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    Please help me finish my PAS-2 upgrade

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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Tue Dec 04, 2018 8:53 pm

    A replacement board of the same kind may not be necessary and will not help if the problem is a defect in the design of the board that may have gone uncorrected.  And, it is not clear that your board or its parts are defective.

    The diodes are for the filament circuit only, so I don't think the diodes are part of the problem.

    With axial leaded PCB parts, you can usually desolder and lift one lead at a time.  This isn't very feasible with radial or snap-in leads, and this makes it difficult to remove them.  The best way I know of to remove radial-type leads is to use two soldering irons at the same time and melt the solder on both leads simultaneously, then have someone else standing by to pull out the part while the solder is melted.  But, you'll likely get solder splashes which could short out other things on the board, and this makes for more work to correct.

    If it were mine, I would not want to proceed with buying anything else until I could try to narrow the problem down.  Guesswork should be minimized.  But, I am not sure that's feasible in this case.  A working knowledge of electronics and of the PAS circuit would really come in handy.  Without that, we could be at this forever.  You could try buying a different cap board or a different transformer or something, but I'd hate to see you spend the money and still have problems.

    Have you thought about sending it out to someone to work on for you?
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Tue Dec 04, 2018 10:37 pm

    Thanks for the "graphic" description of  the problems/dangers with unsoldering radial caps.

    I would be very willing to send it to someone to work on it, but that would mean shipping it internationally. And that's out, since the freight alone would come to more than the preamp is worth.
    I can find no qualified techs here.  I live in a city with a population of 1.5 million, and I can bet that mine is the only Dynaco equipment in town.  When I Google "Dynaco repair / restoration" (in Portuguese, of course), I get no hits from anywhere in the country.  The Brazilian equivalent to eBay is called "MercadoLivre".  A search there for "Dynaco" gives me just one hit  - some guy a thousand miles from here trying to unload a Stereo 120 for $600.  So, I'm not going to get any local help to narrow this problem down.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Tue Dec 04, 2018 11:44 pm

    My suggestion would be to try to streamline the way you do things when someone is trying to help you remotely, such as in forums.  For instance, you might try to study some basic electronics and how to read schematics at a basic level.  You might also read the manual for your meter to make certain you are using it properly in all situations where you need it.  Use a second meter to check measured values.  Studying the entire original Dynaco PAS manual is, IMO, essential, as it should help you to become more familiar with the PAS.  IMO, these are basic things that need to be understood.

    Otherwise, I guess you are left with just changing some parts and hoping it will work out.  But, this requires PCB reworking skills and proper equipment to do it without damaging the PC board.  And, you need to be able to recognize correct replacement parts and make sure they make it into the correct locations on the board, properly oriented, and properly soldered.  It's detailed work, with plenty of opportunities to do things the wrong way.

    If it were mine, I'd want to want to perform continuity checks for all the circuit pathways starting with the cap board, for instance, to see if it matches up with the schematic.  However, it is rather difficult to guide someone remotely though this level of detail, especially if you might not be reasonably proficient at reading the schematic and understanding if it matches your continuity checks.

    Or, you could go over the wiring for the umpteenth time.  Or, maybe post somewhere else to see what ideas others would have.  You would certainly need to totally refrain from going off-script and making independent decisions like running the preamp at 127 VAC mains, especially while there are bugs that need to be worked out, or maybe other things you might be inclined to do without prior discussion with someone.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Dec 05, 2018 12:00 am

    Admittedly, I am running short on ideas for an easy fix.  Since pins 1 of both tube sockets on PC5 are running too low, you could try verifying the values of the resistors off of pins 1 for both sockets on PC5.  How to do this...  You could look at their color bands.  But, some colors can be mistaken for others.  If this might be the case, then, to be certain, one end of each resistor would need to be unsoldered and the lead lifted clear of contact with the pad or adjacent trace.  Then measure the resistors (again, with one lead hanging in air).  What we want here is certainty of the values of those two resistors.  Crosscheck readings with a second meter.  Note that your meters may have some sort of procedure for zeroing them before taking measurements.  Please zero them, accordingly, then take measurements.

