Dynaco ST-70 / Dynaco Pass-2 Value

Good morning . . . and as a new member of this forum I'd like to say thanks for the opportunity to join in.  

I've toyed with the idea of buying an old tube system for years but always decided against it because there is so much I don't know.  Instead, I've been quite content to play my vinyl through an old Sansui 9090 and Klipsch Heresy's.  A week ago I had never heard of Dynaco but ran into an old friend who said he has the ST-70 and Pass-2 units that he'd sell me for $600.  He said they work fine and have not had any modifications - and will be glad to audition them for me after the holidays.  He said that they are a little more valuable due to them being 'factory wired' and he told me to read up on the Dynaco's to see what I thought.

After spending some time online and in this and other forums, I've convinced myself that this might be a good entry-level tube amp / pre-amp - and that I might at some point down the road be interested in learning more about the potential modifications that are out there.  
 
This being my first post, I hope that I'm following the protocol for posting questions, etc.  I understand that condition is very important and as far as appearances go, these two components are very, very clean.  Original brown patina is unmolested, the original lettering not worn away.  Assuming that I hook up my Heresy's to these and they play nicely and all functions operate correctly, would any of you please tell me what you think of the $600 price tag?

Thanks for any opinions or comments,

PopaTop
Nashville, TN

.

I think the price is fair for stock equipment, factory wired, in pristine cosmetic condition (modified Dynacos invariably go for lower prices), but be aware that you may have to see to some work on the electronics to get them to original factory performance and for reliability.  The tubes must be considered an unknown unless they have been replaced recently, or tested and verified good.  The selenium rectifiers in both the Stereo 70 and the PAS are known to age over time, and these units are probably fifty years old by now.  Their failure mode is high internal resistance resulting in low voltage, so that the tube filaments in the PAS don't run at their proper voltage, resulting in flabby, loose sound; and in the Stereo 70 they can make it difficult or impossible to bias the output stage properly.  I know that some say not to do this, but in a stock unit, modern silicon diodes can be soldered in across the existing selenium rectifier, using its terminals as connection points, effectively bypassing the problem.  I have NEVER had a selenium short out after this is done and I've been running Dynaco tube equipment this way for almost that whole fifty years. In effect it becomes a terminal board, the silicon diodes,being of lower resistance, do all the work.

The original power supply filter capacitors in the Stereo 70 are well past their life expectancy by now, so if the ones in this equipment have not been replaced, they are like a ticking time bomb.  A filter capacitor that suddenly arcs over and shorts is not a good thing.  In the Stereo 70 such a failure could take out the power transformer which is an expensive part to replace, though at least now, very good replacements, better than original, are available.  

Something I insisted upon doing in any stock PAS I serviced (when I was in the business of repairing them) was to add a line fuse.  You don't want to use the power transformer as a fuse! And make sure the fuse in the Stereo 70 is according to the factory rating. A too-big fuse doesn't protect the internal circuitry and the transformer properly.

Good luck with the Stereo 70 and PAS.  You'll notice a distinct difference in sound between good tube equipment...which this is...and mid-grade transistor equipment. I like it, but I have to admit having ditched transistor amplification in my home system a long time ago.

Best advise I can give you as a newbie to tubes myself (about a year) the hardest part is figuring out what you really want, Regardless of brand all tube equipment will need to be serviced at some point so do you want to learn how or pay others to perform?
Old or "vintage" tube equipment is a gamble and will more than likely need service sooner rather than later, nothing wrong with going this route if you have the skills or want others to do the work for you.
Since I was starting with very basic electrical skills I choose to go with a new kit (ST-120) with all new parts and assemble/learn as I assembled using this forum as my daily go to (No lack of help and guidance here good group).
I have to tell you the sense of accomplishment and pride I felt when the kit was completed and working was unbelievable the new kits offered by Bob & Roy are Top notch quality, if you can read and follow clear concise instructions you could be listening to a new better quality sounding ST-70 in 12-15 hours check out tubes4hifi web site.
I'm listening through a pair of mid 70s Heresy's and the sound is amazing.
I will caution you once you experience the sweet sound of tubes there is no turning back.
Good luck.

Thanks all for the input.  I've spent most of the day mulling over the options and based on the feedback from you guys . . . while I like the idea of the vintage stuff, I agree that repairs/upgrades would be something to expect sooner or later.  I guess I was wondering if the $600 price was such a killer deal that I'd be smart to jump on them.  That doesn't appear to be the case.

I did go to Bob's site and saw what he was building and selling and the ST-120 intrigued me.  I think I could assemble a kit and agree that building my own would be rewarding in itself - and the icing on the cake would be "the sweet sound of tubes".  I've never listened to a record played on a tube amp, at least not that I know of. I'm a fairly new convert to vinyl and in the group who believe vinyl sounds superior to digital recordings. I fully expect to find that once I hear a decent tube amp, my Sansui won't see much action.

Thanks again for the input. I'm sure if I buy one of Bob's kits, I'll be a regular on here.

Best regards and Happy New Year!

