The Dynaco Tube Audio Forum

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


    Started down the road.

    Share
    avatar
    CNCfan

    Posts : 31
    Join date : 2018-08-13
    Age : 70
    Location : Houston Texas

    Started down the road.

    Post by CNCfan on Mon Aug 13, 2018 2:58 pm

    Hello everyone,  new here so please excuse my lack of knowledge.

    Been interested in a Dynaco ST70 for longer than I can remember but the price has always held me back.
    Was wasting my time on ebay and came across a parts chassis, it has the cage and bottom,  a few sockets
    and a few other parts.  Decided to get it and start picking up parts to finish it as I can afford them. (going to be a long journey)

    Also snagged a  Pas preamp that the seller said was mostly original and in working condition. Figured the preamp and
    parts chassis would be a good start.  

    Will be asking a lot of pretty basic question most likely but will be researching youtube and this forum before I do.

    My plans as of now is to get the ST70 up and going. Will need power xfmr, output......well to make it simple, I will need everything
    that has a wire connected to it.

    On the preamp,  I plan on doing a once over and buying any upgraded parts that are available.  

    Also want to get a Dyna FM receiver,  any suggestion on which version to get?  

    I am only an expert in one area of electronics.  I have first hand knowledge on what happens when you grab the
    bare wire going to the "on" light on a 220 volt electric stove even when it is off.   Have no plans on finding out
    what happens when you touch 350+ volts.
    avatar
    Peter W.

    Posts : 966
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Started down the road.

    Post by Peter W. on Mon Aug 13, 2018 4:05 pm

    Please note the interpolations - and I hope you are high-and-dry in the face of the coming storms!

    CNCfan wrote:Hello everyone,  new here so please excuse my lack of knowledge.

    Been interested in a Dynaco ST70 for longer than I can remember but the price has always held me back.
    Was wasting my time on ebay and came across a parts chassis, it has the cage and bottom,  a few sockets
    and a few other parts.  Decided to get it and start picking up parts to finish it as I can afford them. (going to be a long journey)

    On the positive side, every part as was ever made for the OEM 70 is available in the equivalent today. Do a little bit of comparison-shopping before making choices in the driver board - I would never suggest anyone purchase an OEM Phenolic board (the orange ones with the raised solder traces) for latter-day installation, as one example. I would also suggest that you look for an alternative to the OEM 7199 as they can be both scarce and expensive - as well as being microphonic on occasion.

    Also snagged a  Pas preamp that the seller said was mostly original and in working condition. Figured the preamp and
    parts chassis would be a good start.  

    Start with a full recap and consider replacing the original power and bias-supplies. There are some fairly elegant and easy to install options out there. Also, do clean the controls and make sure that the wiring is all good and tight. Many of these were kits, so QC varies quite a bit to that regard.

    Will be asking a lot of pretty basic question most likely but will be researching youtube and this forum before I do.

    My plans as of now is to get the ST70 up and going. Will need power xfmr, output......well to make it simple, I will need everything
    that has a wire connected to it.

    See above. Transformers are available from several sources, including those numbered as the OEMs, and from US-made sources. DO TRY to avoid Pacific-Rim transformers at almost any cost. There are also EDCOR and Hammond equivalents - I have heard, but not used them. Superficially, they seemed fine.

    On the preamp,  I plan on doing a once over and buying any upgraded parts that are available.  

    Start with caps and power supplies. Don't go overboard until you have heard it in its originally designed state. You may be pleasantly surprised and not need to go any further.

    Also want to get a Dyna FM receiver,  any suggestion on which version to get?  

    An FM-3 (Tube) would be the natural partner to the above. These are pretty basic tuners, and surprisingly mellifluous for what they are. I keep one (1) heavily tweaked unit and one (1) very nearly stock unit. If you are going to go Solid-State, the FM-5 is not half-bad, and the AF-6 is very good indeed if you can find one of the two-dozen or so out there that are actually properly aligned. But, in terms of something subject to amateur care-and-feeding, the FM-3 hands-down.  

