💬 OT The (not really) official electronics workbench thread

[Mr_Roboto]

With the house for sale etc. I think I ended up doing some shopping therapy. I blew up one of my arduinos trying to make an LCD display work so I decided a real bench PSU with current limiting wasn't a bad idea. This is definitely an older model but considering you can get a NIST Certified version I figured it was likely high quality. I guess I get to see if the caps in it are shit or not in all probability. Gave 60 bucks for it, I should have bought the Square Trade Warranty for $6. It probably would have taken em to the cleaners on this one if they had to fix it I mean it blows my mind that they'd even offer it on lab gear. Slip through must be super good even for such things.

https://www.ebay.com/itm/255106365392

 

[Mr_Roboto]

Got the bench rebuilt, not sure on layout. Am testing some 807s. Home made PSU for hv, the variable for bias. Left Simpson is v, the right current and the green meter is bias.

 

[Mr_Roboto]

Tested my 807 tubes. Either one is a ringer or the rest are clapped out. Betting the latter. It may be this was done at 250v too. May just bump the drive to them.

 

[Ron Vogel]

Any of you guys do SMD? I'm thinking of looking for a hot air gun to do SMD. Looking for something budget friendlyish.

I bought this one on Amazon to do the mosfets in my car's DME. It's not professional by any means, but it works pretty well. If you do end up buying one of these or the offshoots, beware of how the incoming power polarity is wired. Plenty of tutorials out there on the net on how to test and correct.

Amazon.com

 

[Mr_Roboto]

[

Did some testing today. Found out my power supply regulation was not up to the task of dealing with an 807. I bypassed the regulation and ended up fixing my nonlinearity.

I had 5.6368vpp and 70vpp out for a voltage gain of about 12.5 via the resonant circuit and the tube. I need to find/get my dummy load hooked up to this so I can get an idea of Pout. I will probably split the plate and screen supplies then run higher voltage (750ish) on the plate. I probably also need to figure out the second tube too and really get some watts cranking.

I may have to short a couple coils or something as the maximum frequency I can get to with this setup is 7100Khz and it needs to get 400K or so higher so I have some margin. I probably need a load and it set up as push pull to be sure.

Lastly, I need to secure the tuning capacitor. There is hv on it and it needs to be operable to tune. You can isolate it from the DC but at 750v the rf voltage on it will probably be significant.

 

[Mr_Roboto]

FINALLY found a chassis that is a good size to build this into. Goal is a dual 807 40M radio amp that i can run on 80 and 20 as well with old school interchangeable coils. I need to get a tuning circuit for the input and get things moving here. I also need to finish my home brew PSU I was making for my HW-101 as it will probably power this fella too.

 

[Mr_Roboto]

I've been busy tinkering but not busy posting. I think I want to buy a PCB etching setup, just haven't gotten there yet. I think that the debate now is the annoyance of dealing with SMT parts vs the annoyance of drilling holes. I may just say hell with both and have some boards made at some point.

I downloaded LibrePCB and so far it seems interesting enough. Trying to get my sea legs with it.

I'm thinking I want to rebuild the amp/filter chain for transmit in my ubitx. The more I look at it, the less thrilled I am with it. I'm debating doing a few things for power conservation at some point and wanting to possibly add some features. I think it's interesting that the ARRL Hand book has people using the same transistors they do and getting say 65-75W out of them while I'm lucky to get 10ish. I think I have an idea or two to play with especially more towards 28MHz but I'll have to get there first. I have a way to break the board out and will add a daughter board in all liklihood.

 

[Mr_Roboto]

Getting somewhere I think. Had real, tangible gain even loaded on this stage. Class A, single ended running at about 7 MHz. I want to add a stage or two, then get the IRF510s to make me some real power. I am going to use this to hopefully redo the amp stages of my ubitx and likely the filter stages too. Got LibrePCB I am playing with, I mally go back to Eagle but am not sure yet. This may be hybrid smelt through hole, just not sure yet. Goal is to run this from 1.8MHz to about 28MHz.

 

[Mr_Roboto]

Did some more messing around today, I have about a whole 1.8W output! It's progress in the right direction though. The big lesson I seem to be getting here is that the output toroids are VERY particular in the way that they're wound and used. I also think I need to evaluate adding stages at this point, but haven't gotten there yet. Everything I've been playing with is single ended, not push-pull. I may have an oscillation at 20mHZ as well, but I haven't gotten around to playing with it yet/trying to squish that yet. I should also really fire up the TinySA and see what I'm dealing with. I bought a 40DB attenuator that's good for 10W which should get me where I need to go initially to see how spectrally pure I'm not. I'm probably seeing 40DBm or more gain through the stages so that's good.

