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    Dynaco PAS restoration issues.

    peterh
    peterh

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    Post by peterh on Tue Jun 02, 2020 6:10 pm

    Freddie_Freekowtski wrote:
    peterh wrote:I contacted the seller "re-engineer" and asked if the potentiometers in the
    pas potentiometer kit. Did they have correct values .
    The answer was not to my satisfaction :

    The question you're really asking is:
    Are they the same resistance as the
    originals.
    The answer is:
    If they were, there would be no need for the
    kit.
    Thanks for stopping by...C


    In other words he refuses to tell what he sells.
    Maybe better to skip this seller.

    He was quite problematic during communication. His instructions for troubleshooting werent exactly clear, and they did did change...I had reported a value across pins 5 that was in the 30's and he freaked. sent back explicit step by step instructions which differed from the first set which stated to take out the tubes  and power unit off....which then changed to remove rectifier and 12ax7's in the phono board, power on and measure. We then got an acceptable value, at least to him, of 28.66 VDC. He has not replied since we got the phono stage working by bypassing his buffer. We followed his supplied instructions to the letter and still had a wire that originally ran from point 1 on the line board to RCA ground. His instructions never mentioned what to do with it.

    The brightness issue still exists. When I was listening, it seemed to become more of an issue as the thing was running. The line stage never experienced that issue. Another poster in a different forum said the selector switch could be at fault. I wouldnt be surprised if it was. It was literally frozen in place when I got the unit. My guy had to soak it in something to dissolve the gunk that crippled it. I am not a fan of its feel, it doesnt seem to sit properly in the phono spot. slight turns to either the left or right can cause a channel to drop out completely. The line stage, on spare, seems to feel like it rides its groove better, but you can still cause noise and dropouts by the slightest turn. Edited to add that all resistors were within 10% tolerance of their original values. Bass pots read 71.2k for left and 71.5 k for right..now treble is 368.6k for left and and 345.2k for right.
    I assume the bass pot is 710k
    But, as you suspect, if the selector has been troubling, yes that may very well happen, and
    the riaa equalisation is done via a few of it's connectors.
    Cleaning the selector is possible, with care and some mild cleaing oil. 5-56 comes to my mind,
    i'm sure better advices may com ( peter ?).
    The selector is delicate but not impossible to get working again. The good thing
    with the selector ( that none of thereplacement parts offer) is that it shorts unused
    inputs to proevent them from "bleeding throu". This bleeding can be quite annoying
    in an amp that lacks this shorting feature.
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    Freddie_Freekowtski

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    Post by Freddie_Freekowtski on Tue Jun 02, 2020 6:16 pm

    peterh wrote:
    Freddie_Freekowtski wrote:
    peterh wrote:I contacted the seller "re-engineer" and asked if the potentiometers in the
    pas potentiometer kit. Did they have correct values .
    The answer was not to my satisfaction :

    The question you're really asking is:
    Are they the same resistance as the
    originals.
    The answer is:
    If they were, there would be no need for the
    kit.
    Thanks for stopping by...C


    In other words he refuses to tell what he sells.
    Maybe better to skip this seller.

    He was quite problematic during communication. His instructions for troubleshooting werent exactly clear, and they did did change...I had reported a value across pins 5 that was in the 30's and he freaked. sent back explicit step by step instructions which differed from the first set which stated to take out the tubes  and power unit off....which then changed to remove rectifier and 12ax7's in the phono board, power on and measure. We then got an acceptable value, at least to him, of 28.66 VDC. He has not replied since we got the phono stage working by bypassing his buffer. We followed his supplied instructions to the letter and still had a wire that originally ran from point 1 on the line board to RCA ground. His instructions never mentioned what to do with it.

