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Old 16th October 2013, 10:10 PM   #1
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Default Studer B67 follies

I just acquired one of these (7.5-15-30ips) through ebay for pretty cheap, but it is missing some pieces which I found replacements for, except no back or top or bottom panels which I still would want to find original parts for. (if somebody knows a person with some spare B67 back/top/bottom panels cluttering up their storage space, I would like to know) The heads in the unit look surprisingly unworn, so I wonder what its history was - did something major give out early in its life and so it was put in storage early? IAC, I should get some idea tonight when I power it up for the first time. Unfortunately, it has no pinch roller at the moment so I can't actually run a tape on it yet (I've got one on order from Germany, though.)

One thing I was considering was converting it to vacuum tube audio, so I pulled its tech manual. I was shocked to see that this high level mastering machine merely used around 2K Ohm resistance at the output of a NE5532 type amplifier (TDA1034B) to drive the music signal to the record head and that the playback amplifier first stage has a 330 ohm cathode, er...emitter resistor. The good news about that is that it should make conversion to tube audio much more straightforward than feared. I was afraid that these 'solid state' heads might be much harder to get good signal in and out of using tubes, but that may not be so much the case, given this.

Might get the vacuum tubes in the original box if I move the bias oscillator board over to the end - it was apparently set up to run with a separate bridge panel in a cart (which is why no back panel, etc), so I can punch out the existing bottom front panel for pots/meters for a more portable arrangement. I plan to keep it as a pretty basic line level deck, although adding two tube mic pres is a possibility - space and heat are probably already fairly marginal without tube mic pre's but I can work on that possibility.

I plan to add a couple playback features also including a tube phase correction circuit and a tube peak unlimit circuit that should extract 2-3 more headroom from tapes, potentially including those recorded on other machines. I've successfully prototyped both of these circuits a long time ago (need to find any notes), and was able to restore the peaks on a triangle waveform recorded 3 db into saturation with the peak unlimit and to get linear phase response to 21 Khz at 7.5 ips with the phase correction circuit (have an old scope photo of a 7 khz square wave with correctly phased 3rd harmonic with a record/playback signal). I also acquired a half worn set of EIA type 'butterfly' heads 'cheap' for it for another db of S/N so might be able to get overall SN equivalent to 2 track half inch with this quarter inch machine.
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Last edited by thoriated; 16th October 2013 at 11:03 PM.
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Old 17th October 2013, 08:40 PM   #2
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Some kinda bad news after power up. I noticed the left reel rotor always ran at full torque when enabled, and a few minutes into operation, a part on that side let its magic smoke out, whereupon the left reel rotor began running at full torque whenever power was on.

My initial response will be to replace all the more susceptible components for that reel motor torque control schematic (which are all located on a fairly small pcb next to that reel motor where there was a failure, except for a TO-3 case power transistor, which I may also replace) and hope the damage is limited just to that location.

Everything else appeared to come up normally except for a couple sticky tape lifters and the counter pushbutton - no fuses have popped so far.
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Old 21st October 2013, 10:31 PM   #3
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Still waiting on some parts to fix the left reel motor drive, as well as the pinch roller. I came across a Modern Recording and Music review of the B67 where they measured an A-weighted SN ration of 77 db with presumably a NAB eq'd machine using an Ampex 456 equivalent tape.

With EIA heads and my peak unlimiting circuit and a hotter tape than Ampex 456, SN's exceeding 80 db seem quite possible. Actually, I found one way to gainseverl db beyond this. If a tape is bulk erased, and then the record head is turned off during recording, that seems to drop the background noise by several db when recording. Anybody else notice this? Possibly mid-80's then if the electronics are quiet enough.
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Old 22nd October 2013, 04:42 AM   #4
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Ooops. In my last post, I meant 'turn off the erase head', not the record head for lower noise on a bulk erased tape. This makes me wonder if an erase head with a more slowly diminishing field might result in quieter tapes since it would approximate the slow field decrease of a bulk eraser a bit better?

Well, this evening, I got some of the replacement parts for the left reel driver board. When I pulled the board out to test it, a chunk of filter capacitor fell out, providing a clue. It turns out that one cap (0.47uf, 150 VAC) had gone short. There were three of them, so I replaced all three with 275VAC Grade B 0.47uF, and did a diode check of the power transistor and diode bridge which appeared ok. So I put it all back together and powered it up. It now appears both reel motors are working properly. So, all I need is to receive the pinch roller to start rolling tapes, it appears.

Of course there are still a few problems with the transport. It appeared to have been dropped at one time since there is a little distortion of the lower frame which shouldn't be too hard to deal with. The digital time counter has a couple of dead segments which I attribute to the display LEDs - need to troubleshoot that, plus its binding reset switch. And an anti-magnetic shield that is supposed to pop up in front of the playback head isn't working. However, the practical headstack I ordered also has one, so that might be a simple swap.

