Ampex Stereo Amplifier, “6973” model, with upgrades.
Stereo version of the late 50’s, early 60’s Ampex console amps, *****detailed photos available,. incl. before and after mods and upgrades, original schematic
They were made in very small quantities for the huge and extremely expensive consoles built by Ampex in the ‘fifties and early ‘sixties. A search will show that they no longer ‘show up regularly on eBay,’ but are now in the collections of connoisseurs around the world. For many decades, the 6973 output tube, which was mostly used in guitar amps and juke boxes, was out of production. NOS specimens were rare and expensive. Recently, however, Electro-Harmonix came out with a true 6973. Tubedepot.com is selling matched pairs for just $39.95, and they are reputed to be excellent. Info on this amplifier most often gets referred back to an entry on Arthur Salvatore’s website, High-endaudio.com.
From Arthur Salvatore’s High-endaudio.com website/Reference Components-Vintage Audio:
AMPEX VINTAGE TUBE AMPLIFIERS
I received a letter from a reader regarding these amplifiers, which I barely even remember. I don't have any clear memory of ever hearing, let alone owning, a pair of any of their models. "I wanted to ask if you had ever had any experience with any of the Ampex made amplifiers that were used in their high-end consoles? NOT their industrial/theater amps NOR the amps used in the "famous" suitcase amps fitted wit the JBL D216 speakers. There are 5 models that I know of. Monoblock amps running 6V6, EL34 (2 versions, one tube rectified), 6L6 and finally both stereo and mono-block amplifiers using 6973 tubes. (very different amps.) In my own system, I was running Manley Neo Retros, and did a blind substitution with the 6973 monoblocks with 5 local audiophiles whose ears I trust. Even though we disagree on what we LIKE, we all tend to hear similar differences in sound. It was with some sadness when I revealed to them that they had unanimously voted the Ampex monos as besting the Manley amps! (running in both SET and PP) Frankly.....given what I had paid for the Manleys...I didn't want to believe it! I have been a tube collector for years, and so had shuffled through DOZENS of different tubes in the Manley's (Primarily the 6SN7 and 6SL7 input tubes where I had gone through about 40! matched pairs of different types over about 3 years of listening. But I accumulated 6-8 different quads of 300Bs, and a dozen or so 5U4 rectifer quads along the way. As you know, the input tubes can make an enormous difference, but even the best combos did not compete with the stock tubes installed in the Ampex when I received them. I later sold the Manley's, and used some of the proceeds to have the Ampex completely rebuilt for me on custom chassis that were suitable for display. Like the Altec/Tutay amps...they were never really meant for display and so were not "finished". Just bare metal chassis... I now own one set of each of the other amps just for collector's sake. And while they are certainly not "common", it appears that many hundreds of each were sold and so they regularly show up on eBay. At least for the 6973 based mono amps, I understand that Ampex had the iron custom wound by Triad...which probably explains a good deal of their quality. In any case, I am extremely pleased with the quality of these amps in MY system. (Stacked Quad ESL's / Wyetech (prototype) Preamp / SME 10 / Musical Fidelity DAC / CD / Genesis Digital Lens / REL Tuner, Wasatch cabling, Bybee filters on the amp inputs etc.), but was curious to hear whether you had ever experienced any of them. I am convinced that (when properly updated) they can compete with quite a few of the mega-dollar components out there. In any case, I thought they might appeal to you as a somewhat extraordinary audio value. Meaning I believe them able to compete FAR outside of their price range." Personal Notes [from Arthur Salvatore]:
- tIf the above is true, these Ampex amplifiers, or at least the reader's 6973 monos, are one of the finest vintage amplifiers ever made. Even better, they are totally unknown, and/or ignored, by the vintage crowd (though for how long now). Accordingly, as the reader states, they could be one of the very best values around, outperforming many amps that are far more expensive (even after the mods). Considering this reader's (and his friends!) surprising experiences, and their still reasonable initial cost, I would say these amps are well worth making the effort, time and financial investment to do a total rebuild. That means Teflon coupling caps, high quality resistors, all film B+ power supply caps, a chrome chassis, new RCA females, an AC receptacle and speaker binding posts etc., A.S.”
My Ebay photographs show the “before and after” parts that have been replaced, volume pots bypassed so as to run with a preamp. Sound on this amplifier is glorious when mated with my custom built Doge pre and vintage Coral 8’s …but I presently have eight amplifiers in my home, so it must go.
(My original Ebay listing had noted this amp had a noticeable hum in one channel; finally, after some time trying to figure it out I tried swapping the tubes out to the opposite side ...Voila! The hum disappeared.)