar with the theory and can calculate it or at least give some guidance I will be grateful to him.

Better solution is the output transformer just to be measured. I very well understand that this may be annoying task for most of you. But if anyone wants to do it will help me a lot. I also wrote to the manufacturer, asking to sell 2 transformers or send me some basic data about them. Honestly, I do not believe they will answer me. They must keep this information secret and I understand them.

Well, that's all. Thank you for your cooperation.
I wish you a nice day

 

[DejanM]

mr. Vagabond,

I cannot help you with dimensioning of the trainnies but I can recommend you a good replacements. For the input transformers the best choice are Jensen JT-11P1-HPC. For the output there are now three Lundahl options: LL2754, LL2765 and LL2774. The choice will depend on the phones that you are using as well as from the tubes at the output stage. There are though some other transformer producers on the market that are providing some good options especially built for headphones ... Sowther, for example. Lundahl is though well known for a good quality transformers and that would be my first choice. All these transformers are not cheap, but the transformers on both ends of the circuit influence the quality of sound reproduction considerably. Therefore, I believe that it is not a very good idea to save money on them ...

 

[mr. Vagabond]

Thanks DejanM
But how can you be sure these transformers are suitable? I am inclined to accept the input transformer proposal as good.
But when it comes to the output I have no idea what the transformers should be. According to the data, the internal resistance of the 6SL7 tubes is about 44K, or for both in parallel is about 22K. In the example circuit they are loaded with plate resistor about 100K. As I said, because of the feedback it is difficult to calculate the appropriate load resistance. And without it, it is impossible to choose a suitable transformer.

 

[DejanM]

I would write an eMail to Lundahl and ask them which one is the most appropriate for your application. Things are really a bit complicated as every of these transformers has PP and SE verision with different output options depending on the headphone impedance. I am sure Lundahl will be glad to help. Another option, if you are living in US, is to contact KandK audio - Kevin is a very nice and competent guy and he will surely help you to make a right choice.

 

[mr. Vagabond]

Thanks, but I do not think this is a solution. The scheme requires a serious analysis to determine which transformer is appropriate. Hardly anyone will devote so much time and effort. Measuring the original transformer is much easier. Anyway, thanks for your efforts.

I live in europe, not in USA.