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    Please help me finish my PAS-2 upgrade

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    billinrio

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    Please help me finish my PAS-2 upgrade

    Post by billinrio on Mon Nov 26, 2018 8:36 pm

    It's been quite a while, but I've finally entered the home stretch in upgrading my PAs-2. I've installed new boards (from Erhard), a new transformer (from Triod),
    and a capboard from tekdevice. I'm now finishing the project by re-connecting the selector switch, using the original manual as a guide.
    I just came up against the following: on page 12, instruction No.24 states: "Connect the short black wire from wafer C lug #3 to PC-6 eyelet #11 (S). (In addition to the wire already
    soldered below the board)". Well, I see no wire "already soldered below to the board" at eyelet #11 on PC-6. When I search through the manual to find a reference to such
    a connection, i find nothing else. As far as I can tell, the quote above, from page 12, is the only reference in the manual to that particular eyelet. Am I missing something?
    Is the manual wrong? Thanks very much for any help.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Mon Nov 26, 2018 11:03 pm

    See step 17, page 7.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Tue Nov 27, 2018 6:52 am

    PeterCapo wrote:See step 17, page 7.

    Quiet right. My PAS-2 manual is in .pdf format.  So much for my relying on the "find" command of Adobe Acrobat Pro.  
    Because the original manual deals with installing and wiring a quad capacitor and a selenium rectifier, and since I have discarded these in favor of a new cap board, I assumed that many of the original wiring instructions no longer apply. For example, many of the main chassis wiring instructions in the manual (including step 17, page 7), refer to running wires to the ground lug of the quad capacitor.   I have retained the quad cap, unwired, for aesthetic purposes. Should I still use its grounding lug?  Now I'm not sure which original grounding instructions still apply and which don't.

    In the same vein, regarding wiring this unit, Roy Mottram wrote, "In the original PAS amp, PC6 eyelets 4 and 11 have 2 separate connections to chassis ground. When I service these preamps I cut both
    ground wires out and run a single ground connection to eyelet 10, and then connect eyelet 4 and eyelet 11 together with a wire".  Should I do this? If so, which "chassis ground" should I use?


    Last edited by billinrio on Tue Nov 27, 2018 5:27 pm; edited 6 times in total (Reason for editing : clarification)
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Tue Nov 27, 2018 7:24 am

    Here are a couple photos. Please let me know if anything looks out of place.

    "


    Last edited by billinrio on Wed Nov 28, 2018 9:41 am; edited 4 times in total
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Tue Nov 27, 2018 9:08 am

    "
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Nov 28, 2018 2:45 am

    billinrio wrote:
    PeterCapo wrote:See step 17, page 7.
    Because the original manual deals with installing and wiring a quad capacitor and a selenium rectifier, and since I have discarded these in favor of a new cap board, I assumed that many of the original wiring instructions no longer apply. For example, many of the main chassis wiring instructions in the manual (including step 17, page 7), refer to running wires to the ground lug of the quad capacitor.   I have retained the quad cap, unwired, for aesthetic purposes. Should I still use its grounding lug?  Now I'm not sure which original grounding instructions still apply and which don't.

    Certain parts of the original assembly instructions may not apply in the sense of doing step-by-step assembly if you're substituting a cap board for the quad cap and filament supply.  But, electrically, the necessary connections still need to be made.  I am not too familiar with the new parts you are installing.  If they comprise a different circuit from the original Dynaco PAS, then I'm not sure what to tell you except go back to whomever you bought them from and ask for some guidance, or maybe someone here will know about them, specifically.  But, I am sure they still need proper grounding even if they are different.

    For a cap board intended to emulate, or duplicate, the original Dynaco circuit, then from an electrical standpoint the connections called-for in the Dynaco manual still have to be made in some way.  The quad section capacitor provided a grounding point for the circuit.  If the quad cap is not used, then you need to establish a ground point in relation to the cap board and then make the connections to it that would have gone to the quad cap ground.  When I installed my cap board, I picked a convenient hole in the chassis and bolted several ground lugs to it and attached the ground wires there.  I still have some hum, though not enough to be bothersome.  It might be due to wire routing, but I must admit that grounding can be vexing.

