Jonny Tubetronics: amps and synth stuff now in one thread

Do a skid!

Great looking line up of valve gear and good musical taste 👍

My username comes partly from the diminutive of my name and a tribute to the MAN, I've used it that way for over 50 years, it was sign written on the side panels of my Lambretta back around 1967/68



I'm pretty sure I have the 45 single of "All Along the Watchtower" (and Hey Joe & Purple Haze) in the attic,I need to get up there as well, my vinyl has been up there that long I've forgotten all the stuff I have 🤭
Apologies for the thread distraction 😉

To make a system sing you can't go wrong with Yello.
The Album 'Baby' is teriffic, Jungle Jim or Ocean club sound amazing with the volume cranked and really work your system.

Ok, I got this working. It just needed a reference to 0V adding in and now it works.

I tested this by patching in a 1M resistor with a croc clip while putting a 100mV 1khz signal in the input:



That went from the coupling capacitor output to 0V which was a nice easy fix. You can see the fan on the tube on the left is wide - that's because the correct voltage is now getting through. I didn't have two 1M resistors for on the board, so 820k resistors had to do:



And that meant with a music signal on the input, the fans dance to the music:



A quick video with music going through it but no sound:



I'll need some piggyback connectors to be able to run it and have sound at the same time. I wanted to put two sets of connectors on the back but there isn't quite space. Note how the two tubes are slightly different in real life. Both face slightly different directions and the colours aren't the same! Quality control at its best.

Gain-wise, with 100mV input at 1khz, the ECC83 puts out 7.3V. So the gain is about 70x. Full fan appears with 460mV and 29V output. I haven't put a scope on it, but I suspect it's clipping at that point. I'm glad I opted for an ECC83 over an ECC81, because the signal is only just high enough to drive the circuit. I think when I put it on the preamp at home, it might struggle a bit.

Last month when the Ukrposhta postman visited, I tested out the IV-6 VFD tubes but not the IN-3 indicator tubes or the MTX-90 tubes.

The IN-3 tubes are indeed similar to the IN-35 luminophore lamps on page 7. They look ever so slightly different. They have a sort of reflector cup and the glass is smoked like a nixie tube. The difference for running is the IN-35 is around 5mA at 240V but the stated voltage and current for the IN-3 is lower. Again, I don't fully understand the datasheet. It shows an anode and a cathode side, which presumably relate to the bits inside that look like a plate a reflector. Two voltages (90V and 55V) are stated, which might be the trigger voltage and minimum voltage to sustain the lamp. Current 0.2mA compared to the IN-35's 0.5mA.

I decided to hit them with 240V on the breadboard and limit the current to 0.2mA, which meant a 1.2M resistor. It lit but was a bit dim, so I added another one next to it with an 820K resistor



So as far as I can work out, they're just a lower power indicator lamp, maybe which fires at a lower voltage than the IN-35. It can be viewed front-on or from the end. Only comes in orange. I think they were used as the dots in nixie display equipment, clocks etc, since the trigger voltage is the same. I've got 25 of them.

Next up are the MTX-90 thyratron tubes...




These aren't an indicator lamp like I originally thought but they do light up when triggered. A thyratron is in fact a type of switch and these tubes can perform a number of functions, most of which I don't understand yet. It has three pins. There's an anode, cathode and grid. High voltage goes between the anode and cathode, then when sufficient voltage is applied to the grid, the device switches on (and lights up). It doesn't need much, because the grid is sensitive enough to be used as a touch-sensor. This is what it looks like - the tube is about 30mm long and 10mm diameter:



Here's a video showing some of the things it can be made to do:



I'm guessing it could do simple logic as well. I have ten of them. No idea.

The solder balls aren't solder either, they seem to be solid and tinned. I've made it easier to play with one by soldering it to some PCB header pins:



So, uh, yeah. Still got no idea what to do with these so watch this space I guess!

So a couple of posts ago I said I was worried about the input level for the VU meter well ive literally had two nights no sleep thinking about this and how I might end up having to deal with the whole Christmas break without a properly working VU and its been getting me down and this morning I decided to call the doctor because I don't want to slip into a depression over this and he goes to me yeah I think ur gonna need an op and I was like WHAT and he goes hold on let me finish I think you're going to need an op AMP on the input to bump the voltage up a bit. You know, from 1990s A Level electronics, remember? Well, sort of. I had a rummage in my scavenged box of outdated bits at work and indeed found some 1990s 8-pin DIP dual op amps. Dual 741s, no less, the real deal!

I present to you, the MC1458:



Perfect. One side for left, one side for right. Lunchtime project time before I finish for Christmas.

So, rough plan. Tap into the 6.3V heater supply. Bridge rectify it and split it down the middle with resistors to make about a +/-3V supply with 0V in the middle. Make a pair of non-inverting amplifiers with a gain of about 5x which should give me plenty of extra input voltage. Don't want to amplify as much as 10x because that much might make adjusting it difficult and 5x gives me plenty of headroom with the low supply voltage. An additional bonus of having an op amp on the input stage is if the VU meter introduces any hum into my system through the signal lines, the op amp will effectively isolate the rest of the circuit and eliminate any hum. It's not fully tube, but it is fully in the spirit of my bodgey builds made with outdated toot.

Non-inverting amplifier for those who have forgotten (like I had):



Equation for those who have forgotten (like I had):



From here, many thanks random website. I used a 180k resistor for RF and 39k resistor for R2, which should give a gain of about 5.6.

I also found a random/handy DIP-sized bridge rectifier which made my veroboarding much easier. I also added on a couple of 100k resistors to divide in the 0V point and a couple of 47uF smoothing capacitors and this is what I ended up with:



Testing on the analogue bench supply:



Obviously it didn't work first time - I'd put the two resistors on the right-hand channel round the wrong way so I only got a gain of 1.25. Glad I checked. Once I'd swapped them around, with an approximate 100mV DC input I got an output of around 540mV from each channel. Spot on.

You wont need any heating in that room when its switched on...

How's the x-former handling being enclosed ?

I'm with you on the slots, look much more professional IMO similarly with passive cooling.
Although sometimes active is the only way, what I've done in the past is to put in a 12v fan but run it on a lower voltage (probably still run at 5v) I had good results with a fan at the bottom sucking air in and vents at the top.
I installed this one (its 12v and running on 12v) on my Topfield PVR, with the PSU and HD side by side they tend to run hot and the original caps on the PSU were poor quality, they normally fail after a couple of years and cause all kinds of problems with the PVR operation. Mine have all been replaced and I put the fan in to try and prevent future problems,it's virtually silent and reduced the HD temps from average 53degC to 30degC according to the HD S.M.A.R.T. info. Must have worked PVR is still running trouble free over 11 years later and its on virtually 24/7