    If the resistors are okay, then you might try different tubes, as I believe you had mentioned.

    If new or different tubes do not help, then I suppose you'd want to decide on whether you want to try to examine your existing cap board and changing the capacitors, or just buy a different cap board, drop it in and give it a try.

    But, right now you might try focusing on the two resistors on PC5 and then the tubes.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Dec 05, 2018 9:16 am

    First of all, I want to thank you sincerely for your patience and your time spent on this thread. You are a generous guy, and make me feel that you "have my back" and thus a bit less isolated here with this problem.
    I have lots of tube equipment, including a pair of factory Dynaco MKIV's, and a pair of Heathkit W5M's (with the Peerless 16458 transformers) that I've collected beginning with my teenage years in the U.S. While I was there, it was always easy to buy tubes, quality caps and resistors, and whatever I needed to keep the equipment functioning.  My soldering skills are quite adequate, I think, and I have a good soldering station that allows me to control the temperature of the tip. I use desoldering wick, brought from abroad, of which I have a good supply. My meter is a simple one - a Wavetek DM5XL. I no longer have its manual, lost somewhere during various international moves, and I've searched for, but haven't found a copy on the internet.
    I speak, read, and write a number of languages (I'm a linguist), but schematics are in a "language" that I've never mastered, and I much admire those who understand them (can one begin to learn this at 75?)
    I will pursue verifying the values of the resistors off of pins 1 for both tubes on PC5, and see what I might discover.
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    DynakitParts
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    Re: Please help me finish my PAS-2 upgrade

    Post by DynakitParts on Wed Dec 05, 2018 10:14 am

    Billinrio,
                I have been following all these Posts and I must commend Peter for his continued efforts to help a fellow member. This is what this Forum is all about.
    Anyway...do not overlook the possibility that the power transformer is the culprit. If you can...Measure all the secondary voltages of this power transformer under "No Load"
    with your line voltage set a 120 vac. Let us know what you measure.

    Regards....Kevin
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Dec 05, 2018 10:18 am

    DynakitParts wrote:Billinrio,
                I have been following all these Posts and I must commend Peter for his continued efforts to help a fellow member. This is what this Forum is all about.
    Anyway...do not overlook the possibility that the power transformer is the culprit. If you can...Measure all the secondary voltages of this power transformer under "No Load"
    with your line voltage set a 120 vac. Let us know what you measure.

    Regards....Kevin

    Thanks Kevin.  I'll check the transformer.  I just assumed that since it's new, it's good, and thought that this was confirmed by the fact that that all of the 12X4 pinouts are correct.
    What are the "secondary voltages" compared to what, I guess, would be "primary voltages?  
    I assume that by "under no load" you mean that I should take the transformer's ouput leads out of the circuit.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Dec 05, 2018 1:53 pm

    Your 12X4 readings we have seen thus far fall into the 20% tolerance range that Dynaco mentioned in the manual.  They are nevertheless kind of low.  For instance, when I take measurements in my PAS, the readings at the 12X4 (from the power transformer) are much closer to spec.  

    I had considered that some problem you are having downstream (cap board, possibly PCBs 5 or 6, or some other unknown factor) might be dragging down your readings.  But, you should definitely take Kevin's suggestion, as the power transformer could be the problem.  Just kind of hard to tell for sure in the midst of everything.

    Keep in mind that the Triode USA power transformer is not precisely the same as the original Dynaco transformer.  Where the original spec calls for 335 VAC from each red lead to ground (red-yellow grounded center tap lead), the Triode USA transformer specs at 330 VAC.  Not a big difference, but worth noting.  The Triode USA transformer's filament spec at 12 VAC is also higher than the original I believe, but Kevin would know that better than I.

    Make sure you take proper precautions not to get shocked, or worse, trying to take measurements on the disconnected secondary leads (or anything else pertaining to this project, overall).  It is assumed that you have conducted your own study of safe practices around dangerous voltages and you are aware of how to protect yourself.