    Whichever wires were eliminated by disconnecting original parts need to find their equivalent connection with the new parts.  Ground loops could be an issue.  The cap board I used has its ground plane in contact with the standoff it mounts upon.  I therefore used a nylon standoff in an effort to reduce ground loop.  Anyway, as I have said in other posts online, cap boards can offer performance advantages, but you can run into complications with the grounding.

    billinrio wrote:
    PeterCapo wrote:See step 17, page 7.
    In the same vein, regarding wiring this unit, Roy Mottram wrote, "In the original PAS amp, PC6 eyelets 4 and 11 have 2 separate connections to chassis ground. When I service these preamps I cut both ground wires out and run a single ground connection to eyelet 10, and then connect eyelet 4 and eyelet 11 together with a wire".  Should I do this? If so, which "chassis ground" should I use?

    It would be interesting to know if Roy measured a reduction in noise doing it that way.  Without knowing this, then I'd say either way will work.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Nov 28, 2018 6:35 am

    Thanks very much for your response.  In regard to the cap board, I would like to attach its written instructions and schematic, but this message editor doesn't seem to allow for attachments, so I'll include them as images.  The instructions, coming from China, are in a sufferable English. They mention grounding, but I find the language confusing. Should I make the screw to chassis connection of the cap board as the main ground point for the preamp? Since the quad cap is out of the circuit, should its grounding tab not be used? What do I do with the "Ground" 01 and 02 connections on the cap board?  The schematic, for those able to understand it (I can't include myself in this privileged group), may be more edifying. " />


    Last edited by billinrio on Wed Nov 28, 2018 9:43 am; edited 7 times in total
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Nov 28, 2018 6:38 am

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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Nov 28, 2018 10:23 am

    It looks like it recreates the original PAS power supply.  With regard to the grounding "instructions," my interpretation is as follows...

    Where it says "make sure the mounting hole is SHORT with chassis - 0 ohm," it suggests that the cap board has a ground plane that its metal, mounting standoff, or screw, will be in contact with.  And, you want to make sure the cap board's ground plane is a dead short to the chassis via the mounting standoff (which I assume it came with?).  In this case, they're probably expecting that the original ground wires are still all connected to the quad can, and therefore you want a dead short to chassis for the ground plane of the cap board.

    Where it says "if not mount Cap board to chassis, connect a GND wire from PAS2/3 to the GROUND terminal block," I take it as a general note saying that if for whatever reason you don't establish a dead short from the chassis to the cap board's ground plane via a metal standoff, that you can connect to the cap board's ground plane at that terminal block.  The other end of such a wire to the ground terminal block needs to connect to chassis somewhere, such as to where all the other ground wires are connected to chassis.

    Since you appear to have removed all of the ground wires that were going to your quad can, you need to make sure that all of the ground wires that went to the quad can somehow find a connection to the ground plane of the cap board (and also to the chassis).  Think in terms of the ground plane of the cap board substituting for the original grounding at the quad can.  The filaments also need a ground reference, but I assume it is incorporated into the cap board's ground plane.

    So, that's my interpretation of it.  Anyone else, please jump in to confirm or deny.  I would also add that there could be other issues.  Can't promise you that I have thought of everything to look out for.  Since you have removed some of the original wires, I'd go through the entire manual again, step by step, thinking about what each step is connecting and how its equivalent may need to be duplicated given the incorporation of the cap board, with emphasis on each step that involves a ground somewhere.

    BTW, in step # 1, it says to "connect 12X4 pin 7 to CN1 pin 1 (12X4)" with a handwritten [yellow].  What is "yellow" referring to?
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Wed Nov 28, 2018 2:01 pm

    Thank you for the useful information and advice.  
    Yes, the cap board is fastened to the preamp's chassis with a metal standoff tightened from the metal bottom of the chassis with a screw.  When I measure resistance from that screw to the chassis I get a "O" reading.

    I haven't removed all ground connections to the now merely decorative quad cap.  The red/orange ground wire from the transformer is connected to one of those quad tabs (as seen in the photo I included of the bottom of the chassis). Should I move it somewhere else, and try to establish a single ground connection for the preamp?

    The hand-written "yellow" is a reminder that I wrote to myself of the color of the wire I used to connect pin 7 of the 12X4 to the CN1, connection 1 on the cap board (labeled "12X4") as seen the top view photo, close to the transformer, next to the two red wires from the transformer.

