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  1. #1

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    Default Altec 1570B project

    Hello, Here's some shots of the Altec 1570B I'm modifying.
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    Last edited by Jed Leland; 06-02-2008 at 09:34 PM.

  2. #2

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    Hello,
    I didn't offer much of an explanation of what the photos were. This is one of two 60's era tube amps that I am slowly rebuilding from scratch. This is an amp that was used everywhere from Greyhound bus stations to the Houston Astrodome. It uses two large directly heated 811A triodes in a push-pull configuration to produce around 165 Watts. It uses a 12AX7 as the input tube a 6SN7 as the next stage and triode connected EL34s for driver tubes. I began by completely stripping down the chassis, saving the phase splitter inductor, output transformer and the massive power transformer (big red, now). In order to produce such high power the output tubes have 930 Volts as B+. I then had the chassis powder coated a textured black finish and the protection screen a nice silver color. Now I'm doing the point-to-point wiring mostly using a silver coated wire with Teflon sleeving. The two sets of coupling capacitors are V-Cap and all of the other passive parts are chosen for their sound character. Input loading done with Vishay 102S metal foil resistors. The original 4 pin output tube sockets were pretty groady, but well made, so I dissassembled them, cleaned and polished all the contacts. All of the inductors and transformers have been dissassembled and fish paper replaced, any rust eliminated and sand blasted the bell housings and repainted or powder coated. The AC tube heater connections are all done with shielded twisted pairs of wires all grounded to prevent AC contamination.
    I have yet to pick out the type of output terminal strip to use, I like good old fashioned positive/negative lugs as opposed to binding posts. The amp will have a times turn-on delay to save the output tube life and a seperate power supply for the EL34s.
    If anyone is interested I can continue posting photos as the work progresses?
    Cheers, Jed

  3. #3

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    Nice attention to detail in the rebuild. PTP wiring is fun when you have the time to make it look as good inside as it does when you fire it up to listen to it.

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    Thanks, Dennis, i appreciate the comments. When I make a connection between two points it fairly labor intensive. I first cut a short piece of wire, then polish it with Flitz to get a good clean surface. Then I cut a corresponding length of Teflon sleeve and put the shrink tubing (pre-cut a whole bunch to the same size) on one end and heat shrink it. Then I have a set of round nose pliers that make a very nice circle for the connection to the terminal post. My goal is to have the wire wrap complete around the post and end up with the cut end of the wire neatly meet the par with the sleeve. This get pinched in place and carefully soldered. I leave this set for around a half an hour to make sure there's no cold solder joint. I don't move a thing while its cooling, this also forces me to be careful, thinking about what happens next. I can be too speedy and try to do too much at once. Zen soldering. then I make the other end of the connection, the length has already been determined by measuring. The other end is just as carefully wrapped. After this has cooled I measure the resistance from point A to point B, for zero Ohms.
    I know its anal, but its the way that works for me. It's also a good way to unwind from a work day. Audio meditation.
    Cheers, jed

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    Beautiful! I have two 1570BTs a friend and I are starting to get up and running--nothing like the rebuild you're doing. they were trash finds. I'm planning to do a stock rebuild with modern caps and resistors. Please post as many pics as you want!

    Than

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    Hello Than,
    It's good to hear from another Altec owner! There's an article in an older issue of VTV magazine about the amp and a modification offered by Tom Tutay. If you'd like it just let me know.
    I'll take some more photos after I've done some additional work. I'm putting in the test points and the large cap.
    Cheers, Jed

  7. #7

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    Quote Originally Posted by Jed Leland View Post
    If anyone is interested I can continue posting photos as the work progresses?
    Please, by all means, keep posting photos. Nice work on the point to point wiring.
    The world is full of answers, some are right and some are wrong. - Neil Young

  8. #8

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    Thanks for the offer! I bought a copy of that VTV issue (#7). It's a great magazine in general. I'm not very skilled with electronics--I can solder a bad joint with the best of 'em, and I can kind of tell what's going on in a schematic--but my friend Chris is a trained EE and has built a number of tube amps and other projects. He's the brains behind getting the brawn of the 1570Bs actually working.

