The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    PAS-2 woes

    Share
    avatar
    billinrio

    Posts : 8
    Join date : 2018-01-03

    PAS-2 woes

    Post by billinrio on Thu Jan 04, 2018 11:51 am

    This is my first post to this forum.  A little background:  I'm an American who for many years has lived in Brazil.  When I came here, I brought a good deal of vintage tube equipment with me, including Dynaco (PAS-2, MKIV, FM3 and Heathkit (WM-4's, WM-5's) that usually drive AR2a's and AR4ax's.  Tech assistance for tube equipment is pretty much impossible where I live.
    To give you an idea, no electronic stores in the city (of more than 3 million) where I live sell caps that are appropriate for tube equipment. This besides the question I get from them, "tubes, what are they?".
    My concern right now is in regard to my PAS2.  About 3 years ago the transformer burned out, and I bought a regulated power supply from Roy Mottram.  Once it arrived, Roy and I exchanged a good number of e-mails, many of which involved me complaining about the scant nature of his written instructions, and him expressing amazement at my lack of basic technical know-how.  In any case, I finally got the unit to function, and have used and enjoyed it for a couple of years.  Last week, I turned it on, and only the rectifier tube lit up.  The unit's power has always been derived from a variac set at 117vac (the power from the wall is 128vac).  I checked the tube pin-outs and got the following:

    Tube     12X4      PC5 12AX7 (1)    PC5 12AX& (2)    PC6 12AX7 (1)    PC6 12AX& (2)

    Pin 1     273          190                     190                      243                    243
    Pin 2  
    Pin 3    13.3ac
    Pin 4    13.3ac
    Pin 5
    Pin 6    273           254                     254                      254                     254
    Pin 7    364
    Pin 8
    Pin 9

    Pin values not indicated read 0.

    Once again I emphasize that there's no tech capable of working on this unit within thousands of miles of me.
    Shipping it off internationally is also not an option, due to high shipping costs and high duty charges i would have to
    pay upon its re-entry into the country.
    I would much appreciate recommendations on how to proceed.  Many thanks for your attention.


    Last edited by billinrio on Sat Jan 06, 2018 7:38 pm; edited 5 times in total
    avatar
    peterh

    Posts : 892
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: PAS-2 woes

    Post by peterh on Thu Jan 04, 2018 12:42 pm

    billinrio wrote:This is my first post to this forum.  A little background:  I'm an American who for many years has lived in Brazil.  When I came here, I brought much vintage tube equipment with me, including Dynaco (PAS-2, MKIV, FM3 and Heathkit (WM-4's, WM-5's) that usually drive AR2a's and AR4ax's.  Tech assistance is pretty much impossible where I live.
    To give you an idea, no electronic stores in the city (of more than 3 million) where I live sell caps that are appropriate for tube equipment. This besides the question I get from them, "tubes, what are they?".
    My concern right now is in regard to my PAS2.  About 3 years ago the transformer burned out, and I bought a regulated power supply from Roy Mottram.  Once it arrived, Roy and I exchanged a good number of e-mails, many of which involved my complaining about the scant nature of his written instructions, and him expressing amazement at my lack of basic technical know-how.  In any case, I finally got the unit to function, and have used it for a couple of years.  Last week, I turned it on, and only the rectifier tube lit up.  The unit's power has always been derived from a variac set at 117vac (the power from the wall is 128vac).  I checked the tube pin-outs and got the following:

    Tube     12X4      PC5 12AX7 (1)    PC5 12AX& (2)    PC6 12AX7 (1)    PC6 12AX& (2)

    Pin 1     273          190                     190                      243                    243
    Pin 2  
    Pin 3    13.3ac
    Pin 4    13.3ac
    Pin 5
    Pin 6    273           254                     254                      254                     254
    Pin 7    364
    Pin 8
    Pin 9

    Pin values not indicated read 0.

