Hi to all, wondering if anyone would have a tuning dial or scan of to suit what could be a 1954 4 valve Tecnico radio. Valve line up is 6AN7, 6ARGT, 6X4 & 6M5. Transformer marked 26 Oct 54. Also after schematic if possible as it is rather deaf, please email
Thanks in advance
Paul

There is a Tecnico 1140 in the AORSM Volume 10, Page 293, 294 & 295 with that valve line-up.

Click on circuit diagram for larger resolution

Thanks heaps for posting, my email appears to have stopped working again,time for a change I think.CCT appears to correct,will check when I'm back in Melbourne ....currently in Halls Gap. If anyone has a spare case or even complete radio I could use for parts etc that would be great......still require dial glass. Cheers Paul

It's been a happy ending for this Technico after some work!!!

After replacing all out of tolerance resistors & capacitors & trying valve substitution from working radios the Technico still refused to receive anything other than the ABC at a weak level!

In the end I found one of the IF transformer cores had come away from the adjuster screw throwing it right out of tune, suspect someone had tried to fiddle somewhere in the past & gave up on it by the look of the mess!!

The IF transformer was made of a glass tube with wooden ends where the adjuster traversed, made it easy to see how the adjuster worked but a bit scary to fiddle with!!

A bit of a clean up was needed to remove loose material in the tube & to free the thread which was extremely tight on the screw, next some careful injection into the core with some high temp two part epoxy glue & carefully turn the the adjuster down into the core & glue careful not to squeeze any out the sides & after waiting a couple of days all was good

While the casing was off the IF I also removed the small mica caps & found they were off value significantly as well. After replacing them I attempted to align the unit before re-install into the radio by disconnecting the cap off one side & using this a primary to feed in the sig gen. I hooked the CRO to the secondary winding & tuned for peak o/p, then reversed the procedure to tune the primary coil, seemed to work ok on the CRO....but after re-installing the IF into the radio it was still mostly deaf & required some aligning to maximise performance......the radio can now suck in 7BU from Tassie using only the units internal antenna which is as bout as good as it gets from where I am in Melbourne.

What I am asking however is if anyone has a technique for pre-tuning IFs that they are willing to share with us all, it would be most appreciated! Any learning accomplished will save time & frustration for us all...especially enthusiasts like me who learn as we go....usually the long & the hard way :/

This radio was a gift to the owner from his parents as reward for finishing his higher ed courses many years ago... so it was well worth the effort to repair & see the smile on his face...

There are not too many ways of presetting the IFT without expensive equipment. The reality is that when it is put into a circuit, or parts are changed in its circuit, it will change frequency.

That in itself is a primary cause of set deafness and why adjustment is recommended by manufacturers. The other mistake is to use too much signal & have the AGC cut in. This is also noted on the Data Sheet.

Always start at the last IFT first, injecting into the signal grid of the valve feeding it.

Marc

Thought it might be the case, it was fun & a good bit of experience to try though!
First time run with my recently refurbished honor valve freq generator which is amazingly stable in its output. Had tried to use a friends early 80's era HP clone but it drifted all over the place.....even when left on overnight to warm up!
Did note as you stated to use as little as possible o/p on the sig gen.....however in the initial setup I had to turn off the mod & up the o/p a little for my freq meter to correctly read the base freq.
It has been a fun exercise all round....builds a bit of confidence in using my gear as ancient as it may be! just need a valve Cro to complement the set up.....