I decided to try build amp by myself but I will need some help...

First, the parts...

1. OPT transformers- I posted mails to:

Tribute, lundhal, intactaudio, ae-europe, and today to promitheusaudio

I ask them for transformators that Romy mention somewhere on this forum:

 "8 or more secondarys, 8:1 in the middle mapping, DCR primary > <50R, 350mA amorphous"

I got answers from lundhal and intatctaudio.

lundhal proposition is  LL1693/350mA but it cant by amorphous

http://www.lundahl.se/pdfs/datash/1693.pdf

He can make amorphous  LL1627 

http://www.lundahl.se/pdfs/datash/1620_3_7_9202.pdf

intactaudio asked me a question:

"I do not like the procedure of "remapping" the secondaries since it 
forces compromise. I can do it, but would need to know what the 
"preferred" decondary load would be"

So what should by decondary load?

Best

Dominik

I got email from promitheus:

"The transformer for this would be a double c-core
nanocrystalline core which is better than the amorphous core. The
nanocrystalline core is where the grain material is smaller in the nano
region'

Still waiting for reply from lundhal- delivery time.

Price for LL1627 and intactaudio transformers is almost same.

I make decisoin next week.

Dominik 

Dominik wrote:

Tribute give me best price... Romy, Can You help me with choosing L1, L2, L3, L4? http://www.hammondmfg.com/5cchk.htm And DL1, DL2 http://www.magnecraft.com/time_delay_sensor_relays.php

Dominik,

The Magnecraft relays are excellent, so the Hammond chokes. In fact the Hammond chokes in my view even better then they shall be. The Tribute transformers are very fine but I am bit not at ease with what I see. He specified the 350mA amorphous transformer for 260Euro. That is very conservative price and therefore I wonder what the core size he will be using. Current offsets inductance and inductance offsets LF. If he whatever core size he uses gaps it for 350mA then how much inductance will be left? He needs to give you the inductance number at 350mA, 300mA, and 250mA. I afraid that at 350mA it will be 7H-8H left and it will be too low. If you drive this thing at 200V then at 300mA you are already at max plate dissipation, so unless you go for 160V-170V (that I feel a bit too low) then you would not need 350mA. Probably the optimum for a full range operation to have 200V and drive the tube at 200-250mA, that would make a cup for 270A-280mA good enough. With all of it you need to have 10H and up. An amorphous transformer for 260mA and 11-12H and with a price tag of 260Euro? Sounds too good to be true. Hm, can I have one extra pair for myself? For a full-range operation you need to target LF cut off at 15Hz, you will end up with 17Hz-18Hz, at full-power of cause.

Dominik, I think you took it a bit wrong and delivered to Tribute a message with a wrong accent.

As I understated that was the reply from the Tribute guy. No one accuses him in cutting down core size but based upon the available inductance you will be available to choose what currant you would like your transformer to be gaped at.

The higher currant you drive the lower plate impedance and it might be useful in some cases. You chose 8:1 load that is in the middle of the road and you shall be OK with 200-300mA or with gap of 230-330mA.  Now how the “core size” play in all of it? Amount of lowers cut off frequency (at full power) is a subject of inductance. Inductance is a subject of 3 derivatives - core size, gap size, amount of wire. The amount of wire is fixed by the turns ration. The core size is fixed by the selection of the Tribute’s laminations. The only variable you have is to moderate the gap size (or the max DC currant the transformer will be handling). The higher currant the lower inductance. So, asking Tribute to make it 200mA, 250mA, 300mA or 350mA you will be changing your LF cut off. The in here is to know if it will be from 12Hz to 25 Hz or from 20Hz to 40Hz. To answers this question you need to know what is the core size Tribute uses. The “total weight for one transformer” is not accurate and in mostly irrelevant number, the size of the enclosure it will fill is also very abstract number. He needs to give you the inductance numbers at let sat 200mA and at 300mA and it will instantly show you very objectively the core size. Some manufacturer do not like use inductance numbers and they more accustom to talk about lower cut off at full power. That is inductance too.

I kind of supplied a lot of thing but it shell give you a basic idea what you need to look for. If you would like “your friend … to order a pair too” then he needs to give to the friend the inductance number at 250mA – that will let the friend to know what he will be requesting. Do not forget that Tribute guy knows very much what he does and he do not need your or mine help. However, knowing the objective capacity of Tribute core from a perspective of LF is something that will help you estimate what to order.

Dominik,

I do not think that you need suggestion from me. If Pieter looked at the schema then everything is very much identifiable in there and he shall know what to do. Let me to give you alternatives that are not at the schema.

The 12,6V/5A, 6,3V/1A filament transformer might be as proposed but it might be also just simple 6,3V transformer with 8-10A secondary. You see, the 6C33C has two pair of heated and you might connect them in series or in parallel. There are many debases what is better, both camps have own reasonable arguments. I made the experiment and I was not able to hear difference between series or in parallel. I had 12V because I would like to keep current down (six driver filaments and six 6C33C filaments, each of 6C33C them 6A) but in your case what you have one 6C33C per amps you might stay with 6.3V only and use parallel heaters. The benefit of the parallel heaters that is you have good speakers that do not need a lot of power then you will be able to disconnect one heater and use just one anode of 6C33C – it will sound better….

The bias and the B+ for the first stage are fine.

The power supply chokes need to be warned. I do not know how Pieter does his chokes but some of the chokes do not work well in input choke application as they are too “loose”, not well varnished perhaps and in input choke application they have noise  - something that I hate very much. Explain to Pieter that the chokes will be work right after rectifiers and will see very high ripples. So, the chokes need to be made that they would not buzz. Pieter or whoever will do it will knows what to… Ironically the very cheap Hammond chokes are very well made from the perspective of “none-buzzing” in input choke application. They have even a custom version for each choke (10% more expensive) where they double-dip choke in epoxy (separate coil and separate assembled choice). They look ugly but you can drive the Hoover Dam currant across them and they still will be silent.

Dominik wrote:

Hi, From Pieter: "For me it is normal practice to do good specifications. I go for 10 Hy's at 250mA. 10 Hy's with 512 ohms source impedance will give 8 Hz cut off frequency."

Dominik
 Any further progress on the project of the Melquiades? Curious about the transformers from Pieter. Any comments?

perrew wrote:

Anyone know if Tribute still in business, and if not can recommend company that has double coil on single c core for 2A3?