    Last edited by PeterCapo on Thu Dec 06, 2018 1:12 am; edited 2 times in total (Reason for editing : Review post for accuracy.)
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Dec 05, 2018 3:10 pm

    For my transformer (http://www.triodestore.com/pa522.html), then, I should de-solder the red leads from pins 1 and 6 of the 12X4, and remove the two blue transformer leads from the cap board.  I assume that the transformer's ground wire (red/orange) can remain connected to the preamp.  Then, having powered up the preamp at 120VAC, I will measure the VAC voltage from each red wire to ground, (which should be 330VAC) and the VDC of each transformer blue lead to ground (which should be 12 VDC).  For the meter, I'll use cables with alligator clips on the probe ends, which seems to me safer than trying to touch the transformer's wires with a needle probe.


    Last edited by billinrio on Wed Dec 05, 2018 5:17 pm; edited 1 time in total
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    DynakitParts
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    Re: Please help me finish my PAS-2 upgrade

    Post by DynakitParts on Wed Dec 05, 2018 4:19 pm

    I believe you can just remove the rectifier tube, and all the other tubes on PC-5 & PC-6 plus the pilot lamp to reduce he current load as opposed to de-soldering any leads for you to take these measurements. I do not have a PAS unit in here to confirm this (I'm out of the office) but I believe this to be correct.

    Kevin
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Dec 05, 2018 4:32 pm

    Thank you, Kevin, it is much easier pulling the 12X4.  

    The filament electrolytics should still charge even with the bulb removed, correct?  I wonder if the voltage ratings of the filament electrolytics might be exceeded without the load from the 12AX7s?
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Dec 05, 2018 5:25 pm

    I received Kevin's message after I had already unsoldered the to leads to the 12X4. At 120VAC measured out of the variac, I read 324VAC at both of those leads. I will now solder them back to the 12X4. How is the voltage from the blue transformer leads measured?
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    DynakitParts
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    Re: Please help me finish my PAS-2 upgrade

    Post by DynakitParts on Wed Dec 05, 2018 5:27 pm

    Peter,
    I would expect all the secondary voltages to be much higher with the tubes removed but you are correct about the charging of the electrolytics. I just wanted to make this an easy task for Bill to measure these voltages. I'm suspect of the Triode power transformer....as I'm suspect of anything these guys now currently sell. I will say no more but you most likely know what I mean.

    Kevin
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Dec 05, 2018 5:46 pm

    Yes, indeed. Thank you, Kevin.
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    DynakitParts
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    Re: Please help me finish my PAS-2 upgrade

    Post by DynakitParts on Wed Dec 05, 2018 6:27 pm

    May I call you Bill?
                               Voltage readings on the high voltage secondary's should be about 345 vac (Red to Red/Yellow) no load volts.... full load volts should measure about 330 vac.

    Measure the filament voltage across both Blue Leads....no load volts should be about 12 vac.....full load volts about 10.9 vac

    Keep in mind that our PA 211 transformer was wound to closely match the secondary voltages of the original Dynaco PA 211 at 120 vac. We did some comparison testing of Triode's version and found it to be also quite close to the original voltage specs but the current rating of this unit was a bit low @ 800 mA. We raised this on our PA-211 version to 1.25 A which allowed this unit to run somewhat cooler than the original. I have some data in support of this somewhere in the archives.

    Anyway...It appears to me that the secondary (NLV) voltages are about 20 volts too low...Defective transformer?

    Kevin
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Dec 05, 2018 7:39 pm

    Of course you can. All of my friends call me Bill (although in Brazil it comes out "Be-uw" ( at the end of words,Portuguese doesn't have our "L" sound with the tongue touching on the front of the palate).

    I've already re-connected the red transformer wires to pins 1 & 6 of the rectifier tube.
    I measured 324VAC from the unsoldered red leads to ground. Should I have involved the red/yellow transformer ground lead?

    Measuring the filament voltage across the Blue transformer leads, I get 11.7 vac with a 120vac input.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Dec 05, 2018 8:45 pm

    billinrio wrote:I've already re-connected the red transformer wires to pins 1 & 6 of the rectifier tube.
    I measured 324VAC from the unsoldered red leads to ground. Should I have involved the red/yellow transformer ground lead?

