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Metal base EL34s sounded very good tonight.

Posted by Michael Samra on January 25, 2017 at 01:58:44:

Every once in a while I get the urge when I'm up grading class assignments when I can't sleep,to try some of my more forgotten vintage output tubes.
Tonight,the amplifiers were my Eico HF60s that I had rebuilt about 10 years ago.In the Eico HF50s and HF60s and HF35s,a 50uf film cap off the rectifier in place of the paralleled first two 20uf sections is a must to really get these things to open up.The cap I have been using is a 51uf at 630v Solen and it's one of my favorite caps because you don't have to increase the hole size to put the connections thru as you would with a motorrun cap.Downstream I went with a dual 100uf F&T and I will change those over to a pair of 60uf panasonic film caps that will fit underneath the chassis just fine.These amps need a polishing and a repaint on the Acrosound transformers along with the power transformers.I will also be putting in a choke as I did in my HF50s with the Gilespie mods to run KT88s..You can see I didn't put new cords on yet and those will be the standard 14gauge,2 conductor. The bias and balance pots are all new as well.
What I have realized tonight when running the old Philips metal base EL34s is,you have to have bias and balance spot on.The tubes also have to be matched pretty well within at least 10% of each other because they are not as forgiving as a 6L6 or a KT88 even if you have them balanced and biased.
I was streaming jazz radio on my I pad and I was going direct into the amps and I wasn't using the DAC either.
I was using the Newform Research 645 ribbons and then I switched over to the TDL transmission line monitors we just picked up.Both speakers sounded very detailed,very controlled,and very open with depth from here to a back alley.To be fair,I have always liked the EL34 on the HF50s and HF60s because it is done right because of the iron and the circuitry.
Steve-0 told me try the EL34s in these amps as opposed to the HF87 I was always using for the test and he was right.The amp really does make a difference.Tonight I will try the Genelex Reissue KT77 once again in these amps which I call old faithful because they sound fabulous in any amp I've put them in. It should interesting.