    You may have noted in the bottom view that the power supply wires to the transformer (black, black/white, and purple, purple/white) are quite long. I didn't cut them.  Should I?

    I hope I'm not testing your patience with this.  Local help, here in Brazil, is unavailable. The same goes for any e-mail assistance from the Chinese manufacturer of the cap board.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Wed Nov 28, 2018 6:17 pm

    billinrio wrote:I haven't removed all ground connections to the now merely decorative quad cap.  The red/orange ground wire from the transformer is connected to one of those quad tabs (as seen in the photo I included of the bottom of the chassis). Should I move it somewhere else, and try to establish a single ground connection for the preamp?

    A single ground point would be preferable.

    billinrio wrote:You may have noted in the bottom view that the power supply wires to the transformer (black, black/white, and purple, purple/white) are quite long. I didn't cut them.  Should I?

    They could be a source of hum.  I would refer to the original Dynaco manual’s pictorial wiring diagram for guidance in routing wires including such as these carrying AC, like filaments and AC mains.  Shortening them in the process would probably be a good idea but don’t cut yourself too short.  You might need to rework it someday, so leaving some slack would probably be a good idea.

    billinrio wrote:I hope I'm not testing your patience with this.  Local help, here in Brazil, is unavailable. The same goes for any e-mail assistance from the Chinese manufacturer of the cap board.

    Not even close to how my patience is tested by the unfortunate prejudice and misperceptions around the Internet about the original Dynaco circuits.  According to some, you’d think the original Dynacos were the result of an 8th grade science fair project and suitable mainly as audio pablum for newbies to cut their teeth on Rolling Eyes but I digress...

    Glad to help if I can.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Thu Nov 29, 2018 2:05 pm

    I thought I had finished, having checked and completed all of the ground connections indicated in the PAS2 manual.  So I connected the unit to my variac and brought if up slowly to 117V (the line voltage here measures 129V; I'm not sure if it's wise to run that much voltage into equipment that was designed for 117V).
    Anyway, no fire, no smoke.  The new blue LED pilot light glows nicely, and all of the tubes show some glow as well, which I take to mean that at least they are receiving some voltages.  But measuring the tube pin voltages shows  0V in the case for pin 1 on all the tubes.  I note that there are only 3 wires connected to the 12X4 - to pins 3,4, and 7.  Pins 1 and 6 should have connections, right?  The cap board instructions, a photo of which I included in a post above, state "pay attention/make marks for a pair of wires goto (sic) 12X4 heater, transformer supply wires and the wires connects (sic) to PC-5 & PC-6 circuit board".
    My not being able to make sense of that instruction might be the source of my problem.
    I note that there is no reference to the 12X4 tube in the cap board schematic, a photo of which is also above. How to proceed?
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Thu Nov 29, 2018 4:32 pm

    Looks like the board has the option of replacing the 12X4 with solid state diodes (D1 and D2 in the cap board schematic), but your photo does not show such diodes in place (not to be confused with the other two diodes for the filament supply).  Doubt the accompanying instructions covered this with any clarity.

    I am not familiar with the power transformer you are using.  The original schematic shows two red leads off of the high voltage secondary going to 12x4 pins 1 and 6.  Whichever two wires from your transformer correspond to these should be connected to 12x4 pins 1 and 6 respectively (one red lead to each pin - do not connect the pins together).  I think at the moment you have the red leads connected at CN1-2 and CN1-3, which are at open circuit for lack of the aforementioned solid state diodes.

    Please locate the voltage chart in the manual.  It is along the right hand side of the same page as the schematic for the power supply, probably page 11.  Read the notes at the top of the chart.  When you next power it up, bring the variac up slowly and measure all the voltages indicated for the 12X4.  Check the filaments, also, at pins 5 and 9 of all four 12AX7 tubes.  Take these readings at, say, 25%, then 50%, then 75% of full 117VAC mains.  If anywhere along the way the readings exceed the values in the chart by 20% or more, then stop.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Thu Nov 29, 2018 4:43 pm

    Probably should also monitor all four 12AX7 pins 1 and 6 on the way up with the variac...
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Thu Nov 29, 2018 6:09 pm

