Re: The secret to using iron IT's (like Lundahl 1660)

Posted by RonSS (A) on May 14, 2002 at 12:59:43

In Reply to: The secret to using iron IT's (like Lundahl 1660) posted by Kurt Strain on May 11, 2002 at 19:47:40:

Ah, a post for me as I've been struggling with the bench measured performance of the 1660/10mA IT's.

I have discovered a few things.
1. Loading each section of the secondary with 500pf makes the square waves look pretty good. This with a 2.5k Rp drive impedance.
2. Resistive loading only really drops the output amplitude, and increases the distortion.
3. The split at the secondary is right on at 1khz, but at 20 khz it is always off by about 1-2dB side to side. This is without any sort of loading on the secondary. This concerns me.
4. The response at the output is highly dependant on the Rp of the driver tube. I verified this by simply driving the IT with a 50ohm tracking generator in series with a 10k pot that I adjust while watching the output with a spectrum analyzer. I get the same results with a tube as the driver while varying the cathode resistor.
5. I measure 800pF of capacitance from the input to the output of the IT when wired in SE/PP grid configuration. This explains the peak in the frequency response near 100khz, and accounts for the ringing when viewing square wave response.

So I guess these things just aren't going to measure well on the test bench. Are they.
Despite it going against my technical background, I'm just going to have to go ahead and build the amps with the IT and listen.
And....things will behave different when the IT is driving the 300B, I haven't done that part of the experiment yet.
I still think though, that better IT's could be made. At least then it would seem to justify using the best OPT's available.

And Lynn, I'll get a couple of the ECC99's from Matt to play with. It's his fault I own 300B's and LL1660's now anyway! Ha!

Ron Selberg

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Follow Ups Full Thread

Topic - The secret to using iron IT's (like Lundahl 1660) - Kurt Strain 19:47:40 05/11/02 (24)

Re: The secret to using iron IT's (like Lundahl 1660) - RonSS 05/14/0212:59:43 05/14/02 (1)

First time I checked out the LL1660/PP with some measurements... - Kurt Strain 14:12:15 05/14/02 (0)

Re: The secret to using iron IT's (like Lundahl 1660) - Paul D. Scearce 08:22:52 05/12/02 (0)

Re: The secret to using iron IT's (like Lundahl 1660) - Lynn Olson 20:17:53 05/11/02 (17)

Yikes! I stand corrected! - Kurt Strain 21:04:28 05/12/02 (0)

RC Network trick - Lynn Olson 15:30:45 05/13/02 (0)

I took out the damn 220 pF cap and... - Kurt Strain 21:06:10 05/13/02 (8)

Re: I took out the damn 220 pF cap and... - dave slagle 21:13:54 05/14/02 (0)

Mo' tweaks for PP45 Man ... - Lynn Olson 02:02:52 05/14/02 (6)

TV dampers and regulated supplies. - Mark Kelly 17:27:12 05/14/02 (2)

Re: TV dampers and regulated supplies. - Lynn Olson 01:12:29 05/15/02 (1)

Re: TV dampers and regulated supplies. - Mark Kelly 23:49:59 05/15/02 (0)

Re: Mo' tweaks for PP45 Man ... - Kurt Strain 07:59:13 05/14/02 (2)

Re: Mo' tweaks for PP45 Man ... - Lynn Olson 15:59:21 05/14/02 (0)

Re: Mo' tweaks for PP45 Man ... - Eli Duttman 11:49:40 05/14/02 (0)

Re: RC Network trick - dave slagle 19:50:28 05/13/02 (0)

Re: Yikes! I stand corrected! - Danny T 03:26:12 05/13/02 (0)

Re: Yikes! I stand corrected! - Kurt Strain 10:43:23 05/13/02 (0)

It definitely does - Danny T 15:17:00 05/13/02 (0)

Re: It definitely does - Paul D. Scearce 07:13:11 05/14/02 (0)

Re: It definitely does - Danny T 01:41:40 05/14/02 (0)

Kurt give me some tips for my experiment.. - Yoon 19:57:39 05/11/02 (1)

I really couldn't say for sure. You have to try them and hear. nt - Kurt Strain 22:59:50 05/12/02 (0)

Re: Kurt give me some tips for my experiment.. - Yoon 19:58:44 05/11/02 (0)

Follow Ups

Re: The secret to using iron IT's (like Lundahl 1660) - RonSS 05/14/0212:59:43 05/14/02 (1)

First time I checked out the LL1660/PP with some measurements... - Kurt Strain 14:12:15 05/14/02 (0)

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