mfrench
Addicted Member
Let me start with this image of the finished TT as a hook; Then, I'll start over with the build from the start.
I've had a few postings about this deck in various threads, here at AK; but I've not started a feature thread about it yet. A few of you Lencophiles have likely already seen this buildup over at LH. There will not be a pop quiz following the presentation.
So without further adieus and ramblings,....
This is my Presto Recording Corporation - Pirouette T18DC_mod, c. 1955; reborn 2009/2010; An idler drive TT for the 21st century.
It started as a 3-speed, three wheel idler drive TT, circa 1955; and is of the last of the true vintage pre-Bogen era Prestos.
It bears the mark of his noodliness, the Flying Spaghetti Monster:
That mark, ^^, made it a holy divine piece, and I endeavored to restore it to its former glory - little did I realize that it was in no mood for any such restoration; It was going to demand a far more intensive effort! It demanded a complete drive-line redesign to drag it out of mid-20th century mono era, and into the second decade of the 21st century.
The first thing to do was look under the skirt to see what I was in store for.
OK,... So it had three idler wheels,... interesting.
What drove these wheels?
The black cube from hell, thats what! I picked up on a nickname from it, coined by another member here, mopic5, as he is involved in a similar deck project, with the same motor. He called it, most appropriately, the Borg Death Cube. The name resonates in infamy.
The Borg Death Cube had a three step capstan-pulley that was seized to it, and it took forever to get it freed.
Well, in dissecting the OE drive-line, I found that the motor mounts were shot, and had been improperly hung, with washers that caused a rigidity of the motor to the top plate, rather than as a suspension as had been designed.
OK,... So, motor suspension is shot.
I'd removed and had already sent the idler wheels out to the overhauler, Ed Crockett, for some new tires.
Lets take the bearing off and clean it; great condition, but with some wear; not egged - solid.
I lubed the motor, actually drilling out some rivets to open the motor, and deep lube it, regrease the thrust plate, polish the bushings, etc. Problem: there was pitting on the upper motor spindle within the bushing, and matching corrosion in the upper bushing.
The idler wheels returned, hook it all up and give it a spin,...
rumble, and lots of noise. Damn.
So, I take the motor out, and flip the bushings top-to-bottom. This helped, but the damage to the spindle shaft seems to have reduced its diameter to a degree that its sloppy on the top of the bushing.
I tried every trick in the book to quiet the motor, but, all I could do was reduce the amount of noise, but it was still at an unacceptable level.
After months of trying to fix the motor, I gave up on it, and, decided to install a new motor into the old original three-wheel driveline.
So, I started shopping out motors and had a hankering to build it with a DC motor, and a precision controller.
I found a motor, based purely on its size comparison, to ensure that I could fit it into the same space as the original assembly. It was from a local company that designs and builds the controllers here locally, and imports the motors that they re-badge.
And it had a matching driver that offered intimate monitoring and control:
The driver has three hall sensors around a 360º circumference. They monitor the speed of the motor, and keep it locked at an unwavering dead-to-speed locked RPM. It does not slightly wander off speed. I can carry speeds from a zero-stop to hundreds of RPM at the platter.
A new motor mounting plate is built, and new motor mount suspension grommets are installed at each point.
A new mounting achieved:
New stainless steel vs. old mount:
OK,... So, new high tech motor and mount finished; Check, test.
Result: Newly realized driveline noise; AND, worse -- A realization that the original geometry of the three wheel design favored the newly developed 33 and 45rpm speeds, and only included the 78rpm speed as a nice added speed, as it was still so close to that era. The deck was fundamentally flawed and noisy if you tried to adjust the motor tensioning to accommodate all three speeds in a single adjustment.
The design is best described as a power take up from a rotating platter and its interface with the wheels and capstan. The power uptake regime was designed to transfer the capstan -> wheel -> platter at approximately two positions; 5 o'clock and 7 o'clock, with a crucial center point line being marked by the 6 o'clock to 12 o'clock center line, from bearing to capstan. Look at the image above, and mentally draw a line between the bearing center and the 33prm graphic on the top plate, with the bottom of that line being 6 o'clock.
The 33/45 rpm speeds power take-up were on the 5 o'clock side of the 6 o'clock line, and the 78 rpm wheel was at the 7 o'clock mark - you can see that in the last image, above.
At the 5 o'clock position, the wheels are captured by the downhill motion of the platter, and driven into the capstan, in an ideal, forced-into-compliance motion. The 78rpm wheel, however, was on the uphill swing of the platter, past 6 o'clock, and, the only way to properly engage that wheel was to adjust for it; But by adjusting for it, 33 and 45 rpms became noisy. A vicious cycle ensued.
By adjusting to 33/45, you barely engaged the 78 wheel. Ideally it would need a spring to engage the 78rpm wheel, but its design precluded any spring, as such force would only pull the wheel further away. Believe me, I looked at many options.
Presto designed this deck with two wheels too many.
The drive-line is flawed in that regard, and it wasn't until I'd dropped a few hundred dollars into the project that I realized the flaw; it was too deeply buried to be able to detect in the early stages. It would be a decent enough 33/45 deck, or a fine 78rpm deck; just not a universal three speed deck.
So, now I have to answer to Sarge about why this project has stalled, despite spending like a drunken sailor up to this point.
