PAS Rebuild

I got an old PAS2 in a trade. I'll eventually get into restoring/customizing it, but it works pretty well for the moment. I'll take some pictures and post them soon. But the one thing that looks like it requires immediate attention is the power outlets on the back panel. They've crumbled. I'm wondering if anybody knows of a source for these. Of course I checked Dynakitparts and TubeNirvana, but I don't see any. I know these aren't necessary, but they're kind of nice to have, and these broken ones are a fire hazard.

This may or may not be helpful, If you can live with something modern rather than "authentic-vintage" I'm guessing Mouser or DigiKey will have something functional, but there will be issue of fitting in your existing chassis opening.  Better than burning down the house though.

(With Mouser website you may also grow old and die before being able to locate your best option part from among the half million SKU's they seem to stock - My personal experience is I can very quickly narrow search down to 30-70 virtually identical items at which point they are all pretty much the same with minor variance and I get sucked into reading spec sheet PDF's . . . .)

Before picture:

Here are 329 possibilities offered up in a quick Mouser search:

http://www.mouser.com/Power/AC-Power-Entry-Modules/_/N-6g7mp?P=1z0vlot

vtshopdog wrote:Here are 329 possibilities offered up in a quick Mouser search:

http://www.mouser.com/Power/AC-Power-Entry-Modules/_/N-6g7mp?P=1z0vlot

You're a better man than me, vtshopdog - I gave up there after 2 minutes. I figured if there was such a thing, it would be available from the affiliates here, since it is sort of old school. I know I'd be better off just putting in one of those IECC thinks, or whatever they're called - 3-wire computer style.

Why not just eliminate them?

audiobill wrote:Why not just eliminate them?

Too easy? Not much reason to worry about them, and there's good reasons for not wanting to run a lot of extra current through my preamp, but if they were available, they'd fill the holes.

daveshel wrote:I got an old PAS2 in a trade. I'll eventually get into restoring/customizing it, but it works pretty well for the moment. I'll take some pictures and post them soon. But the one thing that looks like it requires immediate attention is the power outlets on the back panel. They've crumbled. I'm wondering if anybody knows of a source for these. Of course I checked Dynakitparts and TubeNirvana, but I don't see any. I know these aren't necessary, but they're kind of nice to have, and these broken ones are a fire hazard.

I recommend to remove them. The power switch does not seem to be capable of reliably turning on and off todays poweramps.
Instead use +12V from the filament to control an SSR inside the poweramp , or , as
an alternative, see if the PAS can trigger one of these powerstrips that uses current
drawn on a "master outlet" control the other outlets.

IN short, don't fix the outlets - remove them!

I removed them. (Acually I removed three of them and left one that was still intacct.) I put in a terminal strip to handle some of their connections.

Moving on.

I cleaned up the front panel today, as good as it's going to get anyway. Next I want to replace the power supply. I was going to go with the TubeNirvana replacement, but you have to commit to whichever circuit boards you will end up with, and choose the power supply accordingly. I see this project as an evolution, with long listening intervals between stages. I want to keep the original phono and line stage boards for a while. The power supply board from Dynaco Designs seems to be a bit more versatile, as in it can handle the original boards as well as their Aikido board.

Thoughts, anyone?

My PAS 2 was stored outdoors under a picnic table--before I acquired it. Re-working the front panel was low risk for me as the cosmetics were ~zero on a scale of ten. I built a small fixture to apply horizontal brush marks to the panel. I think I prefer this result to the polishing option.

" alt=""/>

daveshel wrote:I removed them. (Acually I removed three of them and left one that was still intacct.) I put in a terminal strip to handle some of their connections.

Moving on.

I cleaned up the front panel today, as good as it's going to get anyway. Next I want to replace the power supply. I was going to go with the TubeNirvana replacement, but you have to commit to whichever circuit boards you will end up with, and choose the power supply accordingly. I see this project as an evolution, with long listening intervals between stages. I want to keep the original phono and line stage boards for a while. The power supply board from Dynaco Designs seems to be a bit more versatile, as in it can handle the original boards as well as their Aikido board.

Thoughts, anyone?

our power supply will work with the original PC5, but not with the PC6. The reason is, for some weird reason, one side of each 12AY7 filament on the PC6 is tied to B+ ground. The voltage regulator we use, LM350, and I believe this would apply to most voltage regulators out there, does not like to have its 24VDC referenced to B+ ground, as the 24VDC circuit is totally separate from the B+ circuit.
The original PC5 does not have one end of the 12AX7 filaments tied to B+ ground, they are just in series, as it should be!
So correctly speaking, you do no have to 'commit' to whichever boards you wish to upgrade to, all our other upgrade pcb's will of course work with our fully regulated power supplies.

j beede wrote:My PAS 2 was stored outdoors under a picnic table--before I acquired it. Re-working the front panel was low risk for me as the cosmetics were ~zero on a scale of ten. I built a small fixture to apply horizontal brush marks to the panel. I think I prefer this result to the polishing option.

Looks great, j - much better than mine. Not sure what you mean by a small fixture. How would I go about achieving this kind of results?

