MRL_Audio
RIP 2022
I am excited for you Bill. But one must first know that Perfectempo is one word.
That’ll be critical to proper restoration.
Another Stromberg Carlson Perfectempo Restoration...
- Thread starter hirscwi
- Start date
That’ll be critical to proper restoration.
That’ll be critical to proper restoration.
Yes. To restore requires some form of searching and if you Google "Perfect Tempo" you will only get non turntable results. But it is with jest as I am working closely will Bill to share my Perfectempo restoration experiences.
This gets a little tricky. If you only want mono, then any of the vintage correct carts would work. Stereo on the other hand was just emerging at that time and the number of proper compliant carts is limited and would only be conical. First to consider is the compliance. Here is a chart showing the best ones in green for best resonance:
Second to consider is the tracking force. Since the Stromberg Carlson unipivot does not have anti-skate, a cart with heavy tracking force (3 - 5 grams) should be used but that will pretty much limit you to a conical stylus. But if you retrofit an anti-skate, then you can get away with less tracking force and go with a plethora of elliptical stylus carts. Elac was one of the very early manufacturers of carts that would work but are very expensive and replacement stylus are hard to get. I picked a Shure M44C as the price was reasonable and replacement stylus' are available.
The Denon 103 might work as it is #5 compliant but specs a tracking force of 2.2 -2.8 grams. It would work for sure with anti-skate. There is a handy search tool for carts over at vinylengine that is quite handy.
Btw, I use 600,000 cst silicone damping fluid in my RA-498 tonearm.
John
Last edited:
Hi John,
Thanks for the info about possible carts. I would prefer stereo and it can be a bit more modern than the table/arm. I want to make the anti-skate for sure as it will allow some more choices.
It's helpful to know the viscosity of the silicone oil. I may have some about that weight already.
Thanks for the info about possible carts. I would prefer stereo and it can be a bit more modern than the table/arm. I want to make the anti-skate for sure as it will allow some more choices.
It's helpful to know the viscosity of the silicone oil. I may have some about that weight already.
I now have the S-C tonearm. It is the RA-498 arm and is the type originally used on this table. It may be the only arm made by Stromberg Carlson.
It does need a bit of work, but it's the real deal. A mere 42 grams of effective mass. Rewiring will be very simple - the wire runs from the headshell to a hol just before the attachment to the pivot. Then down through the hole in the base and to a terminal block where it connects to the phono cable.
This one may need a bearing insert in the upper pivot section.
It sits too low and bumps/impedes on the pivot structure. I think it may have originally had a brass insert. I don't think it will be too difficult to make an insert.
Hopefully I can have the arm replated.
A couple more shots:
It does need a bit of work, but it's the real deal. A mere 42 grams of effective mass. Rewiring will be very simple - the wire runs from the headshell to a hol just before the attachment to the pivot. Then down through the hole in the base and to a terminal block where it connects to the phono cable.
This one may need a bearing insert in the upper pivot section.
It sits too low and bumps/impedes on the pivot structure. I think it may have originally had a brass insert. I don't think it will be too difficult to make an insert.
Hopefully I can have the arm replated.
A couple more shots:
Last edited:
Here's further description of the underlying signal generator that I mentioned in an earlier post. It's called the "SG4"
The SG4 generates 4 low distortion, high accuracy sinewaves suitable for driving conventional audio power amps to create a multi-phase drive for turntable motors. The generator outputs a reference sinewave at 60/81Hz or 50/67.5Hz on the 0° pin. The 90° pin outputs an exact replica of the reference sinewave, but shifted +90° (Cosine) for driving 2 phase AC synchronous motors. The 120° & 240° pins output an exact replica of the reference signal, but shifted +120° and +240° respectively for driving a 3 phase motor. The SG4 is a sinewave generator only. You will need to add the necessary audio power amps and step-up transformers (if needed) to create the final signal to drive the motor. Low cost linear and class D amps are readily available on e-Bay and other on-line sources.
The SG4 uses a 20 bit DDS core implemented in software to generate the reference sinewave. Frequency resolution is 0.01Hz. Frequency range is 40.00-70.00 Hz for 33 RPM and 60.00-90.00 Hz for 45 RPM.
There are four 8 bit phase accumulators to generate the four phases. The reference signal is fixed, but the other 3 are adjustable in 1.5° steps ±15° maximum. D to A conversion for the 4 signals is done with 8 bit PWM at 18kHz. There are 4 LPFs on the board to convert the PWM signal to analog. The outputs are DC coupled, 5VPP and centered at 2.5VDC. Distortion is ~0.5% (-46dB) and frequency stability is 30 PPM.
Update: The firmware has been updated to version 1.02. A 7 bit linear taper attenuator has been added to ramp the voltage from 0 to 5VPP at start up when exiting standby mode. This should prevent the amplifiers from shutting down when first started as they will have time (~650mS) to overcome the core magnetization of the transformers. I also added a reduced output voltage mode, where the output voltage will automatically be reduced to a user programmed level after 5 seconds. The level is adjustable from 128 (maximum) to 64 (half voltage) in ~40mV steps which equates to ~1V steps at the transformer outputs.
The phase adjustment is 1.5°/step. One of the peculiarities of using a 16 bit phase accumulator with an 8 bit DAC (PWM in this case), is the limited precision math can create different points where a carry occurs (and thus an additional phase step). For most frequencies, this isn't noticeable as the difference in phase shifts is usually in the mSec range. In certain cases, the math works out where it becomes quite noticeable and in the audio range where it could affect performance. Using a 16 bit phase accumulator in the SG4, a nasty phase spur will occur on either side of 81.92Hz, which is fairly close to the frequency needed for 45 RPM. The new firmware hasn't hit the field as of yet, so there will be no need to do another exchange. V1.02 will ship with the attenuator capability, but will retain the 1.5° phase adjustment of the original.
