LO1166 technical questions

[moamps]

Hi,

I did my best to try and find the following info but with little luck. I'd really appreciate it if someone could help me out with answers to the following:

1. What's the nominal DC bias current for the transformer in the BA283 circuit?
2. What's the maximum AC output voltage (THD less than 1%) at 50Hz and 15kHz, with the transformer loaded (600ohm) at the nominal DC bias current?

P.S. I was browsing metas and found several dead links to NYD's schematics. Could someone erase the dead links in metas, please?

Regards,
Milan

 

[PRR]

> I did my best to try and find the following info

Link to whatever you did find, because us scatterbrains can't remember the difference between a LL1166, a 707, and a Ford 500.

This thing?

http://www.jlmaudio.com/neve_BA283.htm

What's the nominal primary impedance of that transformer?

 

[Brian Roth]

PRR, according to my notes, the 1166 has split coils for both primary and secondary, and thus can be wired for 200 or 50 Ohms primary to 600 or 150 secondary.

Bri

 

[rafafredd]

so, it´s a 200:600? I always thought it was 250:600...

 

[moamps]

Hi guys:

CJ posted the parameters of the transformer in one of the threads:

http://vacuumbrain.com/The_Lab/TA/Neve/LO-1166.pdf

I'd really appreciate feedback from the people who are familiar with the BA283 preamp and LO1166 characteristics and measurements. My intention is to design a substitute transformer for the preamp, based on the answers to questions 1 and 2.

Thank you for all your time and assistance.

Regards,
Milan

 

[CJ]

Sounds like your after AC and DC flux.

That's a gapped design, I figure yours will be also, unless you get sneaky with the net dc flux, so any math will be a wild estimation due to the nature of a gapped core.

I estimated ac flux on a Neve square stack at 20 hz and dot 4 stacking to be about 344,089 V/T.

 

[12afael]

about the pdf file, I still believe that the sec B is made of 0.010" .

 

[maxwall]

.

 

[sodderboy]

The output circuit was never spec'ed for DC bias current, or Neve never gave any value for adjusting it.  Alignment for that circuit was to drive it with 1Khz sine to clipping, and adjust bias for symmetrical clipping.  I can bet that the current would be different for two channels simply because of the tolerances in components.
Mike

 

[moamps]

If someone has the original technical teardown .pdf on this LO1166, can they send it to my email

Done.

Regards,
Milan

 

[maxwall]

Many thanks Milan !!!!

just wondering , did you ever get your questions answered in your initial first post above.

your website is impressive too !!! I wish I could read in your language to understand explanations
under your audio projects.

Off the subject of the LO1166 a little.......
I especially enjoy your use of the 6C33 tube in one of your projects. I have been wanting to make a single ended
Fender super champ guitar amplifier with that triode power tube using a 12" alnico speaker. I need to find a source for that output tube. I hear the 6C33 tube had production runs at the Svetlana factory that were better than Reflector factory. Any truth to this ?  Also, is there a adapter to use in order to test these 6C33 tubes on a tube tester, the socket is unique to this particular output tube ?

Also, Have you had any success with LO1166 ?

 

[moamps]

Hi,

Thanks for the nice words about the site.

Sadly, I never got my questions here answered but that was 4 years ago and it doesn’t matter any more. At the time, I was working on a NEVE-based preamp design (http://www.moxtone.com/Dual_microphone_preamplifier.htm) and decided to use a substitute Sowter transformer that I had at hand but the results I was getting were not quite what I expected. When I biased the output transistor (using standard procedure, as explained by Mike in his preceding post), I got rather disappointing THD- and bandwith-related readings so I wanted to find out what the nominal transistor current (which is also the transformer magnetization DC current) specified by the manufacturer actually was. Later on, I decided to switch to another brand, which turned out to be a good move, and happily forgot all about the original transformer.

As regards the 6C33 tube, my experience with it has been mixed. The tube can be purchased relatively cheaply but its implementation is far from trivial as it places huge demands on the output transformer and the driver stage of the amplifier, plus it requires a high filament current. The 6C33 tube amplifier shown on my site is an original design by Erno Borbely, slightly adjusted to my own needs. Honestly, I am not overly satisfied with its performance (both sound- and measurement-wise) but the amplifier is very stable and I’m sure it has plenty of tweaking potential (I’ll have to revisit this project someday, time and money permitting). Another issue worth noting with regard to this tube is a relatively high dependence of anode current upon temperature. For instance, when I had an Ayon Spark 6C33 tube amplifier brought in for service a few days ago, I measured a rise of the anode current by over 100% (from 80 to 180mA!!) during the few minutes required for the amplifier and tubes to reach their operating temperature. The Ayon Spark uses fixed bias, which is generally avoided by designers precisely because of the huge current drift. On the other hand, auto-bias would require insanely powerful cathode resistors and cause the amplifier to heat up even more. It’s a no win situation really. Another issue with the 6C33 is its socket that needs to be replaced quite frequently, due to high temperature oxidation. AFAIK, the Russians used this tube in their MIG planes (power supply regulators) and replaced the sockets together with tubes (after about 1,000 hours).

I am not a guitar amp expert so take my opinion as just that but I don’t believe the 6C33 would be the best choice for a guitar amp, and here’s why:
- the 6C33 would require a very complex driver stage to drive it into saturation;
-the output transformer would have to be very complex as well because of the high DC current;
-the 6C33 has been designed to withstand large mechanical loads and vibration whereas guitar amps actually benefit from some mechanical-acoustical coupling-feedback.

I don’t think I have ever seen a 6C33 septar socket adapter. Besides, I’m not sure if there are that many tube testers out there that can actually measure the 6C33 (Ia=200mA, Ua=180V, Vh=12V, Ih=3,5A!!!). Why not improvise an adhoc measurement setup of your own to test the tube, which is precisely what I did back in the day.

Mind you, it isn’t my intention to dissuade you in any way from your guitar project. I just wanted to give you a heads-up about the possible issues and areas of concern should you choose the 6C33 for the project.

So far, I can’t say that I have noticed any significant differences between the Svetlana and Reflektor production runs. IMO, any one will be fine as long as the tube is protected from constant overload and kept at max. 80% of total dissipation.

Regards,
Milan