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Old 14th November 2006, 07:07 AM   #1
sds2000 is offline sds2000  United States
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Default St-35

Ok Im, not a tube god and do not profess to have great knowledge in the field of tube amplifiers. That said, I have just come into a fairly beat Dynaco st-35. There are no tubes in it and the circuit boards look to have been hot for a long time but transformers look OK.

My question is this: Is it worth restoring this thing back to it's original circuitry or has time left this design so far behind it's better to just scrap it for parts (transformers) and build something with a more modern topology. On the one hand I could end up with nice classic amp. On the other hand if it does not sound that great why bother. There seem to be allot of designs around using dynaco transformers with more up to date designs. Is there any sense of agreement on what to do with an old st-35

Thanks
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Old 14th November 2006, 08:16 AM   #2
fergs1 is offline fergs1  Australia
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greetings, I think either approach is valid but to cover yourself you could build a new chassis and try a different topology using the tfmrs (which were always considered very good) so you can always pop them back in the st35. I think you can do much better sound wise t han the original circuits using a seperate phase slpitter rather than that triode/ pentode 7199 tube which while it worked quite well was proobably a cost saving measure in the first place. There is plenty of info on the net and I remeber a site where a guy had a step by step process of doing what you are thinking except he got his tfmrs from a sca35 but same diff. Especially that it a is a beat up one in the first place I think, to coin a well used phrase" out of the ashes the pheonix rises"
cheers and good luck cheers fergs
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Old 14th November 2006, 12:09 PM   #3
SY is offline SY  United States
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Gut and rebuild. The case and the iron are OK, the boards, switches, and connectors are 1962 vintage low bidder.

There is no shortage of push-pull EL84 circuits floating around, so you have plenty of options.
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Old 14th November 2006, 01:10 PM   #4
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I agree with keeping the transformers and tossing the rest. Check out www.diytube.com - they sell a pcb for a st-35 type circuit. It's a good project, especially if you already have the iron for it.
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Old 14th November 2006, 04:46 PM   #5
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My take - restore it... this is one of the the rarest Dynaco amps, and will be worth much more than the cost of restoration. Some think it's the best sounding one too.

If I recall correctly, this used 12DW7s/7247s, not 7199s, and they aren't THAT expensive, with new production available. I think there are new PCBs available in the original color...
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Old 15th November 2006, 03:26 AM   #6
ArtG is offline ArtG  United States
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You owe it to yourself to at least get it operating condition, listen to it, and decide for yourself what you will do. (and I'll bet you'll be quite surprised!) It's not a powerhouse, however, and requires speakers of , at least moderate efficiency. The 17.5 Watts/ch rating is a little bit of a stretch! The output transformers are considered among the best ever built and are in demand! The power transformer is stressed fairly hard and has been know to fail from time to time, although it's not a problem, as improved replacements are easily available. Give it a try!
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Old 15th November 2006, 06:50 AM   #7
sds2000 is offline sds2000  United States
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Default st--35

Thanks to everyone who replied. I suppose I should have guessed before hand that I woulf get near an even split on the rebuild verse gut question. It looks like a new populated set of st-35 boards ould set me back about $100 and and the diytube boards would be about $ 130. But I loose another $35 replacing the 3 section electrolytic with a similar unit (I just guessng its bad but its hard not to believe it shouldn't be replaced anyway).

The new pc board then requires a new chasis for about $80 but the rebuilt original will still be sitting on a chasis which clearly didn't have enough ventilation. Overall it still seems about equal what the best thing to do is.................

Any thoughts on which 6BQ5's represent a decent deal? Seems silly to put premium tubes in a low end amplifier.

PS fist job for this thing if I ever get it working will be to take over driving my old Stax ESL headphones
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Old 15th November 2006, 07:40 AM   #8
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Default Re: st--35

By all means gut it. Personally i wouldn't bother with the chassis either. Leading contenders are El Cheapo, Red Light District & Baby Huey (or mix & match)


Quote:
Originally posted by sds2000
Any thoughts on which 6BQ5's represent a decent deal? Seems silly to put premium tubes in a low end amplifier.
For new, JJs get pretty good mention (i've not tried them). You can also get good prices from some of the Eastern European vendors on the Russian equivalent of EL84Ms (6p15p?).

And then you might just be able to tap someone for junkers during the test phases,

dave
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Old 15th November 2006, 12:44 PM   #9
SY is offline SY  United States
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I've tried 5 quads of the JJ EL84/6BQ5 and recommend them highly.
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Old 17th November 2006, 04:23 AM   #10
sds2000 is offline sds2000  United States
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Thnx again to all who replied. Looks like a quad of JJ EL-84's and some deep thought are in order. Since I work in an optoelectronics releated field I will have to walk the "Red Light District" thread back to see what a dozen or so LEDs are doing in a amplifier full of fire bottles.
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