    Once again I emphasize that there's no tech capable of working on this unit within thousands of miles of me.
    Shipping it off internationally is also not an option, due to high shipping costs and high duties i would have to
    pay upon its re-entry into the country.
    I would much appreciate recommendations on how to proceed.  Many thanks for your attention.

    Your filement is missing, that's why the plate voltages are so high.
    Is there a fuse for filament ? If not it's time for replacement of things.

    triode have transformer :
    http://triodeelectronics.com/pa2powtrandy.html
    and a powersupply board with good instructions :
    http://triodeelectronics.com/sdslacabofor1.html

    Let's see what ray has to offer fixing your existing powersupply..

    avatar
    Peter W.

    Posts : 577
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: PAS-2 woes

    Post by Peter W. on Thu Jan 04, 2018 12:57 pm

    https://www.manualslib.com/manual/1006756/Dynaco-Pas-2.html?page=11#manual    

    OK - clearly you are not getting filament voltage, as all else depends on it. You _are_ getting B+. That your rectifier lights also strongly suggests that your transformer is OK, so no worries there.

    Potential causes are multiple, but start with:

    a) Broken wire/cold-solder/poor connection across the filament pins.
    b) Open SS rectifier diode(s). These beasts used a selenium device for OEM, but you should have replaced this with the revised power-supply. BUT - check the diodes on that board.
    c) Open 12AX7 filaments (unlikely).
    d) Open/shorted 2,000 uF caps.
    e) The voltage regulator chip on the mod-board has given up.

    Also helpful would be a picture of the new board or a link to the schematic.  

    I am leaning heavily to a), followed by b) above. If you need diodes, even airmail to Brazil will be pennies, and for a very few dollars, I could include any caps as you might need. I would need to know voltage and capacity.

    In terms of systematic diagnosis, read the voltages as they come of the modified P/S board. They should correspond to the destination requirements - with special attention to the filament (13.3) voltage. Look for shorts and cracked/broken traces. Look for melt-downs and such.

    Note that ALL the voltages you show are exceedingly high, by very nearly 30% or more.
    And before you do anything else, you need to figure out why this is happening. Start with your line voltage, and make sure that it is *NO MORE* than 120VAC at the wallplate. If you are running at 160 VAC, you will burn everything out on that P/S board, and more.

    Please check the line voltage first and report back. If too high *STOP* there until it is corrected. If OK, move on to the voltages coming off the mod-board. And report back.

    We will then have better information designing a path forward.

    Best of luck with it - and be happy that you have an intact transformer - so far.

    nmchiefsfan

    Posts : 39
    Join date : 2012-03-21

    Re: PAS-2 woes

    Post by nmchiefsfan on Thu Jan 04, 2018 1:06 pm

    I am not familiar with how the boards are layed out but it seems that you have filament voltage for the rectifier so the transformer is okay. Perhaps there is a jumper that sends the filament voltage from tube to tube that is failed. Is the power supply on a different board than the pre-amp stuff. If so there is probably a twisted pair connecting the filament voltage from one board to the next. I would check those connections first.
    avatar
    billinrio

    Posts : 8
    Join date : 2018-01-03

    Re: PAS-2 woes

    Post by billinrio on Thu Jan 04, 2018 2:10 pm

    Many thanks for the very prompt replies.  The line voltage at the wallplate here is 132VAC, 60Hz, but I'm powering my equipment from a variac which is set at 117VAC.  
    Suggestion (a):  I assume you refer to the filament pins of all of the 5 tubes. I will check all tube pin connections for broken wires/ cold solders / poor connections.
    Suggestion (b):  there is no longer a selenium device, since I removed it when installing Roy's regulated power supply board.  Roy's board has four diodes (D1-D4). There are also two other diodes, one running off pin 1 and one running off pin 6 of the 12X4 tube. How do I check them?
    Suggestion (c): The 12AX7 tubes I'm using all read as normal on my tube checker.  Just to be sure, I tried replacing them with other 12AX7 tubes, to no effect.
    Suggestion (d):  Roy's board has no 2,000 caps.  The two larger ones on his board (C4 & C5) are 3300 uF 25v.  How do I check if they're open/shorted?
    Suggestion (e):  I'm not sure about a regulator chip on the mod board; whether there is one, and if so, where it would be.
    I've scanned the schematic and drawing of the PS board, but see no way to include attachments in this message.  Apparently, because I'm new to this forum I'm not yet allowed to include attachments in my messages. i've uploaded the two scans to my Photobucket account, and tried to give you the links but that doesn't work either.

