Looks interesting, at what frequency does HX become sensitive to program content? Out of curiosity how much high pass filtering is used, and break point? (first order, second order?)
I had an Otari with HX at one point, did not have the schematics or neglected to look at them. (Can't remember which.. lol)
I had an Otari with HX at one point, did not have the schematics or neglected to look at them. (Can't remember which.. lol)
Latest update - still evaluating the magnetics for the HX. When I fired up the UTC 0-7, it was starting to roll off slightly below 20khz by a few db, but that appears manageable - that may have had something to do with the fact that I expect to drive it from a tube section that has a 50K Ohm plate resistance.
I also have acquired a decent sized base drive (as in NPN transistor) transformer good up to 500khz up to 0.25A with a 3:1 stepdown ratio. However, I do need to test it with a few milliamps of DC on the primary to see if that causes any negative effects.
I had found an interesting artifact of the B67 head stack which is that there is a mounting position for an additional tape guide immediately at the input that I've never seen populated and also that Studer does not show anything present at this location in their maintenance guide. Basically, the B67 has two tape guides that are both after the playback head - one is before the capstan and one is immediately before the tape leaves the head block. Of course there is a flutter idler between the record and playback heads also, but really nothing to stabilize the vertical tape position before the playback head after the large roller.
So, I tried adding a spare tape guide here and believe it has helped stabilize the tape slightly during playback with improved inner detail in the sound (which I may try to verify at a later date).
Also, with the additional tape guide added, the rewind tape pack is much neater. This is interesting because the B67 tape mechanism has a large roller and a tape tension roller guide between this tape guide position and the supply reel.
If anybody has any feedback on this situation, I would be interested in hearing it.
I also have acquired a decent sized base drive (as in NPN transistor) transformer good up to 500khz up to 0.25A with a 3:1 stepdown ratio. However, I do need to test it with a few milliamps of DC on the primary to see if that causes any negative effects.
I had found an interesting artifact of the B67 head stack which is that there is a mounting position for an additional tape guide immediately at the input that I've never seen populated and also that Studer does not show anything present at this location in their maintenance guide. Basically, the B67 has two tape guides that are both after the playback head - one is before the capstan and one is immediately before the tape leaves the head block. Of course there is a flutter idler between the record and playback heads also, but really nothing to stabilize the vertical tape position before the playback head after the large roller.
So, I tried adding a spare tape guide here and believe it has helped stabilize the tape slightly during playback with improved inner detail in the sound (which I may try to verify at a later date).
Also, with the additional tape guide added, the rewind tape pack is much neater. This is interesting because the B67 tape mechanism has a large roller and a tape tension roller guide between this tape guide position and the supply reel.
If anybody has any feedback on this situation, I would be interested in hearing it.
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I've been working on the new tube power supply for the B67, and believe I've got it to the point where I can get all the HV filtering and the filament regulation and filtering on one vertically mounted PCB that would fit on one of the electronics side panels. The 'breakthough' is when I discovered a line of Panasonic EZPE PCB mount polypropylene capacitors (I plan to use all polypropylene filter caps for the hi voltage) that come in values of up to 110uF at 500Vdc. I can get four of them at 80uF as well as three Hammond C2H package chokes in just over half of the PCB's area and these components should give me about 100 microvolts (or less) ripple at two outputs at 40mA each which is well above the expected circuit current draw. This will leave enough room for two LDO filament filters and regulators on the PCB, and perhaps even a bias oscillator for the erase head. So, all this could fit within 3" of one of the side panels leaving about 6" x 13.5" area for the tube circuitry. Incidentally, I will regulate the hi voltage DC within the tube circuitry section itself. I have a circuit that I've used in the past with good results that uses a single dual element triode (low u/high u) for the comparator and pass sections and should be able to reference two of these off of one 5651.
The power transformer for all of this would have to have the capability to match the input voltage variations that the Studer is rated for, and a company called Talema makes these parts, but unfortunately may not have them available again until January 2014. There is enough room on the Studer transport side panels to fit one of these toroidal transformers. I would probably wind two 7V Rms windings on top of the factory part to get the filament AC voltages.
The power transformer for all of this would have to have the capability to match the input voltage variations that the Studer is rated for, and a company called Talema makes these parts, but unfortunately may not have them available again until January 2014. There is enough room on the Studer transport side panels to fit one of these toroidal transformers. I would probably wind two 7V Rms windings on top of the factory part to get the filament AC voltages.