  9. #9

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    Damn nice work, Jed. I like the wiring. Sounds like a fun project. Keep us informed, and post more pictures.

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    Jed, your workmanship is first class! I may have heard that amp playing a pair of Altec A-7's over 30 years ago in a college town night club. I use to go there all the time. Very sweet sounding amp.
    Carl

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    Hello,
    Thanks, everyone, for your kind words. It's very helpful getting supportive comments. I'll try and take some more shots and post them as soon as I can. These particular amps came from western PA, but they could have been used anywhere. I don't get the feeling they were from the same place. One of them had some rust to deal with while the other had some upgraded coupling caps put inside.
    Cheers, Jed

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    You didn't by any any chance buy them from another Club Polk member? :-) My own 1570BTs were rescued from the junk heap literally as they were being pushed into a waiting tractor trailer AT THE DUMP here in Morgantown WV. They were most likely used in one of West Virginia University's theaters or sports arenas. They are as ugly as or uglier than yours once were. Your paint job and wiring are inspiring.

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    Hello,
    No, I found them at a place called L&M Trading Co. in Slippery Rock, PA the person was named Sumner McDanel that helped me. I located them from the Altec site, but another person who was looking for some said they weren't around any longer. Be careful working inside them, the B+ is over 900 Volts. The original design had a switch that turned the amps off if the screen was removed. The plate caps, on the 811A, sometimes come unglued so most owners epoxy them in place. In ham transmitters they run even higher Voltages for more power. Big tube.
    Cheers Jed

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    Wow,that is some very tidy looking point to point wiring there Jed.Nice work.

    with a B+of 900 volts I guess one must be abit careful where they put their fingers when testing voltages.:D

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    Hi guys,

    Here's some new shots, I'm just about done with the audio part. The amp works fine, 190 Watts of push-pull triode power, low distortion and nice square waves.
    Cheers, Jed
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  16. #16

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    Nice. Very Nice.
    I like speakers that are bigger than a small refrigerator but smaller than a big refrigerator:D

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    Very nice,,noticed those V caps,, is this the same model amp that Tom Tutay is noted for,,among other pieces of gear as well?
    JC approves....he told me so. (F-1 nut)

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    Hello,
    Thanks for the kind comments, I'll take a shot of the amp powered up. Yes, Tom has been a big inspiration on this project and supplied many of the parts. He is extremely generous and couldn't be more helpful. I'm fortunate to also have one of his phono pre-amp designs and it sounds amazing, much better than the one I was using previously, which I had built.
    He certainly know his stuff.
    Cheers, Jed

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    Hello,
    While the camera was warm I took some more:
    Jed
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  20. #20

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    Hello,
    I've made some measurements, of the amplifier, it has a very uniform frequency response. Essentially flat from 64Hz to 18.0kHz, no deviation at all. It is -.9db at 20Hz and -.8db at 42.0kHz. The THD at 1 Watt, 100Hz was .34%, for 10 Watts it was .75% and 100 Watts it was 1.2%. At a 1,000Hz, 1 Watt it was .34%, for 10 Watts .71% and 100 Watts 1.2%. The distortion byproducts were even order and seemed to be mostly second order. I have an older Sound Technology that is getting along in years. I was able to look at the waveform and the distortion product on a dual trace 'scope and can see what the amplifier is doing. While specifications can't predict how a component is going to sound, I don't believe a poor measuring piece of gear will sound good. Conversely a well measured piece of gear doesn't mean it will sound musical.
    Here's a shot looking top down:
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    That baby has some serious tube power,,I'll bet it'll warm up a room on those cold winter nights too.;)
    JC approves....he told me so. (F-1 nut)