    avatar
    billinrio

    Posts : 8
    Join date : 2018-01-03

    Re: PAS-2 woes

    Post by billinrio on Thu Jan 04, 2018 2:20 pm

    billinrio wrote:Many thanks for the very prompt replies.  The line voltage at the wallplate here is 132VAC, 60Hz, but I'm powering my equipment from a variac which is set at 117VAC.  
    Suggestion (a):  I assume you refer to the filament pins of all of the 5 tubes. I will check all tube pin connections for broken wires/ cold solders / poor connections.
    Suggestion (b):  there is no longer a selenium device, since I removed it when installing Roy's regulated power supply board.  Roy's board has four diodes (D1-D4). There are also two other diodes, one running off pin 1 and one running off pin 6 of the 12X4 tube. How do I check them?
    Suggestion (c): The 12AX7 tubes I'm using all read as good on my tube checker.  Just to be sure, I tried replacing them with other 12AX7 tubes, to no effect.
    Suggestion (d):  Roy's board has no 2,000 caps.  The two larger ones on his board (C4 & C5) are 3300 uF 25v.  How do I check if they're open/shorted?
    Suggestion (e):  I'm not sure about a regulator chip on the mod board; whether there is one, and if so, where it would be.
    I've scanned the schematic and drawing of the PS board, but see no way to include attachments in this message.  Apparently, because I'm new to this forum I'm not yet allowed to include attachments or links in my messages.  i've uploaded the two scans to my Photobucket account, and tried to give you the links but that doesn't work either.

    avatar
    Peter W.

    Posts : 577
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: PAS-2 woes

    Post by Peter W. on Thu Jan 04, 2018 2:31 pm

    Please contact me off-group via the personal message function. I am sure we can work this through.
    avatar
    erhard-audio

    Posts : 14
    Join date : 2017-04-07
    Age : 59
    Location : SW Coast OR

    Re: PAS-2 woes

    Post by erhard-audio on Thu Jan 04, 2018 2:32 pm

    billinrio wrote:Many thanks for the very prompt replies.  The line voltage at the wallplate here is 132VAC, 60Hz, but I'm powering my equipment from a variac which is set at 117VAC.  
    Suggestion (a):  I assume you refer to the filament pins of all of the 5 tubes. I will check all tube pin connections for broken wires/ cold solders / poor connections.
    Suggestion (b):  there is no longer a selenium device, since I removed it when installing Roy's regulated power supply board.  Roy's board has four diodes (D1-D4). There are also two other diodes, one running off pin 1 and one running off pin 6 of the 12X4 tube. How do I check them?
    Suggestion (c): The 12AX7 tubes I'm using all read as normal on my tube checker.  Just to be sure, I tried replacing them with other 12AX7 tubes, to no effect.
    Suggestion (d):  Roy's board has no 2,000 caps.  The two larger ones on his board (C4 & C5) are 3300 uF 25v.  How do I check if they're open/shorted?
    Suggestion (e):  I'm not sure about a regulator chip on the mod board; whether there is one, and if so, where it would be.
    I've scanned the schematic and drawing of the PS board, but see no way to include attachments in this message.  Apparently, because I'm new to this forum I'm not yet allowed to include attachments in my messages.  i've uploaded the two scans to my Photobucket account, and tried to give you the links but that doesn't work either.


