Why Altec chose beam power tubes over triodes

I finally got around to scanning an old journal article by John K. Hilliard I felt some of you might find interesting.

OK, my thread title was a hook. You can decide for yourself after reading the article.

I know the subject can be a sensitive one for some, and I don't expect anyone to make any changes of philosophy or preference based on this article. With that in mind, I'll refrain from personal comment other than a reminder to keep in mind the date of publication (1946), and the relative stages of development at that time of the tube types discussed.


http://members.cox.net/notthatstupid/hill12.jpg

http://members.cox.net/notthatstupid/hill22.jpg

http://members.cox.net/notthatstupid/hill32.jpg

http://members.cox.net/notthatstupid/hill42.jpg

http://members.cox.net/notthatstupid/hill52.jpg

http://members.cox.net/notthatstupid/hill62.jpg

I'd suggest that anyone finding this of interest download a copy of the higher-resolution pdf (right click and save target as...), since I have no idea how long I'll be able to keep it posted online.

I debated posting this awhile, knowing that if very many triode lovers got converted, the price of my preferred tubes might soar. Then it dawned on me I already have more tubes than I'll burn up in my remaining years, so who cares. Kinda one of those "I don't play golf, but I'm glad you do" things...

Interesting bfish and thanks for posting. I wonder if the results would be any different with more modern approaches to reducing hum in DHT amps, in other words how much was related directly to that specifically.

I'm a bit confused as he says the way to do it is to use no feedback but it appears to me that both the 6L6 amp and the 807 amp have feedback.

I'm planning to build a 6L6 amp in the relative near future and will definitely reread that a few times, thanks for posting.

Dave

Hi Dave,

Glad you can use it. I'm the wrong guy to ask about triodes though, especially modern variations.

Good question on the feedback thing. The way it's worded is a bit confusing. My read is that the amp design should offer the required bandwith and power output without having to get tricky with feedback application to do so. In other words, more attention to xfmr design, less using feedback as a fix-all, as was common practice in those days. Feedback itself is still required, as you noticed in the schematic.

Failure to follow this thinking is often evidenced by the use of C or RC in (or paralleled to) the feedback loop, a common, cheap way to "fix" cheap iron or other deficiencies, but it comes at a cost, distortion and instability.

Now, variable R in the loop is a different story... (variable damping). http://www.hostboard.com/forums/

<font color="#FFFFFF" size="1">[ October 24, 2007 11:29 PM: Message edited by: bfish ]</font>

This is cool...

http://www.vintagetubeservices.com/page16.html


http://www.vintagetubeservices.com/page8.html

http://www.r-type.org/static/grid14.htm

http://www.r-type.org/static/grid03.htm

http://www.r-type.org/inx/type.htm

http://www.r-type.org/static/grid01.htm

http://www.r-type.org/static/museum.htm

http://www.r-type.org/static/el34.htm

http://www.r-type.org/exhib/aah0003.htm

Yeah it is, thanks!

Kinda emphasizes my initial reservation here too. Hilliards tests were with 1946 6L6s...not GAs, Bs, or Cs, just 6L6s. Just imagine if he'd had some of those TungSol 5881s or 6550s to plug in...Triode developement (those used for audio anyway) had long since neared its' peak by '46, beam power tubes saw another 20 years of signifigant improvement.

Subjective preferences will always have their place. You like what you like for your own reasons, and that's cool. If you'd rather base your choices on objective data though, the jury voted on this one and went home long ago. http://www.hostboard.com/forums/

It's fascinating to me that more Altec lovers aren't into triode amps.
Which explains the lack of comments from informed tube amp owners here.

The article posted was written 50 years ago. Pentodes and Beam power tubes were just coming on line. The draw was more power....

Followed by ultra linear amps...thet haven't been mentioned.

Main differences from power triodes to pentodes/beam power tubes:

Triodes have much lower plate resistance.
Triodes have much lower gain.
The input miller C is greater in triodes. (Takes a great low impedance driver stage to drive them w/o HF loss.)
Power triodes had direct heated filaments. Filament was the cathode.

All that said, really good output transformers didn't come around until the pentodes were in vouge. It was a technology thing...same as today.

Triode amps were passed over in short order. The article justified that by saying a group of experts agreed.

Here is the thing, they had ****** sources in those days. Nothing like we have today.

Good triode amps, with good iron, and good driver stages, with the great sources we have today are a natural fit for the high efficiency, simple crossoves, and reasonably flat impedances of the Altec speakers.

Hum really isn't an issue. Can be fixed either with DC supplies for the filament, or good AC supplies that are very well balanced. Hum is a moot point.

The amps in my avatar are PP 300B, Harmon Kardon Citation II output transformers....(some of the best ever produced), transformer coupled driver stage with an ECC99 low impedance driver. 3 tubes total...not counting the dual 5R4 rectifiers. They make 35 watts. Less than 1% THD below 30 watts, and 7hz-75khz bandwidth, all with no global feedback.

Nothing like this was made back when that article was written.

You guys who listen to your Altecs with solid state high powered amps, ought to take a step back in history and give tube amps a try. Even the pentode amps. Heath W5's (Altec iron BTW....the BEST ever produced IMHO)....Citation II's, Fisher, Scott, McIntosh etc. Give them a chance. Spend some time with them.

I'll tell you, you will fall in love.

Ron

Ron,

I use a combination of triode-wired pentode SET (HF) and PP beam-pentode (LF) for my system. I wouldn't be that surprised if the subjective response was different with a modern triode amp and modern hum levels.

The article does point out that with beam power-tubes the power is a false draw, and it's about proper implimentation of beam power-tubes.

Although I have head SS systems that sound good, I'm a dyed-in-the-wool tube guy and agree that they work great with Altecs.

Dave

Quote:

---

Originally posted by selmerdave:
...The article does point out that with beam power-tubes the power is a false draw, and it's about proper implimentation of beam power-tubes.

Dave

---

<font size="2" face="Verdana, Helvetica, sans-serif">That's really all I hoped to illustrate with the thread, that neither was inherently superior, the final result being dependant on the implementation. With triodes seemingly in the popular forefront, I felt the underdog needed a little support.

Ron had a good point on xfmr devevolpment. It's probably a little more than coincidence that Hilliards article closely paralleled Peerless' progress. (Which I'd love to learn more of, i.e. Peerless' origin, relation to Altec, etc.).

It's nice to see some interest less the commonly-associated flame wars. Thanks, guys!

Quote:

---

Originally posted by RonSS:


You guys who listen to your Altecs with solid state high powered amps, ought to take a step back in history and give tube amps a try. Even the pentode amps. Heath W5's (Altec iron BTW....the BEST ever produced IMHO)....Citation II's, Fisher, Scott, McIntosh etc. Give them a chance. Spend some time with them.

I'll tell you, you will fall in love.

Ron

---

<font size="2" face="Verdana, Helvetica, sans-serif">I have to agree, Altecs and Tubes WORK, YEAH BABY!

Although not really practical for me to use tube amps in my commercial system, I do have a line level device that usess the 12AX7A. When I first got the unit, it had Golden Dragon 12AX7A,s it was good, till I got my paws on NOS 1960,s Amperex 12AX7A,s!

I love tube sound, and hearing good tubes through Altec speakers is a special experience.

http://www.hostboard.com/forums/

<font color="#FFFFFF" size="1">[ October 28, 2007 07:09 PM: Message edited by: scotty j ]</font>