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    Hey George,
    Yes, that's what happens when you use couple of transmitting tubes as outputs and have 930 Volts B+, lots of power. Using EL34s as driver tubes is kind of like using a small block six banger to start the main engine. The amp has three separate power supplies, the one for the EL34s is delayed by 10 seconds after the 811A have come on. When you consider where these amps were used, bus stations, drive-in theaters, sports arenas it's great they can have a second life, all spruced up and powering an audio system.
    The frustrating thing is I only have one done, now I have to start on the second. I wanted to get all of the parts layouts and wire routing done with one amp before I took the second one apart. There are several sub-assemblies that I built two at the same time. I'll drill all of the five terminal mounting holes and binding post holes before I have the chassis stripped and powder coated. I still have to have the two bottom plates done and figure out what's going to be the front. Maybe a thick plexiglass piece so the "tube glow" shows through. I have a while to figure that out, I guess.
    Cheers, Jed

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    I read a long interesting article/story about these amps,, the writer was very explicit when it came to safety,,as I've learned quite abit about DC voltage lately,, good luck on your amps,,as I'm under the impression, that when fifished,it will be the last amp that you ever own,,and I say that in a most complimentary way.Hopefully I'll get my ears on a pair one day.
    JC approves....he told me so. (F-1 nut)

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    Hello,
    Yes you are right, the original amplifier had a pressure sensitive switch on the protective cover. When anyone removed the cover the switch shut off the main power. There's certainly enough voltage to cause harm. I used new ceramic cathode caps that fit nice and tight and won't easily come loose. If I ever built amplifiers for anyone else I would cover all high voltage points under the chassis.
    I can remember hearing some tube amplifiers that had been built by Audionics in the middle 70's that sounded excellent, also the Audio Research D150 of the same era. I'm hoping these will have some of the same effortless quality and lack of strain.
    Cheers, Jed

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    Hi Jed
    I am about to start restoring a pair of 1570s and I was wondering what mods you did on your pair?And how do they sound now that they are modified.
    Thanks
    Amdy

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    Hello Andy,
    The first amp is finished and the second one is completed except for cleaning and painting the AC transformer. The bell housings for this transformer have been powder coated and only need me to sand the laminations to get rid of the old paint lumps and spray paint. I recently retired and needed to set this project aside to repair and modify a friend's Revox A77. Repair on another friend's OTL tube amp and get a Marantz 20 tuner working. As soon as I let people know what my plans were I got quite a few offers for work. Another friend has a Moscode 600 he wants me to look at and someone else has a Sony integrated amp that uses V-FETs for the output. I haven't had a chance to work on my own projects, I had more time before I retired. Funny that's what everyone told me would happen.
    As to your question about the modifications, I am friends with Tom Tutay who has done excellent design work. I followed his article in VTV magazine on the Altecs, I bought the parts from him and followed his instructions. I know a guy who sent him two amps and now has the 1570B hooked to his Quad 989 and has never heard them sound better. I talked to Tom recently and he has two amps available for mods if someone is interested.
    Cheers, Ken

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    Hi Jed
    Thanks for the reply. I haven't retired yet ,still about 8yrs to go, but I am always busy with repairs from friends. I had to turn down a few repairs and mods to get around to my own stuff. I have ordered the VTV issue with the info in it but VTV doesn't move to fast and after reading the internet about VTV and financial problems I may not get it at all. Do you happen to have a copy you can email?
    Thanks
    Andy

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    Hello,
    I can ask my wife to scan the article and I can send it to you. PM me your address and I'll send it.
    Ken

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    Hi
    Haven't got enough messages to send PM yet.Please send to
    atom@altecon.com
    Thanks
    Andy

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    Atom - You may want to drop Polk's recently retired Ken Swauger a line concerning your mods. You can still reach him at kswauger@polkaudio.com as far as I know. If not, drop me a line.

    Jed - Excellent work and great choice of history! I bought a table full of Altec a few years ago for change. A couple were slagged but the rest had enough life to get them spec'd, retooled a little bit and back in B+ shape. I didn't do anything like you posted....wow.
    Last edited by dorokusai; 01-24-2010 at 04:06 PM.

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