DISCLAIMER

DISCLAIMER: Vacuum tube circuits work with dangerously high voltages. Do not attempt to build circuits presented on this site if you do not have the required experience and skills to work with such voltages. I assume no responsibility whatsoever for any damage caused by the usage of my circuits.

All rights of photos and text reserved. Usage of photos or text from my blog on other websites or for any other purpose only with prior permission. If you want to use any material from my blog please contact me by email.



Thursday, March 22, 2012

New Lundahl Line Output / Interstage Transformer

Hi!

In Lundahls line output transformers I always missed one which offers a ratio close to 6:1 step down. There is the excellent LL1660 with 4.5:1, the LL1692A offering 3.5:1 and the LL1689 with a high 9:1 step down ratio. After some email exchange Per Lundahl agreed to develop a transformer which fills that gap. Here is the new LL2745:



It has the same primary windings as the LL1689, only the secondary is wound such that it offers a 2.8+2.8:1+1+1+1 ratio. The transformer can be used for other purposes besides 5.6:1 step down. As with the other types, the winding arrangement can be combined in different ways, for example to get a 2.8:1 step down. It can also be used as interstage transformer, for example offering a 1:1.4 or 1:2.8 step up or step down.

I asked for this transformer as an ideal line output to go with tubes like the 26 or UX201A. For these triodes with a higher rp, the step down ratio gives a lower output impedance as the LL1660, but does not loose as much gain as the LL1689. Especially when a real 600 Ohm impedance should be driven for example wtih the 26, the LL1660 would not provide enough step down.

I got my first pair of the LL2745 gapped for 8mA, to be used with the 26. I will write about this project when it is getting built. Stay tuned.

Best regards

Thomas

No comments:

Post a Comment