    Hi,

    please 'pm' me, and we'll get your PAS back up and running!
    I took over the PAS upgrade kit business from Roy.

    cheers
    Holger
    avatar
    PeterCapo

    Posts : 476
    Join date : 2008-12-05

    Re: PAS-2 woes

    Post by PeterCapo on Thu Jan 04, 2018 2:55 pm

    billinrio wrote:The line voltage at the wallplate here is 132VAC, 60Hz, but I'm powering my equipment from a variac which is set at 117VAC.

    How do you set your variac to 117VAC output? Don't rely on the scale or meter built onto/into the variac. They are calibrated for only one assumed level of AC mains from your wall socket that cannot be predicted by the variac's manufacturer.

    The output of the variac must be set with an external measuring device like a handheld meter, and under the load of actual operating conditions. A power strip comes in handy for this - plug power strip into variac's output, adjust variac output with handheld meter reading one of the sockets on the same power strip.
    avatar
    corndog71

    Posts : 583
    Join date : 2013-03-19
    Location : It can get windy here

    Re: PAS-2 woes

    Post by corndog71 on Thu Jan 04, 2018 3:11 pm

    Sadly, unless you're willing to pay, photobucket is no longer useful for linking pics.
    avatar
    billinrio

    Posts : 8
    Join date : 2018-01-03

    Re: PAS-2 woes

    Post by billinrio on Thu Jan 04, 2018 3:19 pm

    PeterCapo wrote:
    billinrio wrote:The line voltage at the wallplate here is 132VAC, 60Hz, but I'm powering my equipment from a variac which is set at 117VAC.

    How do you set your variac to 117VAC output?  Don't rely on the scale or meter built onto/into the variac.  They are calibrated for only one assumed level of AC mains from your wall socket that cannot be predicted by the variac's manufacturer.

    The output of the variac must be set with an external measuring device like a handheld meter, and under the load of actual operating conditions.  A power strip comes in handy for this - plug power strip into variac's output, adjust variac output with handheld meter reading one of the sockets on the same power strip.

    I completely agree with you, and what you describe is exactly what I always do. My variac ouputs into a power strip into which I plug in my tube equipment. The AC voltage coming out of the power strip, as measured by my Wavetek DM5XL, is 117v.
    avatar
    PeterCapo

    Posts : 476
    Join date : 2008-12-05

    Re: PAS-2 woes

    Post by PeterCapo on Thu Jan 04, 2018 3:35 pm

    Going forward, should you continue to experience difficulty as you described in Post n°1, you might consider reverting to the original Dynaco configuration.  The reason I mention this is because the original Dynaco manuals and their accompanying pictorial wiring diagrams were very thorough and did not assume a considerable level of skill on the part of the kit builder; pretty much everything was explained and it was tough to go wrong.  Many if not all of the original parts are, if need be, replaceable 1:1 with new parts from sources like www.dynakitparts.com Triode USA and other sellers.
    avatar
    billinrio

    Posts : 8
    Join date : 2018-01-03

    Re: PAS-2 woes

    Post by billinrio on Thu Jan 04, 2018 4:12 pm

    I agree with you that the Dynaco manuals and pictorials were quite thorough.  However, for kit builders, one thing that they did lack was that whenever a build manual said to  solder it didn't indicate how many connections should be at the solder joint in question.  In contrast, Eico kits did do this (e.g.,"solder 3") and that was always very helpful as extra protection against making mistakes.
    As for "revert to the Original Dynaco configuration", that's easy in the U.S., but in Brazil it would be very difficult.  Here, any Dynaco replacement part has to be imported.  The duty on most imports in Brazil is 150% of the declared value.  By the time you add international shipping to this, the price becomes prohibitive. Spare parts from other Dynaco owners are non-existent because other Dynaco owners are non-existent.  My PAS2 is very probably the only one in town (and it's a big town).
    avatar
    PeterCapo

    Posts : 476
    Join date : 2008-12-05

    Re: PAS-2 woes

    Post by PeterCapo on Thu Jan 04, 2018 4:16 pm

    Yikes.
    avatar
    billinrio

    Posts : 8
    Join date : 2018-01-03

    Re: PAS-2 woes

    Post by billinrio on Thu Jan 04, 2018 4:17 pm

    corndog71 wrote:Sadly, unless you're willing to pay, photobucket is no longer useful for linking pics.