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Sounds great! I'd love to see some pictures as it goes together.. The capacitors sound very interesting - I'm going to have to check them out. Pretty cool if you can get everything to fit inside the machine.. Schematics if you have time?
I've wound additional filament windings on the Antek toroid that powers the tube electronics in my diy dac in order to get the additional headroom for a regulator. Looks funny, works fine, no additional noise or anything - the toroid in question is lightly loaded.
Digikey has a pretty good selection of those caps all the way up to 1.1kV in some values and the prices aren't exorbitant.. Definitely will be trying some of these soon. Thanks for the tip..
I've wound additional filament windings on the Antek toroid that powers the tube electronics in my diy dac in order to get the additional headroom for a regulator. Looks funny, works fine, no additional noise or anything - the toroid in question is lightly loaded.
Digikey has a pretty good selection of those caps all the way up to 1.1kV in some values and the prices aren't exorbitant.. Definitely will be trying some of these soon. Thanks for the tip..
You're correct - I plan to house all the new electronics in a standard portable B67 package.
I was originally going to drill a gazillion holes in the front and back panels to allow cooling for the tubes like most 'classic' tube recorders have but have changed my mind because drilling all those holes would be a lot of work and probably look like crap - I will find a couple of the most silent 3" diameter 6V cooling fans I can and add some lateral forced air cooling and add holes to one or both of the side panels in the electronics area. I'm pretty sure I can keep the noise level of the fans below that of the B67 transport in operation. My plan is also to allow all the calibration controls to be accessible from the bottom of the chassis to minimize lead length, etc. However, access from the front will allow tube changes, etc.
I've also acquired some padauk wood to make my own side panels, largely since everbody who offers the original B67 wood side panels seems to be asking ~$300 a set. The padauk is a hard and very reddish tropical wood. For moving 'handles', I plan to add an internal upper cutaway to the padauk with a bit having an internal rounded profile so that there will be handholds built into the side panels, rather than the hinged handles that Studer has with their side panels. The side panel center section, similar to that of the Studer B67 side panels, is going to be covered with a metal screen on its inner face to allow improved air circulation, not least for the new electronics!
I was originally going to drill a gazillion holes in the front and back panels to allow cooling for the tubes like most 'classic' tube recorders have but have changed my mind because drilling all those holes would be a lot of work and probably look like crap - I will find a couple of the most silent 3" diameter 6V cooling fans I can and add some lateral forced air cooling and add holes to one or both of the side panels in the electronics area. I'm pretty sure I can keep the noise level of the fans below that of the B67 transport in operation. My plan is also to allow all the calibration controls to be accessible from the bottom of the chassis to minimize lead length, etc. However, access from the front will allow tube changes, etc.
I've also acquired some padauk wood to make my own side panels, largely since everbody who offers the original B67 wood side panels seems to be asking ~$300 a set. The padauk is a hard and very reddish tropical wood. For moving 'handles', I plan to add an internal upper cutaway to the padauk with a bit having an internal rounded profile so that there will be handholds built into the side panels, rather than the hinged handles that Studer has with their side panels. The side panel center section, similar to that of the Studer B67 side panels, is going to be covered with a metal screen on its inner face to allow improved air circulation, not least for the new electronics!
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Hope everybody is having good holidays.
Just thought I'd weigh in - I got the second Studer B67 playing tapes at 3 3/4 ips - 15 ips. It turns out that its audio power regulator board was dead. Since I had the third transport, I checked out its power supply board and the positive +12V rail is out, so I have an order in to Digikey for replacement parts to fix. Once I got that sorted out, and swapped to a stereo head block, I found it was wired to handle stereo audio, even though it was originally a mono machine, so I am good there.
So, out of 3 B67's, I have one good audio regulator board right now. It seems that the playback board on this machine had a large shunt electrolytic cap short out which took out the PS rail, and I have replaced the bad capacitor, but am still waiting on the replacement regulator IC which is a TO-3 package 7812 (or 12V LM340). Good thing I am ordering now since Digikey has the regulator in stock but lists it as 'obsolete'. Probably not that surprising considering these are probably '70's - 80's era transports.
