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    A New ST70 Driver Board Design?

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    scrotuss

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    Post by scrotuss on Tue Mar 26, 2019 6:01 pm

    Have I been asleep, or do we have a new entry in the ST70 driver sweepstakes? I see an Erhard Audio board advertised that includes an octal driver design plus a SS power supply. Anyone familiar with this? Any comments?
    tubes4hifi
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    Post by tubes4hifi on Tue Mar 26, 2019 8:40 pm

    another total ripoff !!
    PeterCapo
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    Post by PeterCapo on Wed Mar 27, 2019 11:37 am

    tubes4hifi wrote:another total ripoff !!

    ?

    Thought you guys were business associates of sorts?
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    scrotuss

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    Post by scrotuss on Wed Mar 27, 2019 12:25 pm

    PeterCapo wrote:
    tubes4hifi wrote:another total ripoff !!

    ?

    Thought you guys were business associates of sorts?


    Have I wandered into a turf war?
    erhard-audio
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    Post by erhard-audio on Wed Mar 27, 2019 2:04 pm

    tubes4hifi wrote:another total ripoff !!

    well actually not. The circuits are different enough to not cause any 'issues'  Smile  plus the power supply is solid state replacing the tube rectifier and multi cap, all incorporated on one pcb. This makes our ST-70 upgrade kit quite different and purely aimed at those who prefer the sound of the 6SN7 family of tubes.
    Peter W.
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    Post by Peter W. on Wed Mar 27, 2019 2:58 pm

    It has been a while since I indulged in a good rant. Be warned.

    Note for the Record - I am NOT writing of modern VTA equipment, but of OEM Dynaco.

    Back in the day, Dynaco was very much the VW of audio equipment, and contemporaneous with VW in their respective heydays. David Hafler designed or hired designers who operated along the lines of Mad Man Muntz (look him up), and when it came to purchasing, squeezed every nickel until Jefferson howled. Where he did not compromise was with the transformers and the tubes, but, like the Saturn 5, pretty much every other part and piece came from the lowest bidder. To the point that boards and parts within the same unit performing the same function would often vary. Until Jefferson Street, and not entirely even then, all the kits and complete units were packed in sheltered workshops. Kits were then sent to dealers. Assembled units were shipped to Drexel engineering students working on consignment. Boards were assembled by jobbers, common in the region at that time. Hence any piece surviving until today is quite unlikely to be identical to another piece of the same model.

    To which we add:
    Phenolic boards - prone to cracking and broken traces.
    Un-annealed solid wire - prone to being nicked in the stripping process.
    Vastly differing soldering techniques, solders used, and care taken.
    Normal human error X each individual assembler vs. actual trained technicians.
    After which, by guess and by God, most of the stuff actually worked!

    Fast Forward 36-or-so years since the last bit of Dynaco escaped from Blackwood, NJ, and very nearly 40 years since the last bit of tube equipment snuck out of Dynaco altogether. Add thousands of heating/cooling cycles. Aging  passive components and so forth. Is it any wonder that vulnerable parts such as phenolic boards started to fail? And (cheap) carbon resistors, phenolic sockets, and on and on. But on items made in their hundreds-of-thousands, that, like VW air-cooled cars became cult-items early on.

    Hence the replacement industry was born.

    Then certain types of tubes became scarce.

    Hence the substitution industry was born.

    The two got together to form an unholy alliance. And the multiplicity of options was developed - only because it could be. Not because it was necessarily good, better, best, worse or worst. And multiple cottage industries were born.

    At its most simple:

    a) An original Dynaco Phenolic Board is able to be salvaged safely and effectively unless: It has experienced physical damage to the point of missing pieces. OR: It has burnt to the point of eliminating traces entirely.
    b) Rare tubes such as the 7199 may be replaced using a simple adapter to the alternate tube. But if all the 7199s hoarded by audio people (GUILTY!) were to come out of hiding, it would rapidly become a $5 tube.
    c) Back in the day, the uniformity between tubes of the same nominal type one-to-another was very nearly infinitely closer than it is today. So, "tube rolling" was not as obvious an exercise as it might be today.
    d) Tube equipment, then-and-now was not and is not an utterly precise process with utterly predictability-to-the-milli-whatever.