    I am only an expert in one area of electronics.  I have first hand knowledge on what happens when you grab the
    bare wire going to the "on" light on a 220 volt electric stove even when it is off.   Have no plans on finding out
    what happens when you touch 350+ volts.

    Purchase reproductions of the original assembly manuals for these beasts. These things were designed to be kits, put together on the kitchen table by everyone from plumbers to lawyers, kids to seniors. Hafler did a fairly good job in his manuals making that happen with a remarkably low failure rate. Measure twice, cut once. Read the directions and understand them *BEFORE* starting. Purchase good tools. Fewer good tools will do you infinitely more good than many poor tools. AND - ABOVE ALL!! Make sure where you work as excellent, shadow-free lighting and excellent ventilation. Use eutectic (37/63 lead/tin solder *ONLY*. You will drive yourself nuts if you try to go lead-free. And, be patient with yourself and with your progress.

    GOOD LUCK! Above all, Enjoy!
    avatar
    CNCfan

    Posts : 31
    Join date : 2018-08-13
    Age : 70
    Location : Houston Texas

    Re: Started down the road.

    Post by CNCfan on Mon Aug 13, 2018 9:13 pm

    Thanks for the reply Peter.

    Will take your advise on all your points. I have noticed driver boards for the ST70, some updated ones have three tubes and others I saw had four. Will have to look into them a bit more to see which I will get.

    The Transformers and choke will be the first items I will buy. They will be from one of the sellers that sell ones build in the States. Been reading up on them past few days.

    On the Pre amp, I plan on re-capping, will also pick up a new transformer as you suggested. Thanks for that suggestion I had not planned on doing it. I will keep it as I received it and give it a good test before I replace anything. Will do caps and transformer no matter the state. Seller stated that the light bulb was replaced with a LED and the leftmost bottom switch was changed out to allow two tape sources? Will put that back to original state. Doing any work on the preamp will come after I get the
    ST70 working. Doing this on a retirement budget so like I said, long journey, but I know I will enjoy it.

    I have just about all the tools I need to work on an amp. Will have to pick up an oscilloscope. I was planning on getting one anyway as I have a few old tube radios I wanted to bring back to life.

    Back in the day I built may Heathkit’s, from a digital clock, 4 channel stereo and a 25 inch color tv plus a number of other things I have long forgot.

    Thanks for the FM-3 suggestion, will keep an eye out for one.

    Will also pick up some 37/63 solder, all I have now is 60/40, (I think that is it), No lead free solder in my plans, have heard to much negative comments about it.

    Oh, yes, so far we have stayed dry, the area I live in (Cypress) is in a 500 year floodplain. Last big storm we had our neighborhood was not flooded. Hope our luck continues.

    Thanks again for taking the time to give me all the pointers.

    audiobill

    Posts : 358
    Join date : 2014-03-13
    Location : Philadelphia

    Re: Started down the road.

    Post by audiobill on Tue Aug 14, 2018 6:16 am

    New driver board, tubes, transformers, choke, recapping, oscilloscope, etc.

    Please think hard about this, since you'll spend as much and end up with an ST70 in an old chassis that will be half the power of a new kit - just trying to be helpful....
    avatar
    Peter W.

    Posts : 966
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Started down the road.

    Post by Peter W. on Tue Aug 14, 2018 7:11 am

    Of the stuff on your list, the scope is likely the least important. Unless you intend to start aligning FM tuners, or you are getting distortion problems, the scope is overkill on most Dynaco products.
    avatar
    peterh

    Posts : 1054
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Started down the road.

    Post by peterh on Tue Aug 14, 2018 7:39 am

    Peter W. wrote:Of the stuff on your list, the scope is likely the least important. Unless you intend to start aligning FM tuners, or you are getting distortion problems, the scope is overkill on most Dynaco products.
    I wouldn't say that. A scope is a versatile and very useful instrument for audio work.
    Just make sure that you have probes for the voltage, 10:1 probes usually
    can cope with 500V, but measuring on powertube plates may easily get into
    the 1000V range.

