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Old 06-26-2017, 10:24 PM
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VintagePC VintagePC is offline
Tube bug got me 05/2010
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Posts: 535
Replacing a flyback?

Apologies for the double post.

Maybe I didn't get an answer because I asked in a more narrow sub-forum so trying here, since I have a hard time believing nobody here has ever replaced a flyback with an aftermarket jobbie

Long story short, I'm swapping in an HVO-7 and am uncertain about how to connect it. I have the original schematic and a copy of the installation guide.
See here:

All provided schematics are variations on that circuit, with either B+ or Boost as the power source for the secondary. I think this circuit is closest to my original one:

However, there are still some pretty significant changes, if I'm understanding this right.

Tap mappings, from what I've puzzled out:
Old tap 9 is now 2
Old tap 8 is now 1
Old HV rect cap had no number, now 3.
Old tap 7 is now 6
Old tap 5 is now 8
Old tap 4 is now 5
Old tap 3 is now ??? (What's the purpose of the lead to the VBO coil? phase/feedback?)

Am I right in that I need to:
1. Change the taps the width coil spans, from 3/4 to 5/8
2. Move the damper filament from (old) tap 4 to the damper cathode.
3. Disconnect the center tap of the linearity coil, and tie the midpoint of the linearity caps (old tap 7) to new tap 6 and the damper cathode (as a source of boosted B+)

Where I'm getting even more confused is the remark to remove the boost from the damper plate. In the alternate version of this (with B+ swapped for boost) as well, new tap 6 and the damper plate connection make note of the same source. However, in my circuit, old tap 7 is attached to boost, and the damper plate (not DC Coupled) is on B+ (differing sources). So what do I do?

->I *think* it's is moving the damper plate to tap 4 instead of B+, moving the yoke to new tap 6. That just leaves the VBO connection on old tap 3...

Or am I completely going about this the wrong way, and is it as simple as mapping the old -> new taps and leaving well enough alone? (based on where they go)
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Old 06-30-2017, 09:57 AM
bandersen's Avatar
bandersen bandersen is offline
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I would map the old to new and give it a try.

Regarding the purpose of the old tap 3 going to the vertical oscillator. I believe that is the boost voltage.
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Old 06-30-2017, 10:03 PM
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VintagePC VintagePC is offline
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Thanks Bob, I'll give it a go and see.
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Old 07-01-2017, 05:20 PM
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VintagePC VintagePC is offline
Tube bug got me 05/2010
Join Date: May 2010
Posts: 535
Gave it a go. First attempt produced no HV at all. Figured I had it out of phase, and swapped the wires. This time I got HV, but it's pretty dim and there's about 1/3 of the image folded over on the left.

Guess that means it's not a drop-in and that rewiring is necessary. Don't want to go down that route given how the original fly still seems to be working ok after doping it.
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