    Whether it is Erhard, VTA, Curcio, Dynakit Part or any of several other suppliers and sources, on an OEM Dynaco device, the results will not be manifestly different from OEM *IF* the OEM is in good condition and up to all specifications. Very nearly certainly not obviously distinguishable via both aural or instrument testing assuming the tests protocols were valid.

    It is my contention that whereas there are valid, useful and enhancing modifications to be made to the power-supply, bias supply, switchgear, pots, parts and pieces, the audio sections are best left within the original design. And, other than the X-type center-null pots, there is NO part or piece that may not be had off-the-shelf today. Even the PECs.

    There is nothing inherently wrong with the 7199 other than scarcity.
    There is no reason for Octal driver tubes on a ST-70. And they also pose a risk to the OEM power transformer.
    100% of the passive parts on the typical Dynaco board may be replaced for less than $10, with parts of far higher quality than OEM - despite the fact that most of those OEM parts are fine today, 50+ years later. And, in making such replacements, one learns some useful skills - soldering and de-soldering, measuring values, placement, polarity - and becomes more acquainted with the device.

    Let me make an actionable statement supported by over 40 years in the hobby:

    80% of the time, "I wonder if" is a blind alley. Of that remaining 20%, 10% will be no-discernible-change. Of that remaining 10%, 8% will be a disappointment. And 2% will be a remarkable positive change *BECAUSE OF* an unrecognized defect in the OEM part.

    Tubes sound different. Especially today. But, it is the tubes, not the circuitry around them. And the "different" sound is not necessarily good. Or, bad, for that matter. Will you like those differences? That, again in my opinion, depends on expectations and internal honesty.

    The after-market audio industry that has been built around Dynaco depends very much on two things: those wishing to maintain what the have in the face of age and wear, and those who believe that what they have may be made to sound better via various forms of magic, black and white, and all shades and hues between. I support the former, and I am dubious of the latter.
    Dave_in_Va
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    Post by Dave_in_Va on Wed Mar 27, 2019 4:19 pm

    I'm disappointed. That rated fairly low on the rantometer (don't worry, it's an expensive one with new batteries).
    Smile
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    Big Harry

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    Post by Big Harry on Wed Mar 27, 2019 6:36 pm

    I replaced the driver boards in both of my ST70's with VTA boards using 12AU7's. Both units were working with the original recapped boards and 7199 tubes which I have few NOS spares. I replaced the boards because I could and wanted to try something different. To me the VTA boards are an improvement, use readily available tubes and have individual bias adjustments which is a plus. Is it worth the expense and effort of building up the VTA boards or a board from another supplier, that is up to the individual amp owner. I do know that using three 6SN7's with an original ST70 power transformer is probably not a good idea.
    PeterCapo
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    Post by PeterCapo on Wed Mar 27, 2019 6:55 pm

    Well said, Peter W. I rather agree. Trying a different circuit board for fun is one thing. But, the original Dynaco circuits are still up to the task and do not deserve the denigration they sometimes get.
    sKiZo
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    Post by sKiZo on Wed Mar 27, 2019 8:24 pm

    I would assUme the new board has some component swaps here and there to tailor the 6SN7 to the circuit? I know there's a camp around here that figure that would also be a good thing for the VTA boards, especially since there's a LOT of tubes in the 12AU7 family. Also that a 12BH7 pretty much requires some resistor swaps to get them into the sweet spot.
    erhard-audio
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    Post by erhard-audio on Wed Mar 27, 2019 8:35 pm

    Peter W. wrote:It has been a while since I indulged in a good rant. Be warned.

    Note for the Record - I am NOT writing of modern VTA equipment, but of OEM Dynaco.

