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    Please help me finish my PAS-2 upgrade

    billinrio
    billinrio


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    Post by billinrio 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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    Post by Guest Mon Nov 26, 2018 11:03 pm

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    Last edited by PeterCapo on Mon Nov 30, 2020 7:42 pm; edited 1 time in total
    billinrio
    billinrio


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    Post by billinrio 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)
    billinrio
    billinrio


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

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

    Please help me finish my PAS-2 upgrade <a href=Please help me finish my PAS-2 upgrade PAS-2%20moded_zps9eu4norr"


    Last edited by billinrio on Wed Nov 28, 2018 9:41 am; edited 4 times in total
    billinrio
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    Post by billinrio Tue Nov 27, 2018 9:08 am

    Please help me finish my PAS-2 upgrade <a href=Please help me finish my PAS-2 upgrade PAS-2%20bottom_zpskdiymeyf"
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    Post by Guest Wed Nov 28, 2018 2:45 am

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    Last edited by PeterCapo on Mon Nov 30, 2020 9:30 pm; edited 1 time in total
    billinrio
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    Post by billinrio 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. Please help me finish my PAS-2 upgrade <a href=Please help me finish my PAS-2 upgrade PAS2%20cap%20board%20instructions_zpsi0a6vxv2" />


    Last edited by billinrio on Wed Nov 28, 2018 9:43 am; edited 7 times in total
    billinrio
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    Post by billinrio Wed Nov 28, 2018 6:38 am

    Please help me finish my PAS-2 upgrade PAS2%20cap%20board%20schematic_zpsqtl170qn
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    Post by Guest Wed Nov 28, 2018 10:23 am

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    Last edited by PeterCapo on Mon Nov 30, 2020 9:29 pm; edited 1 time in total
    billinrio
    billinrio


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    Post by billinrio 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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    Post by Guest Wed Nov 28, 2018 6:17 pm

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    Last edited by PeterCapo on Mon Nov 30, 2020 9:04 pm; edited 1 time in total
    billinrio
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    Post by billinrio 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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    Post by Guest Thu Nov 29, 2018 4:32 pm

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    Last edited by PeterCapo on Mon Nov 30, 2020 6:39 pm; edited 1 time in total
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    Post by Guest Thu Nov 29, 2018 4:43 pm

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    Last edited by PeterCapo on Mon Nov 30, 2020 6:38 pm; edited 1 time in total
    billinrio
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    Post by billinrio 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.
    billinrio
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    Post by billinrio 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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    Post by Guest Fri Nov 30, 2018 11:34 am

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    billinrio
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    Post by billinrio 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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    Post by Guest Fri Nov 30, 2018 6:15 pm

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    Post by Guest Fri Nov 30, 2018 6:44 pm

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    billinrio
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    Post by billinrio 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.
    billinrio
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    Post by billinrio 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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    Post by Guest Sun Dec 02, 2018 12:01 am

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    billinrio
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    Post by billinrio 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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    Post by Guest Sun Dec 02, 2018 12:19 pm

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