One thing I noticed is that Studer has made some significant electronic design changes in the B67 in certain areas during its production run - particularly the capstan speed control board, motor drive control circuit boards and the audio power supply board. For the capstan speed control board, they actually started out with a custom IC motor driver and changed to a standard component implementation later, which is preferable since the custom circuit is not so available, but if necessary, I could kludge a version of the 'standard component' version in its place. IAC, I've acquired a couple extra 'custom' IC's for support reasons. I can imagine that Studer's later decks with full microprocessor control could be even more problematic to maintain, without manufacturer's support, the electronics of once they start having circuit failures!
Another thing I noticed with the B67 I got playing tapes over Christmas (actually, it will probably record, but I'll save checking that out for later since I am only playing some of my old tapes from 20 years ago right now) - It won't move the tape when it sees clear leader tape unless the function button is held down due to its optical sensor. This is somewhat inconvenient for me and different than the original transport I got which I believe is a slightly later manufacture. I'm afraid this may be a 'design feature' in certain B67's but hope to defeat it without losing the optical sense entirely. Perhaps I could add a small circuit to 'gate out' the optical sense if the transport is in play or record mode.
I also ordered parts to start the conversion to tube audio - I'll probably start with playback, then move to record.
Just thought I'd weigh in - I got the second Studer B67 playing tapes at 3 3/4 ips - 15 ips. It turns out that its audio power regulator board was dead. Since I had the third transport, I checked out its power supply board and the positive +12V rail is out, so I have an order in to Digikey for replacement parts to fix. Once I got that sorted out, and swapped to a stereo head block, I found it was wired to handle stereo audio, even though it was originally a mono machine, so I am good there.
So, out of 3 B67's, I have one good audio regulator board right now. It seems that the playback board on this machine had a large shunt electrolytic cap short out which took out the PS rail, and I have replaced the bad capacitor, but am still waiting on the replacement regulator IC which is a TO-3 package 7812 (or 12V LM340). Good thing I am ordering now since Digikey has the regulator in stock but lists it as 'obsolete'. Probably not that surprising considering these are probably '70's - 80's era transports.
One thing I noticed is that Studer has made some significant electronic design changes in the B67 in certain areas during its production run - particularly the capstan speed control board, motor drive control circuit boards and the audio power supply board. For the capstan speed control board, they actually started out with a custom IC motor driver and changed to a standard component implementation later, which is preferable since the custom circuit is not so available, but if necessary, I could kludge a version of the 'standard component' version in its place. IAC, I've acquired a couple extra 'custom' IC's for support reasons. I can imagine that Studer's later decks with full microprocessor control could be even more problematic to maintain, without manufacturer's support, the electronics of once they start having circuit failures!
Another thing I noticed with the B67 I got playing tapes over Christmas (actually, it will probably record, but I'll save checking that out for later since I am only playing some of my old tapes from 20 years ago right now) - It won't move the tape when it sees clear leader tape unless the function button is held down due to its optical sensor. This is somewhat inconvenient for me and different than the original transport I got which I believe is a slightly later manufacture. I'm afraid this may be a 'design feature' in certain B67's but hope to defeat it without losing the optical sense entirely. Perhaps I could add a small circuit to 'gate out' the optical sense if the transport is in play or record mode.
I also ordered parts to start the conversion to tube audio - I'll probably start with playback, then move to record.
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Got the parts and fixed the second power supply "stabilizer" board (as Studer has it). I also recapped the major 'lytics on the reproduce board and 'stabilizer' boards for both machines so now I have two working playback machines.
I have also got materials to do some serious head relapping (as proposed by a Nortronics head lapping how to guide), and figure I'll do a mono set of heads first, and then the stereo IEC head stack (which I plan to use for the 7.5-15-30 ips machine). The IEC heads look like they still have half their life or so in them (which is why I got them fairly cheap). In a way, I got lucky because the heads that came with the 3.75-7.5-15 ips machine are almost brand new Studer heads so all they might need is a demagnetization and maybe azimuth trim.
I also cut out the wood side panels but haven't yet put the ventilation slots in them which I hope to do within a week or so.
Somewhere in all this, I will start making up a set of prototype tube electronics - I actually plan to mount them on a perf pcb on the back of the 3.7-7.5-15 ips machine and will start with the playback circuits.
I have also got materials to do some serious head relapping (as proposed by a Nortronics head lapping how to guide), and figure I'll do a mono set of heads first, and then the stereo IEC head stack (which I plan to use for the 7.5-15-30 ips machine). The IEC heads look like they still have half their life or so in them (which is why I got them fairly cheap). In a way, I got lucky because the heads that came with the 3.75-7.5-15 ips machine are almost brand new Studer heads so all they might need is a demagnetization and maybe azimuth trim.
