mod st70 sound?

[crispycircuit]

Yes, your intitled to your opinion. But I wouldn't go so far to recommend old trannys over new ones...??.... Transformers have a limited life. Maybe you've been lucky. How long have you been building tube amps? Heyboer makes a living at rewinding old trannys.....

[burnedfingers]

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Yes, your intitled to your opinion. But I wouldn't go so far to recommend old trannys over new ones...??.... Transformers have a limited life. Maybe you've been lucky. How long have you been building tube amps? Heyboer makes a living at rewinding old trannys.....

First of all I'm sure Heyboer will appreciate the plug. :) :) and the added business Yellow_Light_Colorz_PDT_07

What do you base your experience on? Transformers have a limited life Yellow_Light_Colorz_PDT_05

Transformers either work or they don't. Its very easy to set up a test senereo and evaluate a transformers operation. Replacing a working transformer might give a paranoid person some piece of mind and at the same time take a chunk out of his pocket book. Common sense would recommend not replacing something when it is fully functional and working correctly.

I have been playing with electronics over 35 years. I do it for a living as I repair large commercial sound systems. I fix what others screw up. They trust me to repair their million dollar sound systems. I either own or can access about any piece of equipment I need to make any tests needed. I do believe that I have both the knowledge and experience to evaluate a power transformer and make a recommendation as to using or replacing it.

I base my "OPINION" as you would call it on my experience to make the correct judgement call.

[burnedfingers]

crispycircuit

I would suggest dropping into a Antique Radio Forum and asking the old boys if they replace their working antique transformers. I believe the common answer is going to be a NO.

[Slartibartfast]

Yes, your intitled to your opinion. But I wouldn't go so far to recommend old trannys over new ones...??.... Transformers have a limited life. Maybe you've been lucky. How long have you been building tube amps? Heyboer makes a living at rewinding old trannys.....

Can you put a number on that "limited life"? Just because the power transformer is suspect of a number of things, that is no reason to replace the output transformers or not buy an older Dynaco unit. They do not have near the amount of current flowing through them and will last a long time.

My ST-70 still has all original iron and performs admirably. I see no reason to replace any of the transformers.

I agree with Burnfingers, the OPTs in the ST-70 will probably outlive any of us on this forum.

[EWBrown]

The old OPTs should last about forever, unless they were used to listen to Led Zepp, Black Sabbath or Deep Purple at full volume 24/7/365, powering AR-3As. :o

The only indication that they should be replaced is if the fabric covered leads are cracked and crumbling (short circuit hazard) or if they exude that well-known lovely aroma of impending electrical death, and that would be caused by overexuberant hot-rodders deciding that if 50 mA per tube is good bias, then 70 mA each is even better, never nmind those glowing red plates and frequent rectifier tube replacement :o Yellow_Light_Colorz_PDT_09 Yellow_Light_Colorz_PDT_07

The original PA-060 power trannies and the C354 chokes are probably darn near used up and should be replaced, and the Triode PA-060 replacements have more in the "testicular" department ,as far as current capability, and not just burning up like an incoming meteor (as did the old ones).

If the old trannie still functions, it can serve a light-duty retirement in a lower powered amp. Nope, I NEVER throw anything away... Yellow_Light_Colorz_PDT_06

Oh, yeah, back to the original question, any of the newer VA / LTPI driver boards, using 12AX7 & 12AU7s, or all 12AT7s, will sound a lot better than the original "crispy" phenolic and leaky cap 7199 or 6AN8 driver boards.

/ed B in NH

[crispycircuit]

This is one of best forums. The members share a wealth of knowledge, are very informed and passioniate. The finished product from this website is excellent. The help available is amazing. I thank all that keep this place #1..... Basically my point was if your building a Dyna amp and are buying parts, I would not pay too much for old trannys, when you can buy new for a few more dollars. I WOULDN'T REPLACE GOOD trannys if they're working fine. Everyone has their own formula to fit their needs/budget. This is fun stuff!!!

[TomMcNally]

I like the nice long leads on the new ones ! Yellow_Light_Colorz_PDT_03

[EWBrown]

Geez, I was digging through the "archives" last night and found another ST70 OPT that I forgot that I had... Just a single one, with cloth covered leads which were reasonably long... Also an ST-35 OPT with a weird DCR reading, one side of the primary measured "normal" resistance, the other side was about twice the expected resistance. This one has the vinyl / plastic insulated leads. Yellow_Light_Colorz_PDT_09 IIRC I pulled it out of a long ago built amp, when I was restoring it.

I expect as the packing / moving process progresses, it will be like digging up king tut's tomb, lots of forgotten treasures yet to be found...

/ed B

[crispycircuit]

Old trannys! Weird readings! It's all my fault. I was in your basement lastnite chewing cloth covered leads and beating the shit out of any old tranny! Sorry.... Yeah your right, it does look like a tomb..... Guess you'll have to buy new ones...... ho ho ho........

[Ty_Bower]

This is one of best forums. The members share a wealth of knowledge, are very informed and passioniate. The finished product from this website is excellent. The help available is amazing. I thank all that keep this place #1.....

Basically my point was if your building a Dyna amp and are buying parts, I would not pay too much for old trannys, when you can buy new for a few more dollars. I WOULDN'T REPLACE GOOD trannys if they're working fine.

Amen to both points. I got lucky and scored a pair of Mk3 amps with original Genalex tubes in them. I sold the tubes on eBay for more than I paid for the amps, effectively getting the iron for free. How can free be too much to pay for a full set of Mk3 iron? Do you think I'm worried if the transformers are too old and worn out? Maybe a little after reading this thread. Do you think I'm gonna go buy new iron? Hell no!

Of course, I still ended up paying a small ransom to replace everything else in the amp (driver boards, power supply, , and I'm still not done the project after half a year. Oh well, good thing it's only a hobby!

[crispycircuit]

Nice find! To bad those finds don't happen more often?.... It took me a 1 yr to finish my DIY Mk3s. They came out great and use original cloth covered wire trannys. The leads were stiff, but the price was right. So I'd say your doing good. 6 months to keep the money bleed under the radar........ Yes, a DIY board, SDS board, tubes, tube sockets, and a good list of $5 items, and you've got more money invested than you expected/wanted. The ladies don't get moved by this stuff, maybe that's why we like it??

[rockable]

"Transformers have a limited life. Maybe you've been lucky. How long have you been building tube amps? Heyboer makes a living at rewinding old trannys....."

The guys over at the Fender Forum would have a great time with this. Especially all the guys that are still playing the living daylights out of their original tweed amps with the original trannies.

Either a transformer works or it doesn't, as was stated before. Now, if you force it to perform outside its design envelope, you can expect the inevitable meltdown. I imagine most of the trannies out there in the Dynacos will work just fine for most people's applications. If you're driving inefficient speakers to high volumes, you might step over the line. Otherwise, Rock On!