The SG4 generates 4 low distortion, high accuracy sinewaves suitable for driving conventional audio power amps to create a multi-phase drive for turntable motors. The generator outputs a reference sinewave at 60/81Hz or 50/67.5Hz on the 0° pin. The 90° pin outputs an exact replica of the reference sinewave, but shifted +90° (Cosine) for driving 2 phase AC synchronous motors. The 120° & 240° pins output an exact replica of the reference signal, but shifted +120° and +240° respectively for driving a 3 phase motor. The SG4 is a sinewave generator only. You will need to add the necessary audio power amps and step-up transformers (if needed) to create the final signal to drive the motor. Low cost linear and class D amps are readily available on e-Bay and other on-line sources.
The SG4 uses a 20 bit DDS core implemented in software to generate the reference sinewave. Frequency resolution is 0.01Hz. Frequency range is 40.00-70.00 Hz for 33 RPM and 60.00-90.00 Hz for 45 RPM.
There are four 8 bit phase accumulators to generate the four phases. The reference signal is fixed, but the other 3 are adjustable in 1.5° steps ±15° maximum. D to A conversion for the 4 signals is done with 8 bit PWM at 18kHz. There are 4 LPFs on the board to convert the PWM signal to analog. The outputs are DC coupled, 5VPP and centered at 2.5VDC. Distortion is ~0.5% (-46dB) and frequency stability is 30 PPM.
Update: The firmware has been updated to version 1.02. A 7 bit linear taper attenuator has been added to ramp the voltage from 0 to 5VPP at start up when exiting standby mode. This should prevent the amplifiers from shutting down when first started as they will have time (~650mS) to overcome the core magnetization of the transformers. I also added a reduced output voltage mode, where the output voltage will automatically be reduced to a user programmed level after 5 seconds. The level is adjustable from 128 (maximum) to 64 (half voltage) in ~40mV steps which equates to ~1V steps at the transformer outputs.
The phase adjustment is 1.5°/step. One of the peculiarities of using a 16 bit phase accumulator with an 8 bit DAC (PWM in this case), is the limited precision math can create different points where a carry occurs (and thus an additional phase step). For most frequencies, this isn't noticeable as the difference in phase shifts is usually in the mSec range. In certain cases, the math works out where it becomes quite noticeable and in the audio range where it could affect performance. Using a 16 bit phase accumulator in the SG4, a nasty phase spur will occur on either side of 81.92Hz, which is fairly close to the frequency needed for 45 RPM. The new firmware hasn't hit the field as of yet, so there will be no need to do another exchange. V1.02 will ship with the attenuator capability, but will retain the 1.5° phase adjustment of the original.
biscuithead
Me likes the eargasm retroplasm...
Here is a bit of information about the Papst motor used on this table and others (e.g. Empire and some ROK). The source is Bill Carlin, owner of Phoenix engineering (creator or Roadrunner and Falcon devices).
"The Papst motor is a 3 phase hysteresis type which is synchronous, but has some differences from a typical AC synch motor. It does not use a permanent magnet for the rotor, so it does not exhibit cogging. Because of this, it is smoother, but can fall out of synch at higher torque loads (an AC synch motor maintains speed until it stalls), is less efficient and has a lower power factor than a similarly sized AC synch motor. Both motors require higher voltage to maintain torque at higher speeds, the the Papst motor can start to "slip" similar to an AC induction motor at 45/78 RPM (drop below speed, but still spin), where an AC synch motor would stall.
IMHO, the Hurst motors are cheaply constructed, the bearings and rotor being the weak points, both inconsistent from one motor to the next. The rotors do not appear to be well balanced and coupled with a sloppy bearing (and only one bearing at that, on the top only), some motors exhibit unacceptable vibration as well as the expected cogging."
Much more information is available
"The Papst motor is a 3 phase hysteresis type which is synchronous, but has some differences from a typical AC synch motor. It does not use a permanent magnet for the rotor, so it does not exhibit cogging. Because of this, it is smoother, but can fall out of synch at higher torque loads (an AC synch motor maintains speed until it stalls), is less efficient and has a lower power factor than a similarly sized AC synch motor. Both motors require higher voltage to maintain torque at higher speeds, the the Papst motor can start to "slip" similar to an AC induction motor at 45/78 RPM (drop below speed, but still spin), where an AC synch motor would stall.
IMHO, the Hurst motors are cheaply constructed, the bearings and rotor being the weak points, both inconsistent from one motor to the next. The rotors do not appear to be well balanced and coupled with a sloppy bearing (and only one bearing at that, on the top only), some motors exhibit unacceptable vibration as well as the expected cogging."
Much more information is available
mr_fixer
Active Member
Mine came with Pickering Stanton MkII which dates from that time, I found a needle for mine but have never listened to it yet.
biscuithead
Me likes the eargasm retroplasm...
Was it a Pickering Stanton 380?
mr_fixer
Active Member
I don't see anything that says 380, just Pickering MK II Stanton. I found a archived advertisement for this around 1959. Here are a couple pics of mine.
orthophonic
Super Member
Pickerings first stereo cartridge, Called the MarkII and the Stereo 90, also a version called the 371.
I don't see how powder coating could work on this arm as it would fill the gram scale on the wand. Also the counterweight is a precision fit over the wand. Plating is the way to go but pricey. Another alternative may be Cerakote.