Valve circuit in new EPE mag

[britishrocket]

Has anyone seen the latest EPE? It has a valve amplifier project with what looks like two ECC 83's.

Not looked closely at it but seems pretty interesting.

Carl.

[Radio Wrangler]

EPE?

David

[Alf]

Here we are

[britishrocket]

Everyday Practical Electronics (International, probably...).

[Bobdger]

I ordered the pcb for the valve pre amp, it arived last week. More intresting is the way that the HT rail is derived from a 15v power supply. They use a MC34063 switch mode reg with a 100µH choke this is set to give a free running output of about 265V. Note the diagram that is in EPE has its + and - mixed.. With a bit of feed back and a timing cap change I can see a very nice, cool running 90v supply for battery radios. Only now waiting for my 0.33R resistors from RS. Out of stock until next week.
Bob.

[David G4EBT]

Most EPE projects are sourced from the excellent 'Silicon Chip' magazine in Oz, but as such, often tend to feature components which can't easily be sourced in the UK, which is compounded by many projects being quite complex and having a high component count. Sometimes, if Jaycar think there will be enough demand, they'll stock kits or components, but as often as not sourcing the bits takes longer than building the projects. About 15 years ago Jaycar were going to establish a UK based supply chain but nothing came of it - there's nothing in it for Maplin, nor was there for Tandy, so I guess Jaycar wised up. It's only a few weeks ago that I binned my out of date Jaycar catalogue.

Now that Elektor has disappeared off the bookstands, EPE is the only electronics magazine left standing in the UK. (Can't really count PW - it's exclusively ham radio). EPE was originally 'Everyday Electronics' then absorbed Practical Electronics and Electronics Today International to become 'EPE'. (EPE's 'sister magazine' is 'Radio Bygones' - subscription only).

Every success with the pre-amp.

[alanwin]

Practical Electronics magazine itself was created by the publishers (Newnes) of Practical Wireless, who wanted to focus on radio and spin off analogue and digital electronics projects into a new title. Everyday Electronics was written by the same team as PE, designed to cater for simple constructional and educational projects. Both titles went their separate ways before EE took over PE to form EPE. If anyone's interested I recently posted a reprint of my articles describing the 50 Year history of EPE available as PDFs at http://www.epemag.com/resources.html

-- Alan Winstanley

[Diabolical Artificer]

So it's a preamp?

Elektor gone? Sad, but then I haven't bought a contempory electronics mag since 1982. I buy old copies, but that's not going to keep the current electronic magazines going. Just looked up Elektor and it's still going - https://www.elektor.com/magazines/single-issues-print/

Andy.

[David G4EBT]

Elektor hasn't 'gone' - it's gone from shops such as WHS, so unless you subscribe to it, there's no longer the option to buy it, so as I said, the only electronics magazine on the book stands is EPE, in which most of the contructional articles are from Silicon Chip mag in Oz. Quite a lot are based on PICs, which are wonderful devices, but not in my sphere of competence or interest - there's only one PIC driven project which is currently of interest to me and that's an LED magic eye project which featured on the forum some months ago using a circular LED array.

As to valve amps/pre-amps, the best design I've seen in a long time was that by Tony Thompson, ('Aerodyne') which featured is Radio Bygones a year or two ago. Excellent design and a very comprehensive constructional article. (R. B - started by the late Geoff Arnold, former editor of PW, has of course only ever been subscription only. (Recently reduced from six issues a year to four).

[Terry_VK5TM]

Slightly OT, but a few years ago, there was a BIG editorial in Siliconhip about how valves were old hat and that they would never, ever publish a valve project, despite numerous requests.

How times have changed.

Terry

[Wendymott]

I subscribed to Elektor "on line" but it has gone from 10 issues a year to 6... i.e Bi monthly. The content too... is not to my liking... the serious professionals got hold of it..so as simple.. "amateur" projects are not covered anymore... it bye bye Elektor for me..when my sub runs out.

[Radio Wrangler]

Don't forget to send the editor a letter explaining why you're not renewing. Otherwise they just see falling numbers without any explanation and can just assume it's market trends and not something they've done.

David

[Ed_Dinning]

Hi Wendy, try Silicon Chip (Oz) or Nuts & Volts (US).
They have a range of both simple and advanced projects.

Ed

[britishrocket]

I agree with Wendy, find Elektor to be more like a trade mag than a hobbies one.

The Everyday Practical Electronics Today Internationals valve amp Psu is interesting. Seen a similar nixie tube Psu that gets 200 odd volts from smps chip.

Thing is, I'm told by them that know that pcb layout is critical for a circuit like that to work. That matters to me as I had thought to use something similar in a valve prototyping system I want to make.

[Bobdger]

The track lay out to the feedback input needs to be routed away from the inductor. Texas have a very good data sheet including a pcb layout for evaluation. The inductor I have used is from RS 800 4426. The MC34063 is a through hole 8 pin version RS 828 9872. I am now altering the values of the control loop as I need to get to about 90 volts.

[mole42uk]

A problem with EPE is that it doesn't seem to be readable on any computer other than a Windows box. I've written to ask if that's true but no answer yet.

[David G4EBT]

Theres an EPE Chatzone a bit like this forum where you can post queries about EPE or Radio Bygones which might be of interst.

[MrBungle]

Just a heads up with respect to the MC34063 used in this. I've had a fair bit of experience with these. It's a pretty dumb switcher. Fundamentally all it does is use the voltage spike from the field collapse on the inductor to charge the output capacitor and turn the oscillator on and off when the output voltage is a multiple of the reference voltage derived through a voltage divider. However unless the output is properly filtered, all sorts of nasty transients are present on it. I haven't looked at the schematic for this but if there's not at least a pi filter on there with very low ESR capacitors I wouldn't poke it with a stick. Tantalum are best but are no good for high voltages unless you go wet tantalum and have lots of money!

You can actually make one of those ICs with a 555 as the oscillator, an LM311 as the voltage comparator and any low gate voltage MOSFET (think this was an IRF510). Here's one I made a while back. Generates 50v at 50mA from 5v+. Don't use 50v electrolytics like I did if you do this; they get a bit hot.



Edit: Also the current limit seems not to work at all on some of the cheap Chinese clone ones (ST / CHN branded ones) leading to self destruction.

Edit 2: also make sure you use an external MOSFET/transistor if you are dealing with more than about 30v and add a zener between the reference input and ground to clamp it below 30v or so or they pretty much instantly snuff it if it doesn't shut down properly. The voltage just goes up until something explodes.

[Terry_VK5TM]

Originally Posted by mole42uk

A problem with EPE is that it doesn't seem to be readable on any computer other than a Windows box. I've written to ask if that's true but no answer yet.

Correct, their pdf's require a special Adobe plugin that only runs on Windows (won't open in an ordinary pdf viewer).

It does say this near the bottom of the subscriptions page.

Terry

[britishrocket]

Originally Posted by MrBungle

Just a heads up with respect to the MC34063 used in this.

Very interesting indeed, thanks for posting. Definitely something I am going to investigate, even if it just turns out to be a simulation. I've several good switching regulator ICS sitting on pcbs that I could use for real, or implement my own as you have done.

For my valve test bed idea Psu I am going to incorporate means to run 6.3 v heaters for E prefix types and 16v for the P types.

Carl.