    Thanks, I've been waiting for your response.  I bought the transformer from Triode.  It's a replica of the original one, in this case they sent me the bi-volt version, which I didn't request, but it's nice, since some parts of the country here supply 220v mains.  Here, it's nominally 127v.  I've now connected the two red transformer leads to pins 1 & 6 of the 12X4.
    I have the preamp's voltage chart in front of me, and I'll connect the variac, bring it up slowly, measuring the voltages of the 12X4 as well as the filament and other voltages of the 12AX7's. I would cross my fingers, but it would be hard to carry out these procedures that way.  Again, thanks.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Fri Nov 30, 2018 1:27 am

    Here are the pinouts @ 127V:

    12X4        
    spec         335 / 0 / 10.5VAC / 0 / 335 / 405
    measured 306 / 0 / 11.4VAC / 0 / 306 / 383

    PC-5 12AX7 (2)

             
    spec         175 / 0 / 1.45 / <1 / 11 / 200 / 0 / 1.25 / 5.5
    measured 116 / 1.5 / 1.0 / 1 / 12.7 / 166 / 0 / 1.30 / 5.8
    measured 123 / 1.6 / 1.0 / 1 / 12.7 / 173 / 0 / 1.23 / 8.2


    PC-6 12AX7 (2)

       
    spec         115 / 0 / .7 / 0 / 11 / 135 / 0 / .8 / 5.5
    measured 136 / 0 / .9 / 0 / -12 / 162 / 0 / 1.2 / 6.2
    measured 132 / 0 / 1.0 / 0 / 15 / 164 / 0 / 1.2 / 7.5

    The 12X4 measurements seem pretty much in the ballpark, but I'm not sure what to make of many of those on the boards, some of which are off by more than 20%, and particularly that -12 on pin 5 of one of the PC-6 tubes.  I've tried a number of tubes, but the pinouts don't change.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Fri Nov 30, 2018 11:34 am

    billinrio wrote:Here are the pinouts @ 127V ...
    Were the readings taken without the variac in use and the PAS plugged directly into 127 VAC mains?  Just to confirm, we'd want the readings while using the variac.

    By the way, I looked up your power transformer and I believe its primary winding is intended for 120VAC, not 117VAC.  So, when using the variac, you'd want to set it for 120VAC.  But, don't go by the scale on the variac.  The best way I know of to adjust the variac is to plug a power strip into the variac's output (socket on the face of the variac), then plug your PAS into the power strip, and then take a measurement with a separate, handheld meter at an unused socket on the power strip and adjust the variac accordingly. Equipment, such as your PAS, plugged into the power strip should be powered on during the fine adjustment of the variac. You should be able to obtain a reliable measurement at the unused power strip socket since it is in parallel with equipment that is plugged into it.

    Please comment on the above.

    The -12 reading on the filament is okay in and of itself.  If you notice in the voltage chart, the reference is +/- 11 VDC.  I'm more interested in the inconsistency among some of the readings, like the 15 Volts at the other filament on PC6, which, other than being inconsistent, is too high.  Pins 1 of the 12AX7s on PC5 are notably low while pins 6 are tolerable.  12.7 for both filaments on PC5 are consistent with each other (good) though a bit high (not unexpected with the replacement of the original selenium rectifier), but then when measured at pins 9 are inconsistent.

    Let's make sure the procedure you're following is verified, such as how the variac is being adjusted and identifying other possible inconsistencies in measuring technique.  Beyond this, a recheck of wiring would be in order, though I suppose you've already gone over it several times.  I'd then look at component values on the cap board, on PC5 and on PC6 compared to the component values in the original schematic.  Are your PC5 and PC6 boards exact reproductions of the originals?

    I may be delayed in responding during the next several days, not sure.  Perhaps someone else will pitch in some ideas, too.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Fri Nov 30, 2018 3:25 pm

    I took your advice and measured by slowly upping the variac voltage, from 30v, to 60v, to 90v, and finally to 120v. The final pinout readings are with the variac connected and at 120v.
    I have been using the variac, attached to a power strip, to power all of my equipment for some time, figuring that I could thus have some control over the varying (and, I think, high, line voltage here.
    Good to know about the +/- indication.  I had assumed that it meant ("more or less").

