Coils for valve IF's are any available like TOKO coils?

[AdrianH]

I am struggling to get my next home brew project going, the problem is small 470KHz IF cans for valves.

So I was wondering if there were ever available small TOKO style cans suitable for valve sets and if anything is still around?

I have been trying to make my own coils basically winding pri and sec on formers but I end up with something that approx 50 mm long with tuning slugs in it and about 13mm diameter, without the screening cans. Making my own small cans is an issue, 15 mm copper tube would not work, well it would but it reduces the inductance that much I would need to wind well over the normal inductances needed, I will be trying tin next. Aluminium I can not form up to the required shape or solder to the board.

I am also making assumptions
1) That transistor IF cans would not be suitable as many only have a few turns on the secondary, (pri tuned, sec un tuned) which would be OK for low impedance transistors but a major waste for Valves.
2) Valve IF cans are typically tuned primary and secondary, with same turns on both.
3) I doubt I could see the wire on a small TOKO type coil to rewind it let alone solder something that thin.

If anyone has worked a simple small solution I would like to hear from you.

Adrian

[Ed_Dinning]

Hi Adrian, valve cans tend to be bigger to get the turns in. I believe the rule of thumb for screening cans is that they should be 3* the dia of the winding or they cause damping. They are also much thinner than normal Cu pipe. Popular choice used to be Al film can or similar. Tin/ steel may be much worse.

Some valve set coils as used on Double Decca were used unscreened but top and bottom of chassis for 1st and second. These were 2 coils mounted side by side on a paxolin strip.

Some MIL stuff had pri and sec coils mounted in pot cores with high Al figures so self screening.
Basically the higher the Al figure the fewer turns (but other drawbacks then come into play!)

Ed

[woodchips]

Have a look along the pharmacy shelves in the supermarket, if not aluminium then plastic tubes that can be painted or wrapped with foil?

[radiomobile]

Hi Adrian, The Motorola transistor car radios models 114 /112/122 series, around 1970's, have very small IF transformers which are double tuned and have the full tuned windings available on the pins as well as the low impedance taps. I have successfully used these for valve applications in the past.

Lester

[G.Castle]

Hello Adrian.

I have read that it is possible to use the transistor style IF transformers back to back. this may be a matching dodge but would also help with the problem of voltage differential between the anode circuit of one valve and the control grid of the following one.

I'd personally avoid tin plate or similar for home brew cans, thin copper sheet is probably the best bet to "roll your own, though zinc, roofing gun metal, or shim brass could do as well, and of course can be soldered.

A young friend made some excellent replacement IF transformers using copper shielding cans and molded chokes, I was going to link to a thread on GVR she started in the homebrew section, but noted you were first responder!

[Herald1360]

You could try using pairs of trimmer tuned off the shelf miniature fixed inductors with a low value top coupling capacitor à la R1155. Mount in a tin of your choice!

ISTR someone on here had a penchant for using such inductors in rather beautifully built homebrew designs.

[AdrianH]

Thanks all for the comments.

This is why I was asking: -

Found on this site http://www.hi-ho.ne.jp/ux-45/russian.html and all credit to T. Kawabata for his page, main index page is http://www.hi-ho.ne.jp/ux-45/index.htm

I have some Russian Rod Pentodes and wanted to get something smaller in the IF can area, even if similar size to the valves, it looks like he has re-wound the cans, must be with some mighty fine wire?

I like his attitude of just wanting to do it and I found his site after searching for superhet circuits with rod pentodes.

Anyway a few comments on previous: -

Thanks Ed for the 3* size, you have made me wonder about pot cores for some reason, but not seen any that would allow for two windings and ferrite tuning. If I overwind the secondary would I need a second slug?

Woodchips, there used to be aluminium tubes of antacids at one time, wonder if they still exist, but I will look around next time shopping, thanks for the idea.

Radiomobile, I would not like to scrap a car radio, plus they are costing quite a bit on the auction site.

G.castle, Yes that was Amie's thread, I have kept that in mind, I do not think results with a screening can were shown? Wonder what happened to Amie?

Adrian

[G.Castle]

Originally Posted by AdrianH

Thanks all for the comments.


G.castle, Yes that was Amie's thread, I have kept that in mind, I do not think results with a screening can were shown? Wonder what happened to Amie?

Adrian

I think she mentioned later in the thread about the screening cans making little difference to the results, they were made from a strip of copper soldered into a box with an end soldered in with punched holes for the trimmers, it doesn't seem that they were pictured... They are about 8 times the volume of the Toko component so may not be small enough for what you're looking for.

Amie is fine, she and her mum moved to the midlands and is concentrating on her education at the moment.

Cheers.
Greg.

[VT FUSE]

May be worth a look on eBay, item 334281123941.
No connection to seller etc but have bought several times ( Plessey PTR175 )
and always had good experience as a satisfied buyer.
I seem to recall that the seller has posted on this forum.
I May have some pieces such as if X'formers from these if only I could get 5 mins to look.
Mike
p.s regular contributor Andy M0YFA could probably point you to circuit info? my worsening memory tells me that there was a ground based set and info is out there.

[G6Tanuki]

I've done the 'two single-tuned-IFs-coupled-together-by-their-untuned-secondaries' thing in the past when needing to build something to fit inside the aluminium case of an otherwise-wrecked valve-type IFT.

It works.

If you're looking for small-ish-bore seamless brass tube, ask any of your hunting/shooting friends; Cartridges from spent rifle-rounds are freely available.

[AdrianH]

VT Fuse, I have the guts out of some of them guard receivers, they led to my first project using 6021 valves, a small audio amp. The can you can see marked pri and sec are 1.8 MHz if transformers, they are using a ferrite pot, I have one in pieces and not sure if I can get it back together, but it is worth another go at it. I need to get some thinner wire as the smallest I have is 0.16mm. The other side of the receiver under the cans are another two sets of IF cans, very close to the former, these are at 35 MHz and I have wound the if coils on these, but over all would be big with decent cans to shield them.


G6Tanuki, Unfortunately I have not shooting buddies for for the casings, I do have some 303 casings found while detecting but way to small an diameter.

I will have a re-think of what size I need to get to and will send an email to Mr T. Kawabata to confirm if he wound his own and what gauge wire was used?

Adrian

[Ed_Dinning]

Hi Adrian, some of the small pot cores that were available had sectioned 4 section bobbins, so it may be possible to have 2, disc shaped windings in there. I suspect you will only be able to fit a single adjuster and would need capacitive tuning for individual windings

Ed

[VT FUSE]

Adrian
Totally correct, had a mind lapse as to frequency of interest and core properties in the ones suggested.
Have you seen these on same auction site? 112916773621 advert shows internals including bare bobbin. Also several other variants of same can. It ought to be possible with some dexterity needed, obviously again only single adjuster.
Mike

[AdrianH]

Thanks Mike, they looked familiar and after looking at them for a while I remembered a box of coils I got from Ed (I think) there are some similar if not slightly bigger at 15mm high marked Weyrad L205/206 and a few Weyrad 207.

The 205/206 is a single coil max inductance of 0.7 mH.
The 207 again a single coil max inductance 24 mH.

OK bigger than the TOKO coils but smaller than I have now but also I think I can still see and work on them.

I really must sort out my parts boxes and list what I have were!

This brings me to another thought and I will need help on it, will these not over couple if the two coils are next to each other and provide for a double hump response.
How does it not do it in these small cans. For example in say a battery valve portable there is a gap between coils of around 6 or 7 mm which I guess has been done to stop the over coupling, it is a case of the secondary has to be an un tuned coil to stop this?

[Station X]

Thread closed at OP's request.