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    My ST70 rebuild progress

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    j4570

    Posts : 141
    Join date : 2010-08-30

    My ST70 rebuild progress

    Post by j4570 on Thu May 12, 2011 9:39 pm

    I've been rebuilding an ST70.

    Basically all new except chassis, cage, and output trannies.

    I posted my board build last week. Here's this weeks progress. A little each night (most nights I should say):











    If I did it again, I'd ask Bob for some hook up wire too. While the cloth covered is nice, and presented no problems, it's thick to work with. But obviously doable. The attenuator and pentode/triode switches were the worst.

    One of the tube sockets came with the mounting plate on backwards, and it's on the front of the amp. so you see some odd looking wiring on the left until I can get a replacement socket and do it right.


    Fire Up will have to wait. I'm tired tonite, and I know I'll be fooling around with it a while. Gotta work on the car on Saturday, so maybe can fire up tomorrow nite in the garage and listen to it Saturday for burn in.

    Jason


    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: My ST70 rebuild progress

    Post by Bob Latino on Fri May 13, 2011 5:07 am

    Hi Jason,

    Nice job on the rebuild ... Thanks for the photos ...

    Somehow a TOP MOUNT socket must have gotten mixed in with the bottom mount sockets. I don't even stock the top mount sockets at all. I buy the bottom mount sockets a few hundred at a time. The distributor must have inadvertently mixed in a top mount socket with the bottom mounts.

    I will send you out a new bottom mount octal socket and new screws and nuts today.

    Bob

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: My ST70 rebuild progress

    Post by j4570 on Fri May 13, 2011 9:50 am

    Bob,

    Feel free to use any photo you want, at your own risk of course! Of what to do, and what not to do......

    Thanks for sending out a new socket. No problem here, things happen. And thanks for all your help answering my questions.

    Now to fire it up tonite hopefully!

    I've been wanting a Dynaco for probably 10-15 years now......Now it's here.

    Next project, the PAS3 that came with it. But I'll probably limit that to a minimal redo as I don't intend to use it much as I've set this up to be used with no preamp.

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: My ST70 rebuild progress

    Post by mantha3 on Fri May 13, 2011 4:05 pm

    Looks real sharp!

    You could get a coat of paint on the transformers... Use Semi Gloss high temp spray paint. You can just pull the 4 screws and bolts that hold the 3 transforms onto the chasis... just pull them up enough to get some of the blue painters tape... The cover the whole chasis with some plastic. So basically all you have exposed is the transformers. you just want to do this in thin coats. perhaps sand the transformers in any blemish spots if you see any (No I'm not seeing any in the photos.

    Look great!

    The attenuator was a pain to get in. I think the instructions could be tweekend. I think getting the wires on soldered on the attenuator and then putting it in may be some help. Nice feature to have! As is the Pentode/Triode toggles.


    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: My ST70 rebuild progress

    Post by Bob Latino on Fri May 13, 2011 4:24 pm

    Andrew,

    You are quite correct about the instructions to install the stepped attenuator. After trying a number of methods, I now recommend installing the 6 wires to the attenuator BEFORE installation. The short one page installation instructions have been changed to what is below. The three 3 1/2 inch wires for the LEFT channel may be shortened slightly (although it's not necessary) during installation since the LEFT channel's input jack and driver board eyelet are closer to the attenuator.

    Bob



    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: My ST70 rebuild progress

    Post by j4570 on Fri May 13, 2011 6:12 pm

    mantha3,

    I thought about painting the transformers, but they were in spotless condition and I decided agaisnt it. I only decided to replace the power transformer after inspecting the wiring and it was falling apart. The amp was given to my friend along with the PAS when he sold the guy some stereo equipment when he "upgraded' to solid state. I think it was a thank you for setting up everything at his house and going over it with him. But the guy said the left channel (or was it the right) was blown, and he was tired of fooling with it. He had built it himself 30+ years before. And it was his only amp for that time. Anyway, I purchased it from my friend last year.

    I wanted the amp to look old, hence the old chassis (which I did clean a lot), and the amp will use the original cage too, not repainted either. I'm a different kind of person than most I suspect, I like things that have a little character, a few scars if you will, but only if it's vintage.