    I pay a monthy fee to Photobucket. I need to have it because of my classical music blog. But if I give you a link to an image I keep in Photobucket,
    you pay nothing to download it.
    avatar
    Peter W.

    Posts : 577
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: PAS-2 woes

    Post by Peter W. on Thu Jan 04, 2018 4:41 pm

    OK - I am going to issue, unilaterally, a STOP WORK order until we get to the bottom of the 30% higher voltages than stock. If I had to diagnose from several thousand miles, I would expect that the modified power-supply is DOA and is passing what would be expected when running wide open.

    https://www.ebay.com/itm/HV-B-And-Heater-Capacitor-Power-Supply-Board-For-DYNACO-PAS2-PAS3-Pre-Amplifier/391736076646?hash=item5b354a2966:g:uhYAAOSwZQRYfb2q  

    While not endorsing this option, I am presently running it in my "extra" PAS-3X - which is the one I use to test various options and configurations. It runs cool, provides spot-on down-line voltages (118 at the wallplate) and has caused me no regret to date. It also eliminates the 12X4, taking that load off the filament winding. I pick this of several options as it all comes from Hong Kong, and shipping is irrespective of destination country.

    With all that in mind and a potential cure a short time away, let's figure out why those voltages are so high before going any further. This will be a tubes-out testing regimen until the cause/culprit is discerned.

    Starting with verifying your VOM/DVM against a known voltage to eliminate it as the source of bad readings. I admit to being spoiled with all sorts of meters right-to-hand including an ESR meter. But, you can test capacitors with a VOM in the resistance setting, however, they must be out-of-circuit.

    What will happen is that the meter will go to low resistance, then slowly climb to infinity, or something in excess of several megs. If it does not, the cap is leaky, full stop. This is not a 100% reliable test, just an indicator-test. But it does separate the wheat from the chaff at least.

    Diodes can be tested, more-or-less in circuit with the diode setting on your meter. High in one direction, not so high in the other. Look for parallel resistors as that will be the reading in one direction.

    How do "gifts" work via your customs service? Were something sent to you with a 'no-value' or 'gift' declaration, are their duties or tariffs?
    avatar
    peterh

    Posts : 892
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: PAS-2 woes

    Post by peterh on Thu Jan 04, 2018 5:52 pm

    I see that erhard also have a psu board :
    http://www.erhard-audio.com/Power_Supply_Kits.html
    it cost usd35 , add postage and customs and sure it will be costly. But you will have a "simple board"
    where the components are of modern type that you should be able to find in brazil. Just replace .

    ( unless the present board could be fixed, that would be the best of course)
    avatar
    billinrio

    Posts : 8
    Join date : 2018-01-03

    Re: PAS-2 woes

    Post by billinrio on Thu Jan 04, 2018 7:20 pm

    Peter W. wrote:OK - I am going to issue, unilaterally, a STOP WORK order until we get to the bottom of the 30% higher voltages than stock. If I had to diagnose from several thousand miles, I would expect that the modified power-supply is DOA and is passing what would be expected when running wide open.

    ebay dot com/itm/HV-B-And-Heater-Capacitor-Power-Supply-Board-For-DYNACO-PAS2-PAS3-Pre-Amplifier/391736076646?hash=item5b354a2966:g:uhYAAOSwZQRYfb2q  

    While not endorsing this option, I am presently running it in my "extra" PAS-3X - which is the one I use to test various options and configurations. It runs cool, provides spot-on down-line voltages (118 at the wallplate) and has caused me no regret to date. It also eliminates the 12X4, taking that load off the filament winding. I pick this of several options as it all comes from Hong Kong, and shipping is irrespective of destination country.