    The brightness issue still exists. When I was listening, it seemed to become more of an issue as the thing was running. The line stage never experienced that issue. Another poster in a different forum said the selector switch could be at fault. I wouldnt be surprised if it was. It was literally frozen in place when I got the unit. My guy had to soak it in something to dissolve the gunk that crippled it. I am not a fan of its feel, it doesnt seem to sit properly in the phono spot. slight turns to either the left or right can cause a channel to drop out completely. The line stage, on spare, seems to feel like it rides its groove better, but you can still cause noise and dropouts by the slightest turn. Edited to add that all resistors were within 10% tolerance of their original values. Bass pots read 71.2k for left and 71.5 k for right..now treble is 368.6k for left and and 345.2k for right.
    I assume the bass pot is 710k
    But, as you suspect, if the selector has been troubling, yes that may very well happen, and
    the riaa equalisation is done via a few of it's connectors.
    Cleaning the selector is possible, with care and some mild cleaing oil. 5-56 comes to my mind,
    i'm sure better advices may com ( peter ?).
    The selector is delicate but not impossible to get working again. The good thing
    with the selector ( that none of thereplacement parts offer) is that it shorts unused
    inputs to proevent them from "bleeding throu". This bleeding can be quite annoying
    in an amp that lacks this shorting feature.


    funny you say that, but their is some bleed. I had a line source connected, my laptop, and was spinning an album and you could faintly hear one of those facebook notification chimes. laptop was hook to "spare" . You can also hear the phono bleed on other channels
    PeterCapo
    PeterCapo

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    Post by PeterCapo on Tue Jun 02, 2020 8:29 pm

    It is possible that if the pots and selector switch were treated with some kind of contact cleaner, or a lubricant, or something like that, they may have been damaged.  Vintage pots and vintage selector switches use phenolic materials that just don't do well with chemicals.  Treating them can do as much or more to hurt than to help.

    Old selector switches can be a problem.  Other than seizing and needing cleaning, the open contacts can lose good contact, and I have never heard of a way to retension them.  Tugging on a wire going to the selector switch can result in contact problems.  The selector switch contacts are riveted to the phenolic wafers.  They can loosen and rotate on the rivet.  If they don’t rotate, the contact can otherwise lose pressure on the sliding contact, and, again, I’ve never figured out a way to retension these riveted contacts.

    Some have disassembled the original selector switch for cleaning.  I have not done this, so I cannot say much about it.  See Reply #7 here: https://www.audiocircle.com/index.php?topic=58900.0  You’re still stuck with the phenolic wafers, though.   But if the selector switch is not behaving well, then you might as well try to take it apart, clean it and then reassemble.  The best thing to do is to get a new rotary switch, but you’d then need to figure out the wiring – no simple task, especially for the low-level inputs.  Wish I had better news, but old age takes its toll on switches and things.

    Here's a short Caig Labs document that includes commentary that demonstrates how important it is to pick the right product and use it sparingly for the purpose we are discussing, and how picking the wrong product would be a mistake: http://store.caig.com/s.nl/ctype.KB/it.I/id.316/KB.215/.f


    Last edited by PeterCapo on Tue Jun 02, 2020 8:38 pm; edited 1 time in total
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    Freddie_Freekowtski

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    Post by Freddie_Freekowtski on Tue Jun 02, 2020 8:37 pm

    [

    Yes, Ive heard the original switch is now unobtanium. I have found a replacement from curcio audio. here's a snippet of their install pdf:

    The original Dynaco selector switch has six positions. Three of these six positions (Tape Head, Special, and Magnetic Phono) are routed to the input phono module. Consequently, these inputs are not available for “line level” signals normally provided by CD players, tape recorders, video sources, tuners and other “high level” sources. Today it is very unusual to have a need for more than one RIAA magnetic phono input. Consequently, in its original configuration, the stock Dynaco selector switch wastes two inputs.  As part of the design to route three of its inputs to the phono pc board, the original Dynaco selector switch incorporates a third section. This third section was included to provide the associated equalization to the phono module when one of the three low level inputs is selected. This third section combined with the inexpensive materials of construction (open switch phonelic materials) causes the switch to be a frequent source of problems with the preamp. This document describes the procedure to remove and replace the original PAS Selector Switch with a much higher quality switch. It will be wired to convert two of the low level inputs (Tape Head & Special) to line level inputs suitable to accept Tuners, CD players or other line level sources. The result will be elimination of pops, hum and other compromised switch problems along with two additional useful inputs as well as higher long term reliability.

