Byer Logo

Rola 77 Mk III Revisions

The Rola 77 Mk III like other products was revised during the life of this model, 1962 to 1972/3. All of the advertising refers to the machine as a Rola 77 Mk III however, there are two versions Rola 77 Mk III and Rola 77 Mk IIIB. There are at least four public releases of the schematics, amplifier drawing number 12-0072, revisions "F", "N", "R", and "W" and the transport drawing number 12-0073, revisions "A", "H", "J", and "O".

Note: Not all schematic versions are currently available for download, please contact me if you need a specific schematic.

Unfortunately, apart from one revision I've not found any other records relating serial numbers on tape machines to drawing revision numbers, however, we do at least have dates for the revisions. You may be asking yourself what is so important about these circuit changes? If you want to correctly restore a machine or if you want to use a tape transport with an amplifier that have different serial numbers then you will need this information. It is important to note that if a 77Mk IIIB amplifier is used with a 77Mk III tape transport then record amplifier mute circuit can be damaged when the machine is placed in record mode. The best course of action is to check the transport circuit and upgrade it to the revision "E" schematic or later.


28 Dec 61Initial drawing release
A12 Feb 62C3 was 47nF now 22nF
A12 Feb 62C12 was 100pF now 68pF
A12 Feb 62R35 was 390k now 240k
A12 Feb 62R52 was 2k2 now 1k5
B9 Apr 62C11 was 47nF now 100nF
C10 May 62Mains indicator added, F1 deleted
D16 May 62CT2 was CV1, CT1 was CV2, CT3 was CV3
D16 May 62Functions added, C.N. 88
E24 May 62R86 and R87 were 220R now 150R
F22 Aug 62R45 was 1M now 100k, R46 was 680k now 270k
G-MNo information
N15 Dec 64Redrawn, no alterations
O4 Feb 66C46 was 22pF, deleted
P13 May 68C3 and C13 were 22nF now 47nF
P13 May 68C20 was 100pF now 47pF
P13 May 68C22 was 56pF now 22pF
P13 May 68Major revision to record eq circuit refer schematic
Q17 Jan 69Chang of earth point for R91 1k2
R27 Mar 69C12 was 68pF now 100pF
R27 Mar 69C46 added now 100pF
R27 Mar 69R34 was 180k now 390k
R27 Mar 69R53 was 3k3 now 2k7
R27 Mar 69R85 was 150k now 220k
*27 Mar 69Added C50 220pF, C51 56pF, R102 47k, R103 470k
S23 Feb 70C25 was 5n6F now 10nF
S23 Feb 70C29 was 25uF now 50uF, 25V
S23 Feb 70C50 was 220pF now 330pF
S23 Feb 70C51 was 56pF now 180pF
S23 Feb 70C52 added 56pF between C12 and RV3
S23 Feb 70C53 added 22pF between C15 and RV2
S23 Feb 70C54 added 56pF across R63
T14 May 70MB10 bridge recifier was 4 x 10B1
U16 Nov 70C55 added 100nF, 160V
V23 Feb 71Position of C55 corrected on the schematic
W15 Oct 71R13 was 56R now deleted
W15 Oct 71R18 and R19 was 10k now 100k
W15 Oct 71R4 and R5 was 270R now 1k2
W15 Oct 71R4 and R5 are now in parallel across R18 and R19

* The components are on drawing Rev R but are in listed in the change record.


16 Jan 62Initial drawing release
A10 May 62C35 added 0.1uF
A10 May 62R35 added 22R
A10 May 62Pole 2 added to SW1
BNo information
C-EMajor circuit revisions
C31 May 63No information except C.N. 269
D26 Jun 63No information except C.N. 293
E24 Jul 63No information except C.N. 294, applies to:
E24 Jul 63S/N 1771, 1772, 1803, 1811, 1812, and from 1838 inclusive
F17 Dec 63No information except C.N. 321
G29 Jan 64R33 was 1700R, 20W now 1000R, 20W
H24 Feb 64Rectifier diodes were 10B1 now 10B2
J16 Dec 64Redrawn, No alterations
K18 Jun 69R23 & R25 were 400R, 20W now deleted
K18 Jun 69R42 was 1k5, 10W now 2k 10W
K18 Jun 69R46 700R, 20W added
L14 Apr 700.5uF, 400V capacitor added (no info as to where in the circuit)
M14 May 70Rectifier diodes were 10B2 now EM402
N27 Jul 70R15 was 220R, 1W now 150R, 1W
O27 Jun 710.5uF 400V deleted
O27 Jun 71C31 2uF, or 2.5uF for PAPST capstan motor
O27 Jun 71R33 was 1k, 20W now 2k, 20W
O27 Jun 71R42 was 2k, 10W now 1k5, 10W
O27 Jun 71R46 was 700R, 20W now 1k, 20W
O27 Jun 71R47 400R, 20W added for PAPST capstan motor only