Altec tube amp, model 1570-B

[capt.khz]

Yes indeed. I'm sure there is a Radio Shack nearby in your town open late, where you can buy a safe audio product with that thumping bass!

Anyway, about what Altec did right in these amplifiers', first of all, the class AB2 set up of the 811A at approx. 950v instead of class B at 1200 v. anode is the right choice, keeps the transfer curve away from the "crossover distortion" region. No need to go class B to get this 160 w. The 6W6 driver pair is a better choice than most other beam power tube triode connection cathode follower circuits. The 6W6 has a very low plate resistance triode connected,and these are affordable now. As a cathode follower, choke loaded, this offers a rock solid low imp. drive for the 811 positive bias grids. 811s biased this way draw much grid current that has to be supplied by the driver. Altec's choice to have a separate DC supply for this 6W6 driver arrangement is a must for regulation. This low B+ supply is not tube rectified...a little engineering trade off.... if you like all tube rectified supplies. The usual B- supply was avoided by getting the -30 for the 6W6 grids by a "back bias" arrangement with a 600 ohm resister. Change of this 600 ohm value rebiases the 6W6 pair. The 811A grids are clamped to zero bias ground rail save for the voltage drop in the driver choke windings. The 811A grids have a positive bias in AB-2.

If you really wanted a cathode follower driver to end all drivers, check out the Gates BC-1 broadcast Am transmitter modulator driver using 807s that drive 833A! Anyway, back to the Altec, as to the front end, not so great to use a 12AX7 as the split load phase splitter, however, it helps to add the 6SN7 2nd audio pre-driver to take the voltage swing demands off of the ax7 splitter. Engineering trade-offs, that is where the cleverness is in many designs and the 1570 is a very good example of this. The 1570 is not over OR under engineered. Right on.

[sheltie dave]

Capt.kHz, if you are going to flash some attitude, there are many dumber people to goad than djk on this forum.

There are also a number of people who have inquisitive kids who love to explore stuff, including tube amps. Having heard the Tutay amps as well, I chose to save my money and buy a cheaper set of tube amps that sounded better, and were intrinsically safe.

[capt.khz]

Sorry, not impressed with djk. The safety issue is a straw dog. Disagree is to goad? Interesting!

[capt.khz]

I lost a buddy-peer who came into contact with 230 V mains and was caught between a cinderblock wall and the transmitter frame so he could not move to free himself. Also knew a gent who worked in television, suffered lasting disability from electric shock. I have serviced gear running 5,000 volts at over 20 amperes. You do not get a second chance if there is contact. Any tube amp. is a hazard...point is, false sense of security if you think a typical lower...say 450v tube amp. is OK. keep any tube gear out of reach of others, children as well. 200v is as much of a hazard as 1000v. Wet hands, salty hands, wet feet, shoes can mean the difference between survival or death. The one hand rule has saved me many times. Always have one hand in your pocket when you are handling this gear, even when you think it is safe.

[PWR]

ITS ,KIND OF FISH TUBES FROM AMAZON RIVER .HIGH VOLTAGE .

[sheltie dave]

Capt., when you come across as a pompous jerk, the rest of your post is neglected. You are setting up the straw man to make yourself look good. Puffery does not suit you.

[capt.khz]

Odd responses to a technical article, life is short.......take it easy! Really.

[Bryrohr]