    Im thinking it is worth a try
    PeterCapo
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    Post by PeterCapo on Tue Jun 02, 2020 8:45 pm

    It's a sensible approach. But there are a couple of problems. First, you'd have to get a hold of Joe. He hasn't posted in his forum for some time - is he still in business? Second, when I ordered this replacement selector switch from him some years ago, he sent a very cheap switch that I ended-up having contact problems with. I replaced it with an Electroswitch rotary switch - a high quality product. Grayhill is also quite good (Cary Audio used them as upgrades). The trick is figuring out how rotary switches can be configured and then map the original PAS wiring to it. No easy task.
    Midwestside
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    Post by Midwestside on Tue Jun 02, 2020 10:57 pm

    peterh wrote:I contacted the seller "re-engineer" and asked if the potentiometers in the
    pas potentiometer kit. Did they have correct values .
    The answer was not to my satisfaction :

    The question you're really asking is:
    Are they the same resistance as the
    originals.
    The answer is:
    If they were, there would be no need for the
    kit.
    Thanks for stopping by...C


    In other words he refuses to tell what he sells.
    Maybe better to skip this seller.

    When i first got my PAS i kind of rushed out and got the tone control kit, and led power light replacement from this user.
    I just figured since Dynakit linked to Dynaco designs site, that it was an endorsement.
    My bass and treble pots dont have a marked value on them from this seller.
    I realized after purchase that these would not be the same values and asked if i could cancel my order.
    He told me if i canceled , i would have to cancel ALL orders, including the led lamp kit i bought seperately, and if i did cancel please never buy anything again. lol
    I ended up kind of thinking.. 'well i could have some spares for one reason or another' getting them.

    I ended up taking my original tone pots apart , which actually looked fairly unused and cleaned them.
    I also kind of also bent the wipers to make better contact. It was not hard to pry up the little tabs and put them back together.
    This did make an improvement.
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    Freddie_Freekowtski

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    Post by Freddie_Freekowtski on Wed Jun 03, 2020 8:10 am

    PeterCapo wrote:It's a sensible approach.  But there are a couple of problems.  First, you'd have to get a hold of Joe.  He hasn't posted in his forum for some time - is he still in business?  Second, when I ordered this replacement selector switch from him some years ago, he sent a very cheap switch that I ended-up having contact problems with.  I replaced it with an Electroswitch rotary switch - a high quality product.  Grayhill is also quite good (Cary Audio used them as upgrades).  The trick is figuring out how rotary switches can be configured and then map the original PAS wiring to it.  No easy task.

    The re-engineer seller told my tech he would send the transistors to fix his module, but he insists my Dynaco was never wired correctly and wants my guy to literally go thru every connection and fix it before he does. My tech does not have that kind of time to dive way into it. After replacing the original power supply can cap and the filter caps, it was playing just fine, save for the brightness on the one side, which others are saying could be caused by one of the caps used to achieve RIAA equalization. Tech said he would check the cap values on the Phono, Tape Head, and Special. He also wrote the guy to ask if he had an idea where to start looking for the bad wires. I am almost ready to bail on this board and chalk it up to a leaning experience and concentrate on the brightness issue. It only exists on the phono stage. Thanks agin for the suggestions and advice. The thing will sing again one day.
    PeterCapo
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    Post by PeterCapo on Wed Jun 03, 2020 9:47 am

    Midwestside wrote:
    peterh wrote:I contacted the seller "re-engineer" and asked if the potentiometers in the
    pas potentiometer kit. Did they have correct values .
    The answer was not to my satisfaction :

    The question you're really asking is:
    Are they the same resistance as the
    originals.
    The answer is:
    If they were, there would be no need for the
    kit.
    Thanks for stopping by...C


    In other words he refuses to tell what he sells.
    Maybe better to skip this seller.

