A quick note of thanks to everyone

Well I just fired up my rebuilt early ST-70 (with cloth wires) for the first time since I was a teenager. Man did I abuse that poor amp back then! I wasn't 100% sure the transformers were good (they measured ok), but after a momentary scare (poor speaker connection) both channels played music! Next was a brief but intense web search for "the right" speakers to pair with the '70. The audioholics forum was a friendly and information-rich resource. Thanks to Craigslist I acquired a vintage pair of Dynaco A-25VW's in short order. Well I must have done something right because I'm really liking what I hear! I have access to hundreds of thousands of dollars worth of fancy test equipment and I'm not sure that I could quantify the fact that what I hear sounds "sweet, smooth, airy and pleasing! You guys probably know it as "sound-stage" or any of a dozen other official words that get thrown about this forum! I'm presently only feeding my amp with an iPod (don't cringe) as my PAS-2 gets ready to be overhauled. Once that is done I believe that I can say that I have a pretty good "baseline" system with which to start the infinite "upgrade" journey! Oh yeah, and to enjoy my music, some of which sounds like I'm hearing it for the first time!

First I need to thank my dad who was one of the early "DIY geeks". I grew up watching him build everything including our first color TV (Heathkit). I then need to thank him for storing away the long forgotten ST-70/PAS during the years that I was "smarter" than him! Now as my dad struggles with Alzheimers, I'll be able to fire up some Herb Alpert for him to enjoy again on his old amp! Finally I need to thank all of you, the members of this forum, for being tolerant and welcoming of us newbs, most likely asking the same set of questions over and over as we come up to speed. After only a week, my new old stereo has become a treasure. No Dolby 7.1, wiz bang, HDMI menu systems! Just two speakers powered by a little glowing space heater! Less is so much more!

Eloquent testimonial.

November 3
Again, welcome to the loony bin.
Never built the Heathkit colour TV but built one of their B&W ones, which was quite an experience! Never could get that choke over the CRT quite straight, so we had to crook our heads a bit to watch it. Also built Heath's AR-15 kit, which was even more complex -- 69 transistors and 2 ICs, all installed and soldered in individually. Quite the party. Then some Dynakits. Then went wrenching on some old Collins gear in later hamming days.
A wonderful tribute to your father.
Now that you're in to Dynaco stuff your next trespass will likely be into tube-rolling. I would ask Bob or Roy about power supply issues as you progress. Output and driver tubes very much affect the quality of sound, but all have their own special needs. Make sure your transformers are up to the task.
Cheerio,
-d-

as you've said, this is hopefully the start of a fun and full filling journey for you in the world of tubes!
Once you get started, it is hard to stop....I know...I speak from personal experience!
In time, you may wish to look at the many options available to you to upgrade your ST70...you think it sounds good now?...wait until you start the upgrade, especially the driver board. The improvement in sound will astound you, then....well then who knows.....enjoy!!

The reason why I rebuilt this ST-70 without much modification was due to the inherent shortcomings of the original design. Given the expense of the transformers, I can't see the use in overtaxing one that is barely able to keep up as it is! If I'm going to extensively modify the amp I might as well just buy the kit with everything including the larger main transformer and the nice shiny stainless chassis. Then the A-B comparisons can really begin! I think there will always be a home (and a market) for an original and functioning ST-70 out there.

n3ikq wrote:The reason why I rebuilt this ST-70 without much modification was due to the inherent shortcomings of the original design. Given the expense of the transformers, I can't see the use in overtaxing one that is barely able to keep up as it is! If I'm going to extensively modify the amp I might as well just buy the kit with everything including the larger main transformer and the nice shiny stainless chassis. Then the A-B comparisons can really begin! I think there will always be a home (and a market) for an original and functioning ST-70 out there.

