Pristine II restoration

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  • #365
    Nolafile
    Participant

    Greetings, I’m restoring a set of Pristine II’s and currently in the process of replacing the burnt resistors. Luckily it appears the wiring in the same area has survived. So it should be fairly straightforward installation of new resistors and perhaps replacement boards. This time around providing slight spacing between the resistors and the boards. Which should reduce the current drama. At this point I’m assuming the panels are still functional. So the question is what other weak areas should I be investigating while I’m in there? Perhaps the wiring connection points at the panels? I’m noticing discoloration on the back of the vented brilliance pots? I’d say chances are high that they are fouled internally from the pollutants created by the burning fiberboards. So I’m considering installing a resistor in place of them? Which I suspect would also be a sonic high frequency upgrade as well. So what would be the best size resistor to employ? Also does a detailed instructional exist on correctly connecting the bias taps? Anybody happen to have schematics or service data handy? These are serial 89 and I believe were produced in 2005.

    This is quickly becoming quite a project. But I suspect the results will be well worth the time invested. And many thanks in advance for any assistance.

    DD

    #366
    yoshi
    Participant

    Hello DD:

    I have been fully updating my Pristine 2 this past year.

    1. Bypassed the tweeter pot with a 50 watt , 4R metal fin resistor( Mills 4R, MRC50 50 or 75 watt). Very cheap cost for a significant upgrade in HF presentation. $5.00 each…

    2. Factory installed Toroid 1: the Toroid 2 will not fit in your backlplate housing, and you may even have to put a spacer piece of wood to raise our the backplate housing up to accommodate the greater depth of the Toroid 1 transformer. I did with 3/4” thick strip.

    3. Replaced the bias supply module with the new regulated supply. This was installed my me. Roger will provide you all the parts, new bias control pot and wiring schematic. The new module will not fit in flat, so you must cut of one of the flanges ends and mount it on end for it to fit. 2 way tape, hot glue and a new small door hinge on the existing mounting screw works perfect to securely get it in. Has at least 30% more bias capability, and is voltage regulated.

    4. New bass-focused panels, mounted in the current pristine 2 frame. The pristines have 60 degree dispersion angle and you will need to provide Roger with the exact width of panels to have them specially made, due the wider panel than the current 545.
    They can be installed by you at home. The new panels take some time to break in, but are quite an upgrade, particularly the bass area. However, the original panel worked great for me for over 20 years. I had to turn up the old bias supply almost 100% to reach a full bias on the new bass focused panels. The new bass focused panels have a wider spacing of the grid wires, which Roger says enhances low frequency production. Consequently, I have found that the old bias modules a little under capacity for the bass focused panels.

    5. Clean the 3 banana plugs form the backplate to the panels and check the tension on the plugs for secure fit.

    6. I also had a panel arching repair before I purchased new bass focused panels. A repair is home doable if you have an issue there, with a degree of difficult and a lot of time. The Mylar is extremely delicate. If you have to wade into the panel for investigation, do not touch the mylar or even hard blow on it. You will pierce the Mylar with almost no tension on the membrane. I did… they will still work, but you will likely never be satisfied with a pierced panel membrane.

    7. If you do not the tip toes for these frames, get them. Big difference on this speaker.

    8. sallie home made backwave panels. firm rigid insulation panel,5’ H x 4” ( double up on 2”) thick, just placed behind the frame bas, angled parallel to the panel, centered, will improve acoustics and the front wave launch. I made a a stand with wood base, 2 dowls on the plate for rear support, and 2- 4 ‘ dowls mounted and glued vertical in the base, for panel support. works great and you can’t see them from the listening position.

    I would also suggest you figure out why the resistors blew and if there other electrical component issues in there.

    Good luck and keep us posted.

    Ken

    #367
    John V
    Participant

    Hi,

    I’ve attached a wiring pictorial for you to peruse. The diagram may not match the wiring of your Pristines so I would suggest you contact the factory to obtain the correct one for your speakers.
    It would help if you posted a few pictures of your backplates to give us a better idea of what your describing.