    When i first got my PAS i kind of rushed out and got the tone control kit, and led power light replacement from this user.
    I just figured since Dynakit linked to Dynaco designs site, that it was an endorsement.
    My bass and treble pots dont have a marked value on them from this seller.
    I realized after purchase that these would not be the same values and asked if i could cancel my order.
    He told me if i canceled , i would have to cancel ALL orders, including the led lamp kit i bought seperately, and if i did cancel please never buy anything again. lol

    IMO, that's just outlandish - even pathological.
    Midwestside
    Midwestside

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    Post by Midwestside on Wed Jun 03, 2020 1:51 pm

    I had wondered which area on the selector switch shorts the unused inputs.  I have a tiny bit of bleed through, only say when move to an album and the cd player is on. Sometimes while testing i have forgotten to stop the cd playing, but switched the knob to phono, this is how i know there is bleed through. Its not the worst thing and perhaps this is normal and that shorting other inputs only helps with low level noises (cd still playing music). I realize its common sense to stop the CD source, but was curious if the shorting feature was designed to actually quiet another source's full signal strength.
    peterh
    peterh

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    Post by peterh on Wed Jun 03, 2020 2:30 pm

    Midwestside wrote:I had wondered which area on the selector switch shorts the unused inputs.  I have a tiny bit of bleed through, only say when move to an album and the cd player is on. Sometimes while testing i have forgotten to stop the cd playing, but switched the knob to phono, this is how i know there is bleed through. Its not the worst thing and perhaps this is normal and that shorting other inputs only helps with low level noises (cd still playing music). I realize its common sense to stop the CD source, but was curious if the shorting feature was designed to actually quiet another source's full signal strength.
    Yes, i think it should totally silence unused inputs.
    AT the time this was designed tuners were tubes. They had no crystals and
    drifted somewhat during warm up. Thus one wanted the tuner to be
    warm and active all the time, but when listening to records the tuner
    should not be heard.

    If it bleeds through i think some cleaning of the selector is needed. Look at
    the schematics to identify which contacts to clean. And be careful !
    i know only of one spare selector in existence !
    Midwestside
    Midwestside

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    Post by Midwestside on Wed Jun 03, 2020 4:01 pm

    peterh wrote:
    Midwestside wrote:I had wondered which area on the selector switch shorts the unused inputs.  I have a tiny bit of bleed through, only say when move to an album and the cd player is on. Sometimes while testing i have forgotten to stop the cd playing, but switched the knob to phono, this is how i know there is bleed through. Its not the worst thing and perhaps this is normal and that shorting other inputs only helps with low level noises (cd still playing music). I realize its common sense to stop the CD source, but was curious if the shorting feature was designed to actually quiet another source's full signal strength.
    Yes, i think it should totally silence unused inputs.
    AT the time this was designed tuners were tubes. They had no crystals and
    drifted somewhat during warm up. Thus one wanted the tuner to be
    warm and active all the time, but when listening to records the tuner
    should not be heard.

    If it bleeds through i think some cleaning of the selector is needed. Look at
    the schematics to identify which contacts to clean. And be careful !
    i know only of one spare selector in existence !

    Thanks, just out of curiosity , are you saying modern replacement selector switches just dont seem to take shorting the other inputs into consideration?
    peterh
    peterh

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    Post by peterh on Wed Jun 03, 2020 4:10 pm

    Midwestside wrote:
    peterh wrote:
    Midwestside wrote:I had wondered which area on the selector switch shorts the unused inputs.  I have a tiny bit of bleed through, only say when move to an album and the cd player is on. Sometimes while testing i have forgotten to stop the cd playing, but switched the knob to phono, this is how i know there is bleed through. Its not the worst thing and perhaps this is normal and that shorting other inputs only helps with low level noises (cd still playing music). I realize its common sense to stop the CD source, but was curious if the shorting feature was designed to actually quiet another source's full signal strength.
    Yes, i think it should totally silence unused inputs.
    AT the time this was designed tuners were tubes. They had no crystals and
    drifted somewhat during warm up. Thus one wanted the tuner to be
    warm and active all the time, but when listening to records the tuner
    should not be heard.