Its probably time for a break about now,....
[/page one]
I've had a few postings about this deck in various threads, here at AK; but I've not started a feature thread about it yet. A few of you Lencophiles have likely already seen this buildup over at LH. There will not be a pop quiz following the presentation.
So without further adieus and ramblings,....
This is my Presto Recording Corporation - Pirouette T18DC_mod, c. 1955; reborn 2009/2010; An idler drive TT for the 21st century.
It started as a 3-speed, three wheel idler drive TT, circa 1955; and is of the last of the true vintage pre-Bogen era Prestos.
It bears the mark of his noodliness, the Flying Spaghetti Monster:
That mark, ^^, made it a holy divine piece, and I endeavored to restore it to its former glory - little did I realize that it was in no mood for any such restoration; It was going to demand a far more intensive effort! It demanded a complete drive-line redesign to drag it out of mid-20th century mono era, and into the second decade of the 21st century.
The first thing to do was look under the skirt to see what I was in store for.
OK,... So it had three idler wheels,... interesting.
What drove these wheels?
The black cube from hell, thats what! I picked up on a nickname from it, coined by another member here, mopic5, as he is involved in a similar deck project, with the same motor. He called it, most appropriately, the Borg Death Cube. The name resonates in infamy.
The Borg Death Cube had a three step capstan-pulley that was seized to it, and it took forever to get it freed.
Well, in dissecting the OE drive-line, I found that the motor mounts were shot, and had been improperly hung, with washers that caused a rigidity of the motor to the top plate, rather than as a suspension as had been designed.
OK,... So, motor suspension is shot.
I'd removed and had already sent the idler wheels out to the overhauler, Ed Crockett, for some new tires.
Lets take the bearing off and clean it; great condition, but with some wear; not egged - solid.
I lubed the motor, actually drilling out some rivets to open the motor, and deep lube it, regrease the thrust plate, polish the bushings, etc. Problem: there was pitting on the upper motor spindle within the bushing, and matching corrosion in the upper bushing.
The idler wheels returned, hook it all up and give it a spin,...
rumble, and lots of noise. Damn.
So, I take the motor out, and flip the bushings top-to-bottom. This helped, but the damage to the spindle shaft seems to have reduced its diameter to a degree that its sloppy on the top of the bushing.
I tried every trick in the book to quiet the motor, but, all I could do was reduce the amount of noise, but it was still at an unacceptable level.
After months of trying to fix the motor, I gave up on it, and, decided to install a new motor into the old original three-wheel driveline.
So, I started shopping out motors and had a hankering to build it with a DC motor, and a precision controller.
I found a motor, based purely on its size comparison, to ensure that I could fit it into the same space as the original assembly. It was from a local company that designs and builds the controllers here locally, and imports the motors that they re-badge.
And it had a matching driver that offered intimate monitoring and control:
The driver has three hall sensors around a 360º circumference. They monitor the speed of the motor, and keep it locked at an unwavering dead-to-speed locked RPM. It does not slightly wander off speed. I can carry speeds from a zero-stop to hundreds of RPM at the platter.
A new motor mounting plate is built, and new motor mount suspension grommets are installed at each point.
A new mounting achieved:
New stainless steel vs. old mount:
OK,... So, new high tech motor and mount finished; Check, test.
Result: Newly realized driveline noise; AND, worse -- A realization that the original geometry of the three wheel design favored the newly developed 33 and 45rpm speeds, and only included the 78rpm speed as a nice added speed, as it was still so close to that era. The deck was fundamentally flawed and noisy if you tried to adjust the motor tensioning to accommodate all three speeds in a single adjustment.
The design is best described as a power take up from a rotating platter and its interface with the wheels and capstan. The power uptake regime was designed to transfer the capstan -> wheel -> platter at approximately two positions; 5 o'clock and 7 o'clock, with a crucial center point line being marked by the 6 o'clock to 12 o'clock center line, from bearing to capstan. Look at the image above, and mentally draw a line between the bearing center and the 33prm graphic on the top plate, with the bottom of that line being 6 o'clock.
The 33/45 rpm speeds power take-up were on the 5 o'clock side of the 6 o'clock line, and the 78 rpm wheel was at the 7 o'clock mark - you can see that in the last image, above.
At the 5 o'clock position, the wheels are captured by the downhill motion of the platter, and driven into the capstan, in an ideal, forced-into-compliance motion. The 78rpm wheel, however, was on the uphill swing of the platter, past 6 o'clock, and, the only way to properly engage that wheel was to adjust for it; But by adjusting for it, 33 and 45 rpms became noisy. A vicious cycle ensued.
By adjusting to 33/45, you barely engaged the 78 wheel. Ideally it would need a spring to engage the 78rpm wheel, but its design precluded any spring, as such force would only pull the wheel further away. Believe me, I looked at many options.
Presto designed this deck with two wheels too many.
The drive-line is flawed in that regard, and it wasn't until I'd dropped a few hundred dollars into the project that I realized the flaw; it was too deeply buried to be able to detect in the early stages. It would be a decent enough 33/45 deck, or a fine 78rpm deck; just not a universal three speed deck.
So, now I have to answer to Sarge about why this project has stalled, despite spending like a drunken sailor up to this point.
Its probably time for a break about now,....
[/page one]
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