Capacitor Tester and Reformer Unit - Stefan Niewiadomski

[Stevie342000]

Just for clarity and to make sure that I have got this right.

The outer foil end in valve or tube circuits goes to the anode end and the other end goes to the grid or the outer foil goes to ground end, right?

As one of the another clip using the amp method that I just looked at had this the other way around (he says the outer foil goes to grid...hmm I think he is wrong), I trust Mr Carlson, he's very good, if somewhat long winded or thorough depends on your viewpoint.

[pwdrive]

In audio situations to avoid or reduce stray pickup by the capacitor the outer foil would be connected to the lower impedance part of the circuit and the inner to the higher impedance part.

For bypass situations such as screen grid bypass etc the outer foil would be connected to chassis.

Doing the 'scope or amplifier test for the outer foil is straight forward.

Lawrence.

[Diabolical Artificer]

Mr Carlson does indeed know his onion's ( though I think he was wrong about heater flash - https://www.vintage-radio.net/forum/show...p?t=122438 ){ he's doing a patreon electronics course at the mo which is good }.... however there is a simpler way to test for the outer foil on a cap as Lawrence imply's. Turn on your scope, turn to lowest setting 50mV or whatever connect cap across lead, IE earth clip on one cap lead, probe tip to tother. Pince cap body with fingers, you'll see a trace/hash/crap of about 100mV amplitude or whatever, now reverse leads. The outer foil is the one with the smaller amplitude trace when connected to the black ground lead.

AFAIK the outer foil goes to the "earthy" end or as Lawrence says the lower Z end of a circuit, which in the case of a de-coupling cap from anode to control grid with a 1 meg or similar R to ground would be outer foil to control grid end. Not sure if I have that right. To find the Z of the output of the first valve you times the dynamic anode resistance in parallel with the anode R by the gain, yes? The Z of the following stage is the grid resistor. so for your bog standard triode gain stage output Z is around 30 - 100k so if it was 79k say and the following grid R was 1meg then the outer goes to the 1 meg end. But if for instance you had an OP Z of 35K and had an grid R of 100k on the following stage then the foil would go to the preceeding stage end.

Not entirely sure about this myself, could someone do some real world example's please?

Andy.

[Stevie342000]

Thanks Andy & Lawrence that was fine as far as I can tell, the explanation made sense and I've not had my first sip of fresh coffee yet - waiting for my friend Gaggia to warm up.

It confirms what I have learned already, yes Mr Carlson is doing a Patreon group/course it's rather good actually he has a simple but effective teaching style and he is very easy to understand, no complicated maths as he simplifies it as much as he can. After all these years I can now figure out what and why certain components are placed in a circuit and what they do, as of yet I do not have the full maths for the calculations for gain or maths involved in each stage of a circuit but I could read that up.

In the members only clip, I figured what the extra capacitors and resistors were for in the schematic, aside from which he had given a very broad hint when he took his measurements on restricted bandwidth. I just watched and waited for him to confirm what I had thought and indeed it was right.

A circuit valve or solid state is just a set of building blocks, I prefer valves simpler to understand the schematic and less components but more expensive to build than solid state. Now I understand better how those building blocks work and fit together.

So the foil end goes to the lowest resistance point in the circuit full stop, well off I must go Mr Gaggia is calling.

[pwdrive]

Given the impedances involved and the reactance of the capacitor with anode to grid coupling it probably wont make a great deal of difference which side the foil is connected to.

Lawrence.

[Diabolical Artificer]

Yep, the Maas 50 amp video was good Stevie. You might try building your own amplifier from scratch, it teaches you a lot.

Dig what your saying about valves. The thing I like about mucking about with valve's is that they're very forgiving if you screw up and make a mistake. As you say there are less component's too; it's tricky as a beginner to read a busy transistor amplifier schematic as compared to a valve amp.

It's not resistance (DC), it's impedance (AC)which is the trickier part of the circuit.

As you say Lawrence, it probably doesn't matter, it's gilding the lilly. In practice a lot of times I stuff cap's in any which way, in an audio amplifier, makes no difference. Would think it matter's more at RF where the frequencies are higher and as a result the reactance's are bigger.

Andy.

[Stevie342000]

Why I say thank you my Diabolical friend, yes agreed it probably makes no difference in audio circuits but there must have been a reason (and RF usage may be it) why old style caps were marked with outer foil end but it may answer why modern ones are not.  It was probable best practice in the day so you did not think about it when you working on equipment and thus avoided pitfalls and issues when it did matter.

Yes I agree the MAAS 50 looks interesting once you take all the R/C bandwidth limiting parts out of it.  I did build some amps in the past my first project I seem to remember (and the only one I can recall to date) was an ETI project for a hybrid preamplifier.  It used something like BC109 in front end to boost signal for MC cartridges and then used an ECC88 for the next or line stage it was about the late 80s or early 90s (the issue is on the American Broadcast site), I think it was November or December 1990.

