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This Month's Meeting @ VALVE
September's meeting was another of our small and therefore very informal meetings (which are among the most pleasant we have). Dave and Steve supplied the audition pieces, a PAS 3 stereo preamp, a Fisher 50C mono preamp, a McIntosh MC40 monoblock, and a wacky Hungarian bookshelf speaker made to look like a book, called the Musical Encyclopedia.
The PAS 3 was brought In response to the requests for a tube preamp to use Instead of my Apt/Holman. In an NB comparison of Beethoven's Violin Concerto on vinyl, the two sounded pretty close, with the expected results of a slight sweetening of the strings with the PAS and a slight increase In detail and transient clarity with the Apt.
I must say that this was the first PAS that I liked, and I have listened to several this year, getting the same impression of wiryness to the highs. This PAS 3 was stock, as were the others, so I don't have an explanation for the lack of wire this time, other than guessing that the Mklll's we used were better In combination with the PAS than the other amps (Stereo 70, Ampex 6973 Ultralinear, homebrew Williamson) tried In the past. This makes sense if one considers the Mklll's strengths to be in the mid and low ranges, as I do.
I found a PAS 2 in a pile of Junk a while ago, and will experiment further. It will function as a simple preamp to compare against a rather complicated HK Citatlon I acquired this week for restoration. We also NB'd Dave's MC40, which had new caps, against the modded Mklll. A detailed three page description of this circuit can be found starting on page 606 In the Audio Cyclopedia. The facing page Is a schematic reproduced from this article. Results were petty close, except for a bit of veiling and grunge in the Mac. Part way through the comparison the Mac stopped playing. Eventually our massive combined intelligence figured out it was just a loose contact in the signal chain, but I managed to talk Dave into replacing the rectifier diodes so It looked like we really made a decisive repair. Well, darned if that simple replacement didn't clean away the veiling and grunge!
I happened to mention this to Charlie Kittleson the other day and he heartily concurred that all components, not just capacitors, as most restorations focus on, deteriorate with time. A typical diode checker on a DVM puts so little voltage through a high voltage silicon rectifier that the positive result you may get indicates little about the diode's actual performance in circuit. At 50 cents a piece for 1kV 2.5A PTC205's, I say don't even bother to check the old ones, just replace 'em.
Which leads to another point. Any auditions or comparisons involving vintage equipment are valid only if the equipment has been gone through. A comparison of tube tuners vs. new tuners In a well known audiophile publication used a tube tuner that was essentially untouched, meaning It was probably full of leaky caps, drifted resistors, and detuned coils. Sure the new stuff sounded better!
Please keep this In mind when reading reviews of vintage gear, even in this rag. I can't vouch for the condition of every piece I opine about. I will try to Include a little info on what's been done to it when I can. The next fun piece was Dave's Fisher 50C, which he had thoroughly gone through. We connected it to the Mac, which was Dave's planned usage, and he set the EQ switches for LP's. We dug up some nice mono recordings. most notably an old Decca "Melmac" LP of Segovia.
Boy, that is a NICE preamp1 I used to own it, and liked it OK, but now it sounded great. Proof again that you gotta restore 'em to really enjoy 'em. Dave has since bought a Mac C-8, and we'll have a shootout when it's ready. Should be a close call. The last item we auditioned was a vary silly novelty speaker Dave found In a thrift store. It was about a foot tall, four inches wide and maybe eight deep. Two three inch mid woofers and a two inch tweeter pretty much covered the whole front baffle. The foam surrounds on the woofers had turned to a texture resembling shredded wheat, but the surprise was that the wacky thing sounded pretty decent. the Baltic ply used for the cabinet may have something to do with the lack of boxiness (as well as the leaky surrounds!). The 'binding' was actually a deceptively real looking grill cloth, printed to look like a book cover and fastened with Velcro A true 'bookshelf' speaker.