|
#1
|
||||
|
||||
Price perhaps? There was a good bit more metal on the plates than your standard 5V4...I have a hard time imagining a 6AS7 as being cheaper.
Also, your forgetting IMO the most interesting audio application of the part: Output transformerless Amplification. I designed/built an OTL amp based on those tubes several years ago...It has been my main amp ever since (it is that good).
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#2
|
||||
|
||||
What sets used the 6AS7G as a damper? I would like to see if it was just connected as a diode or if the grid control actually served some purpose.
Sure, a diode or double diode would be cheaper to fabricate than a double triode. Bean counters usually win. jr |
#3
|
|||
|
|||
Quote:
IIRC, the RCA 648*** projection set used one as a damper. I just scrapped a mid-60's Techtronics that had one. I is a "G" type branded RCA, with a mid-60's code date. |
#4
|
||||
|
||||
Quote:
How stable is your OTL? I've toyed with the idea of building one, a variation of the Dickie and Macovski circuit from 1954, but I really don't like the idea of running the 6AS7s fixed bias, nor do I like the idea of having B+ at the speaker terminals... |
#5
|
||||
|
||||
Quote:
I went with a reverse Futterman circuit with some negative feedback in the driver stage. With proper adjustment, I was able to achieve almost no DC voltage across the speaker terminals (someday I may rework the bais adjustment circuit to require less finesse). After a year of heavy service, I rechecked the bias balance and tube emission and there did not seem to be a change. My amp is a 2/4 channel with the rear outputs AC drive path and feedback switched over to parallel with the front when in stereo mode. I was very conservative with DC quiescent current in the outputs...I expect output tube life to be close to heater life. My output rails are only +/-60V so there is not much more risk to the speakers in the event of a rail short than some transistor amps. I built that amp during a summer break in college when buying the outputs at $5 a pop, the chassis sheet metal, wood, and pots (most everything else was from my junk box) was a great stretch of my budget. The power supply evolved with the amp...Eventually utilizing SS regulators for nearly all B+ and B- rails. I could not afford the right power trans so I engineered around the junk box transformers I had....That box has every valid internal mounting point utilized to it's utmost....Probably weighs as much as an RCA 630.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
Audiokarma |
#6
|
||||
|
||||
Quote:
I only ever recall seeing that circuit in Audio Engineering and Orr's handbook however. |
#7
|
||||
|
||||
Quote:
With +60/-60 rail voltages I would feel a hell of a lot better about such a topology. The one 6AS7G amp. I'm familiar with uses +140/-140 volt rails. That makes me nervous and for good reason. It also calls for a potentially lethal hot chassis design. No power transformer, no output transformer, hell, no inductors at all! A bit scary to have something like that plugged right into the wall... |
#8
|
||||
|
||||
Quote:
OTLs are IMO the best of both worlds in amps; combining and balancing the redeeming traits of the characteristic sounds of tube and SS gear.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#9
|
||||
|
||||
I like Tom's idea , the cheaper the better for the Bean counters and a kinda big triode VS a smaller diode wouldn't fly . While the TV's screens themselves kept getting bigger , smaller & cheaper circuitry was the driving force behind such design changes since the beginning of mass market electronics . Yep , price gets my vote .
|
|
|