On My Bench.

[Dave the bass]

What's the background in photos, is it a mat?

Yeah, exactly as our-Ray mentioned. It's just a soft silicone rubber mat to stop equipment sliding about on the bench. Every so often I have to vacuum clean it to get bits of wire and solder blobs out of the pores as the mat has chemically reacted with the varnish I used on the bench and the 2 are stuck together. Doh! I'll replace it one day.

Re the DC DC buck cct, I've tested the other working example on a 12V filament bulb and the start up is instantaneous, I hadn't thought of any problems regarding firing up DHT filaments with it.

The query was more about the buck converters effect sonically if any? I didn't know if it was a known no-no.

[Mike H]

Re mat, cool.

If the SMPS is ultrasonic, can't see how. Well I could, you could have a difference frequency product from mixing with audible HF.

The analogy is like the ultrasonic AC bias of a tape recorder, it could mix with HF in the audio and make an audible difference signal, but in practice it never happens. The HF frequency component in the signal would have to be really high.

[Nick]

Just to repeat what I found when trying (years ago) a HF switching supply for a 211 heater, you could hear the beat between a 18kHz audio tone and the 40kHz or so heating signal. However that was with the supply producing 40kHz AC output, so you may find its very very different with DC and a bit of switching noise.

But also remember when Andrew was designing his DHT heater supplies, Mark J could tell the difference between (two different dielectric) a cap in the feedback loop of the supply. So YMMV.

[Dave the bass]

Ta for your thoughts Mike and Nick. Hmm, I'm leaning towards repairing the faulty module (so I have 2 working) and just trying it to see if this approach has got any legs.

EDIT. The specs on that board from the web, they run the switching frequency at 180KHz,

Voltage regulation method: PWM modulation
Input voltage: DC4-40V
Output range: DC1.25-36V
Maximum current: 8A
Maximum power: 200W
Conversion efficiency: 94%
Switching frequency: 180KHZ

[Dave the bass]

Just to repeat what I found when trying (years ago) a HF switching supply for a 211 heater, you could hear the beat between a 18kHz audio tone and the 40kHz or so heating signal. However that was with the supply producing 40kHz AC output, so you may find its very very different with DC and a bit of switching noise.

Coming back to ^^^. I wonder if the 180kHz switching frequency of the Buck convertor board is far enough out the audio range to stop any beat interaction with the audio signal? I get what you're saying in that you were going for a HF heater supply and this is a different kettle of fish.

So YMMV.

It's this that makes me want to pursue it

[Nick]

Yep, no reason why you should not try it. You could add a current limiter in series with the output if there was any DHT startup worries.

[Mike H]

To avoid a cap directly across the filament, as my idea earlier, a series resistor, or even, if you're feeling adventurous, a linear regulator.

That's not so daft, you could have a LM317 as a CCS, but will need Voltage overhead.

[Dave the bass]

Right, so while I'm waiting on parts to repair the faulty Buck convertor, this little (in a physical sense) project came up. Its a 5 band HF Transceiver

https://dl2man.de/



A chum in the amateur radio club asked me if I'd like to build his kit. So I did, luckily the SMT bits were done previously which had been been requested by the fella who organised the buying of these kits for the club but its been pretty intense, I've never had to wind little torroids before.

A pile of bits, some sheets and YouToob tutorial helped, the support seems very good for this kit.


End of 1st session.


The 2nd session was spent doing lots of these...


...there's 5 bands (20,30,40,60 and 80m covered) and each band has 2 coils which have a different nmber of turns on them then theres 2 x SWR transformers.

RF board coming together...


Many hours later, whahey!


See how its even got a CW/Morse decoder built in? I'm taking it up to radio-chums house so he can align and calibrate it properly on his test kit. I'm not geared-up for RF and also unlike me he's licensed (not for off-sales...) so he can test it on air.

Phwoaar! Its been a good winter-electronics wise.

[Nick]

Holy wound components batman. Very nice. Almost shoddy.

[andrew Ivimey]

Snigger...almost!

[Dave the bass]

Ta.

Almost... you brutes!

[Mike H]

Wow toroids for radio coils. Well I guess, since there's a lot of them around nowadays.

[Dave the bass]

So, at the weekend I took the little transceiver around to its owner's home. He's really into old valve radio gear and rebuilds old 'stuff' as a hobby, there's a lot of parallels to DIY audio which is great IMO.

After a couple of function tests into a 50R dummy load he connected it up to his properly fettled and tuned 40/80m centrefed dipole. Bearing in mind that little box has ~5W RF output on SSB (single sideband) his first CQ (call) got him into Germany and his 2nd into Belgium Blimey!

He's stoked on it, happy bunnys all round.

Next!

[Ray P]

Schlampige!

[andrew Ivimey]

Nein , ausgeseichnich - bugger can't speel. That's shoddy!