    Scope may be used to compare 2 signals by the "adding signals" function where
    one channel is inverted. This shows what distortion consists of. Scope is also
    very handy when diagnosing a silent amp ( where does the signal stop question)

    A modern scope also shows voltage / frequency thus may be used instead of a DMM.
    avatar
    bluemeanies

    Posts : 260
    Join date : 2015-02-09
    Age : 68
    Location : Folsom Pa.

    Re: Started down the road.

    Post by bluemeanies on Wed Aug 15, 2018 5:33 am

    Hello,
    and
    WELCOME!
    Large endeavor you intend to take upon youself. Just reading YOUR intial post I have to say I wish I had the talent to undertake such a task...and it is a task!
    However you seem confident and somewhat knowledgeable and I am sure you have had experience with DIY kits in the pass.
    Me...I still a newbie to this stuff after 3years. A lot of evolution with electronics over the years.
    It's all good.
    The point is that when reading your post (without reading anything else) I thought between labor and costs is it worth the RESTORE. Is there value $$in this project or personal satisfaction...which is fine.
    I just thought if it were me I would at least look into the cost factor for each part. I would not (realizing all the work involve cut corners) by that I mean cheap vs top of the line.
    In the end the cost analysis and your time MIGHT not be worth it compared to buying something NEW.
    Just my thoughts and something to be considered.
    If it's sentimental go for it, but if it is just a dust off, rehab of an old amplifier....well ??? to think about!

    I did do model planes very well when I was a kid! lol!
    avatar
    CNCfan

    Posts : 31
    Join date : 2018-08-13
    Age : 70
    Location : Houston Texas

    Re: Started down the road.

    Post by CNCfan on Wed Aug 15, 2018 1:07 pm

    Audiobill

    I was under the impression I could buy one of the new driver
    boards and power transformer and have a ST70 that is on par as far as components
    go as an “upgraded” ST70 kit. That is of course included buying
    the quality caps, resistors and other items that it takes to build the ST70.

    Just wondering if I have missed something that did mach 3 when it went over my head.




    Bluemeanies

    Thanks for the welcome.

    Value in doing the build the way I plan or worth the price of restore from just a parts chassis? Most likely no value. But I do not plan on selling it and I am always looking for hobby projects to do since I am retired and have more time on my hands than money.

    No plans on cutting corners, at least I knowing won't. Embarassed

    Will it cost more buying components as I can afford them, instead of buying a kit with everything included. Yes, been there done that on other hobby’s I have played with in the past. Some I regret, some I don’t. (There once was a KZ1000 that I took apart to rebuild…….never mind different subject) Very Happy

    Right now I am looking at two web sites that cater to people building or buying ST70 kits, already wired, and individual parts. Comparing what is in the kits and the parts available to build one , I am thinking I can get one built and it will be just as good as if I bought the whole kit in one order.
    Will it cost more, like I said above, yep, I’m thinking it will. How much more, not sure but we are going to find out

    I am confident on the hardware side, now once I get it together and for some reason it sound like it came from ebay with a $6 buy it now option………. lets just say I will have lots of questions. Very Happy Very Happy Very Happy


    Thanks again for everyone's input.

    audiobill

    Posts : 358
    Join date : 2014-03-13
    Location : Philadelphia

    Re: Started down the road.

    Post by audiobill on Wed Aug 15, 2018 1:16 pm

    Many miss the fact that although Dynaco advertised the ST70 at 35 watts per channel, the 1974 FTC requirement that both channels be driven from 20-20khz resulted in the ST70 producing only 17-19 wpc.

    Bob's VTA version sports substantial power supply upgrades as well as a much larger power transformer that allows the amp to produce, and has been tested, at least 35wpc.  These transformers are not available separately from Bob.

    So, for those refreshing "vintage" ST70s, please realize that you will likely spend as much and end up with half the power of Bob's VTA version.


    Last edited by audiobill on Wed Aug 15, 2018 1:17 pm; edited 1 time in total
    avatar
    Peter W.

