Dynaco PAS-3X tube preamp

[kach22i]

Tomorrow after work I'm going to look at, and most likely buy a working Dynaco PAS-3X tube preamp for $200. Owner claims some "service" was done to it five years ago, and it's been sitting around all that time because he has two of them. I called him up, he said he was listening to it now.

I had a line on one locally for $150 (which started this), but the guy is not returning my e-mails, even tried a PM (different forum) and it's been a couple of days.

What should I know about this unit?

What should I look out for?

I will be able to test /audition it and will have to bring my own turntable.

This will be a temporary fix until I get my GRAAF tube pre-amp repaired. Like the Dynaco ST-120A SS amp I bought a while back, I hope to recoup my investment when I get my main system back in order. At least that's the current plan.

 

[cjfrbw]

Unlikely, but if the tubes have the telefunken triangle on the bottom, they could be worth more than the preamp. I still have a couple of the tele 12ax7's from a unit I paid $120 for in the 70's.

 

[kach22i]

I cannot tell from the photo provided what the tubes are, but will look at them when I get there. Tubes are not cheap, not the good ones anyway.

There is a non-stock volume control knob, but it's somewhat era appropriate and vintage looking. I'm not worried about knobs, I just don't want to be buying another project in need of immediate servicing.

 

[Bill Hart]

This was a 'go-to' preamp back in the day, and sounded better than its solid state sucessor from Dynaco, as well as a host of other solid state preamps back in the day. Things I would be sensitive to:
was the unit factory built or built by a home user as a kit? (Remember, Dyna was one of the handful of companies that allowed you to build your own, so build quality, soldering, etc. could be an issue, regardless of how well kept the unit is);
many of these units were modded over the years, with varying results;
state of the tubes; as Carl pointed out, if you are lucky, it may have valuable tubes in it already, but if the tubes are past their useful life, retubing is going to add to the expense;
I would suspect that the schematics for these are readily available, and the units are fairly easy to work on, but i would assume you are looking for a useable unit as a stop-gap, and not a project.
I had a bunch of Dyna equipment back in the day, it served me well. There is also a site that sells part for Dynaco. Here's their site: http://www.dynakitparts.com/store/
You might ping them and ask them where the likely vulnerabilities are- switches, caps, etc.
And obviously, if you can fire it up and hear it run for a while before you buy, that would be good.
Van Alstine still makes a modded version, I think. He's probably the other 'guru' on these preamps.

 

[kach22i]

Thank you whart, I'll keep your comments and information in mind.

What of the phono section?

Is it as good as the rest of the pre-amp?

One person told me the RIAA equalization curve is so out of date that you are better off using an modern outboard unit.

 

[Bill Hart]

Thank you whart, I'll keep your comments and information in mind.

What of the phono section?

Is it as good as the rest of the pre-amp?

One person told me the RIAA equalization curve is so out of date that you are better off using an modern outboard unit.

Don't have a clue. I think the last time i fooled around with a PAS 3 was in the mid-70's. I'll bet there is some info on the web, that preamp has a following, and there must be mucho info re the phono section given all the modifications that have been done over the years. As far as adherence to the curve goes, not sure a lot of record companies really adhered that closely to it anyway.

 

[DonH50]

I do not recall where the 3X lands but I think the phono EQ may be OK. Some of the earlier units do not follow the RIAA curve and were tweaked. I have many fond memories of modding PAS-3_ preamps, from minor tweaks to complete rebuilds. I even have a bunch of little pamphlets with various mods in a box someplace.

Tube phono stages, I think the PAS was a little noisier than SOTA but quite acceptable. Tube phono inputs have the advantage of having gobs of voltage headroom, one of the shortcomings of many SS stages. They have the disdvantage that they are rarely cascoded, and many exhibit very high input capacitance due to Miller effect. That causes a HF roll-off that many actually like.

 

[kach22i]

I'm going to buy the PAS-3X.

I have it working including phono, it's muddy and noisy compared to anything else I have (as it now sits).

My local hi-end dealer tested it on his bench, called it a "project", and be prepared to sink money into it.

He also said some capacitors are bad and need to be replaced, but did not say which ones when I asked, indicating to me that it may be best to do them all if possible.

I know that when I had the cover off, it looked like a bunch of cheap (small) blue capacitors where bundled together on the right side to achieve the proper rating. It looked pretty messy, and doubt that it was stock.

It's a starting point, that's about it.

 

[Bill Hart]

I'm going to buy the PAS-3X.

I have it working including phono, it's muddy and noisy compared to anything else I have (as it now sits).

My local hi-end dealer tested it on his bench, called it a "project", and be prepared to sink money into it.

He also said some capacitors are bad and need to be replaced, but did not say which ones when I asked, indicating to me that it may be best to do them all if possible.

I know that when I had the cover off, it looked like a bunch of cheap (small) blue capacitors where bundled together on the right side to achieve the proper rating. It looked pretty messy, and doubt that it was stock.

It's a starting point, that's about it.

I think that link to the dyna kit site i posted earlier in this thread has various upgrades, including circuit boards, etc. that you could do yourself if you have basic skills. It's been around 40 years since i built a dynakit, but it was fun and surprisingly, the damn thing worked when i completed it. Maybe your tech could tell you where to focus, and what needs to be upgraded or repaired, and you could do it yourself with some of the pre-fab kit stuff from that site.

 

[Dirty Larry]

From a service aspect, the PAS power transformer seemed to be the most common failure - they run hot.

After my second failure, I went with a small xfmer for the filaments to take some of the load off.

 

[rbbert]

I owned one of these from '74 -'77, although it was stock only for about 6 mos. I had Ike Eisensohn (who published a pamphlet "Tu-be or not Tu-be") rebuild it (I'm pretty sure all that remained from the original was the case, faceplate/knobs and transformer) with very noticeable sonic improvement. I don't think the stock PAS-3x is competitive with even good pre-amps from the 1980's (like the PS Audio 4.6 that John in Canada recently purchased), much less even "budget" pre-amps of today. OTOH a well-modified one might be. JMO, YMMV, etc.

 

[Shaffer]

My local hi-end dealer tested it on his bench, called it a "project", and be prepared to sink money into it.

I had an AVA-modified PAS in the late-80s. At the time it sounded somewhat euphoric, rolled-off at the extremes with powerful (albeit loose) upper bass. I suspect that it may play well today in a system with vintage horns, where its particular flavor can compliment the overall presentation.