    Back in the day, Dynaco was very much the VW of audio equipment, and contemporaneous with VW in their respective heydays. David Hafler designed or hired designers who operated along the lines of Mad Man Muntz (look him up), and when it came to purchasing, squeezed every nickel until Jefferson howled. Where he did not compromise was with the transformers and the tubes, but, like the Saturn 5, pretty much every other part and piece came from the lowest bidder. To the point that boards and parts within the same unit performing the same function would often vary. Until Jefferson Street, and not entirely even then, all the kits and complete units were packed in sheltered workshops. Kits were then sent to dealers. Assembled units were shipped to Drexel engineering students working on consignment. Boards were assembled by jobbers, common in the region at that time. Hence any piece surviving until today is quite unlikely to be identical to another piece of the same model.

    To which we add:
    Phenolic boards - prone to cracking and broken traces.
    Un-annealed solid wire - prone to being nicked in the stripping process.
    Vastly differing soldering techniques, solders used, and care taken.
    Normal human error X each individual assembler vs. actual trained technicians.
    After which, by guess and by God, most of the stuff actually worked!

    Fast Forward 36-or-so years since the last bit of Dynaco escaped from Blackwood, NJ, and very nearly 40 years since the last bit of tube equipment snuck out of Dynaco altogether. Add thousands of heating/cooling cycles. Aging  passive components and so forth. Is it any wonder that vulnerable parts such as phenolic boards started to fail? And (cheap) carbon resistors, phenolic sockets, and on and on. But on items made in their hundreds-of-thousands, that, like VW air-cooled cars became cult-items early on.

    Hence the replacement industry was born.

    Then certain types of tubes became scarce.

    Hence the substitution industry was born.

    The two got together to form an unholy alliance. And the multiplicity of options was developed - only because it could be. Not because it was necessarily good, better, best, worse or worst. And multiple cottage industries were born.

    At its most simple:

    a) An original Dynaco Phenolic Board is able to be salvaged safely and effectively unless: It has experienced physical damage to the point of missing pieces. OR: It has burnt to the point of eliminating traces entirely.
    b) Rare tubes such as the 7199 may be replaced using a simple adapter to the alternate tube. But if all the 7199s hoarded by audio people (GUILTY!) were to come out of hiding, it would rapidly become a $5 tube.
    c) Back in the day, the uniformity between tubes of the same nominal type one-to-another was very nearly infinitely closer than it is today. So, "tube rolling" was not as obvious an exercise as it might be today.
    d) Tube equipment, then-and-now was not and is not an utterly precise process with utterly predictability-to-the-milli-whatever.

    Whether it is Erhard, VTA, Curcio, Dynakit Part or any of several other suppliers and sources, on an OEM Dynaco device, the results will not be manifestly different from OEM *IF* the OEM is in good condition and up to all specifications. Very nearly certainly not obviously distinguishable via both aural or instrument testing assuming the tests protocols were valid.

    It is my contention that whereas there are valid, useful and enhancing modifications to be made to the power-supply, bias supply, switchgear, pots, parts and pieces, the audio sections are best left within the original design. And, other than the X-type center-null pots, there is NO part or piece that may not be had off-the-shelf today. Even the PECs.

    There is nothing inherently wrong with the 7199 other than scarcity.
    There is no reason for Octal driver tubes on a ST-70. And they also pose a risk to the OEM power transformer.
    100% of the passive parts on the typical Dynaco board may be replaced for less than $10, with parts of far higher quality than OEM - despite the fact that most of those OEM parts are fine today, 50+ years later. And, in making such replacements, one learns some useful skills - soldering and de-soldering, measuring values, placement, polarity - and becomes more acquainted with the device.

    Let me make an actionable statement supported by over 40 years in the hobby:

    80% of the time, "I wonder if" is a blind alley. Of that remaining 20%, 10% will be no-discernible-change. Of that remaining 10%, 8% will be a disappointment. And 2% will be a remarkable positive change *BECAUSE OF* an unrecognized defect in the OEM part.

    Tubes sound different. Especially today. But, it is the tubes, not the circuitry around them. And the "different" sound is not necessarily good. Or, bad, for that matter. Will you like those differences? That, again in my opinion, depends on expectations and internal honesty.