    Posts : 966
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Started down the road.

    Post by Peter W. on Wed Aug 15, 2018 1:17 pm

    Consider the primary reasons that I generally choose vintage over new - and I am, emphatically, writing only for myself:

    a) It is always something new, and always a bit of a challenge.
    b) I know it worked at some point, so making it work again is only a matter of getting to that point.
    c) I learn something with each challenge.
    d) It keeps stuff out of landfills.
    e) It is, very nearly always, cheaper than a new equivalent.
    avatar
    Peter W.

    Posts : 966
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Started down the road.

    Post by Peter W. on Wed Aug 15, 2018 1:24 pm

    audiobill wrote:Many miss the fact that although Dynaco advertised the ST70 at 35 watts per channel, the 1974 FTC requirement that both channels be driven from 20-20khz resulted in the ST70 producing only 17-19 wpc.

    Bob's VTA version sports substantial power supply upgrades as well as a much larger power transformer that allows the amp to produce, and has been tested, at least 35wpc.  These transformers are not available separately from Bob.

    So, for those refreshing "vintage" ST70s, please realize that you will likely spend as much and end up with half the power of Bob's VTA version.

    Latest specifications, per OEM Dynaco, c. 1980:

    Power Output: 35 watts continuous, 80 watts peak each channel.

    Frequency Response: ±.5 dB from 10 hz to 40 khz.

    Power Response: 20 hz to 20 khz within 1 dB of 35 watts at less than 1% distortion.

    Intermodulation Distortion: Less than 1% at 35 watts (normally about .5%). Less than .05% at 1 watt.

    This is not to suggest that OEM units were not run at the bleeding edge of their capabilities, or that the VTA power-supply is not a significant improvement. But, a vintage unit, properly configured, will produce 35 wpc/rms. Keep in mind that the 70 remained in production through the 80s.

    audiobill

    Posts : 358
    Join date : 2014-03-13
    Location : Philadelphia

    Re: Started down the road.

    Post by audiobill on Wed Aug 15, 2018 1:46 pm

    Please see this link:

    http://dynacotubeaudio.forumotion.com/t1468-differences-between-the-original-st-70-and-my-vta-st-70

    Peter, I understand that the power you describe came in later units, with Japanese transformers, not the originals that I assume the OP has.

    Bob has posted Dynaco's original FTC confession on his facebook page:

    https://www.facebook.com/vta.amp.kits/posts/956306401144557:0


    Last edited by audiobill on Wed Aug 15, 2018 6:05 pm; edited 2 times in total
    avatar
    Pillo69

    Posts : 158
    Join date : 2012-04-11
    Location : Granada (España)

    Re: Started down the road.

    Post by Pillo69 on Wed Aug 15, 2018 1:57 pm

    If you are looking for components to replace the originals look at the following link.

    https://www.dynakitparts.com/
    avatar
    corndog71

    Posts : 673
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Started down the road.

    Post by corndog71 on Wed Aug 15, 2018 2:22 pm

    Dynakitparts is my choice for Dynaco transformers. And Tubes4hifi / VTA sell (in my opinion) the best driver circuits. I also recommend Jim McShane for tested and matched tubes.

    While I can appreciate the choice to go with the original circuit for that vintage look and sound, the newer parts and circuits are so reasonably priced, easy to source, and perform so well that it seems silly to choose otherwise.

    But hey, to each their own.
    avatar
    CNCfan

    Posts : 31
    Join date : 2018-08-13
    Age : 70
    Location : Houston Texas

    Re: Started down the road.

    Post by CNCfan on Fri Aug 17, 2018 6:35 pm

    audiobill:

    Yes I realize I will not end up with an amp as good as Bob’s VTA version.  On a retirement budget (ie SS)  and for my use I will be more than happy when I get my ST70 together and it works as good as an original.   As long as I can get crisp clear voice, and not too deep bass that is clean and not muddy like you hear in a lot of cars going down the street, I will doing a happy dance.  