Who says valve amps are not quiet, it operated from a stone still silent blackness, even thought it was a sat under a table for safety's sake of course and not in a box of any description, looking more like a rats nest than an amplifier.  At the time I used it to drive a pair of Vortexion PA No.1 amps (From WW2), massive iron in those (it was in production from about 1936/37, later rebadged as CP20). I went straight in with the signal on the volume pot wiper (as I have the original user manual with War Department warnings and schematic - there is only local feedback around the 6V6 output tubes - no global feedback at all) , worked absolutely fine and was jaw droppingly good.  Source Ortofon MC10 cartridge, Rotel RP830 turntable, Philips CD player, Philips 1970s tuner, a cassette deck and Kef Cantor III speakers.

One other kit I remember making and selling in the end was an Audio Note Preamplifier and I do not think there is anything else, the  last one was sort of PCB hard-wired.

Anyhow I digress I am looking to rebuild my 3 Williamsons with Woden WOT-25 output transformers, and yes it might be gilding the lily (which was name of a similar project in Audio Magazine) but in that design it may make a difference as it tends to be a bit marginal although I never had an issues with it motor boating.  I know it may not make any difference but knowing that the components should be fitted in a preferred way (is a good habit and practice to get into) - well how can I put it if it is not done that way it triggers an OCD area of my functionality.

Plus I am looking to build 3 150 watt OTL Power Amps to drive my cutter heads for disc recording, there are other projects in the pipeline as well.

Ah yes which brings me to my final point, how do you work out the gain of a stage (simple maths please) and what its impedance is?  I assume Mu comes into it somewhere or not?  I assume if you were doing a block diagram of each stage then that would be expressed in dBs (at 600 R?)? That the voltages would be looked up on a table (or on-line calculator these days) and one figure would be taken away from the other or added?  Ah yes now that I am getting older it is time to do the things I never did when I was younger, so it is time for me to tinker with my boys toys.

I could look it up in a book but they tend to be overly maths heavy (my maths is not as bad as I think it is) however the BBC technical books and documents are easy to read (mostly).

One of the reasons in the past I stayed with tube/valve equipment is that it was much more difficult to read a solid state design and not so easy to make PCBs, now with the advent of on-line tools, silk screen printing I am revisiting that area as well.  Valves are easier in that sense as they are hard wired, plus with more components comes more errors and so on.  The Mullard and the GEC books on audio amplifiers and layouts warn of issues and what is good practice in component layout for the novice at least.

[Terry]

One of the reasons in the past I stayed with tube/valve equipment is that it was ... not so easy to make PCBs ...

It wasn't exactly difficult, though.

Take a pad of 0.1" graph paper to suit components with a mounting pitch of 2.54 mm and multiples thereof.

Work out the component locations and mark on the sheet then add the track layout in pencil, in case changes are needed.

Secure the finished work to a sheet of copper laminate and transfer the mounting hole position to the copper by pressing hard with a very sharp tool - I used to use a bradawl.

When the paper is removed, the pad layout should now be clearly visible.

Take a bottle of nail varnish - as dark a colour as possible - mix thoroughly then use the applicator brush to place a dot of the varnish on each pad then add the track layout.

Etch as normal and remove the varnish with acetone. The previously transferred hole pattern should now help to guide the point of the drill to get the holes in the right positions.

I used this method successfully for a wide variety of boards and modified it slightly to allow me to make multiples of the same board - some quite complex - without having to redraw the layout.

[Stevie342000]

Agreed absolutely but I did not have that knowledge or information until just passed it on. Plus some of the on-line applications analyse the circuit layout on the pcb and will move any components if there are issues with layout.

It all comes down to experience and that seems long winded but a method that works but probably no more long winded than printing on acetates and photo etching which from what I can gather is similar to silk screen printing, which makes duplication easier should I wish to make more than 1 or 2 copies of the PCB layout. Unless of course I have not fully understood your method which looks like a one off method.

[Nick]

I haven't made a PCB myself for years. Making your own PCBs, if they're simple, can be done in a day, but if you can wait a few days, most folk I know now just use one of the on-line shops.

I mostly use PCBway, who are disgustingly cheap, good, and very fast. I've had many designs and many 100s of boards made by them with no problems at all.

https://www.pcbway.com/pcb_prototype/

Current deal is for 10 x double sided, silk screened, solder masked (choice of colours), plated through vias, HASL tinned, 6mil minimum spacing, FR4, boards - max size of a board is 10cm x 10xm...

...for USD 5 for all 10 boards + P&P (typically about USD 20 if you use DHL)

I have a slightly used top quality heated bubble tank for sale should anyone want to buy one...