Comments on: Audio Anthology: Collected Hi-Fi articles from AUDIO ENGINEERING in the 1940s

By: mike

mike — Fri, 07 Aug 2020 22:32:52 +0000

In reply to rrusston.

The 6AS7 and the 6080 will run happily at 300 VDC ! I don’t know why people make the assumptions that they can only handle 200VDC, unless lurking in the OTL fog of circuits has corrupted the mind. I wish people would not publish misinformation about tube circuits, this happens all over the net these days. I have built tried and true circuits using these tubes off and on for 40 plus years at plate voltages of 300+ VDC range without sacrificing lifespan of the tubes, it’s a no-brainer even without interstage transformers. I would like to know why you “feel or think” the 6AS7 is “only” good for 200 volts B+… Please let me in on the reasoning behind your statement. Thank you

By: Kimbal

Kimbal — Sat, 06 Sep 2014 06:13:38 +0000

Some years ago a customer of mine bought in a small bench top stereo AM/FM Tube Receiver which he purchased off eBay, and wanted me to give it a general service. Unfortunately I can’t recall the brand name now, as it was so long ago. I do recall it was not a brand I had seen before and possibly a USA model. It did not need very much servicing at all – as it was quite functional and well looked after. The main thing I noted with it when having it run in the workshop on test was the amazing sound quality when operating on FM. It was smooth and very mellow with a solid but not overpowering bass, running through a very lo-fi amplifier we had as a test amp in the workshop. The tubes used as I recall were very standard 6X4/ 6AU6 / 6BE6 / 6AV6; etc. Even on AM it was very good and quite noticeably better than a standard AM tube radio. It was stable and had no hiss or crackling as normally heard on almost all AM and Cheap FM sets. As a result – I took it home and used it for the following week on a much better amplifier, where it certainly came to life with some half decent speakers. After about a day of using this receiver, I was hooked on its quality and the amazing sound it was capable of delivering. I did not want to turn it off. Even my wife noted on how good it sounded.
The point of this post is – that I have a lot of respect for Vacuum Tube Equipment and the sound quality it produces.
It’s so rare to see anything with tubes nowadays, so when one does find such, the sound quality is immediately apparent to a good ear. Even a humble tube receiver can sound very “addictive” when used and well worth the time and trouble to find an old unit and resurrect it OR build your own from an old schematic.

By: Keith John

Keith John — Fri, 03 Feb 2012 00:29:49 +0000

Not to change the subject but one of these articles covered the conversion of a tube AM car radio to an exceptionally good home radio receiver. The standard rectifier, vibrator and power supply were removed and the output transformer was replaced with a larger unit or the power tube replaced with a cathode follower for use with an external amp. A small B+ and filament supply was fabricated or the old mono power amps had a socket providing B+ and heater power. These old radios could be had from junkyards for a dollar or two even then because the early ones would fit only the car they came from. Any old tube AM radio or any solid state AM only set from the earliest ones to the early eighties will perform very, very well much better than say a Superadio III or a CCRadio. The tube ones do sound better. I used to have one from a fifties Chrysler that in northern Nevada would get stations in Chicago, St. Louis and oftentimes Vancouver BC-every night. Avoid “Wonderbar” sets, GM hybrid sets and non-Big Three factory radios and stick with AM only sets.

By: rrusston

rrusston — Sun, 29 Jan 2012 23:52:13 +0000

There were actually seven “Audio Anthology” books issued, six of which were reprinted by Ed Dell’s OCSL/Audio Amateur apparat. They published a fair number of 6AS7 projects-all transformer driven, and without feedback because you can’t put a NFB loop across two transformer stages. And without NFB there is no fidelity, not without some even more exotic techniques.

The coupling transformers are not made anymore-Tango and Tamura in Japan make a couple, but usually not the right ones, and they are very expensive.

And a guitar amp with 6AS7s isn’t going to sound like a guitar amp-it might be useful for jazz, country or steel guitar players, but they’re perfectly happy with their Peaveys and Polytones.

You could build a RC coupled 6AS7 amp if you used a driver stage with about 400 volts and enough gain stages. The 6AS7 will only take about 200 volts though so you will need to design a unorthodox power supply. You could cut that down if you used a choke coupled stage like the Brook triode amps or the Altec 1570B.