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: My ST70 rebuild progress

    Post by j4570 on Tue May 17, 2011 9:00 pm

    I got the replacement socket yesterday, but it being late I decided to wait and install it when I was a little less tired tonite. Here it is:





    I also took a pic of the upgraded binding posts installed that Bob and/or Roy offers. I mounted the PCB on the outside, though it might have been possible from the inside, the binding posts were simply too close to the metal on the chassis for my comfort, so I went outside. The posts are nice. I'm very happy with them and gives me the 4 and 8 ohm taps.

    I had a little hum before, and now it's gone, it's probably due to cleaning up the wiring with that one bias socket.....

    I just put some Valve Art EL34B's in there to test run, and a Ruby Rectifier. I got the 12AT7's from Bob (JAN's) but also tried some Sylvania's I had, and I have 2 Westinghouse Canada tubes I tried on the outboard. I think I may like the Sylvania's the best, but I need to sample more music to make that call.




    anbitet66

    Posts : 131
    Join date : 2009-12-23
    Location : Valley Stream, NY

    Re: My ST70 rebuild progress

    Post by anbitet66 on Wed May 18, 2011 3:56 pm

    Way to go J4570.

    I like that you are using the Valve Art EL34 in your amp. I have a set I got at Antique Electronics Supply but I am using a quad of Electro-Harmonics EL34's. The VA's at under $11 each is a steal Cool , and this month they are offering free matching. Give us your impression of these tubes when you can.

    Tony

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: My ST70 rebuild progress

    Post by j4570 on Wed May 18, 2011 8:07 pm

    Tony,

    The tubes sound great. Best set of EL34's I have ever owned. OK, so it's the only set of 4 I own.

    Seriously, I have no reference. I do have some Russian tubes from BSA_79 on Ebay I'm gonna try too. They are about the same price since I bought 8. But unmatched. Anyone near TAMPA,FL want to match mine for a 6 pack (and I'll buy something other than Pabst, unless that's your thing)? I only have an emission tester.

    And if I could find a set of RCA 6CA7's to match the two that came with the amp for a decent price, I'd probably get two to try those. I need to look thru my tube box and see what else I have that might work, but I don't think I have more than 1 or 2 of anything unless it's something I specifically bought.

    I have a bunch of Tung-Sol 5881's too I might roll, when I get a chance. I know they aren't ideal, but a few people like the sound I hear.

    I got my Valve Art's from AES last fall when they offered free matching as well. Seems they do it every 6 months or so. Only on current production tubes, no NOS. AES is a good place. I have bought some stuff here and there over the years and directed a bunch of people there too. Mainly old radio guys, don't know any tube audiophile guys except on the net.

    But for the person building their own amp, and not wanting to toast a nice set of tubes, these are great for testing. $44 for a set is less than you pay for one premium tube, and if you start talking NOS Mullards and Telefunkens, forget it.

    Oh, and consider the music sampling has been limited to Warren Zevon in my portable CD player on the test "bench", it's really not a test at all. I have a few Telarc CD's that are my favorites for testing. Some of their "Sampler" CD's. And to really test it, I need to hook it to my Polk M10's, which I love, just a personal thing.

    Jason


    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: My ST70 rebuild progress

    Post by j4570 on Thu May 19, 2011 9:39 pm

    Tony,

    I tried the Russian 6n3cE from BSA_79 tonite, and even not burned in, I don't think I'd go back to the Valve Art. The Russians had more bass and lower mids that the Valve Arts didn't have. However, there seems to be less treble than the Valve Arts. Vocals sounded better, but I didn't try any high pitched females.......

    I like these Russian tubes. Also, I understanded Jim McShane offers burned in and tested 6n3cE tubes for a little more money which many believe is worth it.

    JW


    anbitet66

    Posts : 131
    Join date : 2009-12-23
    Location : Valley Stream, NY

    Re: My ST70 rebuild progress

    Post by anbitet66 on Thu May 19, 2011 11:13 pm

    Jason,

    I have been thinking of buying another quad of EL34's but I'm not sure what to get. The 6n3ce's sound interesting. They are a version of 6L6GC, right?

    When cash becomes less scarce these would be an ideal set to roll to see how they compare. I also have an original ST70 with 2 Dynaco branded mullards, and 2 Gt Britan GE's (also Mullards) that match very nicely, and can be used as a reference to the new production tubes to see which I'd like better.
    Tony

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: My ST70 rebuild progress

    Post by j4570 on Fri May 20, 2011 7:11 am

    Tony,

    That's my understanding, they are a 6L6 type.

    Now as to the translation, I typed it in like it looked, not cryllic translated.

    Jason

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