    Also, what got me going in this directions was I saw a guy on ebay selling the cage, base, bottom,  a few tube sockets plus a few caps I most likely will not use unless they test good.  That is it, no driver  board , power or output transformers and no tubes.  Quick check on sites where I found the cage, base and bottom for sale told me I could save a little over $100 instead of buying new.  They look in pretty good condition so went with it.  Well “save” might not be the correct word, will most likely put that on something else.

    I was planing on putting in an upgraded driver board which if I understand will require the upgraded transformer which I see by your post Bob does not sell by itself.  So I will stick with the two tube driver board and get the version that takes 6GH8A  tubes.  (still looking into this, have not been able to spend any time researching this project for the last week.  Wife has me cutting hedges and putting in a “ring” door bell.  For some reason she now wants to see and talk to people at the front door without going to the door.  (told her my may need another tube amp for the talk part.)

    Peter W.

    Looks like I am on the same page as you on my current project.  I like the vintage aspect but was
    also hoping to do an upgrade or two as I went along.  But if I can’t all is still good, original was good enough for thousands so it will more that work for me.

    Pillo69 and corndog71,

    yep have both sites bookmarked.

    Thanks again to everyone for your comments and suggestions much appreciated.
    Been a great help


    Last edited by CNCfan on Sat Aug 18, 2018 11:46 am; edited 1 time in total

    audiobill

    Posts : 358
    Join date : 2014-03-13
    Location : Philadelphia

    Re: Started down the road.

    Post by audiobill on Sat Aug 18, 2018 5:23 am

    CNCfan, best of luck with your build. Certainly lots of good advice on this board!
    avatar
    peterh

    Posts : 1054
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Started down the road.

    Post by peterh on Sat Aug 18, 2018 5:30 am

    Regarding the preamp PAS3 you write :
    On the preamp,  I plan on doing a once over and buying any upgraded parts that are available.  

    My comment is : leave it in original shape as much as possible. Avoid snake-oil "enhancements" and "improvements" unless proven otherwise .
    Use it if possible untouched until the rest of
    your gear is working and you are in position to judge any changes.

    ( the best pas is an original one in proper working condition )


    Last edited by peterh on Sat Aug 18, 2018 5:32 am; edited 1 time in total (Reason for editing : Spelling, formattimg)
    avatar
    PeterCapo

    Posts : 561
    Join date : 2008-12-05

    Re: Started down the road.

    Post by PeterCapo on Sat Aug 18, 2018 1:15 pm

    CNCfan,

    Tossing my hat in the ring here.  With regard to power output, power supplies and such, it is often overlooked that the power supply improvements touted in reimagined versions of the Stereo 70 can be applied to the original Dyanco Stereo 70 circuit, as well.

    For instance, there have been "cap boards" available that substitute higher performance, low ESR electrolytics (discrete) with polypropylene bypasses in place of the traditional quad section can (Swiss roll type internal construction).  You can also use a fast or zero recovery diode in the original bias circuit.  These and other parts upgrades benefit the original Stereo 70 just as they do the reimagined versions having different driver boards.  If you value originality, then another nice thing about at least some of the cap boards is that they also retain the basic topology of the original power supply.  But, I am not sure there are as many cap boards available as there used to be.  I think Triode USA still sells one.  As another option, dynakitparts.com sells an upgraded version of the quad section capacitor built out of discrete electrolytics inside the can.

    In any case, before you do anything else, I’d like to recommend the landmark studies of the original Stereo 70 and PAS done by Dave Gillespie and George Ronnenkamp.  They are eye-opening and cut through popular misperceptions of the original Dynacos.  They are "must reads."  Have a look along the left side of the following webpage: http://www.audioregenesis.com/

    zx

    Posts : 205
    Join date : 2011-08-05

    Re: Started down the road.

    Post by zx on Sat Aug 18, 2018 5:25 pm

    I have to say, I am ….100%...With Petercapo recommend read!....
    If you wont a diff amp are preamp than the Stock dynaco pas an St70....or MK4s are Mk3....Get One of Bobs amps....


