My Second Radialva Groom Restore

[Geaney]

Thanks guys - plenty of food for thought and options to play around with. I especially like the idea of replacing R12 with the field coil, etc. I also go a PM speaker just in case

I'll post an update once I get a satisfactory result.

Cheers, John

[Geaney]

Bit of an update - I finished off the wiring and gave it it's first power up. Lots of howling and high pitched noises. But nothing went bang, caught fire, or otherwise set things back seriously. By a happy coincidence I had been browsing Chas Miller's great repair book a few nights earlier so the topic of phasing was fresh in my mind. Because of the physical construction I had fitted my coils in a different orientation to the originals. I swapped over the connections to the output transformer secondary and all was quiet apart from a slight buzz that varied with volume. Touching the grid of the 6Q7 gave a nice audio buzz through the speaker so I couldn't resist feeding some audio to it. It was with a certain excitement that I heard the set blare out some Glenn Miller at very respectable volume and with no distortion. Touching the aerial causes changes to the audio output so there is some level of continuity through the set. Still tons to do as my problems are clearly in the RF/IF stages and there's no guarantee I'll get there in the end - but one is suitably motivated to persevere!
For the speaker connection I just added a 2.5K resistor in series with the field coil and for now that seems to work fine. I will experiment with the other suggestions you guys made if and when I get the set working properly.

My first valve scratch build - so far so good!

Cheers, John

[Geaney]

Set now works on medium wave and long wave but no local oscillator on shortwave. The main fault turned out to be the fact that I'd missed off two components in the rebuild - a resistor and cap on the output of the second IF transformer (Doh!).

I had to put it aside for a while so I could look at it with fresh eyes. After a week I saw what was blindingly obvious but didn't see it last time. After spending so much time on it I couldn't look objectively anymore but after a break I was once again able to see the wood and the trees!

Hopefully the SW oscillator problem won't be too big a problem to resolve.

Cheers, John

[Geaney]

Well after almost a month of frustration trying to find out why the shortwave local oscillator refused to work I finally got it sorted with some help from one of my YouTube subscribers. So, with a decent tailwind, completing the rebuild should be straightforward from here on (he said optimistically).

Details here:

https://www.youtube.com/watch?v=cRjDTwNyh6I

Cheers, John
I'm curious as to why none of the coil slugs can be adjusted - perhaps the 'occupying powers' did not want people modifying the sets in any way.

[pwdrive]

Looks like the osc grid coupling capacitor along with the stray capacitance of the wiring to the grid was acting as a voltage divider, enough to stop shortwave, anyways all fixed now so congrats John.

Lawrence.

[Geaney]

Looks like the osc grid coupling capacitor along with the stray capacitance of the wiring to the grid was acting as a voltage divider, enough to stop shortwave, anyways all fixed now so congrats John.

Lawrence.

Thanks Lawrence, yes it's nice to have it finished at last and I'm always glad when I learn something new along the way.

Cheers, John

[Geaney]

Both sets now more or less finished - except for the backs which I'll get to sometime soon (he said hopefully). On the right is the restore that belonged to my neighbours grandparents, on the left is the 'donor' set that ended up as a complete rebuild.

I certainly learned a lot on these little sets so thanks for all the help. I feel like my apprenticeship is coming along!

Cheers, John

[Radio Fixer]

Well done John. Good effort and now nice looking radios: much more attractive than a DAC 90 in my opinion.

Gary

[AlanBeckett]

They really do look splendid. It's just as well you know which is which.

Alan

[Yorkie]

Excellent end result John - Ben Djikman did a splendid job on the new glass dial - you can see how well it stands out in comparison to the original.