8bitPower
Active member
Thank you! I did this last year on an asteroids with a failing voltage doubler that was causing the monitor to bloom and do all kinds of weird things, it worked great. I was trying to find the site earlier today.
G05-801 panic attack ..
- Thread starter GA61XX
- Start date
Hi,
I am going to build a replacement HV Doubler (VD900) and was guided to a video showing the process:
The build is different that it uses 2 capacitors as opposed to one as in the above diagram.
Obviously the above one (this thread) worked but would it be better to build it with the 2 capacitors as in the attached schem?
This site also shows the two capacitors in the circuit (although polarized) and explains the theory.......
Jeff
I am going to build a replacement HV Doubler (VD900) and was guided to a video showing the process:
Obviously the above one (this thread) worked but would it be better to build it with the 2 capacitors as in the attached schem?
This site also shows the two capacitors in the circuit (although polarized) and explains the theory.......
Jeff
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Just thinking out loud.... how would the original design work without the second capacitor?
Is the CRT acting in place for the second cap?
Is the CRT acting in place for the second cap?
Sourcing components.......
Cap: HVCC203Y6P101MEAX
100pF @ 20kV DC
Diode: DD1800
Vr = 18kV
If = 20mA
Vf = 40v
Ir = 5uA
Max surge current = 3A
Since I am not an EE I would appreciate if someone could confirm this would function as expected.
Thanks in advance
Jeff
Cap: HVCC203Y6P101MEAX
100pF @ 20kV DC
Diode: DD1800
Vr = 18kV
If = 20mA
Vf = 40v
Ir = 5uA
Max surge current = 3A
Since I am not an EE I would appreciate if someone could confirm this would function as expected.
Thanks in advance
Jeff
andrewb
Well-known member
The cap value is confusing. In the doc for this hack (linked on the previous page of this thread), he says '102', which in cap lingo means ten with two zeroes, so 1000pF, or 1nF. This is what I use. (And mine are rated 15kV.) I got them on ebay years ago.
In the doc he incorrectly prints it in Step 4 as 10pF, which isn't what 102 would mean. I don't know if 10 or 100pF would work, and maybe a wide range of values could be used, but I know 1nF has worked fine. (I'm wondering if he actually was using 1nF, but was just reading the value wrong.)
Those diodes should be ok. The ones I use are 2CL2FM 20kV 100mA 100ns. But IIRC 100mA is way overkill, and even 20mA should still be fine. The H1802 diodes used in 802/v2000's are only rated for like 4.6mA (which I found in the original Varo catalog), so 20mA should be fine here.
Also, the second cap isn't needed. The tube itself is one big cap and does the smoothing, so adding another one to the output isn't necessary. You just need the two diodes, 1 cap, a box to fit them inside efficiently, and epoxy to pot them in. I'm sure cheaper stuff can be used, but I bought an MG Chemicals potting kit, which comes with the black epoxy, mixing tools and accessories, and instructions. Digikey P/N 473-1082-ND:
Awesome!
Thank you for verifying the components.
Unfortunately during this time I have discovered that the Doubler is not my problem, it is looking like the HVT......
Thank you for verifying the components.
Unfortunately during this time I have discovered that the Doubler is not my problem, it is looking like the HVT......
andrewb
Well-known member
How do you know?
I placed the HV probe on the output of the HVT right before the Doubler and received a reading of 0vac - tried dc as well - still zero....
I am bench testing this set-up without the CRT, is that OK with a G05-801 set or does it need to have the CRT in circuit to produce the output??
andrewb
Well-known member
I never fire HV's up (intentionally) without the tube attached. But I would expect it to just arc to air if it were working.
However having no HV at all could mean any part of the circuitry driving the flyback is dead. The only way to know if the fly is bad for sure is to swap it into another known-good cage. But if you're getting nothing at all I would suspect the rest of the cage components first.
However having no HV at all could mean any part of the circuitry driving the flyback is dead. The only way to know if the fly is bad for sure is to swap it into another known-good cage. But if you're getting nothing at all I would suspect the rest of the cage components first.
andrewb
Well-known member
All the more reason something could be incorrect. The more you replace, the more opportunity to make a mistake.
I've never seen one of these that needed that much stuff replaced. If you still have the old parts, I'd hang onto them.
What did you use for D901 and 902?
I've never seen one of these that needed that much stuff replaced. If you still have the old parts, I'd hang onto them.
What did you use for D901 and 902?
D901/902 = MUR2100EG
andrewb
Well-known member
Not the same part. The original VG-2X's have a 10V forward drop. See attached datasheet. You might have tested them and thought they were bad because you didn't see a drop in either direction, but that's because they're more like an HV diode than a regular diode. But I've never seen one of those actually fail, so the originals are probably still fine if you have them.
I would dig as many of the original parts out of the trash and reinstall them, unless you can prove they're bad. Like I said, I've never seen most of what's in the cage go bad, aside from the electrolytic caps, the doubler, and the occasionally a transistor (PCB or cage-mount).
I have used these parts in many many builds without issue...... I am going to have to check all the components again to prove them out....
Thank you for helping out - it's good to be able to talk to someone with these problems.....
Thank you for helping out - it's good to be able to talk to someone with these problems.....
The tube is essentially the storage capacitor in the HV (rectified flyback output) circuit. Without the capacitance (and load), how can you be assured the voltage is correct?
I'd also never power up a HV cage without the anode attached (to the tube). Also doesn't seem safe to do so either.
andrewb
Well-known member
You've used them in these?
The same part can be used in 6100's. But I've never tried them in these. (Not saying they can't work. But they aren't exactly the same, and I haven't tried them, mainly because I've never needed to.)
The HV is basically just an oscillator that gets stepped up through the HVT. If anything in the oscillator circuit isn't right, it won't oscillate, and nothing will work.
andrewb
Well-known member
Not sure if you're agreeing, disagreeing, or questioning anything. But in general I agree. To make sure everything is fine in the end, you do need to measure things with it connected to the tube.
I only know what happens when you don't connect the anode because I did it once (accidentally). It'll just arc to the air. (Assuming there's no grounded metal close enough to it.)
Clay Cowgill had a post once (maybe on Vectorlist?) about working on HV's without the anode connected, where he'd put the anode in a thick ceramic mug and tape it in there. But I've never found the need to work on any HV while powered. If they don't work after a standard rebuild, I can usually figure out what's wrong by just checking everything passively. (And one of the most common things are cracked traces in those cases.)
I've seen maybe 3 cases over the years where a b/w flyback was actually bad, and eventually had to prove it by swapping it into a known-good cage.