    Measuring the filament voltage across the Blue transformer leads, I get 11.7 vac with a 120vac input.

    As I recall, you left the red-yellow lead connected to the ground connection point on your chassis, correct? If so, that was fine. I take it that you measured each red lead in turn to ground, correct?

    The blue leads don't really matter at this point. Given the readings from the red leads, it looks like you need a new transformer.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Dec 05, 2018 8:58 pm

    Yes, Peter, I did leave the yellow-red transformer lead connected to ground on the chassis.  And I did measure each read lead to ground, and got that 324vac result for each.
    It's very disappointing to discover that a new component that I purchased from what I thought was a reliable source, is defective.  I don't know whether Triode backs up their products with any kind of guarantee. I purchased the transformer, and the cap board, and the new PC boards, when I was in Portland OR in April visiting family. It's only now that I have been able to be back in Brazil with access to my PAS2 that I have tried to install the transformer with the results we know. Not being in the U.S. makes everything a bit complicated.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Dec 05, 2018 9:07 pm

    You might still inquire with Triode USA.  If they don't help, you can try asking the credit card company for help, though too much time may have passed for this.

    Sorry for not figuring this out sooner.  Kevin is the "man of the hour."
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    DynakitParts
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    Re: Please help me finish my PAS-2 upgrade

    Post by DynakitParts on Wed Dec 05, 2018 9:23 pm

    Bill,
    It's now more than (6) months since Triode sold you this transformer. I doubt you will be getting anything back from them although if you made this purchase with a credit card you may have some recourse as Peter suggested. Good luck.

    Email me if you decide to purchase a replacement transformer. Another option would be to purchase a regulated power supply from Erhard Audio.

    Best regards,

    Kevin

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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Dec 05, 2018 9:32 pm

    I just read the description on the Erhard Audio webpage, and if I correctly understood, his regulated supply won't work with the original PC5 and 6 circuits? http://www.erhard-audio.com/Power_Supply_Kits.html
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    DynakitParts
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    Re: Please help me finish my PAS-2 upgrade

    Post by DynakitParts on Wed Dec 05, 2018 9:53 pm

    Peter,
    When in doubt....read the instructions....you are correct. I trust Bill is still following all of this?

    Kevin
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Dec 05, 2018 10:03 pm

    DynakitParts wrote:Bill,
         It's now more than (6) months since Triode sold you this transformer. I doubt you will be getting anything back from them although if you made this purchase with a credit card you may have some recourse as Peter suggested. Good luck.

    Email me if you decide to purchase a replacement transformer. Another option would be to purchase a regulated power supply from Erhard Audio.  

    Best regards,

    Kevin


    According to the description of the transformer on the Triode USA site (http://www.triodeelectronics.com/pa522.html)
    "Secondary is 330-0-330VAC at 15 ma DC rectified current, plus 12V at 800ma for filaments & pilot lamp. Primary is dual 120/240VAC 50/60 Hz."
    Are my measurements far from these specs?
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    DynakitParts
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    Re: Please help me finish my PAS-2 upgrade

    Post by DynakitParts on Wed Dec 05, 2018 10:59 pm

    Bill,
    The 330-0-330 secondary voltage spec is based on full load. You measured 324-0-324 vac under no load. Figure about a 20 to 25 volt drop under full load.

    So...the high voltage secondary under no load should have been roughly 350-0-350 vac to 355-0-355 vac.

    The transformer appears to be defective. Why did they send you a dual voltage unit to begin with...did you request this?

    Kevin



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    erhard-audio

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    Re: Please help me finish my PAS-2 upgrade

    Post by erhard-audio on Wed Dec 05, 2018 11:13 pm

    PeterCapo wrote:I just read the description on the Erhard Audio webpage, and if I correctly understood, his regulated supply won't work with the original PC5 and 6 circuits?  http://www.erhard-audio.com/Power_Supply_Kits.html

    that is correct. The original Dynaco filament supply for the PC6 has one end tied to ground. The regulated DC filament power supply will not work with one end of the filaments tied to ground. It could work, but one would need to mod the pcb, cut tracks...too messy. Very Happy

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