I also cut out the wood side panels but haven't yet put the ventilation slots in them which I hope to do within a week or so.
Somewhere in all this, I will start making up a set of prototype tube electronics - I actually plan to mount them on a perf pcb on the back of the 3.7-7.5-15 ips machine and will start with the playback circuits.
Sounds like a lot of progress has occurred lately.. Would love to see a pix or two, put me in touch with my inner R2R fan..
I have never attempted to lap a head, and truthfully the one tape head I might have lapped had a shorted coil as well so the only recourse was replacement, with the acquisition of Magnetic Head Company (Nortronics replacement heads) inventory by jrfmagnetics replacement heads have become even more expensive.
I got rid on my ReVox G36 a few months ago, so I am now tape free..
Would love to see a pix or two, put me in touch with my inner R2R fan.. I have never attempted to lap a head, and truthfully the one tape head I might have lapped had a shorted coil as well so the only recourse was replacement, with the acquisition of Magnetic Head Company (Nortronics replacement heads) inventory by jrfmagnetics replacement heads have become even more expensive.
I got rid on my ReVox G36 a few months ago, so I am now tape free..
So, what did you not like specifically about your G36? Are you still recording digitally?
One of the things I like about the B67 transport is that it is rated as one of the lowest flutter transports out there, and it also handles tapes pretty gently having all roller guides (this is something I actually added to the Ampex 351 transport I was using, as well as an AG440 servo capstan motor 20 years ago to handle the latest high bias tapes at lower tape speeds which were having shedding problems with the original fixed Ampex guides).
One thing I noticed when playing my tapes from 20 years ago, even using the solid state B67 pb electronics through my HT system is how good the imaging is on many recordings made from LP, even compared to DTS pro live recordings. Even my cat was initially reacting to a good deal of program material where she didn't to the all digital recording chain signals. In particular, there is much more lateral imaging outside the front channel speakers, and more center imaging specificity, and this is through an all solid state HT system. Of course, without 5.1, the back channels aren't doing as much.
When I get the tube playback electronics going on the slower speed machine, I plan to move it up to my high-end audio only system for more critical evaluation. I'll see if I can get something going pix wise- my digital camera died out a few months ago
One of the things I like about the B67 transport is that it is rated as one of the lowest flutter transports out there, and it also handles tapes pretty gently having all roller guides (this is something I actually added to the Ampex 351 transport I was using, as well as an AG440 servo capstan motor 20 years ago to handle the latest high bias tapes at lower tape speeds which were having shedding problems with the original fixed Ampex guides).
One thing I noticed when playing my tapes from 20 years ago, even using the solid state B67 pb electronics through my HT system is how good the imaging is on many recordings made from LP, even compared to DTS pro live recordings. Even my cat was initially reacting to a good deal of program material where she didn't to the all digital recording chain signals. In particular, there is much more lateral imaging outside the front channel speakers, and more center imaging specificity, and this is through an all solid state HT system. Of course, without 5.1, the back channels aren't doing as much.
When I get the tube playback electronics going on the slower speed machine, I plan to move it up to my high-end audio only system for more critical evaluation. I'll see if I can get something going pix wise- my digital camera died out a few months ago
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Working on the cooling scheme for the tube electronics -have settled on two Evercool 70mm x15mm fans for each machine. I also want to run the fans at reduced speed to keep their acoustic noise less than that of the transport, so am looking at desiging a little speed controller for each. I don't want to go PWM because I don't want that noise close to the tubes, and am not sure a simple resistor dropper would do because these are 5V fans (to be run from 6V filament supply) and I notice they cog a lot more on startup than the 12V fans (so the 5V fans will run at a significantly lower speed than they'll start at), so am looking at a linear regulation scheme based off the fan's Hall Effect speed monitor so they start up as well as run at a speed perhaps lower than achievable with a simple resistor divider.
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Sounds like a lot of progress has occurred lately..
I have never attempted to lap a head, and truthfully the one tape head I might have lapped had a shorted coil as well so the only recourse was replacement, with the acquisition of Magnetic Head Company (Nortronics replacement heads) inventory by jrfmagnetics replacement heads have become even more expensive.
I got rid on my ReVox G36 a few months ago, so I am now tape free..
I lapped the heads on my old TEAC once and it worked great. I didn't follow anyone's instructions as I recall. It's time consuming but not technically difficult.