Pop-a-Top Smith
Nashville, TN

Then again, you could get lucky, and the stuff will last another 20 years without having to put a dime more into them.

Hey, it could happen!   

With either option, new kit or refurbing the old stuff, you could expect to have to put several hundred into labor if you have someone else do it. Might be the excuse you need to get your feet wet. You'd still need to put a couple hundred into tools if you're starting out from scratch. You'd want a decent soldering station, snips and strippers, screwdrivers and such, as well as a well lighted bench to do the work.

Worth noting, Bob's kits have VERY nice step by step instructions for assembly and testing, and there's always help available here on the forum. I recently put together an ST120 and am currently enjoying the fruits of my labor. Killer amp it is. LOT more guts with major improvements over the original Dynaco stuff. You also have the advantage of knowing it'll last and not worry about the whole ticking time bomb thing that comes along with "untouched" vintage equipment.

In an amplifier old advice is that you make an update for your peace of mind.
You may contact Bob for installing an updated VTA board.

My advise is "get your friends units".

You really should look after the few things mentioned ( replace selenium rectifiers) in buth. It's
an easy task. Replacing caps is more involved, but you can let them bee for a while becouse:

When your ears have adopted you might wany to moderize, i VTA-70 ( or 120) from bob would
be an obvious choice. Then you have the benefit of 1/ music during buildtime 2/ a suitable
comparation unit when the build is ready.
At that point you most likely sell the st-70 and loose no money.

The pas2 might be the next object, here a psu board is available that replaces all caps
and diodes, check tubes4hifo and others. Or, you might want to build something, again
you have something to compare with after building.

My 5 Kronor

PopaTopSmith wrote:I've toyed with the idea of buying an old tube system for years but always decided against it because there is so much I don't know.  Instead, I've been quite content to play my vinyl through an old Sansui 9090 and Klipsch Heresy's.

I had a 9090DB once, the Hafler DH-101 preamp run into the 9090's amp section was a revelation.  Imagine a well restored tube system.

PopaTopSmith wrote:A week ago I had never heard of Dynaco but ran into an old friend who said he has the ST-70 and Pass-2 units that he'd sell me for $600.  He said they work fine and have not had any modifications - and will be glad to audition them for me after the holidays.  He said that they are a little more valuable due to them being 'factory wired' and he told me to read up on the Dynaco's to see what I thought.

A little pricey, but truly factory wired, unmodified units that are in pristine condition would be worth it, IMHO.

PopaTopSmith wrote:After spending some time online and in this and other forums, I've convinced myself that this might be a good entry-level tube amp / pre-amp - and that I might at some point down the road be interested in learning more about the potential modifications that are out there.

Quit reading and start listening to them!  
 

PopaTopSmith wrote:This being my first post, I hope that I'm following the protocol for posting questions, etc.

Our Moderator, Bob Latino, will certainly let you know if you're misbehaving. 

PopaTopSmith wrote:I understand that condition is very important and as far as appearances go, these two components are very, very clean.  Original brown patina is unmolested, the original lettering not worn away.  Assuming that I hook up my Heresy's to these and they play nicely and all functions operate correctly, would any of you please tell me what you think of the $600 price tag?

Kinda sounds like a decent deal.  My recollection is that the Heresys are quite efficient - Paul Klipsch built most of his speakers that way.  His favorite saying was "What the world needs is a good five watt amplifier" - that's how efficient most of the speakers he designed were.  An ST-70 will not even break a sweat on those speakers; even my little 17 watt Dynaco ST-35 could drive you out of the room with Heresys.

Bob Latino sells amp kits that are as modern as you can get using vacuum tubes.  If you go that route then his smallest stereo amp should be more than enough power for the Heresys.  It goes without saying that they will sound better than a 55-year-old design with vintage (dying and hopelessly out-of-specification) parts.  Roy Mottram (also a member) sells highly regarded vacuum tube preamps, with and without phono sections, that are an extraordinary value.  Full Disclosure: I have no financial interest in any of the above items or sellers; I don't own any of their products, but I do own some old Dynaco equipment I bought over 20 years ago.

One last note:  The phono section of the PAS-2 will need to have some parts changed to correct values to adhere to the RIAA curve.  Without these changes you're listening to your vinyl through incorrect RIAA de-emphasis.  There is a "Sticky" that addresses this issue.

So there you are, my two cents.  Enjoy the tyranny of choice.

I agree that it boils down to choice.  

$600 for a Pas and ST70 is a great price.  But buying old gear means doing lots of homework should anything go wrong.  The things that will need replacing eventually will be the fuses, diodes, quad cap, 5AR4 rectifier, and EL34 power tubes.   The pas from what I've read is not a great preamp but it's ok.

Or you can build one of Roy's preamp kits and one of Bob's amp kits and skip a lot of pain and frustration.

If I seem a bit biased it's only because I've learned a lot the hard way.  Of course if this all seems like the kind of hobby you might want to jump into, then go with the older gear, put your thinking cap on, and enjoy! Either way will bring you the glorious sound of tubes.