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    Coming Soon: Pas-3X

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    Peter W.

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    Location : Melrose Park, PA

    Coming Soon: Pas-3X

    Post by Peter W. on Sat Sep 15, 2018 2:22 pm

    https://www.ebay.com/itm/253857174566

    Just snagged this PAS-3X (or so it is represented). From the description, it will either be the rectifier tube, open selenium rectifier or bad transformer. I have the former and the latter, the middle one (and the associated caps) will be replaced out-of-hand.

    "They" are suggesting an October 1 arrival.

    Wish me luck.
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    PeterCapo

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    Re: Coming Soon: Pas-3X

    Post by PeterCapo on Sat Sep 15, 2018 2:37 pm

    Gadzooks! Keep us informed, eh wot??
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    peterh

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    Location : gothenburg, sweden

    Re: Coming Soon: Pas-3X

    Post by peterh on Sat Sep 15, 2018 3:10 pm

    Peter W. wrote:https://www.ebay.com/itm/253857174566  

    Just snagged this PAS-3X (or so it is represented). From the description, it will either be the rectifier tube, open selenium rectifier or bad transformer. I have the former and the latter, the middle one (and the associated caps) will be replaced out-of-hand.

    "They" are suggesting an October 1 arrival.

    Wish me luck.
    No need, you will fix this one. Selenium rectifier is my guess, forget 12x4,
    maybe transformer.
    Good price btw.
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    Peter W.

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    Re: Coming Soon: Pas-3X

    Post by Peter W. on Sat Sep 15, 2018 7:40 pm

    peterh wrote:
    Peter W. wrote:https://www.ebay.com/itm/253857174566  

    Just snagged this PAS-3X (or so it is represented). From the description, it will either be the rectifier tube, open selenium rectifier or bad transformer. I have the former and the latter, the middle one (and the associated caps) will be replaced out-of-hand.

    "They" are suggesting an October 1 arrival.

    Wish me luck.
    No need, you will fix this one. Selenium rectifier is my guess, forget 12x4,
    maybe transformer.
    Good price btw.

    If it is an X, yes, good. Otherwise it will be o its way back to Canada. This is targeted as the office system, with a CD changer, an ST35, and A35 speakers.
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    PeterCapo

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    Re: Coming Soon: Pas-3X

    Post by PeterCapo on Sat Sep 15, 2018 7:54 pm

    It's a 3X. It has the two small, original electrolytic DC blocking capacitors. It also has the notches in the bass and treble pots.
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    Peter W.

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    Re: Coming Soon: Pas-3X

    Post by Peter W. on Sat Sep 15, 2018 8:10 pm

    Trust, but verify. Smile Y
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    PeterCapo

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    Re: Coming Soon: Pas-3X

    Post by PeterCapo on Sat Sep 15, 2018 8:13 pm

    Right-o.
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    Peter W.

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    Re: Coming Soon: Pas-3X

    Post by Peter W. on Mon Sep 24, 2018 9:25 am

    The unit arrived Thursday while I was at Kutztown. I unpacked it Sunday morning, and ran the basic tests last night. Only the 12X4 was lighting - dimly, the others not visibly. I had 5 VDC on the filament line. When I disconnected one of the blue transformer leads from the bias supply, I got 13 V on that winding at 110V input, about right. And the very slight mechanical buzz from the transformer went away. New bias supply (diodes and caps) are in the cards - I suspect that is all there is to it.

    Otherwise, yes, it is an X. and remarkably clean on the outside. I will strip the top and sand out the very little bit of rust, and fleck-paint it black, and replace the line-cord with a two-lead polarized cord to keep the hot on the switch. Then, it will live in the office mated to a ST-35 and either the Dynaco A35s or an AR Athena sub-sat set - space is at a premium, so common sense may prevail over "all Dynaco".

    rjpjnk

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    Re: Coming Soon: Pas-3X

    Post by rjpjnk on Tue Sep 25, 2018 8:38 pm

    You got a great buy there Peter! I could see from the pics that is was, in fact, an X. I have the same as you know, and I like it very much. I like how it makes records sound. Be sure to adjust the output resistors to match whatever amp you decide to connect it to, and if it is a SS amp you will need an output buffer if you plan to use the tone controls. But I know you already know this.