    If it bleeds through i think some cleaning of the selector is needed. Look at
    the schematics to identify which contacts to clean. And be careful !
    i know only of one spare selector in existence !

    Thanks, just out of curiosity , are you saying modern replacement selector switches just dont seem to take shorting the other inputs into consideration?
    True, the ones i have seen offered don't have the extra contacts.
    If you think of purchasing one, contakt seller and ask explicitly if
    their switch shorts unused inputs.


    Last edited by peterh on Wed Jun 03, 2020 4:16 pm; edited 1 time in total
    PeterCapo
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    Post by PeterCapo on Wed Jun 03, 2020 4:15 pm

    If the original selector switch is failing to function and is beyond repair, there's no choice than to get a new one. It may be possible to get a new, multi-deck switch and wire it up the same way as the original with the shorting. But determining whether this would be possible, and, if so, how to do it, would take detailed analysis.
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    Freddie_Freekowtski

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    Post by Freddie_Freekowtski on Wed Jun 03, 2020 5:27 pm

    PeterCapo wrote:If the original selector switch is failing to function and is beyond repair, there's no choice than to get a new one.  It may be possible to get a new, multi-deck switch and wire it up the same way as the original with the shorting.  But determining whether this would be possible, and, if so, how to do it, would take detailed analysis.

    curcio audio is still in business and Joe was quick to reply to my inquiry. I guess his selector switch was an issue because he is now selling a higher quality one
    PeterCapo
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    Post by PeterCapo on Wed Jun 03, 2020 6:51 pm

    Glad he's still there.  The archives in his Dynaco Doctor forum are, IMO, the best on the Internet.  Such a wealth of Dynaco-related topics were explored, and the search feature works well.  Hope his forum archives never go away.
    tubes4hifi
    tubes4hifi
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    Post by tubes4hifi on Wed Jun 03, 2020 8:40 pm

    all of these problems are exactly why I quite selling PAS preamp upgrades 5 years ago, it simply is not worth the cost and bother
    when you can buy a brand new preamp for less money
    PeterCapo
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    Post by PeterCapo on Wed Jun 03, 2020 9:34 pm

    tubes4hifi wrote:all of these problems are exactly why I quite selling PAS preamp upgrades 5 years ago, it simply is not worth the cost and bother when you can buy a brand new preamp for less money

    It's all part of the DIY landscape.  Restorative work is part of the hobby, if one so chooses.

    The problems are not the nature of the restoration.  What's the difference if you replace a selector switch in an original PAS vs. installing and wiring a selector switch in a brand new preamp kit?

    What is not always readily available are the necessary procedures explaining how go about restoring an original.  But once you get it figured out, it's not that difficult.  My frustration is that a few years ago I had that selector switch figured out.  I should have documented replacement procedures, then.  If I had, I could just give it to whomever might benefit from it.  And, when you know what needs to be done, it can probably be done relatively inexpensively - probably at a lower or comparable cost than some other new preamp kits and almost certainly a lot less than most fully assembled preamps.

    Other than restoration being part of the stock-and-trade of DIYers, the finished result is a handsome reward for your efforts.  The original PAS circuit, properly restored to its original glory, is a truly fine-sounding, classic all-tube preamp that can compete with other preamps in its price range and even beyond that.

    These are all valid reasons for carefully, systematically restoring an original Dynaco - and probably other vintage gear, as well.
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    rjpjnk

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    Post by rjpjnk on Thu Jun 04, 2020 10:18 am

    I agree there is something special about restored vintage gear that something new will never have even if it sounds better. This is why in general I prefer to not upgrade the PAS with modern parts unless necessary. That is, make the PAS the best PAS it can be, and if you want a "better" modern preamp buy a new one. Personally I don't see the value in compromising between the two, but I realize many others do. The main thing is to have fun in your hobby. Building stuff is cool. Smile
    KeyserSozo
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    Post by KeyserSozo on Sun Jun 14, 2020 1:32 pm

