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.


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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:

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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

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<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:

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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

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<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>

Dave,

You ought to investigate DHT triode output stages. True, Pentodes or beam power tubes can be wired as triodes, but it's sort of like having a bunch of extra stuff in the way. (screen grid connected to the plate) Pentodes are better than beam power tubes when wired this way. But still not a real triode.

I have 4 Heath W5M's converted to 6B4G's. They make about 9 watts. I converted the driver stages to low impedance 5687's. Tons of bandwidth. (Better than 100khz) Perfect square wave response. And they are oh so sweet. But don't have enough power to get the model 19's cranking in the low end. At least not when you want to really rock and roll the blues, or big band.

The 300B PP amps on the other hand have plenty of power. The drawback of the 300B's? The long grid and plate structures are michrophonic! The output from the speakers tend to modulate the output. In fact, the structures are michrophonic w/o even being near the speakers. Something I doubt ever gets noticed with low efficiency speakers. It might be why folks find 300B's so sexy.

Still, they sound **** good.

Both sets of amps sound even better with the duplexes.

I have had SET amps in my system...borrowed from friends. All 300B. I personally didn't hear any real benefit over the PP amps. But I didn't have them long enough to give a fair comparrison.
Hum of course is tougher to tame in an SET, especially when my buds don't have high efficiency Altecs.

I'll never trade my tube stuff. I'm from that era. And although I'm sure there is high end SS stuff that sounds great, I would have to buy, not build it. And building my own, is just the way I am. Tubes sound great, I can roll my own, and shoot, they are just wy more sexy than SS amps...they glow!

Ron

Hi Ron,

I've heard some DHT amps, 300B, 845, 2A3 and PX25 or whatever that one is. Those were all single-ended. I'm not saying I don't prefer them, or that I think beam-power tubes are better (or triode-wired pentodes for that matter). Most triode amps are above my budget as are the tubes, and most of the equipment that I have has higher impedance OPT's so not really triode-friendly.

So I'm not passing judgement on triodes, the ones I heard sounded great, particularly the 845 which was Sakuma's amp and was really impressive. I happen to have a few amps that use beam-power tubes and found the above article interesting with respect to their application.

Dave

I will Have a Special Quad of Pre-Production
JJ KT-77's for Sale. I will post more in the 'Classified'
section. You can PM me.

I am on the SET camp!

I had tried some commercial SS amps in my system. All I can say is that in my experience, nothing comes close to the clarity of DHT's (I prefer 2A3 and 45) using my Altec drivers.

As for hum, an educated layout of the components and circuit design is the key. I have 1.9 mV of hum on my 2A3 with the amp vol pot fully open and preamp volume fully open! Around 1mV when using 45. For 300B, I use Pete Millet's DC filament circuit after trying many schemes to make the hum less than 2.5mV on the amp. With Pete's circuit, I have 0.4 mV maximum hum, not even audible, just measurable.

If you have not tried DHT SET (not triode strapped pentode!!) amp, then I would suggest to borrow one and see for yourself especially an AC heated 2A3.

Abe

I'm a believer in the flea amp too. Of course it helps when you have speakers that can sing with 1-2 watts. I'm not running anything too fancy but the simplicity of a SE 45 amp on some vintage Altecs is magic.

I'm still figgering out what the best pre amp might be, but the current one is nothing more complicated than a modded Bottlehead FP II.

analog addict,

I have a preamp for you! I mean, a suggestion only of course. I am thinking of saying a type 26 preamp, but it is too complicated to make it quiet.

The next best thing , for me is a type 76. I can send you the schematic as published in Sound Practices magazine way back, or the improvised schematic from a personal friend of mine(Joseph Esmilla of JE Labs). It will cost around $700 to build. I have, and some of my friends, compared this to a Supratek Syrah/Chenin(I own one), Manley, Aikido, Bottlehead, Cary, AES, CJ and a S&B TX series passive preamp, etc. in the under $5000 range and to us, it comes on top everytime, especialy when using Altec drivers for speakers.

Let me know.

Abe

26s are cool and sound fantastic? but yeah, they are hard to get quiet. 71A sounds great and the filament is easy to supply. With a choke load on the 71A you get about the same gain as a 26 with a proper output transformer which is about none. Zout is reasonable and the right plate choke is considerably less expensive than a good output transformer for the 26.

I?m not down with the whole IMD as be all and end all measurement or THD for that matter. I?ve heard really good and really bad amps and distortion specifications don?t correlate that well. But if you are into that type of thing triodes are pretty hard to beat as linear low distortion devices.

Are there later Altec Amps that are Powered
by 6CA7's, EL-34's or KT77's ?
I thought a few of the last were?

?Are there later Altec Amps that are Powered
by 6CA7's??

Yep, 1568 and 1569. I like the 1568 better triode strapped.

Quote:

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Originally Posted by martyh45

“Are there later Altec Amps that are Powered
by 6CA7's…”

Yep, 1568 and 1569. I like the 1568 better triode strapped.

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Thanks Again!

1 Quad of Pre-Production JJ KT-77's - Hostboard Classifieds & Auctions

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