    In my 40 years of owning every….Tube amp an preamp I could find...most big buckes..Theses old  Stock setup always have a Magic….you just don't find to day....is there better ...well there diff...for sure..

    The Dyna pas an the ST70 are a steal....yes new caps are needed..
    I just pic up a pas 3X an a Fm3 an St70 for $600...I find the pas3 an St70 going on CL for about $300ea....I like a lot of Older tube people think the 7199is one sweet sounding tube....an work great on the St70 with it... so call week leak  power tran…
    I am using the st70 to drive my Martin Logans ESL Ascent I, CLS speakers an the sound as good as any amp I have ever owned.....Funny...I gess if I had starded my 40 year... Audio quest with the Dynacos I would have miss out on some great sound...

    All just one mans finding....other May differ...good luck...have fun when you can...




    Thanks for the Site Bob......

    rjpjnk

    Posts : 117
    Join date : 2018-07-18

    Re: Started down the road.

    Post by rjpjnk on Sun Aug 19, 2018 11:40 am

    CNCfan wrote:

    I was planing on putting in an upgraded driver board which if I understand will require the upgraded transformer which I see by your post Bob does not sell by itself.  So I will stick with the two tube driver board and get the version that takes 6GH8A  tubes.

    As others have already pointed out, dynakitparts.com is an excellent source for the transformers. Their output transformers are as good as the originals, and the power transformers seem to have been beefed up a bit. The site mentions they are taller due to increased lamination stack. That is a welcome improvement. Bob's transformers are equally good but not available for sale that I know of.

    https://www.dynakitparts.com/shop/st-70-transformer-set/

    Regarding the driver board. I'm pretty sure you can use any of the original 2-tube style boards or the newer 3-tube style driver boards with the original transformers. I am really enjoying Bob's VTA driver board. I have never heard the original.

    One nice thing about the ST70 is you can easily swap the driver board to see what sounds best to you. The new drivers are great, but so are the originals. Depends what you like. As pointed out previously, the Dave Gillespie series is an essential read for anyone considering touching an ST70 or PAS preamp.

    Here is the ST70 study:
    http://www.audioregenesis.com/documents/ST-70%20Base%20Line%20Testing.pdf
    avatar
    CNCfan

    Posts : 31
    Join date : 2018-08-13
    Age : 70
    Location : Houston Texas

    Re: Started down the road.

    Post by CNCfan on Mon Aug 20, 2018 2:25 pm

    Audiobill. Thanks for the “best of luck”, expect I will need it. I have already found this forum to be great. I have had questions about a few things and found the answers by going through old posts. Will most likely find most of my questions answered somewhere in this forum.

    Peterh, will also take you advise on the PAS, seller said it was in good condition and working. Will
    leave it as is before doing any parts replacement if needed, well “needed” may not be the correct work here, more like “I want that”. (caps replacement the exception depending on what I see.)

    PeterCapo, thanks for the link, will check it out. Plan on taking advantage of all the upgraded parts I can find for the ST70. Right now I plan on getting the power transformer and output kit from dynakitparts. Also most of the other parts that are available. One site I saw a board for auto bias, that is also on my list.

    Zx, I have the preamp, parts chassis and FM tuner on the way. End of post are links to ebay on what I have ordered.

    Rjpjnk, Thank for the tip on the 2 or 3 bute style driver board, that is one thing I have been thinking about.

    Links to what I am starting with. Preamp and FM tuner are described to be in good condition, any work they may require will wait until I have the ST70 up and running. ST70 parts chassis should show up today. Preamp is scheduled to be delivered tomorrow and the FM tuner I just bought so it will be about a week until delivered.

    Don’t laugh too hard if you see I paid to much. Don’t think so, but not sure.

    https://www.ebay.com/itm/Dynaco-FM-3-Tube-Tuner-EXCELLENT-CONDITION-SEE-YOUTUBE-VIDEO-OF-IT-WORKING/302842306414?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649


    https://www.ebay.com/itm/Dynaco-St70-Cage-plus-extras-see-new-photos/153134003264?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

    https://www.ebay.com/itm/Dyna-Stereo-Preamplifier-PAS-PreAmp-with-Tape-input-modifcation/142893985311?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
    avatar
    Peter W.