 

[Mr_Roboto]

Book that seems worth downloading if you're into design. SpeedSpeak2me

https://www-f9.ijs.si/~margan/WBA3_4web/Wideband_Amplifiers_FPRL.pdf

 

[SpeedSpeak2me]

Book that seems worth downloading if you're into design. SpeedSpeak2me

https://www-f9.ijs.si/~margan/WBA3_4web/Wideband_Amplifiers_FPRL.pdf

651 pages, oof. I can't even count that high. I would like a UHF amp, for 420-470 MHz, but they're way to damn pricey. Oh hell, everything is pricey. The 2m 50--->160w amp that I got in 1995 for $140 is now almost $630.

 

[Mr_Roboto]

https://www.aliexpress.us/item/3256...sea!US!2771578796!&curPageLogUid=8g6CMbTdQ68H

UHF makes stuff harder honestly. Capacitances and inductances get weird at that frequency range. Get one of these and a tinySA and tell me how the second harmonic looks.

 

[SpeedSpeak2me]

It’ll look like a disco ball with sixteen spotlights on it.

 

[Mr_Roboto]

This is what my tinySA sees from the amp I built above. Need to add negative feedback to it and see if my useable power goes up and the harmonics down. They are bigger than the signal I want to keep. Sigh.

 

[SpeedSpeak2me]

I keep thinking about getting a TinySA. I don't use my NanoVNA-H4 that much anymore, so at the moment hard to justify the cost. Primarily used the Nano for SWR analysis, but found that once you get up into the UHF range it is not very accurate. HF is quite good, VHF is decent, but UHF is too far off, even after a "fresh" calibration. My dad has found the exact same thing after we compared his to the RigExpert.

 

[Mr_Roboto]

I'd believe it, as I said stuff gets harder at UHF levels. The thing about stuff like that is people literally didn't have it back in the day and got by. You'd do stuff like fish around harmonics looking for your oscillation, using grid dip meters to ferret out resonances and so on.

 

[SpeedSpeak2me]

I really like that RigExpert for the antennas. If I ever get the slush fund money I'll give my dad my Stick Pro (up to 600 MHz), and I'd get a higher end model. I'd like for them to update the AA series (over 1 GHz), none of them have built in bluetooth (like the Stick series, and AA-55). That bluetooth really helps when tuning antennas and you need the analyzer on the end of the feed line that's 50' away.

Edit - to indicate the age of the AA series, they're still using USB 2.0 Type-B connectors.

 

[Mr_Roboto]

I don't mind a full size USB connector on something like that. When you're not trying to make it small as possible the durability of the connector is worth it IMO.

 

[SpeedSpeak2me]

The USB-C on mine works great, and is more common these days. They designed the port so it is pretty well protected, and when you plug in the cable its housing fits quite snug. They also provide a rubberized plug to cover the port when not in use.

 

[Mr_Roboto]

Built this today. It is an rf power meter. Basically a dummy load in parallel with a rectifier plus a power smoothing circuit and calibration. What's weird is I am using the 50uA movement on one of my simpson 260s and it doesn't read linearly in terms of power increase by current. The db meter is accurate though. I will have to think on this. In some ways it matters little because my goal is to get peak power on low power amplifiers to tune output circuits.



The idea is to be able to make and measure a smaller version of this circuit.

 

[Jimy Bilmo]

View attachment 184767

Built this today. It is an rf power meter. Basically a dummy load in parallel with a rectifier plus a power smoothing circuit and calibration. What's weird is I am using the 50uA movement on one of my simpson 260s and it doesn't read linearly in terms of power increase by current. The db meter is accurate though. I will have to think on this. In some ways it matters little because my goal is to get peak power on low power amplifiers to tune output circuits.



The idea is to be able to make and measure a smaller version of this circuit.

 

[Lord Tin Foilhat]

Something something "new anal plug" something something... I think.

 

[sktchy]

I ccould probably wrap my head around this if it wasnt the time of day when the tism is kicking in

 

[Mr_Roboto]

That's probably the ADHD you really want the 'tism for this sort of work.

 

[sktchy]

Yep, things that require thought process have to be done in the morning before the fog sets in