regreening of Studer C37 !
Verfasst: Sonntag 24. Juni 2007, 16:15
The STUDER C37 was a modern concept for the time. There are several versions, from the mono full track “play back only”, to the 19-38cm/s stereo butterfly.
This machine was produced between 1962 and approximately 1970, before being replaced by A80. All electronics is modular, entirely with tubes.
The control circuit of mechanism, which uses diodes and 2 power Germanium transistors. 21 tubes equip the stereo machine. The audio part use ECC88-ECC83 charged by transformers.
Tape transport section :
The mechanical part is the most difficult point of a restoration like that. All the spare parts are not provided any more from STUDER. For this reason, it was necessary to manufacture the obsolete wearing parts.
The following parts was manufactured according to original specifications:
- Brake bands.
- Brake linings.
- Pinch Roller.
- Capstan elastic coupling strips.
- PTFE capstan washer.
- Heads (relapping).
- AEG reel adaptors.
Some of the essential measurement tools necessary for the mechanical adjustments :
The new spare parts:
Heads
Bloc heads complete
CINE reel adaptors.
AEG reel adaptors complete.
Pinch Roller.
Brake linings.
New brake linings on reel drum.
Brake bands & Brake linings.
Capstan elastic coupling strips & PTFE capstan washer.
Some mechanical organs of the machine:
First generation of the capstan motor (original condition) :
Capstan shaft.
After 40 years of vertical position, oil is naturally gone down at the bottom of the engine, which was very hard to turn! The engine badly lubricated heating and risk to burn… In addition, the performances of wow and flutter are also degraded. It is advisable to dismount all the unit, to remake a lubrication and to change the wearing parts.
Second generation of the capstan motor :
The last generation of this machine have a system of mechanical elastic coupling slightly different than the older. The flywheel is lighter, with 4 elastic strips. The holes on the periphery of the wheel, are used for balancing the mecanism.
New elastic strips 1 & 2 generation compatible.
Chassis.
The original painting is completely damaged.
The old chassis.
The painted chassis.
Reassembly of all the elements !
Air dashpot.
Reassembly in progress.
Checking of the tape guides. The exentricity is 1/100 of mm!
Checking of the tape transport mecanism.
Adjustment of brake system.
Checking of the brake tension.
Checking of the adjustment of each brake drum using a dynamometer. The use of a band starter is quite practical for this kind of tests… It is better to do this adjustment with the type of reel (metal, plastic, AEG plater) that the machine will use. For a perfect balance of the brakes (moment of braking), it is better to put the same type of reel on the machine on the right and on the left (same weight).
Tape tension balance adjustment.
Capstan idler pressure adjustment.
Checking of Tape tension with a Tentelometer. The pressure on the heads is around 100g (common value to the principal manufacturers of open reel recorder).
Mechanical test with different reels. Continuous run of more than 3H30 to check the stability of the adjustments.
The following stage will be the checking of the wow and flutter and the calibration audio.
Electronics section :
The electronic part restoration is relatively simple, but very long. All the tubes, chemical condensers as well was replaced.
Before:
After:
Several connectors and screw was also changed !
These old machines runing a lot during the last years much. The power supply are burned and not reliable in this state (wire breaking under the effect of heat, blows of heats at many places, etc)... It is essential to completely rebuilt the module of PSU regulation of each machine.
Before:
After:
Twin Chemical caps (40 years old) was replaced by new ones from JJ.
Some Chemical caps are sometimes in difficult places of access. Fortunately that the machine are completly dismountled, it is thus possible to rebuilt each module, in comfortable working condition.
New tubes from JJ, RTC & RSD N.O.S.
Azimuth adjustment:
10KHZ
20KHZ
Central capstan shaft adjustment (3 centering screw)
Wow & Flutter deviations mesurements.
The fluctuation can be bring back very low by action on 3 centrering screw (capstan motor body). Here, the value is approximately 0.1% RMS. This value is conform to the original specifications. With weighting network, the value is even lower. Testify to the quality of the transport mecanism.
Audio calibration on SM900 EMTEC:
0dbm IN= 0dbm OUT
Distorsion : 0.6 to 2% (depending to the speed and curve).
B/W 19cm/s : 16Khz (-1db)
B/W 38cm/s: 20Khz (-1db)
Linearity : +/- 1db between 100Hz et 20 Khz (38cm/s).