    I had hoped that with new PC boards (purportedly exact reproductions), a new transformer, and the new  cap board, I would finally have all of the voltages spot on.

    In order to check the components on the cap board it appears that I would have to remove it from its mounting to the chassis in order to access its bottom and the foil strips. I can, of course, with it in place, measure the output voltages from the cap board to PC-5 and PC-6.  Would that be a suitable path to follow? I have contacted the board's seller, Tekdevice.com, and requested that they send
    me the operating output voltages of the board. I don't know if they will respond to my request.

    By the way, all of the tubes check out "good" on my tube tester.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Fri Nov 30, 2018 6:15 pm

    I have to admit to being a bit stymied, especially not having it all in front of me.  I wouldn't start taking things apart yet.

    Measuring the voltages from the cap board for PC5 and PC6 is a fine idea.  Based upon the readings, might it be that you have them in reverse?

    Are all four of the 12AX7 the same brand?  Can you see a date code on each one, by any chance?  I ask this because I have found that differences among tubes can affect the filament readings.

    Looking at your photos again, the resistors are banded.  You should be able to read the color sequence off of them without taking anything apart.  Same for the resistors off of pins 1 of PC5, though you might have to flip the chassis over and back a few times to keep your bearings.


    Last edited by PeterCapo on Fri Nov 30, 2018 10:52 pm; edited 1 time in total
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Fri Nov 30, 2018 6:44 pm

    Do those connector blocks just use a screw to fasten the wire?  You can try temporarily removing the wires from CN-4, and, if you can get your meter probes down in there, take some resistance and continuity readings.

    For instance, CN4-2 should read short to one end of the 47K resistor on the cap board.  Measuring across the 47K should read 47K.

    CN4-1 should read short to one end of one of the 10K resistors on the cap board.  Then, try measuring across each of the 10K resistors in turn.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sat Dec 01, 2018 11:54 pm

    I haven't yet begun measuring the voltages from the cap board to PC-5 and PC-6, but I will do so.  I don't think I  have them in reverse, but I'll check this.

    The 12AX7 tubes aren't all the same brand, and none of them are of recent manufacture. I've accumulated them from other projects and equipment over the years.  For example, two of them are labeled "Eico" and are from a project long ago, (in the 1960's) building an EICO ST-40 integrated amp kit.  Another is labeled "DYNACO ECC83 MADE IN WEST GERMANY"; another "MINIWATT ECC83"; another "USA 12AX7A", and another "USA 12AX7WA".  As I mentioned, all test "good" on my B&K 600 tube tester, but perhaps that's no guarantee of their suitability.
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sat Dec 01, 2018 11:56 pm

    Yes, the connector blocks on the cap board use screws to fasten the wires. I'll give your suggested resistance and continuity readings a try.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 12:01 am

    A mixed group of 12AX7 might be the cause of the differences in the filament readings...
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    billinrio

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    Re: Please help me finish my PAS-2 upgrade

    Post by billinrio on Sun Dec 02, 2018 12:13 pm

    I would, of course, like very much to have matched sets of new 12AX7 tubes. I can't source anything like that here in Brazil. Ordering from a dealer in the U.S. for delivery to Brazil is always chancy due to the fact of the import duties on anything over USD$50 when coming from a commercial address. I note that tubestore.com has some nice looking Svetlana 12AX7s for $17 each, and maybe I should pull the trigger on them and take my chances. People who pursue this hobby and live in the U.S. or Europe don't realize how lucky they are.
    Now I'm going to do the resistance and continuity readings of the cap board. I wrote to the seller (in Hong Kong) asking for output voltage information for the board, but I don't really expect them to respond.
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    PeterCapo

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    Re: Please help me finish my PAS-2 upgrade

    Post by PeterCapo on Sun Dec 02, 2018 12:19 pm

    Doesn't really matter if they respond, because the voltages are listed in the chart in the manual (last two sections of the quad cap).  Note the voltage readings should be taken with the wires connected.  You're temporarily removing the wires just for the continuity and resistance readings - make sure the PAS has been unplugged for a while before doing this.

    If you order tubes, suggest requesting a matching date code on all four or at least per pair.  Reason being the hope that if they are from the same production run they could be more alike each other than if they were made in very different production runs.  It's an idea I subscribe to, and given the way the PAS works, it could be an advantage.

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