Jonny Tubetronics: amps and synth stuff now in one thread

I made a quick change to the heater centre point grounding resistors:



I was actually trying out a bigger capacitor on the heater DC smoothing and I noticed the two grounding resistors were getting hot. Quick V = I x R showed I was putting 0.2W through 0.25W resistors which is a bit close (I know, I should have done this to start with). I upped the resistors from 100 Ohms to 150 Ohms and used 0.5W instead of 0.25W. Now they just get warm and I'm much happier with it.

I decided the sound quality isn't that bad. This is what it looks like running in my lab:



And with the lights off:



Thinking about the residual hum; it's not the main heater circuit because I added another capacitor to the smoothing and it made no difference. It could be the heater on the rectifier valve which is on a different tap and still on AC. It's not that easy to squeeze in another bridge rectifier and capacitor, but I might temporarily connect the rectifier valve to the main circuit and see what happens. The next place to look is potentially adding more smoothing to the HT. I can do this with a bigger smoothing capacitor but I suspect it would probably prefer a choke inline. It's very low level 50hz hum though, so I suspect it's being picked up from unrectified AC somewhere.

I got to the bottom of it. I added the rectifier heater onto the bridge rectifier and it made no difference. Then I bodged on a 100uF capacitor soldered at one end onto a convenient HT point and using a bolt hole:



That seemed to make a huge difference, so I took out the 50uF cap and replaced it with that one:

Yes, it could just use a bit more capacitance now...

I think this is about the limit of what the rectifier valve can take though, before I start to kill it. The spec sheets state a maximum of 50uF which seems to be due to the inrush current when powering on (particularly when hot?) - effect being to shorten the valve's life. I don't think I'm too bothered by that given how much this is going to get used. 

I made the capacitor mounting bracket out of a Jubilee clip strap. It's secure enough that I could piggyback another capacitor on top to quieten it down further and it would still be secure enough.

Nixie clock musings. Proper nixie tubes are now expensive. I did buy some on eBay on a whim from a Ukranian seller but unfortunately they never arrived and I got them refunded. Something I've been looking at as an alternative are VFD tubes (vacuum fluorescent discharge). They're similar to nixie tubes but the display is greeny-blue instead of orange. They're a lot cheaper, far more abundant and there are loads of them to choose from. Like, literally don't know where to start. They're all Soviet era. So I'm just going to dump a load here for reference.

Most interesting to me are IV-4 (ИВ-4) VFD tubes:





These are a 16-segment display tube, so can display more than basic numbers. You'd be able to make these display complex letter characters as well.

For more basic numbers there's the IV-6 VFD tube. These are 8 segments if you include the dot:





There's an IV-11 which I think is a bigger version of the IV-6:





Then there's a more integrated single display tube, the IV-18, which is pretty cool:





Slightly more basic is the IVLM1-1/7. These would have been used in a matrix to make a larger dot matrix display. Could also use them as VU meters etc:







That's just scratching the surface. There are numerous other displays and that's before you start getting into the pre-LED era indicator lamps like CRT VFD indicator lamps (e.g. ILD3-L), coloured neon-looking filament VFD tubes (e.g. IV-13 NUMITRON ИВ-13), IV-15 Magic Green Glow, multi-coloured small neon luminophore VFD indicator lights (e.g. IN-35):

I'm guessing the 220B/242B may refer to the voltage required to operate them. I have one Nixie tube (neon orange glowing type) that will operate at around 90V, similar to typical neon lamps such as found in mains appliances. Of course, you usually use a current-limiting resistor in series with them when running from mains voltages.

Dumping some links. The fella off Look Mum No Computer has made a short video about VFD tubes:



IV-4 datasheet: tubehobby.com/datasheets/iv4.pdf

Some of that info in English: lampes-et-tubes.info/cd/cd035.php

Russian site wish some of the pinouts (use Google Translate): rudatasheet.ru/tubes/iv4/

I'm tempted to just get some of these to play with...

Decided to waste some money on some IN-35 lamps. Literally got no use for these at all, but I'm intrigued by them. I got a mix of 50 red, yellow, white, purple and orange.

Looks like some of them have the white luminophore coating inside, which dictates the colour, and the orange ones are uncoated. Pictures from eBay seller:









I reckon one will go in the preamp, probably an orange one, as it really needs an indicator to show it's on. What I'm going to do with the other 49 is anyone's guess!

I’m not sure yet. The data sheet seems to suggest they have a firing voltage of around 180V but need a resistor inline to limit the current. The issue I’ve got is the resistor value stated isn’t correct for the voltage and current stated in the specs. I’m going to use the variable PSU I modified and see what happens. I’ve also got a step-up inverter that does up to 180V DC and 250V AC with 12V DC input. Might have a play with that at lunchtime to see if it’ll be suitable.

Well it's not looking promising for the IN-35 lamps arriving. Showing as shipped on 30th May but the tracking is showing they're still somewhere in Ukraine. Probably have to claim this back from eBay on July 12th