    The after-market audio industry that has been built around Dynaco depends very much on two things: those wishing to maintain what the have in the face of age and wear, and those who believe that what they have may be made to sound better via various forms of magic, black and white, and all shades and hues between. I support the former, and I am dubious of the latter.

    my goodness...that is certainly a long way to say you prefer the original circuits Very Happy
    There is no magic, false promises, hocus pokus, snake oil...you get the drift...it is just another option based on using the 6SN7 family of tubes, which many like and prefer to the 12XX7 family of tubes plus going away from using a rectifier tube and multi cap.
    Does it sound heaps better than the original Dynaco circuit or other upgrade offerings out there?....as we all know, sound is quite subjective.
    It is however a great circuit that delivers the sonic goods, nothing more and nothing less.
    PeterCapo
    PeterCapo

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    Post by PeterCapo on Wed Mar 27, 2019 8:37 pm

    So many kits, so little time...
    erhard-audio
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    Post by erhard-audio on Wed Mar 27, 2019 8:40 pm

    Big Harry wrote:I replaced the driver boards in both of my ST70's with VTA boards using 12AU7's. Both units were working with the original recapped boards and 7199 tubes which I have few NOS spares. I replaced the boards because I could and wanted to try something different. To me the VTA boards are an improvement, use readily available tubes and have individual bias adjustments which is a plus. Is it worth the expense and effort of building up the VTA boards or a board from another supplier, that is up to the individual amp owner. I do know that using three  6SN7's with an original ST70 power transformer is probably not a good idea.

    Extensive tests using three 6SN7's which do draw more current were carried out. No negative effects on the power transformer were found what so ever. By also removing the rectifier tube and hence not using the 5V winding, has given the power transformer a bit more 'breathing room' for one of the better words.
    In fact neither of the two 6.3VAC windings had any loss/drop and the power transformer runs surprisingly not really hot.
    If there was ANY doubt, we would not have released our kit. We don't do things half hearted!


    Last edited by erhard-audio on Wed Mar 27, 2019 8:46 pm; edited 1 time in total
    erhard-audio
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    Post by erhard-audio on Wed Mar 27, 2019 8:41 pm

    PeterCapo wrote:So many kits, so little time...

    LOL!!...right? bounce

    I should add, we had a LOT of requests over a long period if we could come up with our own ST-70 upgrade kit, so we decided to Wink
    Peter W.
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    Post by Peter W. on Thu Mar 28, 2019 10:27 am

    erhard-audio wrote:
    PeterCapo wrote:So many kits, so little time...

    LOL!!...right? bounce

    I should add, we had a LOT of requests over a long period if we could come up with our own ST-70 upgrade kit, so we decided to Wink

    Question:

    Does the standard cage fit over the replaced board? Looks close from the pictures.

    PeterCapo
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    Post by PeterCapo on Thu Mar 28, 2019 10:36 am

    I noticed the same. I had a similar issue when I laid out a cap board for my Stereo 35.  Something like this might help: https://stevensproducts.net/products.htm
    erhard-audio
    erhard-audio

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    Post by erhard-audio on Thu Mar 28, 2019 12:09 pm

    Peter W. wrote:
    erhard-audio wrote:
    PeterCapo wrote:So many kits, so little time...

    LOL!!...right? bounce

    I should add, we had a LOT of requests over a long period if we could come up with our own ST-70 upgrade kit, so we decided to Wink

    Question:

    Does the standard cage fit over the replaced board? Looks close from the pictures.


    it does indeed with room to spare Very Happy
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    scrotuss

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    Post by scrotuss on Fri Mar 29, 2019 7:36 pm

    But has anyone (other than Erhard Audio) taken the challenge and installed this board.  Any comparisons?
    erhard-audio
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    Post by erhard-audio on Sat Mar 30, 2019 9:20 am

    scrotuss wrote:But has anyone (other than Erhard Audio) taken the challenge and installed this board.  Any comparisons?

    Question Question that's an odd question....again, we would not be selling this if there was any doubt about its performance, fit, relative ease of construction, installation etc. etc., and yes, we have sold a number of these and the buyers are happy.
    If anyone requires additional information etc., please contact us directly, thank you.

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