    With all that in mind and a potential cure a short time away, let's figure out why those voltages are so high before going any further. This will be a tubes-out testing regimen until the cause/culprit is discerned.

    Starting with verifying your VOM/DVM against a known voltage to eliminate it as the source of bad readings. I admit to being spoiled with all sorts of meters right-to-hand including an ESR meter. But, you can test capacitors with a VOM in the resistance setting, however, they must be out-of-circuit.

    What will happen is that the meter will go to low resistance, then slowly climb to infinity, or something in excess of several megs. If it does not, the cap is leaky, full stop. This is not a 100% reliable test, just an indicator-test. But it does separate the wheat from the chaff at least.

    Diodes can be tested, more-or-less in circuit with the diode setting on your meter. High in one direction, not so high in the other. Look for parallel resistors as that will be the reading in one direction.

    How do "gifts" work via your customs service? Were something sent to you with a 'no-value' or 'gift' declaration, are their duties or tariffs?

    Thanks for your suggestions and tips.  I have 3 different meters for testing voltage (2 digital, 1 analog); so I assume that if they all read the same line voltage, I can be pretty sure about what's coming out of the wall.
    I also have a capacitance meter, recently acquired.  The brand is UYIGAO, model UA6013L, which appears to be a decent device. Googling the name and model will show what it is.  It's made in China (but what isn't nowadays?).
    The people at Brazilian Customs are pretty much on to the "gift" ploy, and will charge for anything of any value sent to me by a company, regardless of what's declared on the export sticker; if coming from a private party they will allow in without charge anything with a value (their determination) of under USD50. However, they do include the cost of postage in their value calculation. In short, this is a high-tariff, extremely protective economy, and living here makes one appreciate (and envy) the availability of inexpensive imports taken for granted by most Americans.
    avatar
    peterh

    Posts : 892
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: PAS-2 woes

    Post by peterh on Fri Jan 05, 2018 5:38 am

    You have  "utsource.net"  ( located in brazil ) for components.

    Also see http://www.usadobrasil.com.br/dynaco for some dynaco related ads
    avatar
    billinrio

    Posts : 8
    Join date : 2018-01-03

    Re: PAS-2 woes

    Post by billinrio on Fri Jan 05, 2018 8:22 pm

    peterh wrote:You have  "utsource dot net"  ( located in brazil ) for components.
    Also see .usadobrasil dot com.br/dynaco] .usadobrasil dot com.br/dynaco for some dynaco related ads

    Unfortunately, these kinds of sites, which are quite common here, aren't of much use for residents of Brazil. In fact, they aren't even really Brazilian. They claim to be able to obtain products (actually, any product, including electronics) for us, from abroad, but we end up paying the exorbitant customs duties, plus expensive shipping anyway.  So, it's not really much of a deal.  Other such links merely redirect us to eBay, Digi-Key, etc., pages in the U.S., to which the same high shipping/high duty problems apply.
    avatar
    Peter W.

    Posts : 577
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: PAS-2 woes

    Post by Peter W. on Mon Jan 08, 2018 10:36 am

    Based on a side-bar conversation with Bill, and a look-over of the power-supply board, I am suspecting that one winding of the filament transformer is shot. What is there is a Triad FP24-500 dual-output 12 & 12 @ 500 each, or 24 @ 500, or 12=12 @ 1A.

    http://www.mouser.com/ds/2/410/media-1068114.pdf    

    As there is filament voltage to the 12X4, and none to the diodes feeding the 12AX7s, that is where I am going.

    NOTE: The schematic shown with the power-supply board shows one (1) transformer, feeding a nominal 12V - unrectified to the 12X4 and rectified & filtered to the 12AX7s.

    Suggestions/thoughts?

    Sponsored content

    Re: PAS-2 woes

    Post by Sponsored content


      Current date/time is Tue Jan 16, 2018 9:45 am