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| Cloning the HP3325A Option 002 - HV Output |
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| TERRA Operative:
--- Quote from: mopa94500 on May 16, 2019, 07:50:18 pm ---Awesome, thanks. Yeah, I thought it would be too big for the cheap boards.. :( Ah well, it's still not tooooo expensive anyway. I wonder if there is anywhere that will do gold plating and also clear or no solder mask to match the old HP style PCB? :D --- End quote --- If you take a look at my boards, you'll see they are gold plated with no soldermask on the top to match the HP boards. They look more brown only due to the internal copper layers from the 4 layer construction. --- Quote from: Neomys Sapiens on May 17, 2019, 05:18:12 pm ---I would use the Kemet. Being of hermetic construction, it will keep it's parameters for a long time. Those are not the failure prone Tants! Also Kemet specs are reliable and conservative. --- End quote --- Yeah, the lifetime of the tants is impressive compared to the electros. The electrolytics I used are only rated to 2000 hours or so. What about squeezing a poly or ceramic cap in, seeing as these are only 3.3uf? |
| Jay_Diddy_B:
Hi, I used a tantalum bead. The capacitor has about 3.7V applied. The current is low, about 1mA peak, during square wave transitions. The current is lower with a sinewave. The value is not critical. A 4.7uF 10V (or greater) will be okay. I used something like this: https://www.digikey.com/product-detail/en/avx-corporation/TAP475K035SRW/478-8986-1-ND/4561852 Regards, Jay_Diddy_B |
| TERRA Operative:
Alrighty. Got it working finally. Turns out that after a bit of head scratching, Diptrace have the Emitter and Collector pins swapped on some of their footprints, or the part I used is swapped from the normal footprint... :rant: The usual story.... |O So that means I have a heap of gold plated 4-layer boards to feed the bin. :( Anyway, it's all figured out and ready for a new PCB order, plus I made a few tweaks to placement for clearances and stuff, just minor stuff, a nudge here and a bump there. Here's the output shown in the pics below. In order: - 1MHz Sine (The device seems to attenuate above 1MHz) - 1Mhz Square - 100KHz Square - Close up of the 100KHz square rising edge Things might need to be poked a bit to reduce that overshoot? Any suggestions? The overshoot seems to stay the same regardless of frequency setting, until it distorts like in the 1MHz image, which starts around 500KHz, where the period becomes the same width as the overshoot ripple. (The 1MHz square wave shape is showing just a portion of the overshoot ripple, hence the distorted shape for example). The triangle and ramp are perfect and boring, so I won't bother with pics. |
| TERRA Operative:
Moar updates. It turns out that the Original HP Option 002 board I have wasn't working, but I traced it down to a faulty transistor Q8, it seemed to test ok in my ebay component tester, but it was nonfunctional enough to bring the whole thing to a grinding halt. Replacing it got the board working perfectly. So, seeing as it works fine with no overshoot, and I need to order another revision of PCB anyway, I ended up just copying the PCB layout with a few tiny tweaks here and there (stuff like neatening up things, 45degree corners, etc). The added benefit of no longer using a 4 layer board is that PCB's will be cheaper. :) I am thinking that the large ground and supply planes were adding capacitance and causing ringing, maybe. Thoughts? I could play with pulling the ground planes back a bit, but I figured 'why bother' when I am holding a working design to copy in my hand.... Anyway, the linked images are the new PCB design, and the output from the repaired original Option 002 board. Once I get this set of PCB's back and the thing tested, I'll be able to start getting some kits made up for those who are interested. |
| TERRA Operative:
New PCB's arrived! I ended up with two batches, first one they ignored the keepout on the top solder mask, so I have a set of 10 boards with and without top solder mask. Since the original HP part has no top solder mask, I wanted the same to make it look the same. Original on the top (already had the electrolytics replaced) and new on the bottom. The traces are a 90% match to the original, and all modern parts are used and substituted and the passives have better specs than the original. Next step, start testing this to make sure my component values and substitutions all work. |
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