    Anyway, great find. Smile

    EDIT: I can vouch for this power supply board (Z-PSU). I have used it and it works great. Replaces both Filament and B+ but keeps the tube rectifier. I did have to add a 1 ohm resistor to the filament circuit to keep the voltage at 11V per tube per Dynaco design.
    http://www.erhard-audio.com/Power_Supply_Kits.html
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    cci1492

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    Re: Coming Soon: Pas-3X

    Post by cci1492 on Tue Sep 25, 2018 9:12 pm

    Fix it up and post some pictures, nice score!
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    Peter W.

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    Re: Coming Soon: Pas-3X

    Post by Peter W. on Thu Oct 18, 2018 1:28 pm

    Update: Confirmed that the selenium diode pair is bad, and that is the only outstanding issue. I will not have time to make complete repairs until next weekend - and I will take pictures.

    As I have to be at work the following weekend, I will take the opportunity to transport this unit, together with an ST35 and an FM3, and the AR sub-sat speakers and Sony CD changer, and set it up in my basement office. I am curious to know how the FM3 will work out 10' below grade, dead-center in a city-block footprint medical and research building. My Zenith RD7000Y does only OK.
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    peterh

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    Re: Coming Soon: Pas-3X

    Post by peterh on Thu Oct 18, 2018 4:30 pm

    Peter W. wrote:Update:  Confirmed that the selenium diode pair is bad, and that is the only outstanding issue. I will not have time to make complete repairs until next weekend - and I will take pictures.

    As I have to be at work the following weekend, I will take the opportunity to transport this unit, together with an ST35 and an FM3, and the AR sub-sat speakers and Sony CD changer, and set it up in my basement office. I am curious to know how the FM3 will work out 10' below grade, dead-center in a city-block footprint medical and research building. My Zenith RD7000Y does only OK.
    Nice to hear that it's a simple repair. As emergency a pair of 1n4005 will do just fine.
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    Peter W.

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    Re: Coming Soon: Pas-3X

    Post by Peter W. on Mon Oct 29, 2018 9:02 am

    Well, it's done. As to the PAS 3X:
    a) Replaced the filament string caps and diodes, unloaded gives me 25 VDC, loaded about 23 V, both at 120 VAC on the variac. Before I install the system permanently, I will discern the wallplate voltage at work, and adjust if necessary. We are a remarkably steady 118 V at home.
    b) Cleaned the controls - all smooth now.
    c) Wiped down the exterior and got the "historical skunge" off it. More later.
    d) Assembled and tested - all good.

    As to the very rough FM3:
    a) Rebuild the power-supply by cutting the top off the multi-section cap and using the base and locking tabs, added four new caps through the original phenolic base.
    b) Cleaned the controls & switches.
    c) Lightly cleaned the exterior.
    c) Assembled and tested. Remarkably quiet, and about as sensitive as typical of these beasts. No need for an alignment!

    Then - took the ST35 out of mothballs and assembled & tested the lot against an AR Athena speaker system.

    Very nice.

    Joined by a Sony 5-disc changer, this will become the office system. I will be in the office at least one day next weekend on a major shut-down, and they let me park in the loading dock on weekends.

    No pictures as all I did, really, was substitute. I have the upgrade kits for both the FM and the PAS power-supplies, but I am staying OEM as this *will* be in the office, and will also be left unattended regularly with possible access by a staff of about 3,500 employees and 4,000 or so medical and nursing students. Not that I am worried, but one knows how it is with pack-rats and shiny objects. So, no repainted cages, no polishing of faceplates and so forth.