S/N ratio : 45/55db
The End !
This machine was produced between 1962 and approximately 1970, before being replaced by A80. All electronics is modular, entirely with tubes.
The control circuit of mechanism, which uses diodes and 2 power Germanium transistors. 21 tubes equip the stereo machine. The audio part use ECC88-ECC83 charged by transformers.
Tape transport section :
The mechanical part is the most difficult point of a restoration like that. All the spare parts are not provided any more from STUDER. For this reason, it was necessary to manufacture the obsolete wearing parts.
The following parts was manufactured according to original specifications:
- Brake bands.
- Brake linings.
- Pinch Roller.
- Capstan elastic coupling strips.
- PTFE capstan washer.
- Heads (relapping).
- AEG reel adaptors.
Some of the essential measurement tools necessary for the mechanical adjustments :
The new spare parts:
Heads
Bloc heads complete 
CINE reel adaptors. 
AEG reel adaptors complete. 
Pinch Roller. 
Brake linings.
New brake linings on reel drum. 
Brake bands & Brake linings.
Capstan elastic coupling strips & PTFE capstan washer.Some mechanical organs of the machine:
First generation of the capstan motor (original condition) :
Capstan shaft. After 40 years of vertical position, oil is naturally gone down at the bottom of the engine, which was very hard to turn! The engine badly lubricated heating and risk to burn… In addition, the performances of wow and flutter are also degraded. It is advisable to dismount all the unit, to remake a lubrication and to change the wearing parts.
Second generation of the capstan motor :
The last generation of this machine have a system of mechanical elastic coupling slightly different than the older. The flywheel is lighter, with 4 elastic strips. The holes on the periphery of the wheel, are used for balancing the mecanism.
New elastic strips 1 & 2 generation compatible.
Chassis. 
The original painting is completely damaged.
The old chassis.
The painted chassis.
Reassembly of all the elements !
Air dashpot.
Reassembly in progress.
Checking of the tape guides. The exentricity is 1/100 of mm! 
Checking of the tape transport mecanism.
Adjustment of brake system.
Checking of the brake tension.Checking of the adjustment of each brake drum using a dynamometer. The use of a band starter is quite practical for this kind of tests… It is better to do this adjustment with the type of reel (metal, plastic, AEG plater) that the machine will use. For a perfect balance of the brakes (moment of braking), it is better to put the same type of reel on the machine on the right and on the left (same weight).
Tape tension balance adjustment.
Capstan idler pressure adjustment.
Checking of Tape tension with a Tentelometer. The pressure on the heads is around 100g (common value to the principal manufacturers of open reel recorder). 
Mechanical test with different reels. Continuous run of more than 3H30 to check the stability of the adjustments.The following stage will be the checking of the wow and flutter and the calibration audio.
Electronics section :
The electronic part restoration is relatively simple, but very long. All the tubes, chemical condensers as well was replaced.
Before:
After:
Several connectors and screw was also changed !These old machines runing a lot during the last years much. The power supply are burned and not reliable in this state (wire breaking under the effect of heat, blows of heats at many places, etc)... It is essential to completely rebuilt the module of PSU regulation of each machine.
Before:
After:
Twin Chemical caps (40 years old) was replaced by new ones from JJ.
Some Chemical caps are sometimes in difficult places of access. Fortunately that the machine are completly dismountled, it is thus possible to rebuilt each module, in comfortable working condition.
New tubes from JJ, RTC & RSD N.O.S.Azimuth adjustment:
10KHZ 
20KHZ
Central capstan shaft adjustment (3 centering screw)
Wow & Flutter deviations mesurements.The fluctuation can be bring back very low by action on 3 centrering screw (capstan motor body). Here, the value is approximately 0.1% RMS. This value is conform to the original specifications. With weighting network, the value is even lower. Testify to the quality of the transport mecanism.
Audio calibration on SM900 EMTEC:
0dbm IN= 0dbm OUT
Distorsion : 0.6 to 2% (depending to the speed and curve).
B/W 19cm/s : 16Khz (-1db)
B/W 38cm/s: 20Khz (-1db)
Linearity : +/- 1db between 100Hz et 20 Khz (38cm/s).
S/N ratio : 45/55db
The End !