MontanaWay wrote:

our power supply will work with the original PC5, but not with the PC6. The reason is, for some weird reason, one side of each 12AY7 filament on the PC6 is tied to B+ ground. The voltage regulator we use, LM350, and I believe this would apply to most voltage regulators out there, does not like to have its 24VDC referenced to B+ ground, as the 24VDC circuit is totally separate from the B+ circuit.
The original PC5 does not have one end of the 12AX7 filaments tied to B+ ground, they are just in series, as it should be!
So correctly speaking, you do no have to 'commit' to whichever boards you wish to upgrade to, all our other upgrade pcb's will of course work with our fully regulated power supplies.

Thanks, Montana. I'm looking into this.

First Step: This morning I removed the old pilot lamp and replaced it with an LED from dynakitparts. I knew that the power supply was the weakest link, but I was surprised how much improvement resulted from just this step. In my initial listening, with the tone controls set as flat as possible, the bass was too prominent and floppy. After removing the old lamp's current draw from the original sagging power supply, the bass is noticeably tighter and in better balance with the rest of the spectrum.

I refinished my PAS-2x, whose front panel was well worn around the selector and volume knobs, with steel wool. By hand in straight-line strokes worked fine.  Spray polyurethane topcoat followed.

My PAS-2x was notably loose and flabby in the bass, and took a long time to warm up when I first got it. Its filament voltage was low. Replacing the selenium rectifier, which typically fails high-resistance, with silicon diodes fixed that. The LED pilot light came later.

GP49 wrote:I refinished my PAS-2x, whose front panel was well worn around the selector and volume knobs, with steel wool. By hand in straight-line strokes worked fine.  Spray polyurethane topcoat followed.

My PAS-2x was notably loose and flabby in the bass, and took a long time to warm up when I first got it.  Its filament voltage was low.  Replacing the selenium rectifier, which typically fails high-resistance, with silicon diodes fixed that.  The LED pilot light came later.

(sounds like the lead in to a joke) How can you tell a PAS2 from a PAS2X?

I used steel wool, Flitz and and an acid bath. I'm not too where I'll end up with it - If I eliminate the tone controls I may get a new face plate, or I could leave them in place but not connected. That's the last step and there are quite a few between here and there. My power supply is supposed to ship tomorrow.

The PAS-2x (and PAS-3x) tone controls have a smaller arc of rotation; they have the special Dynaco controls that teke the tone controls out of circuit at their centered positions.

Stock PAS-2x (and PAS-3x) have NON-SPLINED control shafts on all controls, requiring setscrew knobs. PAS-2 and PAS-3 have splined control shafts and knobs.

Second Step: I completed the installation of the regulated power supply from Dynaco Designs. It sounds very good. The bass is nice and tight and the sibilance is gone. Those old audio boards aren't bad. Nice imaging.

Next step is probably the removal of the tone controls. After I listen for a while.

As I've been listening, I've become more aware of some white noise that I can hear as soon as the preamp warms up - not present with my old preamp. It is independent of the volume control or any other controls. Bear in mind that this is all original except for the pilot lamp and the new power supply - although I didn't really notice this white noise before I installed the power supply. I'm wondering what the most likely source is - if maybe I need to look at my wiring routes for the new power supply.

Tubes?  Resistors?  Especially if they are still the originals.  

One channel? Both channels?

You do say that there was none before, but S#!T Happens...especially if the new power supply has increased the B+ voltage.  

Routing of wires for the power supply is unlikely to cause hiss, only hum.

The tubes are newer Sovetks in the linestage. Both channels are affected.

I wouldn't swear it wasn't there before, as my attention and my expectations both increased after spending so much on the power supply. But I am buoyed by your suggestion that increased B+ has caused increased awareness of pre-existing conditions.

My next step was going to be removing the tone controls, but it seems this power supply board depends on filter caps ahead of it, so I need to deal with that first - the old can cap is still in place. I'm currently evaluating whether to use an expensive new quad can or to try to fashion a network of cheaper caps.

I finally finished redoing the rest or the power supply. It sounds great - very quiet. The original circuits sound very detailed, imaging is holographic.

Hi guys..
           Just a note to say we have stock once again on the AC outlets to fit the PAS & SCA-35. These are hard to find and supply is very limited. I believe these also fit the Dynaco FM 3 tuner & other audio gear from this same era.

Attached Link below:

Kevin @ Dynakit



http://www.dynakitparts.com/dynakit-products/pots-switches-etc/AC-PANEL-OUTLETS-NOS

>>Next step is probably the removal of the tone controls. After I listen for a while.<< Snippage

Look for X-type controls. They are out-of-circuit when in the flat position - and so you may retain them without compromise. Even back in the day Dynaco understood that there was a class of user that would want them out of the way, and so came up with the X-type tone controls in their later iterations.

Bluntly, I do not see any advantage in removing tone controls if properly designed. Not every room is perfect, nor is every recording or broadcast, and not every user has an equalizer. Tone controls give a quick-and-dirty solution to mostly temporary problems without additional hardware, and for that reason alone have their place.