Im not totally clued up about this, but from what I gather the G36 bias Oscillator frequency is 70 kc/s , can this be changed to a higher frequency to erase modern tape? Or am I totally wrong about this and it would require a lot more than a higher bias frequency?
Basically I don't want to be buying old tape of EBay, Id also like the machine to be set up for new tape so I don't need to adjust anything every time I buy old tape, new tape is a bit more expensive but at least I wouldn't have to faf around .
Anybody know if this can be done?
Basically I don't want to be buying old tape of EBay, Id also like the machine to be set up for new tape so I don't need to adjust anything every time I buy old tape, new tape is a bit more expensive but at least I wouldn't have to faf around .
Anybody know if this can be done?
Yes you can increase the frequency and I believe some additional erase current can be had. Try to find Charles King's "Greening the ReVox G36" which was published by Audio Amateur decades ago. I no longer have the article unfortunately.
Increasing the frequency per se will not improve erase, you need more head current and I would be suprised if you can get both with the existing erase head.
However, if someone has done it.....
In the old days there was a rule of thumb for professional machines that the bias frequency should be five times the highest recorded frequency. Whilst it was easy to increase bias freqency it was very difficult to get good erase with the metal heads then available since the losses became too high.
I believe some early machines used a relatively low erase frequency and picked of the third harmonic for bias.
Ferrite erase heads helped a lot here but even so double gapped heads were essential to erase high level tapes below the noise floor.
However, if someone has done it.....
In the old days there was a rule of thumb for professional machines that the bias frequency should be five times the highest recorded frequency. Whilst it was easy to increase bias freqency it was very difficult to get good erase with the metal heads then available since the losses became too high.
I believe some early machines used a relatively low erase frequency and picked of the third harmonic for bias.
Ferrite erase heads helped a lot here but even so double gapped heads were essential to erase high level tapes below the noise floor.
On the moment I"m working on my own G36 high speed and going to try this when I 'm ready with the playback amplifier.
In the article from Charles King he changed the capacitor C32 to 680pf but also the bias trap caps c26/29 250 pf and c48/c76 470 pf.
I have Mr Kings files on my computer, I must read through them again to refresh my memory.
So guys, just so I am clearer, to use modern tape I need a stronger erase current to erase the tape, do I really need the bias to be at a higher frequency to record? I spoke to a member of the Revox fan forum who uses RMG LPR 35 but erases the tape by other means, I have also been told by a technician that RMG SM911 or better SM900 will work fine on the G36 yet another tech told me the bias is too low and the record EQ is all wrong.
I am hearing mixed opinions about this, some people say new tape wont work on the G36 and some people say it does,
So , I am wondering, the G36 was constantly being updated with a MK1 , 2 and MK 3, could this be where the confusion comes from?
I did read that during production of the G36 tape formulations did change and thus so did the G36, they even changed the heads towards the end of production, so , could it be the latter machine's work better with more modern tape?
I guess the best thing to do is buy new tape and find out, if it works then I might be onto a winner.🙂 My machine is a MK 3, serial is 774xx so it is quite late in the production run and at the end of the month I will have the latter type heads for it, its already got a latter type record head that was changed at some point but they are looking very worn.
So guys, just so I am clearer, to use modern tape I need a stronger erase current to erase the tape, do I really need the bias to be at a higher frequency to record? I spoke to a member of the Revox fan forum who uses RMG LPR 35 but erases the tape by other means, I have also been told by a technician that RMG SM911 or better SM900 will work fine on the G36 yet another tech told me the bias is too low and the record EQ is all wrong.
I am hearing mixed opinions about this, some people say new tape wont work on the G36 and some people say it does,
So , I am wondering, the G36 was constantly being updated with a MK1 , 2 and MK 3, could this be where the confusion comes from?
I did read that during production of the G36 tape formulations did change and thus so did the G36, they even changed the heads towards the end of production, so , could it be the latter machine's work better with more modern tape?
I guess the best thing to do is buy new tape and find out, if it works then I might be onto a winner.🙂 My machine is a MK 3, serial is 774xx so it is quite late in the production run and at the end of the month I will have the latter type heads for it, its already got a latter type record head that was changed at some point but they are looking very worn.
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In short:-
You need more erase current but not a higher frequency to erase a high output tape.
You will need a higher bias current and record output level and different EQ to get the best out of a high output tape. The G36 may or may not be capable of this, others may know more about the specific machine.
You do not need a higher bias frequency unless you alter the EQ circuitry to extend the record/ play frequency response of more modern tapes.
You should check that the input circuitry of the replay amps doesn`t overload with a higher input - this was a problem when using some early tape machines with later tape types.
If you only increase the bias current high output tapes will work but without most of the improved performance available.
You need more erase current but not a higher frequency to erase a high output tape.
You will need a higher bias current and record output level and different EQ to get the best out of a high output tape. The G36 may or may not be capable of this, others may know more about the specific machine.
You do not need a higher bias frequency unless you alter the EQ circuitry to extend the record/ play frequency response of more modern tapes.
You should check that the input circuitry of the replay amps doesn`t overload with a higher input - this was a problem when using some early tape machines with later tape types.
If you only increase the bias current high output tapes will work but without most of the improved performance available.
Try this
Hi Guys,
Would agree that the erase current is more "critical" than the frequency.
Looked back in my files and found that Jukka Tolonen recommended checking that R118 in the power supply feeding the erase oscillator be 1K (was 2.2K in some units) to get the B+ up to 215V.
You could also try increasing the 220pf caps (C30and 31) that feed the erase signal to the bias pots to say 330 or even 390pf. That should give you plenty of "umpf".
Regarding the 36 Mark upgrades, per my article, the original "G series began with S/N 35001 and had a lever switch to sense end of tape but no bias traps, the next upgrade (around S/N 48401) added the bias traps and modified the motor control circuitry a bit. The MK 3 series (around 58000) included an optical tape sensor and a redesigned motor/capstan coupling assembly. The tape heads were also "upgraded" from the "epoxy looking" cylinders to the more modern case types used in the Studer decks.
Total aside; Studer/Revox made all their own heads until a fire destroyed that facility in the early 2000's.
Charles King
Hi Guys,
Would agree that the erase current is more "critical" than the frequency.
Looked back in my files and found that Jukka Tolonen recommended checking that R118 in the power supply feeding the erase oscillator be 1K (was 2.2K in some units) to get the B+ up to 215V.
You could also try increasing the 220pf caps (C30and 31) that feed the erase signal to the bias pots to say 330 or even 390pf. That should give you plenty of "umpf".
Regarding the 36 Mark upgrades, per my article, the original "G series began with S/N 35001 and had a lever switch to sense end of tape but no bias traps, the next upgrade (around S/N 48401) added the bias traps and modified the motor control circuitry a bit. The MK 3 series (around 58000) included an optical tape sensor and a redesigned motor/capstan coupling assembly. The tape heads were also "upgraded" from the "epoxy looking" cylinders to the more modern case types used in the Studer decks.
Total aside; Studer/Revox made all their own heads until a fire destroyed that facility in the early 2000's.
Charles King
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Even with the upgrades stellavox suggests I found that bulk erasure first was the best assurance of a good recording result with this deck.
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