So, before the end of this week, I might be able to try running a few tapes through this machine.
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Last edited by thoriated; 22nd October 2013 at 04:49 AM.
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Old 24th October 2013, 08:09 PM   #5
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got the pinch roller last night, was able to roll a reel of tape, and checked the playback audio path. I see that since the unit was previously a horizontal case mount, it presumably once had an external VU bridge and some control switches that are now missing, so there was a break in the audio path for playback going through an external DB connector.

I found the point previous to that where the playback audio was routed to this external connector and tonight will try wiring that up to a pair of rca jacks and try playing through my HT initially. Assuming that works out, I can then try recording, but will have to wire an external potentiometer to the input circuit for that.
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Last edited by thoriated; 24th October 2013 at 08:15 PM.
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Old 25th October 2013, 06:14 PM   #6
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Soldered a pair of RCA jacks to the playback amplifier and ran some tape I had prerecorded from the early '90's. Overall, the operation is pretty sweet, and the machine is not too noisy.

I just found somebody in GB who is selling me the external panels that were missing with the original machine. Problem is, the price he is charging me for the panels actually exceeds the price of the original machine I paid (out of a rollaround rack) which is killing me, but I really felt like I had to bite the bullet here since several inquiries in the US failed to find anybody with spare external panels. I am still going to make my own side panels out of wood, though, since on the market, people are charging $300 and up for a pair.
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Old 28th October 2013, 11:33 PM   #7
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Well, I pulled out most of my old tapes I did on 10.5" reels, and I had forgot that I did most of them on Maxell UDXLII at 3 3/4 ips (mostly recorded from turntable). Of course the Studer won't play that speed since it is 7.5 - 30 ips, so I guess I will stay with my modified Ampex 351 for these tapes for my listening room.

Of course, some people might be wondering how I could have run Maxell UDXLII on a tube Ampex. The answer is that in the early '90's, I bought some Saki glass ferrite heads for it and reworked the bias oscillator to run at about 500 khz into the record head with a tube version of Dolby HX. I believe I was getting decent highs up to 15khz at 3 3/4 ips this way - UDXLII was supposed to be an iron oxide equivalent to 'chrome' or 'metal' cassette tapes back in the day, and really did feature super hot highs at low speeds compared to standard open reel tapes.

Anybody remember Saki glass ferrite heads? They were supposed to be pretty good quality back then, but now I don't see any discussion of them.
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Old 28th October 2013, 11:47 PM   #8
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Never heard of Saki heads until you mentioned it in your previous post, perhaps they were available only for a short period of time.

Sounds like the Studer is coming along pretty well. I spent a lot of time and effort, and some money on the much less worthy G36 a few years ago. I should have started with a better machine..
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Old 29th October 2013, 12:10 AM   #9
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I know there was some debate at the time about whether glass-ferrites sounded as good as some other head construction types, or could take enough bias, but they seemed ok there to me, although I never found out exactly what this debate was about, and I really liked the idea of their not wearing out quickly since I could detect noticeable wear on the original Ampex heads from my use within a couple of years.
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Old 30th October 2013, 10:32 PM   #10
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Well, I really did it this time. I won another busted B67 on Ebay - this one a slow speed model that is supposed to 'not make tape move'. I figured if I could get it going and add tube HX (which I've been working on on paper and believe I've simplified quite a bit) instead of a mic preamp, it would make a good machine for my stereo. I could add a 4-track playback head perhaps (switchable) in place of the stock tape scissors (that make me nervous) & switch at top of head block in that opening, and play tapes recorded that way at speeds down to 3 3/4 ips, as well as my Maxell EE tapes, if I replace the existing PB head with a B77 or PR99 or A700 type which is supposed to have a narrower gap.

I had a fairly easy time bringing up the first B67, so I am hoping for good success with this one also. One area of concern is that the transport operation is supposed to be controlled by a special IC, and if this is blown, I could see some issues/delays in getting it repaired. The person who put it up for auction claims that the motor control transistors could be blown, and that is certainly possible, but to see both reel motors *and* the capstan motor all out at once due to that raises a couple of questions. IAC, I still have some spare transistors and capacitors I didn't need to fix the first machine, so who knows?

It could also be a fuse, but I would assume that he would have ruled that out. However, you never know with the lateral fuse clips. I remember a long time ago that some guy at work wanted to sell me his Hafler DH220 cheap because he said one channel was out. Since we worked in electronics, I opened the amp up right at work and began poking around the fuse holders for each channel. All of a sudden the 'bad' channel came up just fine, and this guy decided he didn't want to sell after all. So, basically, I fixed it for him for free. What a ripoff.
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