6N1P Bass DI - Revisited

[yvus]

Hello guys,

Thank you for this very useful thread. I built 2 units based on the scheme showed in the first message and they sound great. I used Carnhill transormers. Both units are in the same box and are powered by the same PSU.
When i test each unit individually, i get a B+ voltage of about 190 V with about 3 V on the cathode resistor (which is 220 Ohm as stated on the diagram). However, when the two units are feed in parallel from the PSU, the B+ voltage drops to about 150 V with a cathode voltage of 2,2 V approximatively and I can not figure out why ? The low voltage supply for heaters remains quite stable in both cases.

Do you have any idea ?

Thanks.

 

[ruffrecords]

If the HT supply uses simple RC filtering then the additional current draw of two using will drop the HT and alter the operating point which is reflected in the cathode voltage.

Cheers

Ian

 

[yvus]

Since the HT supply in the build I'm testing indeed uses simple RC filtering, it makes sense. Thank you for your answer, I will check this out.

 

[soapfoot]

@CJ

Would this be a suitable transformer for this project?

https://utmindustry.com/utm3590b
Alternatively, are you interested in winding these, or do you have another suggestion for a part?

Thanks so much!

 

[CJ]

16 Henry's is a bit light for bass, even at 100 Hz

175 H at 20 Hz is what I try for. Thus the 1 inch core lams. Looks like they run a European core, 57, whatever that is. I can not get 100 EI endbells, otherwise I would spin some ,

What about that Mesi guy, sheesh.

 

[soapfoot]

16 Henry's is a bit light for bass, even at 100 Hz

175 H at 20 Hz is what I try for. Thus the 1 inch core lams. Looks like they run a European core, 57, whatever that is. I can not get 100 EI endbells, otherwise I would spin some ,

What about that Mesi guy, sheesh.

Thanks so much for the reply!

As for the end bells, is this the right part?

https://www.don-audio.com/Unpainted-vertical-steel-end-bells-for-US-EI-100-1-lamination
It’s sadly not a US supplier, but maybe if enough people were interested shipping would be worth it?

 

[emrr]

@CJ

Would this be a suitable transformer for this project?

https://utmindustry.com/utm3590b
Alternatively, are you interested in winding these, or do you have another suggestion for a part?

Thanks so much!

16H, that requires enough NFB to knock source Z down. A 600:600 UTC A-20 is in the neighborhood of 20H @ 125Hz. Most of the 10-15K vintage primaries I look up at a glance are in the 200-500H range.

 

[CJ]

I will try Heyboer for some end bells. Used to get em for about 3 bucks a set , the tool and die place that used to stamp them got sold. The new buyer relocated so as you might expect, there was an interruption to the supply line.

 

[MicDaddy]

I will try Heyboer for some end bells. Used to get em for about 3 bucks a set , the tool and die place that used to stamp them got sold. The new buyer relocated so as you might expect, there was an interruption to the supply line.

vertically integrate

 

[respo2000]

Hello,
i got a little confused with the various output transformer possiblities mentioned in the original reddi-thread and here (edcor, CJ's, Cinemag). Since i am planning to build one of these di-boxes in the next time and the price of a CXSE25-600-5k is at around 250€-260€ at the moment, i am looking for cheaper alternatives. I know that there is the 2290 from Carnhill which is pretty cheap, compared to the edcor CXSE25.
Therefore i wonder if the Lundahl ll1692A would be another suitable alternative (Alt-Q-configuration) https://www.lundahltransformers.com/wp-content/uploads/datasheets/1692A.pdf ?
I would also be interested in how the 2290 compares sonically to the CXSE25 or CJs "original" DIY-Version. Did anybody do a direct comparison?

 

[CJ]

looks like the 1692 alt q would work great, has about the same turns ratio, mine is about 3.7:1 lundahl is 3.5:1,

primary inductance of mine is about 175 H , lundahl says 95 H which means you might roll off a bit at the ultra low freqs but you can add a cathode bypass cap to get more bass,

that c core might kick ass,

 

[respo2000]

Hey CJ,
thanks for your reply and opinion on the Lundahl tranformer. And of course for the hint with the cathode bypass cap.
At the moment i think i will try both the Lundahl and Carnhill and see what the difference will be. It might take a while to finish that project after some others, but i will report back how it turned out. I plan on doing some sound files of that transformer comparison too.

 

[dmp]

I can not get 100 EI endbells,

You can get them from Edcor!
horizontal or vertical

 

[CJ]

Well I'll be a sonofabitch thanks for that!

 

[beatnik]

Another good shop for transformer parts

http://www.jjyaudio.com/products.asp?sid=16

 

[ruffrecords]

Another good shop for transformer parts

http://www.jjyaudio.com/products.asp?sid=16

And they do covers for toroids too.

Cheers

Ian

 

[CJ]

Looks like 100 EI is EI76 in metric

Used this for info
https://www.leicong.com/en/product-c163225/EI-Laminatioin.html
Hole dims are a bit off on the chrome model but regular covers match up, vertical mount

http://www.jjyaudio.com/productview.asp?sid=8010

 

[Spencerleehorton]

I have a pile of EI75 could probably make about 10 of these if I could work out the total turns per bobbin!!
Could I take the LO1166 Neve OT winding spec and recalculate ratio for 1:3.67 ?

357 turns pri
1311 turns sec

For 1668 total turns as per original sized lams
How could this be adjusted for EI75?

Also is it just the power resistors that need to be 3w right or all?

 

[ruffrecords]

The LO1166 is meant to be driven by a very low source impedance high current source - exactly what you don't want for a tube output transformer and you want it to step down rather than up. You probably something like a 4:1 step down ratio (9K6:600). The LO1166 backwards is not far off but I expect you will need a lot more turns to get a high enough inductance for a 9K6 primary.

Cheers

Ian

 

[Spencerleehorton]

Ive got no inductance specs so working blind here, do you have any ballpark inductance specs?

Yes I was thinking of the LO1166 in reverse and only with the order on winding in the bobbin.

With the EI75 can get a lot more winds in there, at least around double (3000T) with the 0.25mm wire I normally use.

Also can seem to find any 2x170vac PT getting a small txf for the heaters is no problem just the B+ seems to be the problem!!!!