    I will be happy not to be streaming on tiny computer speakers anymore.
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    Sfguitarworks

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    Re: Coming Soon: Pas-3X

    Post by Sfguitarworks on Sat Nov 03, 2018 2:45 am

    Kind of off topic, but how do the stereo dynakit preamps compare to a more modern tube pre? I mean sound wise only. I’d like to get a tube pre to go with my ST-70, and the price of the dynakit units is appealing. Of course I want great sound! Thanks, Geoff

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    Bob Latino
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    Re: Coming Soon: Pas-3X

    Post by Bob Latino on Sat Nov 03, 2018 8:06 am

    Sfguitarworks wrote:Kind of off topic, but how do the stereo dynakit preamps compare to a more modern tube pre? I mean sound wise only. I’d like to get a tube pre to go with my ST-70, and the price of the dynakit units is appealing. Of course I want great sound! Thanks, Geoff

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    This may sound a little harsh towards PAS preamps but this is my honest opinion ..

    Having dealt with Dynaco PAS preamps since the early 1960's, I can say from a "sound quality" point of view that almost any modern well designed preamp will sound better than any PAS preamp. Sure - you can beef up the power supply, bypass the tone controls and perform other upgrades on your PAS preamp but IMHO it still will not sound as accurate as a modern preamp. I love old Dynaco tube gear and a PAS preamp is nice to have as a piece of Dynaco history. To my ears, a PAS preamp sounds smooth, mellow but just not that accurate. It also lacks that "jump factor" on musical peaks that a good preamp has. Buying a PAS preamp off Ebay and trying to turn it into a really great sounding preamp is also not advised from a financial point of view. You buy it and then put a couple of hundred dollars into "upgrading" your PAS and it still doesn't sound that great. OK - so you now want to REsell it on Ebay and find that your upgrades have actually DEVALUED the PAS by you doing upgrades. People will pay on Ebay MORE for an original unmolested PAS than they will for an "upgraded" PAS. Buyers are usually suspicious of upgraded PAS preamps/(and amps also). You are better off just buying one of Roy's Tubes4hifi SP preamp kits. Any of his preamps will sound better than ANY PAS preamp - original or modified.

    Bob
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    Sfguitarworks

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    Re: Coming Soon: Pas-3X

    Post by Sfguitarworks on Sat Nov 03, 2018 3:23 pm

    Thanks bob. Exactly what I was looking for. Since I have you on the line, can you speak to the sonic difference between the stock ST-70 and one with the vta driver board? I think my amp currently sounds great, so I was interested in what would be improved. Thanks!
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    Bob Latino
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    Re: Coming Soon: Pas-3X

    Post by Bob Latino on Sat Nov 03, 2018 4:54 pm

    Sfguitarworks wrote:Thanks bob. Exactly what I was looking for. Since I have you on the line, can you speak to the sonic difference between the stock ST-70 and one with the vta driver board? I think my amp currently sounds great, so I was interested in what would be improved. Thanks!

    Again ... My opinion here .. If others have a different take on things, please express your opinion.

    The stock driver board uses 7199 driver tubes. Some negative things about 7199 driver tubes. (1) they are not linear at all drive levels (2) They are not made anymore and the remaining stock of 7199 tubes is getting expensive ($40+ USD per tube ?) (3) There is no direct replacement for a 7199 - NONE ! Yes - You can get an adapter and use 6GH8A driver tubes but then you are spending a little more money for two adapters. The VTA driver board uses easy to source and relatively inexpensive 12AU7 driver tubes.

    Dynaco designed this circuit to "save a tube" and not for best sound. Using just two driver tubes rather than three saves a tube and a tube socket. Back in the 1960's a 7199 tube and socket costs together about $1.50. Dynaco sold about 350,000 ST-70 amps so they saved maybe $525,000 in 1959 money by using this circuit. (That would be about 4.5 million in today's money). The carbon composition resistors that they used on that original ST-70 board will almost always drift (usually UP) in their value over the years. After almost 60 years the chances are pretty slim that the two channels have resistors that are still closely balanced. The VTA driver board board uses 1 % precision metal film and metal oxide resistors. These modern resistors are much more stable than carbon composition resistors and the channels will stay balanced long after you and I are not around anymore.

    Sonic differences  > The original driver board has a smooth and mellow sound that is not unpleasant to listen to. It is just not "true" when compared to live music. The VTA board has a more accurate sound that is much more like real music.

    Bob

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