    Posts : 966
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Started down the road.

    Post by Peter W. on Mon Aug 20, 2018 2:45 pm



    Don’t laugh too hard if you see I paid to much.  Don’t think so, but not sure.


    a) That is about what I will sell a fully reconditioned FM3 for at Kuztown, I usually ask in the $150 range to allow for some wiggle-room. On the other hand, the buyer can hear, see (and smell) it playing.
    b) My general reaction to the cage is that it is a necessary thing to have - between cats, dogs and grandkids. One in that shape, I would strip, sand, and repaint. The logo may be masked, or removed and re-applied.
    d) That is quite inexpensive for any PAS - that it is a 2 and that it is a brass-face probably contributed to that price. Under the hood, however, there is little to differentiate between any 2 and any 3. It is the X-mod and tone controls that are scarce and make such pre-amps costly. Don't be swayed by the cut-out-the-tone-controls crowd. Even on the PAS2, if clean and undamaged, they are quite neutral in the null position.

    The FM tuner is user-aligning. It helps to have a mono-FM station around, if one exists on your area. I have a small FM transmitter that I use - it can be mono, stereo, right only, left only. All big helps when doing alignments in any case.

    On the 7199, I have been glomming those for 30 years now, as I have four (4) amps that use them. About 50% are somewhat microphonic - so isolation is a good thing.

    Keep in mind that the PAS has an NAB tape-head input that may be adapted for a second phono input, or even a line-level input. It is, essentially, a low-level input with an opposite curve to the RIAA curve.
    The FM/AM input is a standard line-level input set back to the days of simulcasting for stereo.

    rjpjnk

    Posts : 117
    Join date : 2018-07-18

    Re: Started down the road.

    Post by rjpjnk on Mon Aug 20, 2018 3:40 pm

    Peter W. wrote:
    Don't be swayed by the cut-out-the-tone-controls crowd. Even on the PAS2, if clean and undamaged, they are quite neutral in the null position.

    I agree. It seems such a shame to bypass the tone controls. Even on the 3X some people still bypass them fearing they are not pure enough. I think they are the best feature of the preamp. I just wish they didn't have separate L and R controls. That was just dumb.

    Peter, Can the PAS 2 still benefit from the addition of a 1uf capacitor on the output like the 3X uses off the bass control? I think they have a potential DC offset issue otherwise if I am correct.
    avatar
    peterh

    Posts : 1054
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Started down the road.

    Post by peterh on Mon Aug 20, 2018 3:55 pm

    CNCfan,
    a wise decision to keep the PAS for now and concentrate on the ST70.
    When the St70 is "in business" one could adopt the ears, and when time
    is right continue on other things.

    As regards for st70; i guess you can have a original board for close to nothing to
    start with. Yes it's an fragile board, and yes, unless you have working 7199 OR
    adapters to replace with 6U8, you have to cut three traces and re-pin . But as a
    starting point that may be ( or will be ) replaced among the line, it could be a
    starting point.
    You have transformers to buy, dynakitparts is a good source. Working with the
    dynaco build description is a very good starting point. A quad of cheap EL34
    ( yes cheap but a matched quad) to the initial hours is beneficial as you don't cry
    tears if you should damage them.

    Happy building, and observe security issues. B+ is lethal !
    avatar
    peterh

    Posts : 1054
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Started down the road.

    Post by peterh on Mon Aug 20, 2018 3:58 pm

    PAS 2 ( or any non-X) will benefit from a cap at the output post.
    Mount it at the output post, bewtween the gree ( or red) wire, and before the 470k resistor.
    0.5 plastic will do just fine, a 1uF electrolytic also. Aviod tantalum everywhere !

    Sponsored content

    Re: Started down the road.

    Post by Sponsored content


      Current date/time is Wed Nov 14, 2018 11:08 pm