Hello Captain,

I too own a pair of Altec 1570b amps. I appreciate what you had to say about the technical aspects of them as I am always open for new ideas and rarely sell what I have aquired if its vintage gear. A closed mind and a "move on to something else as soon as you don't like what you hear" type personality is not at all my style. I still own gear I bought back in the seventies from my geometry teacher. I still have the Marantz model 7 he sold me in 1978 and somehow it still keeps finding its way back into my system since it sounds better than every other preamp I have tried since then, and I cannot count how many pre's that's been. Well, back to the Altecs. I bought a pair about 10 years ago with the hope they would drive my Martin Logan CLSIIz's to levels never before heard. Back then I had read an article in Vacuum Tube Valley describing what T.T. in Fla was doing to them and I made some of the mentioned modifications (all purely component changes as I wanted to keep them vintage looking) before even listening to them stock. I kept the tube B+ supplies basically stock as I felt going to diodes and the likes would be a step backward, but I did add some additional capacitance along with the 1KV stock can for the B+ as I felt that could not hurt. Along with that I also replaced the caps in the LV supply as it was noisy as hell. The main thing I did though was change the 6V6 drivers to EL34's since in his article Tom felt that was where the real major weakness was. I also replaced all the old carbon composition resistors with low tolerance metal oxide resistors since many of the original resistors had drifted as much as 50% or more in value over time. I also replaced the coupling caps with Hovlands. They work well, sound okay, but honestly, they suffered significantly from high end roll-off driving the large electrosats so I eventually moved on to something with better low Z drive capabilities. Lately though, I have been looking over at them, pondering what they would have sounded like stock. After all, I'm sure the engineers at Altec had nothing but performance and dependability in mind when they designed them. I'm not saying Tom doesn't know his sh!t, but he's one man working with what is there to work with. The Altec engineers were able to design everything as they wanted it to be, they were designers in the "golden age of hi-fi" faced with the challenge of building a product that not only would stand the test of harsh situations, but also be versatile enough to fit nearly any application, and sound like a professional product would be expected to sound like in doing all that as well. I guess, with all that being said, I would have to wonder what they sound like stock. A very close friend of mine bought a pair from T.T and they sounded quite nice driving his highly efficient dynamic speakers but eventually moved on as well. He never keeps an amp for much longer than a year or two anyway so I cannot say he was displeased with Toms re-incarnations, he just had to move on as usual. I hate to admit it, but mine are being used stacked up as an end table in my listening room. I said I never let anything go, and I still have them LOL. I even saved every part I removed from them originally.

So, I was thinking of leaving the supplies as they now are, (basically stock with updated caps) keeping the Hovlands and updated resistors in place, but going back to the 6V6's and associated resistors that were changed to use EL34's as drivers. I somehow feel the 6V6's triode drivers might sound better than the EL34's. And, what would be your thoughts on replacing the 12AX7 phase splitter with a 6DJ8 since the amps seem to have plenty of gain for hi-fi use. I've never been a big fan of the 12AX7 and the 6DJ8 would provide a lower impedance for the input of the 6SN7.

Whats your take on all this?

And by the way, what exactly of any value were those other guys trying to add to your comments, and why were thier panties in such a wad? I thought you were being very respectable in mentioning the obvious EXTREME HAZARDS of working around HV, and those guys acted like you spit in their face or something. All I can say is they must have felt as if their manhood was being threatend in a way that their mothers used to do when telling them to "zip up that jacket or you'll catch a death" LOL

[fini]

Everyone's panties were in a wad back in '09. Funny how fashions come and go.

Welcome to the forum, Mr. Rohr.

[Bryrohr]

Now everyone is just standing around dressed in a wooden barrel wishing they could afford panties!

Thanks for the welcome my friend.

[capt.khz]

Hello, Bryrohr

Lol, I had "written off" this Klipsch site 'cause of all those goofy responses....unreal!

I think you are on the right track, a realistic focus on the weak link of the audio topology of the 1570B-the 12AX7. I am not a fan of the 12AX7! A 12AX7 makes a poor phase splitter in this config. (split load) A lower imp. solution that would require less change than going to a 6DJ8 would be a 12AT7. No pin-out changes, just change cathode and plate resisters for both the first voltage amp. section and the second "split load" phase splitter section. Less is more when it comes to physical changes on classic amplifiers! Agree, plenty of gain, so less gain of 12AT7 would not be an issue, better drive for the 6SN7, and is reversible! The overall moderate approach you describe qualifies as upgrade-modernize rather than to modify, hard to beat the sound of these amplifiers when left very near to "stock"!! They can run 24-7, true continuous-commercial rating.

[Maggot]

I have a pair of these modded by Tom. there is no comparison to the standard ones. Actual output power is listed at 165 watts bu mine didnt clip til 193. Not bad, Tom. Comparable amps built today would sell for $20 K and wouldnt be as good. Old iron is hard to beat. Im including a link to show mine which were part of the system that won best of show at the 2014 Capital Audio Fest. https://youtu.be/CVaazHrDp-w