N3, One thing you might consider, if you don't want to tinker with the amp's circuitry, would be to upgrade the caps on your A-25 crossovers. Not sure about the -VW iteration, but the older A-25s used some pretty cheap electrolytics that over time, especially if the speaks were sitting in somebody's basement for a year or two, go out of value. Cost to replace them is about $12 and a $5 tube of household silicone sealant, plus several hours of grief pulling the woofers out to get to the x-overs. (Dynaco used some form of precambrian Gorilla Glue to seal them in, takes a bit of patience with a putty knife and chisel to pull 'em out so you don't bugger-up the particle board.) Give the new caps about 50 hours to settle in. I think the value is 6 uF at 250V, and you'll like the results.
Cheerio
d

nobody mentioned the avatar?  I want some of those speakers!
We're not talking 8" here guys, we're talking 8 footers!

tubes4hifi wrote:nobody mentioned the avatar?  I want some of those speakers!
We're not talking 8" here guys, we're talking 8 footers!

Think that's a Cerwin. Despite their size they were incredibly efficient, in excess of 103dB/watt. IIRC from a conversation with Andy Bowman, only eight were made and loaded horns.

Looks like somebody was playing with Photoshop again ... kinda stretches credulity that two people would be rolling something like that into a truck ...

OK ... I'll play too!

Here's the amp used to drive those speakers ...

Oh, I dunno.
[img]https://s1270.photobucket.com/user/deepee99/media/househorn_zpsf4efc07f.jpg.html?filters[user]=140276498&filters[recent]=1&sort=1&o=0[/img][/img]

n3ikq, your post resonated with me on a personal level. When I was growing up, my dad used to build TVs, stereos, and so on. He seemed so smart and I grew up listening to his old Dynaco ST-70 in my bedroom.

Eventually I became "smarter" than him and we drifted apart. The old Dynaco ended up somewhere else long before I came to realize that he was struggling with dementia.

Unfortunately, he's gone now, but I am trying to honor him by learning through the process of rebuilding one of these old gems.
I hope you and your dad are able to enjoy your project together for many years. I wish my dad were still around to appreciate just this one thing he taught me.

Best regards,
Colin

Great testimonial! Similar thing here, Lost dad suddenly in 1960 but he loved this stuff. Held on to his Jensen Imperial Reproducer, Heathkit W5M and C3 pre. All mono, prior to stereo. All this sat until 4 years ago when I decided to get back into this stuff (Old DeVry graduate). Well, took apart he amp, re-capped it, measured the output transformer only to find it was shorted. Found a guy in Wisconsin who rewound it for me. Put is all back together, bought new tubes (potato masher rectifier) and it worked. Square wave was real sweet. Local audio shop took it for a few days and said it is pushing 35 watts. Re-capped the preamp and got an Eico tuner, same vintage, 1957-58. Imperial (mahogany finish) is excellent shape, surrounds all in tact!!!. Plugged it all in an "oh my gosh" what a sound that fills up the entire home. Super-tweeter controls needed some cleaning and eventually will re-cap the crossovers but back in business. Great for NPR jazz and mono rocks! Not to mention a great testament to pops -- he may have been proud. Great thing to pass to the kids too if they can appreciate a 250 lb speaker! BTW - upgraded the system with a vintage Garrard mono TT too -- all set!

Thanks for the kind words. It's been a fun/ nostalgic journey with the added benefit of re-discovering good music! I put on a remastered "Dark Side of the Moon" the other night. What a treat!   I can't take credit for that avatar. I found it and thought people would get a kick out of it. A just assumed it was a photoshop job. Are you saying it was a real speaker? Seems like it would be far too heavy for two people! It begs for a nice caption. My favorite so far is: "and this is just the tweeter honey"! Just for fun, I'll show you all a speaker that only you can appreciate! It is quite real!

Sound generators (3)
3-10 kW, electro-pneumatic Horns (3)
25 Hz exponential, 50 Hz hypex,75 Hz exponential
Maximum SPL, 150Db overall sound pressure level
Frequency range:25 Hz to 10 kHz
Interior: 10.0 meters x 8.2 meters x 12.8 meters

Would love to see the crossover!