My "simple" valve tester

[Bushbaby]

Hi All
I know that I am no expert at all when in comes to electronics/circuitry but I thought I would see what your thoughts are with regards to a simple circuit board to cover caps (C3 to C8) and diodes (D5 to D10) with regards to the schematic I'm working from based on  - 

https://valveheaven.com/2015/03/an-inexp...be-tester/

I thought it wise to ask for a review early before I build up the rest of the construction work. It does appears that there are changes to items shown from the original designer builder so I hope I will get this all ok?

Thanks in advance 

Rob


       

[ppppenguin]

For something like this either build it on tagboard or matrix board (aka pin board). I use the latter for much prototype and experimental work. It's like Veroboard without the copper strips. You use pins that are a push fit in the holes. Wiring is with tinned copper wire, with sleeving as needed. Sometimes insulated wire for longer and irregular runs. More flexible than Veroboard and no risk of insulation breakdown between adjacent tracks.

Here's a photo of a PAL coder that I designed and built in 1987 using matrix board. I've still got it and it still works. It was originally designed to give near broadcast grade PAL output from a BBC Micro. My client put it into production, we designed a PCB and it sold quite well.

[Bushbaby]

Wow, what a circuit board....totally impressed.

Good point indeed, I never think about "test" building at all and I do have a pin board etc to do this.
I do like using DIY Layout Creator (DIYLC) but yes, this is latter part of the work. I can still ask though, does this part of the circuit indicate that I'm in the right direction with these connections at all.....it may not be the final judgement.

Many thanks

Rob

[ppppenguin]

You're overthinking this. Just get the components down on some pin board and wire them up. Perhaps sketch it out first so you can do most of the connections with tinned copper wire. Check your wiring against the schematic and you're good to go.

It may not be so relevant in your case, but you may have noticed a run of 18swg tinned copper wire all the way round the edge of my board. That's a nice solid 0V bus. Not as good as a ground plane but very useful indeed.

One thing I've almost never used in the last 50 years is the T-Dec and similar plug-in prototyping boards. I suppose they have their uses but in a professional environment it somehow seems easier to solder it together on pin board and not worry about the bad contacts. It's stuck with me whether I'm doing it as a professional or enthusiast.

It's all change with surface mount, ball grid arrays etc. It straight to multilayer PCB for those, then find the problems, upissue the PCB and repeat. With luck there will be an evaluation kit so I'm not starting from scratch, or an older design I can hack about to try some ideas. Rob, these are not problems that will affect you.

[Bushbaby]

As always, I probably am over thinking this.
I have the majority of components but are awaiting a few more....as you've indicated, I shall give it a try.....I will, keep you posted.

Best Regards
Rob

[ppppenguin]

My main comment on that circuit is that it's an odd way to get HT. I know the parts are cheap and readily available but the regulation will be awful with that amount of voltage multiplication.

If I had a transformer from an old valve radio around with an HT winding I'd use that. If I didn't, I'd probably use a second LT transformer in reverse to step the LT back up to HT. Then use a simple bridge rectifier.

Using optocouplers to switch the power to the DVMs is a clever idea but what's wrong with a switch? OK, you've got to remember to switch it off and on but it's hardly an ordeal.

[Bushbaby]

I've got a Douglas MT3 FT transformer that I picked up as NOS that I'm sure is suitable for the design of the circuit. - does this sound ok?
I don't like the idea of the the optocouplers even though I have them. I was stupid enough (my error??) to buy some cheap DVM but then thought "why don't I use permanent panel meters?" so I've ordered  200uA DC and 200V DC LED panel meters.
       

[Mike Watterson]

There are not enough parts to warrant a PCB, also you are doing only one.

Since the HT is measured, the lack of regulation may not matter. The heater voltage must be accurate as that affects the readings a lot, hence some AVO testers had a load of taps on mains to fine tune.

No need for optocouplers. I've repaired a few testers (3 x AVO, Hickock, another) and built a curve tracer kit. A simple valve tester simply has loads of switches. Some use unsmoothed half wave HT as the calibrated metering is adjusted to suit.V

[ppppenguin]

The circuit specifies a 200mA meter , not 200uA. It's easy to add a shunt to make a 200uA meter into a 200mA meter. I see there's a protection diode so that is survives the inevitable gross overloads.

Mike mentions the need for accurate heater voltage. I would provide terminals where you can easily check it with a DMM. How accurate it will be between the 24V and 30V taps of a transformer is a matter for measurement. If your mains voltage is rather variable your heater voltage will be too.

[Bushbaby]

My error - I have ordered a 200mA and not a 200uA meter.
Thanks for the notes from and Mike regarding the heater voltage....I do hope the mains voltage isn't going to be variable and cause potential issues?