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[dhuebert]

I built up the first of the eiclone halves and have been testing it for the past couple of evenings. I was a little concerned the gain might be low due to the 6SL7 front end. Looking thru this forum I found Shannon's numbers for distortion results. He used 600mV RMS for full power, I tried this and low and behold it made exactly full power @ that input. I started out with KT88s running 72mA @ idle, they made 66Vp-p across 10 ohms for 54 watts RMS. I looked at these numbers and the 475 volt B+ and thought 6L6s could probably do the job just as well. A couple of Sovtek 6L6GBs were found and substituted. The idle current was set to 35mA and the input set to ~600mV. The amp now made 70 Vp-p, for 61 watts; huh, more power. Looks like 6L6GB it is. Although I haven't tried the EL34s.

I would be happy to build the amp with KT88s but would want a B+ of ~550V to make it worth it. I wish I had looked a little closer before I ordered the transformers. The same amp with sockets for a quartet of KT88s and 550V B+ would really kick ass! Or, wait a minute, six of 'em YA! SVT LOOK OUT!!!

BTW:I noticed Shannon changed the feedback resistor and cap, If I made this change, what benefit would I see?

Don

[EWBrown]

KT88s are basically loafing along in this design, even 6550Cs aren't getting pushed all too hard here. 6CA7s and "better" EL84s should run quite happily as well, with the bias set around 35-40 mA, as 50 would be pushing the envelope a bit hard. But then again, EL34 quads aren't all that costly, crank away...

VTL , in their MB-450 monoblocks, which use 8 6550Cs each, says to set each tube's bias, around 30-35 mA, but then they are running the B+ quite high, around 650VDC, IIRC. The PSU has two 1600 uF / 450V monster electrolytics in series. :o LOTS of Joules of stored energy there :o

Since you have changed to 6L6GBs, the NFB resistor and cap may have to be changed to optimize for these tubes. Those 6L6GBs and GCs are about as tough as the proverbial Army boot... Yellow_Light_Colorz_PDT_06

I still haven't yet gotten a full grip on calculating the best RC combinations for this application. If it sounds good to you, I'd just leave it "as is" for now.

/ed B in NH

[Shannon Parks]

Those changes on the Ike lowered the gain and lowered the noise floor a touch (say, 3dB). Stability or overall performance weren't really improved, so if you're happy with it, leave it.

I basically throw whatever tube in there, bias it up agressively (say 85% max dissipation at idle) and run with it. The harder I bias up the EL34s or KT88s, the better they sound and the better they test. It's all in the spirit of the Eico HF87 & HF89 tube eaters. :)

BTW, I've been listening to my 6B4 SET for the last month, but I need to tear it apart to put it in the new FPE/Welborne chassis. I think I'll put the Ikes in the power amp spot and go from 3W to 60W. :o