    I’m unclear as to what you mean by “bias taps”. The bias level is set via a variable resistor. To set proper bias the shaft on the resistor is rotated clockwise to increase the bias to the point where the panel starts to crackle and then backed off to the point where the crackling just ceases.
    A number of people have replaced the brilliance control with a fixed value resistor by setting the brilliance to a level that gives a proper high frequency balance, measuring the resistors value and then replacing the control with the measured fixed value. I would use a 50W non inductive style resistor.

    Good Luck with your restoration, I hope the panels themselves are functional and in proper order.

    John

    • This reply was modified 3 months, 2 weeks ago by John V.
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    #370
    yoshi
    Participant

    DD and John:

    I agree with John’s comments on tweeter value. I normally ran my brilliance control around 12:30 setting on my original Pristine 2. I measured the resistance at 3.9 ohms. The single resistor will sound much more open, so I slight round up to 4 ohms was perfect in my situation. I use all tubes for pre and power.

    Ken

    #374
    Nolafile
    Participant

    Great info! Thanks to all. I seem to have improperly defined the EQ taps as bias. I apologise for any confusion. They indeed are transformer EQ taps. One row for the bass and another for the mid-range. And are ID’ed left to right as -3db 0db +3db. And are also color coded black white red. The previous owner only supplied one jumper per speaker. So I’m assuming I need to source another set to adjust both bass and mid on each.

    The overheated resistors in question are 7.5ohm 20w sand resistors. Which are tightly bundled 4 square and board mounted in each interface. For whatever reason the 2 mounted on the inside of the board seem to have run hotter than the outside facing pair. The 4 pretty well roasted the fiberglass and definitely compromised all solder joints in that area. After removing and sanding all 8 resistors ends. It now seems that only 2 of 8 are actually out of spec electrically. But all are pretty well roasted. All of which I suspect led to higher resistance solder joints along with higher required drive levels. And mucho heating. Unfortunately, I’m clueless as to what the previous owner employed for amps. But I suspect they were sizeable and humping.

    I’m definitely going to disconnect the brilliance pots. As I suspect the improvement in upper reproduction may be substantial. Plus I suspect the pots have seen better days and are polluted via the rear vents. Thanks so much for the great data on those resistors. I’ll get on the research and get them in the mail.

    I have pics which are no doubt worth thousands of words. But presently it seems due to handheld device issues. I’m incapable of uploading at this time. I’ll try later when the desktop is near.

    I’ll get the parts orders underway and let you know the progress. Hopefully the panels are still unburnt and in good shape. The socks are still tight so they should have only been externally exposed to microdust and humidity.

    Again many thanks for all of the assistance.

    DD

    #375
    Nolafile
    Participant

    Well upon researching I just stumbled upon these modern Vishay TO-220 case style resistors. Interesting and high wattage. And I suspect lower overall Z. I wonder if the sonic results would be better than the aluminum cased milspec, or classic sand wirewound types. Being for the topend they might be the ticket.

    Any thoughts of ideas are most welcome. In fact if anyone knows what sonic differences exist between the classic sand type and the aluminum housed modern wirewounds? I’ve yet to experiment with these so I’m officially ignorant on the subject.

    Nevertheless check these Vishays out.

    Thanks,
    DD

    https://www.vishay.com/resistors-fixed/list/product-50050/

    #376
    John V
    Participant

    How are you going to mount them as they need to be heatsinked to meet their power rating?
    Is this as a replacement for only the brilliance control or also the 8
    resistors on the input side of the Toroid?

