Cloning the HP3325A Option 002 - HV Output

[jcline01]

Hi Jared,

Thanks for providing all the work and for the PCB fab information,

I tried to have a company (Pad2Pad) make the board using your gerber files from google drive, but they said it would not work.

Here are their words:
"The top silkscreen is usable, however, the top masking layer provided encompasses the entire board profile and is not usable. We will require a new top masking layer to proceed."

Do you have any insight on a solution?

Also, is there another fab company that can make this happen?

I'm new to PCB fab, so sorry for the questions.

Thanks again,

Joe Cline, KN5U

[TERRA Operative]

There is no top solder mask on this PCB to keep it more accurate to the original HP design, hence the top masking layer to exclude it.
You can tell your fab that they can delete the top mask entirely and only apply solder mask to the bottom layer.

[jcline01]

Awesome - Thanks!

[TERRA Operative]

No worries.

If you look back a little bit in the thread, or in the google drive link, you'll see photos of how it should look with the bare top. All nice and gooollldddd!

[AVO8user]

Hi there, interested in building this, hope you still look at this after all this time. 
My query is about the BOM in the Google drive as there seem to be a couple of questions and comments in the forum which differ from the BOM you have put up.

1 Member P diddy refers to values for R10 and C19 but neither the HP service manual or your BOM have values or have them in the circuit schematic.

2 The next query is using 2N3904/06 transistors, again P diddy refers to the need to use 80v transistors in some locations which you agree with but the BOM lists 3904/06 throughout.

3 And finally in the blog you mention the 10k resistor should be 0.1% and say that you used 1% for the first build and will correct that in the next build, unfiortunatley the BOM still lists 1% parts.

Hoping you can help, is there a newer version of the BOM ?

[TERRA Operative]

Hi,
Yep still here.

1. If there's no R10 or C19 in my BOM or schematic, then they don't exist. J_Diddy_P was playing with his own version so he would have probably had his own part numbering, mine follows the HP design, so to make mine you don't need those two parts.

2. Probably an alright idea to use higher voltage rated transistors, I used the 2N3904/2N3906 as it worked ok, but some headroom is a good idea.
Maybe MPSA06 and MPSA56 transistors can be used. I might try it out myself soon actually.

3. R12 and R13 are the 0.1% +/-0.25 Temperature Coefficient resistors. I still haven't replaced mine (I forgot!) but I'd put them in as they must be there for a reason. HP wouldn't have spent the extra money if it wasn't worthwhile.



Hope that helps.


[EDIT] MPSA06 and MPSA56 transistors work. There is a bit of overshoot on the square wave (all other waveforms look perfect on the scope), but I'll have to dig out my other 3325A with the original HP option board to compare.

[AVO8user]

Hi there thanks for clearing that up.

I was thinking of using MPS8099 and MPS8599 as Mouser are stocking those and they appear to have a slightly better gain /bandwidth product than the MPSA06 and MPSA56. Perhaps I need to make it up with transistors sockets so I can experiment further.

Lots of thes parts are being discontinued now, really frustrating when you look up the specs for a part and it looks really good and then you cannot buy it anymore.

Thanks for putting in the hard work of creating the board files as I know the theroy but don't have the expeience with the software to come up with a board like this. JLPCB have just sent my order to me and they look great.

LTspice looks very useful too-another bit of software to learn!!

[TERRA Operative]

Yeah, all sorts of stuff is getting discontinued revently, seems I get an email every second day almost...

Let us know how your experiments go, it will be nice to have some options on substitute parts for future reference.

[flanneltuba]

I went ahead and spun off a batch of 5 boards through PCWay using your gerber files, built up one of the boards, and shazam! if it didn't work perfectly on the first power up. I ordered some of the higher voltage transistors just in case the 2N390x transistors proved themselves underrated, but so far have not had to use them. It appears to work quite well with the lower voltage jellybeans. It was happy to deliver a full 40v, 10KHz signal into loads as low as ~68Ω (well over 100mA) without significant distortion. Very impressive, indeed.

One trap for young players (I'm 59, but evidently somehow still a young player): Be sure to insulate the legs of the transistors that have the ferrite beads. The circuit will work great while the PCB is upright -- that is while the 3325 is upside down during installation -- but as soon as you smittenly button it all up and heft it back onto your equipment stack, and pile a few other heavy pieces of equipment on it for good measure, the ferrite beads, which are of course conductive (duh) will slide up the transistors and short one or another of the leads.

One other thing I didn't see mentioned was removing the option jumper on the A6 logic board located between the configuration switch block S1 and U43 to let the logic know you've got the 002 HV Option installed.

I do now have a three extra unpopulated PCBs that I probably will never use, if anyone's interested. PM me and I'll send you one. First come first served. Note that I did not opt for the gold plating, so they're just regular tin plated. So call me cheap. See pics.

Anyhow, a huge thanks to TERRA Operative for the Gerbers and associated files and for all the work you put into them. Thanks also to the other contributors who's comments were quite helpful.

- Scott

[TERRA Operative]

Ah yes, the ferrites. I must have forgotten to make a note of them. I coated them with a bit of clear nail polish to insulate them. I also formed the legs of the transistor to help provide clearance. By bending the centre leg straight back towards the rounded side, flat on the base of the transistor, then bending straight down at 90 degrees, I was able to get just enough clearance to not have a problem.

But good to hear you have it all working without too much trouble! And you even made the shield plate too, nice work.

[SilverSolder]

I went ahead and spun off a batch of 5 boards through PCWay using your gerber files, built up one of the boards, and shazam! if it didn't work perfectly on the first power up. I ordered some of the higher voltage transistors just in case the 2N390x transistors proved themselves underrated, but so far have not had to use them. It appears to work quite well with the lower voltage jellybeans. It was happy to deliver a full 40v, 10KHz signal into loads as low as ~68Ω (well over 100mA) without significant distortion. Very impressive, indeed.

One trap for young players (I'm 59, but evidently somehow still a young player): Be sure to insulate the legs of the transistors that have the ferrite beads. The circuit will work great while the PCB is upright -- that is while the 3325 is upside down during installation -- but as soon as you smittenly button it all up and heft it back onto your equipment stack, and pile a few other heavy pieces of equipment on it for good measure, the ferrite beads, which are of course conductive (duh) will slide up the transistors and short one or another of the leads.

One other thing I didn't see mentioned was removing the option jumper on the A6 logic board located between the configuration switch block S1 and U43 to let the logic know you've got the 002 HV Option installed.

I do now have a three extra unpopulated PCBs that I probably will never use, if anyone's interested. PM me and I'll send you one. First come first served. Note that I did not opt for the gold plating, so they're just regular tin plated. So call me cheap. See pics.

Anyhow, a huge thanks to TERRA Operative for the Gerbers and associated files and for all the work you put into them. Thanks also to the other contributors who's comments were quite helpful.

- Scott

Those boards look just the ticket!  Very useful addition to a 3325A.