Well, I may have done it wrong all those years ago, but I used a fine grained white sharpening stone and a lot of oil to reshape the heads. It took forever, pulling the head back and forth across the stone, turning my wrist at the same time to get just the right shape. Good luck. I hope you have a better method.
I strayed away from the B67 project for about a month and am about ready to get back on it. For one thing, I picked up some NOS Teledyne 712 series relays in the $6 range (Newark list is $70 a pop) that ought to work well for the speed compensation matching circuits. They should sound better than anything else except for perhaps mercury relays (which are too orientation sensitive for a portable tape application). They're hermetically sealed 2 Form C types rated down to 10uA/10mV which is about as good as anything else out there. Plus they're quite small and the contacts are rated to 10,000,000 operations at low levels which should exceed any use I plan to put them to. they probably went 'cheap' because they have a 6V coil - not so good for a 5V supply but great for a circuit that has a 6V DC filament supply.
I also picked up an Ampex AG440B-2 pretty cheap which I was planning to borrow the transport from to go with a set of my SAKI Glass Ferrite heads, but that's more of a back burner project. It came with the AG440 Servo Drive instead of the synchronous motor, which is good. This transport has a headblock with a feature I haven't seen on an Ampex pro machine before - it has quarter and half track pb heads in the head block with a switch to select between them. It even runs - needs a little electronic fixup and some tape tension adjust.
Seeing some of the prices the Ampex 351 electronics are going for has got me thinking of selling off most of mine. I could probably get about four together fully functional. I could even do a 'full' 351 with relapped Ampex heads in good shape and get $2-3K for it perhaps. I even have a complete 354 electronics set which I've considered modifying but I'd hate to do that - I would rather modify an empty 354 chassis with all its knobs, connectors and meters perhaps to go with the AG440 transport - anybody have one handy?
I also picked up an Ampex AG440B-2 pretty cheap which I was planning to borrow the transport from to go with a set of my SAKI Glass Ferrite heads, but that's more of a back burner project. It came with the AG440 Servo Drive instead of the synchronous motor, which is good. This transport has a headblock with a feature I haven't seen on an Ampex pro machine before - it has quarter and half track pb heads in the head block with a switch to select between them. It even runs - needs a little electronic fixup and some tape tension adjust.
Seeing some of the prices the Ampex 351 electronics are going for has got me thinking of selling off most of mine. I could probably get about four together fully functional. I could even do a 'full' 351 with relapped Ampex heads in good shape and get $2-3K for it perhaps. I even have a complete 354 electronics set which I've considered modifying but I'd hate to do that - I would rather modify an empty 354 chassis with all its knobs, connectors and meters perhaps to go with the AG440 transport - anybody have one handy?
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Yeah, even used real VU meters on eBay are expensive! If you want to adapt a regular meter for VU use, then you need a driver circuit, which means paying $$ for a custom circuit board and the parts, not to mention making the paper scale for the meter... sigh.
As a mechanical engineer, I can appreciate tape decks a lot. I just don't have a machine shop to make custom parts for them though.... Got a spare $1,200 for a small bench top milling machine? yeah, me neither.
I finished simulation of the playback phase correction circuitry which uses one half of a dual triode. I was able to achieve full phase correction up to 21Khz at 7.5 ips with this approach before where the 3rd harmonic of a 7 khz square wave recorded and reproduced in correct phase and amplitude relationship to the fundamental. This phase correction circuit will include a three speed selection option by using a couple of the Teledyne relays I mentioned above. The other half of the dual triode will include the unbalanced line buffer output and peak unlimiting circuit, the output of which I plan to have accessible through standard RCA jacks somewhere on the electronics assembly. I also will try to use 6SL7's for the first stage input and playback stage amplifiers - if I inset the sockets into the mounting plate, I believe I can get the short bottle tubes in there.
From there I plan to use a dual triode or a compactron to drive a line level output transformer for XLR balanced use - I don't plan to use that part of it for connection to my hi-end audio gear but want to maintain the B67's pro interface capabilities.
I also ordered up all the filter caps I mentioned above so plan to start prototyping very soon.
From there I plan to use a dual triode or a compactron to drive a line level output transformer for XLR balanced use - I don't plan to use that part of it for connection to my hi-end audio gear but want to maintain the B67's pro interface capabilities.
I also ordered up all the filter caps I mentioned above so plan to start prototyping very soon.
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