Some times I start something without any real plans.

[AdrianH]

Knocked up a chassis from some 1mm steel sheet and started sticking things on it, have a vague idea what I want to achieve, but as of yet no drawn out circuits or plans, but bits from magazines/articles. Will have to make a few items as I go. A case of, if I start something I might finish it, or, it will give me something to do.



One question, the old style RFC, generally around 2.5 mH, multiple bobbins on a shaft type choke, seem difficult to get for reasonable money, but the 'looks like a resistor' modern ones seem to be as cheap as chips, would they be OK for valve use, are they any good?

Adrian

[David G4EBT]

I suppose there's a difference in the Q value of each type, but I'm not sure if that's of any consequence (as it would be for example in a tuned circuit). The old-style 'Pi wound' ones tended to be good to about 150mA. The 'resistor-style' ones are available cheaply in .025W, 0.5W and 1W, but they'll be 2.2mH. EG:

https://www.ebay.co.uk/itm/263867106...3ABFBM0N3_k5lh

I've attached a pic of a selection of old-style ones.

I believe they're sought after for replica 'parasets' which might push the price up.

[AdrianH]

Yes they are the style I would like to have, up to 100 mA would be fine. I must see if any of the old mil chassis has anything fitted, but I do not remember anything.

Adrian

[David G4EBT]

Some years ago, I made a little 'Morris Gingery' hand wave-winding coil winder, hoping to be able to wave-wind coils, and chokes like the ones I pictured in my earlier post. However, I soon discovered that trying to get the turns to follow a straight-line trajectory, (which calls for a heart-shaped cam), with the turns laying close to each other, (like Denco coils for example), is next to impossible. The more 'air' in the coil, the larger it becomes for a given inductance.

There are countless DIY coils winders on Youtube, some quite sophisticated, with CNC and stepper motors, but I've only seen one example that wave-winds coils in which the turns are close-wound, and the coil is both narrow and deep, yet the turns don't collapse at the side.

There's a video of it at the link below, creating a pi-wound choke with ten windings.

The explanation states that winding eye is driven by an ordinary servo for modelers and the winder can be programmed for winding of coils with such precision that it's possible to wind coils with thickness as small as 1 mm. No information on its design, construction or how it's programmed:

https://www.youtube.com/watch?v=tg67CvbcHaU

So, for pi-wound chokes, it looks like it has to be NOS on eBay, or to opt for the resistor-style jobbies.

[AdrianH]

Well I have ordered a few batches of the resistor style ones rated at a watt each, so I will see what resistances they are when the arrive and if required stick some in series to build up a required value.. ordering 60 was cheaper then an original.

Adrian

[Cruisin Marine]

ordering 60 was cheaper then an original.
At that price you could use them in series and parallel combo's with many in use to still get the same value (a bit like a matrix if you get me). It may look a little strange, but who cares if it does the job.

[AdrianH]

I watched the video and another, I wonder if the wire was coated with sticky stuff to keep it in position. The coil winders looked good, but not something I could consider making for myself.

Adrian

[Aub]

How do you get those nice rounded corners on the chassis?. Looks good.

Cheers

Aub

[AdrianH]

Nice round corners That is just me using one of the cheap Clarke bench folder that one sticks in a vice, that and use a mallet and corner for the shorter sides..

I think it would be nicer with tight corners, but I did not fancy getting my home made press off the floor onto the bench, It's heavy. But after bending and welding and clean up with the flap disk it looked OK.

If I could have found a cheap baking tin I may have used one of them to play with!

Adrian

[joebog1]

If I could only make round corners !!!!.
I make my chassis, or have them made for me, using a panbrake folder. TIGHT corners and really pointy weld points. Ideally I would love to be able to make say, 1/2" rounded edges AND corners, but apparently there is lots of faffing about to cut and bend them nicely before welding.

Your chassis looks fine

Joe

[Bazz4CQJ]

A friend of mine used to make tin-plate chassis which looked great. With suitable re-enforcement soldered in place, they could be quite strong. A lost art?

I think my problem is that I love to plan stuff and draw it all out, but in my dotage, I don't enjoy construction much these days. Always burning myself with the iron and on things I just soldered .

B

[retailer]

Not quite on topic but interest followers of this thread - how to make a project chassis look presentable and at least semi professional, I've seen amp chassis' made from timber, sheet galvanised steel, 'C' builders purlins and aluminium sheet and extrusions, here's one made from brass sheet, a credit to the builder, it is big - a diy Fender Deluxe Reverb chassis made from brass sheet, the whole chassis has been tinned with solder. At first look I could'nt quite work out what the chassis was made of until I read the whole thread.

https://www.aggh.net/discussion/index.php?topic=53721.0
https://www.***********/photos/195101...n/photostream/

[joebog1]

Heres one of my brass chassis. Another unfinished project.

Its half hard brass and hand buffed to make it mirror shine. Its then painted with automotive two pack clear. Sorry about the blur, it was a half second exposure.

Joe

[kellys_eye]

You can use a circular saw to cut 'grooves' in 1.2mm steel (or aluminium) that allow you to form really tight bends with sharp corners and practically no loss of strength. There's a tube video about it somewhere and all the bending is done by clamping the grooved plate in a vice and some lightish hand pressure.

I bought 4 off 2.5mH pie chokes rated at 170mA a couple of years ago. If you are in desperate need I could spare one!

[AdrianH]

Thanks for the offer of the choke but I am expecting the resistor ones to arrive soon. Postal services do seem slow at present so adding to a bit of frustration. I am awaiting a replacement valve for my Eddy 870 after catching the top pip of a valve and taking it to air, that is 9 days at present. The chokes 5 days.

On the grooves with a circular saw, I do not have a table saw to do that but think I understand what you mean. Guess it could also be done with a milling machine and small end bit.

Adrian

[G6Tanuki]

Originally Posted by Bazz4CQJ

A friend of mine used to make tin-plate chassis which looked great. With suitable re-enforcement soldered in place, they could be quite strong. A lost art?

I've done quite a few chasssis using double-sided FR4; it has the advantage that you can solder things like B7G/B9A valve-sockets [the types with a base shroud to take a screening can] direct to the top of the chassis rather than using nuts/bolts/washers.

Offcuts of FR4 can be soldered in place to make corner-fillets/braces and upstands to take things like switch/potentiometer-spindle bushes or small [up to PL259] sockets/connectors.

[AdrianH]

Originally Posted by G6Tanuki

I've done quite a few chassis using double-sided FR4; it has the advantage that you can solder things like B7G/B9A valve-sockets [the types with a base shroud to take a screening can] direct to the top of the chassis rather than using nuts/bolts/washers.

Most of my home made TV was done with double sided FR4 also using small pieces to support components etc. Then a wooden box to support it all. I still did a power supply and an audio amp on metal chassis, again home made.
https://youtu.be/mImYmATnacg

Adrian

[AdrianH]

Just an update with a few fuzzy pics from the phone.

Have got to the stage where it will no longer run from the small 12 volt to HT plus LT converter, so will have to bring a mains PSU into play. Will see what I can use from a previous project if possible rather then start from scratch.

OA2 and two EF80's and the 6V6G, just initially looking for Top band CW working before I take it further. One step at a time.






Adrian

[joebog1]

Looking nice to me !!!

Joe

[AdrianH]

Had a bit of success last night with a power supply lashed up strung across a board.
I managed to get approx 5 watts of RF into a 50 Ohm load and a lightbulb. The light bulb would load better then 50 Ohms so I guess I need either a change in C or L, but it is a start and will push me to go further with it.

Adrian