    I'm in the process of restoring an old PAS myself right now. I reached out to a few vendors to assemble some parts, and my dealings with 'C' from DynacoDesigns.com was about the same as mentioned above. I inquired to find out a few particular details about pots/switches/PCB's and after a few back and forths it ended with him telling me he 'was not interested in selling to someone like me' lol

    Luckily enough for the Dyna community there seems to be a bunch of other great sellers (DynakitParts/Erhardt/etc...) that carry enough parts to assemble a PAS from scratch.
    PeterCapo
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    Post by PeterCapo on Sun Jun 14, 2020 5:00 pm

    Unfortunate if this seller acts that way. In an age of insane prices elsewhere in audio, we in the Dynaco community should all be pulling together to keep the unbeatable value of Dynaco viable for a long time to come.
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    Freddie_Freekowtski

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    Post by Freddie_Freekowtski on Sun Jun 14, 2020 5:06 pm

    KeyserSozo wrote:I'm in the process of restoring an old PAS myself right now.  I reached out to a few vendors to assemble some parts, and my dealings with 'C' from DynacoDesigns.com was about the same as mentioned above.  I inquired to find out a few particular details about pots/switches/PCB's and after a few back and forths it ended with him telling me he 'was not interested in selling to someone like me' lol

    Luckily enough for the Dyna community there seems to be a bunch of other great sellers (DynakitParts/Erhardt/etc...) that carry enough parts to assemble a PAS from scratch.

    I sourced a switch mod from curcio audio. The original PAS selector switch is unobtanium and mine appears to be damaged and is probably responsible for my RIAA brightness issue I am having. His upgraded switch takes the tape head and special inputs and converts them to line level inputs suitable for things like my laptop and DAT machine. As far as "C" goes and his buffer, he swears my PAS3 is wired wrong and that is why his buffer did not work. He wants my tech to go thru the entire box before he will replace the transistors if they went bad. If the switch solves my issue, I'm going to live and learn and enjoy the thing.
    PeterCapo
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    Post by PeterCapo on Sun Jun 14, 2020 5:39 pm

    Looking forward to hearing how you do with your new switch from Curcio.
    KeyserSozo
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    Post by KeyserSozo on Thu Jul 02, 2020 11:56 pm

    Our friend 'C' let one of his Line Amp boards (and pots) slip onto the auction site ...only 9hrs left!

    For the record both pots are 500k, their bodies are different sizes yet made by the same manufacturer (Bournes), and they look like a decent set... supposedly this board has been modified from the original to work with these pots specifically, if anyone is looking!

    PIC

    PIC

    PIC

    Enjoy!
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    rjpjnk

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    Post by rjpjnk on Fri Jul 03, 2020 10:18 am

    Interesting. I see it went for 38 bucks. Good deal for someone who needs a rebuild.

    274406210665
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    Adnick

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    Post by Adnick on Sat Jul 04, 2020 12:10 am

    I’ve used several of the Dynacodesign tone kits in PAS builds, they work and replicate they original circuit very well.....not many options when the substrate of the original pot is cracked.  

    If the original pots are structurally sound then taking them apart, cleaning/adjustment, is the only sure way to get them functioning like original....If it’s diy, then it’s just time but, if it’s a customer that’s expecting no noise when turning knobs then that’s a completely different matter.

    Never had an issue with any of the other Dynacodesign parts, so can’t  speak to his customer service, good or bad, never had any need....Dynakitparts does recommend them.

    Fender also sells a very decent 500k pot, have used them with equal success on occasion.

    Can also recommend the Curcio Audio replacement instructions for dual pole 6 position switches. Even when taken apart and carefully cleaned, the original selector switch will most likely induce noise.

    Like to keep original parts functioning but, always return them with the amp if replaced.

    Regards,
    Andy

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    Dynaco PAS restoration issues. - Page 2 Empty Re: Dynaco PAS restoration issues.

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      Current date/time is Mon Jul 13, 2020 5:24 pm