    John

    #377
    Nolafile
    Participant

    Hi John,

    I suspect that could be accomplished by attaching it to the backside of the existing pot. Which could be done with a high grade thermally conductive adhesive. Or even drilling the pot backplate for a 6 or 8/32. It definitely has the backside surface area. Or even attaching a standard TO-220 heatsink. I’ve inquired with the Vishay engineering team about audio signal usage. So we shall see what they have to say. They have to be way lower in L & C than the beefy circular wirewounds tracked by a carbon tooth. I was expecting around $30ish each. Looks like they are around for under $10.

    I did just take meter reading off the brilliance pots. And they are dirty with dropouts. But I suspect would survive a carbon tec flushing. So perhaps I’ll just flush them for now to get a closer bearing on where the happy setting is for this room.

    DD

    #378
    Nolafile
    Participant

    Hi John,

    For the brilliance. Sorry I overlooked part of your question. I haven’t considered them for the other 8. But I guess it’s a possibility. So what can I expect to encounter under the bottom panel covers? They appear to be gun stapled on. I guess I should lay them over and closely inspect the terminations for corrosion to the panels themselves.

    #379
    Nolafile
    Participant

    Hi John,

    I just had a look at the diagram you sent. Thanks a million. Very interesting and I wish there was a breakdown of the audio board. By looking at the pic. I’d say they doubled the number of resistors in order to eliminate this burning issue. I may make a board from perf fiberglass using military silver/teflon wire for the traces. The burnt boards are pretty smelly to say the least and have to go. Let me see if I can now post a few pics from the desktop.

    Many thanks again.
    DD

    #381
    Nolafile
    Participant

    Sorry for the delay. Here are the pictures.

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    #385
    Nolafile
    Participant

    Here is the last picture. Thanks for all of your help!

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    #387
    John V
    Participant

    Looks like that is the earlier input circuit. There was a revision to increase the impedance of that circuit to make it easier for tube amplifiers to drive the speaker. At one time there was an upgrade kit which included a new circuit board.
    I would call the factory and speak to Connie to see what is currently available.

    John

    #388
    Nolafile
    Participant

    Hi John,

    I kinda figured they most definitely released a revision. I think I’ll stick with the oem lower impedance. The revision doubles the amount of resistors to redistribute that damaging heat load. Increasing the overall inductance is likely counter productive to overall sound quality. So instead of the oem 3.75 ohm 40w 10% bundle. I’m going to try a single 4ohm 50w 5% ceramic spaced off on a homebrew breadboard. In theory that could be slightly lower in overall Z than the oem. Stepping up to 8 units is a large increase in inductance. I generally strive to keep parts counts to a minimum especially in signal paths.

    Perhaps it would reflect better with tube amps with the higher Z. But that depends on your output xformers. Most will drive the lower Z without complaint granted they may run a tad hotter. The overall plan here is to bi-amp with sealed passive subs. So the stats won’t even see anything below 50hz to begin with. Which should have the added benefit of unloading the panels of large excursions. And in this case it’s the higher frequencys where they dive down. Which leads to a few questions. On these brilliance pots, how much noticable change occurs from say 1 o’clock to wide open? That seems to be a range of around 4 ohms down to .4 on the pot. So the manual states they bottom out at 3 ohms Z. I’m assuming that is with the pot set to maximum? I wonder where it would bottom with 3 ohms added on the pot? I’m assuming around 4.5ohms minimal Z.

    Nevertheless I’ve got plenty to learn in the near future on operating these. And the manuals explaination of employing the EQ taps leaves plenty to be desired. At least it tells you one way how not to blow your amp. I can clearly see why they installed switches on the later models. As deciphering what little instructions lie in the manual is beyond normal human comprehension.

    The parts should be here soon within a week. And with a little luck they may live to sing again.

    DD

    #389
    John V
    Participant

    AFAIK the brilliance control (L Pad) has a linear taper, but that said, the only way to know for sure is to measure it.
    As to mounting the resistor, why not just remove the brilliance control and mount your resistor to the backplate with a screw/washer passed through the controls mounting hole in the backplate? Add some thermal paste for heat transfer and away you go.

    John

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