12 April 2021

Breadboard socket for valve

B9A on breadboard
B9A on breadboard.
To me, playing with vacuum tubes means a lot of trial and error to get where I would like to. Everything is laid on the desk and after a few weeks of fiddling I didn't want anymore to mix the hot soldering iron with the other equipment, cables and so on.

The solution would have been to make a socket so that the tube could be mounted on the solderless breadboard. Nothing easier!

I picked a B9A socket for PCB mount (from the lot that I bought) and soldered terminals that fit the solderless board. I used leftovers from through-hole component leads: they are long and flexible enough to reach the nearest hole.

B9A on breadboard
Filament connection is left out.

Since the filament requires a good amount of current I lifted pins 4&5 and soldered a short length of thick cable. This also allows to have three pins on one side of the breadboard and four on the other side, without overlaps.



10 April 2021

Memory upgrade to HP laptop (15-g005nl)

When the lockdown started one year ago I was fortunate to have enough computers at home to allow simultaneous distance learning and remote working. All home laptops run Ubuntu Linux, that makes them breath with just 4 GB RAM and 5400 rpm spinning hard-disks (that's slow in 2021 terms), plus all updates are under my sole control.

Those computers are about 10 years old and serve 8+ hours a day without a glicth. Almost.

After one year of extensive use the HP laptop needed an upgrade (or a reinstall). The HP 15-g005nl can be upgraded to 8 GB RAM. Linux lshw command shows that there are two slots, BIOS is not so detailed. Still in doubt: do I need a second 4 GB SODIMM, or a single 8 GB module?

I looked online for a teardown video of this model or alike and it confirmed my suspicion: there is only one RAM slot! The video is a lifesaver because, amongst other things, it tells you of 2+1 hidden screws (2 become visible when the DVD reader is removed, the third is under a rubber pad).

Before buying the memory bank I worked my way down to the memory slot, just to confirm that this laptop was NOT made with servicing in mind. Even replacing the HDD requires removing the keyboard and the hand-rest frame.

The picture below shows the main board lifted from the back shell, as if looking at the laptop from the front/normal use position. You need to remove at least 6 cables and lots of screws to get here.


I was so dedicated to the RAM upgrade that I did not notice the backup battery until I reviewed the picture. Hopefully it is a rechargeable and I will not have to deep dive again in the HP anytime soon.

The SODIMM was finally replaced and thrashing (swapping fast memory to the slow hard disk back and forth) has stopped. 


27 March 2021

Help with unknown vacuum tube / valve

In the assortment of vacuum tubes I bought there are few items that look all the same and all without marking. What is worse is that they do not look like any of the almost 40 kinds of tubes that do have a marking!

So I ask my readers for help to give a name to these B9A/noval tubes. All nine pins are connected. There are two identical sections and filament runs happy at 6.3V. The anode/plate is probably connected to pin 9.

Is it a double triode? A double pentode?

Please suggest your answer in the comments or via email to ik1zyw at yahoo.com. Thanks!
 

"Side" view.
"Front" view.

 

23 March 2021

Things got out of control with the all-valve TX project

The more I read about valve (vacuum tube) oscillators and transmitters, the more I understand the inner workings of those relatively simple circuits. Once I realised that a triode-heptode or triode-pentode tube can work both as oscillator and "PA", I concentrated my efforts around a PCL-805. Until my own hands presented me the nest shown in the picture.

One tube CW transmitter (tentative)

Alright. I will take one step back and beam my first venture into the world of vacuum tubes towards two separate stages: the crystal oscillator and the power amplifier. I do have enough tubes and sockets. What I am missing is a decent assortment of high voltage capacitors and high wattage resistors! Let alone RFC!



18 March 2021

Valve sockets!

Now that I got a hundred vacuum tubes and an idea of a project, I needed some matching sockets. Without in-person flea markets, I turned to eBay and with a bit of luck I spotted a lot of assorted used sockets that nobody wanted. I think I got about 100 pieces, which makes it 0.15€ each once shipping is taken into account. Of course I will never need all of them so I probably ended up overpaying just one socket :)

Besides lots of octal, loctal and noval sockets in different shapes, there were few interesting items, proof of a time when electronics were booming and everyone tried to impose their standard (or a technological lock-in).

I've collected them for a group picture (I forgot the ubiquitous *octal).

Numbers represent the # of contact points.

Needless to say that I have no tubes that fit most of these, and some tubes that have no matching socket.

If anyone wishes to give them a name, please do so in the Comments!

 

 

08 March 2021

EF80, EF183, EF184 XTAL oscillator

While passing through forgotten boxes of forgotten components looking for some interesting TTL/CMOS ICs for an artistic project, I found two large XTALs for 2.0971 MHz. I think they were meant for some valve circuit, so I looked for an oscillator circuit with one of the tubes I have most: EF80.

Using the DIY B9A base I rigged together the most promising circuit I found online of a CW TX, with resistors "close enough" to quoted values. The ugly result is shown in the picture as well as the circuit diagram.


Diagram and test circuit.
 

I fed 6Vdc to the filament and 150V HT and it did oscillate. Cool. Time for experiments.

I could reduce filament to 5V at 300mA and everything was fine.

I could reduce the HT to 30V and it didn't stop oscillating, alas the signal picked up by the nearby receiver was much weaker. I couldn't go with a lower HT with today test setup.

Then, while I was at it, I tested all EF80 valves I had already separated from the rest. Not happy with the result, I checked through the list and found out that EF183 and EF184 pentodes are pin-compatible with EF80, so they got tested too. I could even re-stamp a few tubes that had become anonymous.

The result of a couple of hours of fiddling with on/off switched of power supplies is that I have 28 working pentodes waiting to be used in a real transmitter.

Now: VFO or XTAL?

28 February 2021

Checking a static discharge trick with the NanoVNA at UHF

Today I received a question about a post from 8 years ago: how to tame the static build-up in a GP or collinear antenna. Back then I had done some research and concluded that a high value non-inductive resistor could be used, especially at low TX power or RX only.

Now that I own a NanoVNA I can confirm that the impedance is not affected. I quickly reused the LoRA antenna from last Summer, which turned out to be resonating at 750 MHz (if we trust the NanoVNA). This is the curve on a 300 MHz span (well, it stops at 900 MHz on the right):

Just the "open" GP antenna.
 

Then I added a 10 kohm 1/4W resistor across radiator and radials and the result is almost identical (the marker has moved):

After adding the 10kR across. See next picture.

The very (quick && dirty) antenna under test.


So, if we trust the NanoVNA at the upper limit of its working range, this trick does not compromise the impedance. I might also have been lucky on the single experiment I've made, so do your measurements first.