Pristine II restoration

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  • #391
    Nolafile
    Participant

    Ken,

    Thanks for the detailed listing. After examining the diagram it makes more sense. So the toroid is standing on edge and causes you to have to elevate the outer housing. Interesting. At least for the time being I’m sticking with the oem. As I want to get aquatinted with the original sound prior to stepping forward.

    I also notice that the later design has added -6db selections for the EQ settings. Which seems odd and I guess is related to the new design producing higher potentials. So I’ll have to research it, but I wonder if this has increased the older 88db efficiency rating?

    I see you’ve cleaned these banana jacks before. Remarkably I haven’t noticed these yet. Are they located recessed in the HV box? I notice the drawing refers to BJ at the connections on the box. They must be well hidden. I’ll have to have a close look tonight.

    Thanks,
    DD

    #429
    Nolafile
    Participant

    Good idea John. On the brilliance resistors I’m still debating ordering fancy Vishays. So far the engineering inquiry to them has not been followed up on. Half the input resistor order just arrived. The 50w resistors look pretty good. Idk how the original resistors were able to conduct the required input power with such small leads. These should definitely be a improvement. So this weekend the plan is to rework the backside of the EQ taps. Which at a minimum need to be dismantled, decarbonized and resoldered. Plus revarnish the side of the xformer laminations. Which burnt off causing minor light surface rusting. The input connections were also cooked loose and need a good polishing prior to reassembly. I may devise a point to point layout and discard the fiberglass input boards. As it all really need a bit more breathing room. After measurements on the larger replacement resistors. It looks like the input resistance will rise slightly from 7.5ish to 8.2ish ohms. And from 80 to 100 watt in rated wattage. Until recently I didn’t realize that these smaller panels require higher drive than the larger models. I normally run a 260wpc SS amp on my moderately inefficient mains. After this discovery I’m not sure if it is up to this task. But we shall see in a week or so. I think I may mount the interfaces on some filter stock 3/16″ or so off the bottom. And perhaps devise a topside vent. As I suspect a slight chimney flow wouldn’t hurt.

    DD

    #440
    Nolafile
    Participant

    Hey Fellas!

    Well here are the latest updates. The input circuit boards have been replaced with a tidy point2point install. I made solid copper heatsink/supports for the new power resistors. Which corrected the oem layout issues and really opened those resistors up to breath. I decided to stick with the oem 7 conductor twisted solid copper input wire. But paralleled a small silver stranded conductor to them. A few hours ago I got them back together and hooked up.

    One requires about 1/3 on the bias pot to obtain crackling. The other only around 1/5 and develops crackling along with popping. After applying audio it seems the 1/5 bias unit has a bit lower output than the other. Plus perhaps some panel issues. As u see moderate drive I can hear distortions and can see what appears to be a few areas where the membrane appears to be loose. So instead of HOS tonight I’m retreating back to the shop to pull the sock for a close inspection.

    Wish me luck as it seems I’m gonna need it.

    Cheers,
    DD

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