Grundig Transistor Boy from 1956 Part 2 - A very unusual radio.

I dive further into the mysterious workings of this weird little valve / transistor hybrid radio. It's like nothing I've seen before but potentially a very nice little portable. It has a quality feel about it. It's heavy and well built but working on it is, shall we say, a challenge.
Watch & see how I go.
Carl's Capacitors:
www.ebay.com.a...

[@petersvan7880]

That was quite a ride, thank you for showing and the patience with this unique radio!

[@lyntonprescott3412]

Great work Don on a very difficult radio. Grundigs can be a real pain to work on, but having said that I did a 3028 a couple of years ago and it is by far my finest radio. Best wishes Lynton G4XCQ

[@Donno308]

Hi Lynton. Yes I found it fairly difficult but I haven't worked on many portable radios so I don't have much to compare it to. I did enjoy it though and I might do more if they become available. I'm pretty sure there will be an update on the Grundig before long. Cheers

[@DavidTipton101]

Hi Don, I finally got to watch your video now we have finished the cruise. Those Wima capacitors give Hunts caps a run for their money, they are always bad. Tricky of Grundig to put a sticker over the trimmer pot. I did think it odd that you had to remove the can to adjust it though. Haha... I see you managed to get the actual outside photo of your shed in the intro 🤣🤣🤣 You and I will be the only ones to get it. Cheers Don.

[@Donno308]

Hi David and welcome back! Hope you enjoyed the cruise, although I suppose you had a terrible time. Yes I had a little bit of fun with the intro. Nothing like yours though. Looking forward to your holiday videos! 😁

[@quantumleap359]

Nice neat job mate! Very close quarters that!

[@Donno308]

Cheers. Glad you enjoyed it!

[@MichaelBeeny]

The extra voltage could be due to most Philips sets were made for the European voltage of 220 volts. We in NZ and Australia tends to be more on the 240-volt region, possibly slightly more. It seemed an odd choice to use OC72 output transistors, and not a common output valve which were very low cost in those days. OC72s were in comparison quite expensive. Of course, you also needed the extra power supply for the transistors and an interstage transformer. Both options would give much the same output power of around 250mW.

[@Donno308]

Good point,Michael. I think te set is using the 220V primary tap.

[@jimburns348]

Great job there Don. 👍 Didn’t envy you a bit workin in that tiny space 😵‍💫 You’re doing great.

[@domtrimboli6238]

Hi Don, i think you may have been a specialist medical surgeon in your previous life, good luck with the next episode. Cheers. 🍻🍻

[@timetec]

I can highly recommend B-7000 (clear) or T-7000 (black) glue for tacking down wires and components. It can be used as an impact adhesive or simply applied to both surfaces simutaneously and allowed to cure. Supplied in tubes with a fine stainless steel needle for precision application. Typically $6 AU for a 15ml tube. Hope this helps - keep up the great work!

[@Donno308]

Hi That sounds ideal for all sorts of things! Where can you buy it? I guess I could try ebay but would they have it at Bunnings? Or Jaycar? Cheers

[@iantyler4045]

Over 40 degrees in the shed!! I would melt in there. Nice work on a very difficult little radio. Hope you get the battery side of it working (I'm sure you will).

[@Donno308]

It's a bit cooler this week. I'm going to start working on the battery setup this weekend. Cheers

[@BobAndersson]

Hi Don. A fascinating radio but rather you than me with my fat fingers. 😂 Thank you for sharing. I worry a bit about the physical size of that zener you used but without knowing what current is flowing through it it's hard to judge whether it has a high enough wattage rating. It might be worth checking and replacing that zener with a beefier one if necessary as I think the last thing you want is for that zener to fail.

[@Donno308]

Hi Bob. Actually I think you're right. It's a 1N4735 1 watt. I thought 1 watt would be alright but it really is small and was getting warm. The local Jaycar store doesn't have higher wattage ones at that voltage so I'll have to order online. Cheers

[@andybbeck2043]

love it don

[@mackfisher4487]

Don, love your chauvinistic intros, where did you find the spaceship photo of the two ladies in a rocket cockpit? We've come a long way baby, from tube-type "miniaturization" is hell to work on but wait now we have a receiver on a chip. Enjoyed Thanks

[@Donno308]

Hi Mack, I found the spaceship photo on an art website, searching for "retro-futurism" I modified it a fair bit to suit my purposes. Unlike my "usual" bikini girls which I find in swimwear catalogs. I figure that the models were probably well paid and have consented to public use of the photos, so I don't feel I am being too unethical. Yes you can buy a whole radio on a chip for a couple of dollars. If it stops working, throw it away. No fun in that! Cheers

[@techobaz55]

Top job Don, bit sad about that sticker removal though, you should have saved that just to look back on, LOL ! I have a similar all transistor Stromberg for a revamp coming up soon, you have shared a few tricks with this on. Looks great & seems to perform great, Congrats ! Cheers Mate👍

[@Donno308]

Hi Baz. Yes I'm pretty happy with it so far. I would like to get it working on rechargeable batteries and maybe fit a bluetooth board if the power supply will do it. Now I've got this video finished I'll have a bit of time to watch some videos for a change! I'll look out for your Stromberg Carlson video when it comes up. Meanwhile I'm going to have a look at those 2 you did on the Philips. Cheers mate

[@rádiosantigos1958]

Hi Don. I think that the ideal would be to put a resistor in series with the Zener diode to absorb some of the heat from it. Just a guess. Thanks.

[@Donno308]

Hi. Yes I'll give it a try. I've also bought some NiMH batteries so I'll try them out. I guess I'll have to check charge rates etc. Don't want them blowing up!

[@sincerelyyours7538]

Great work on that radio, Don. I don't envy the tight spaces in that one, though. Re the Grundig sticker, could you have covered it with clear tape, then cross-cut the hole with a sharp knife to make your adjustment?

[@Donno308]

Hi. Yes I probably could have doe that, or even soaked it off. Or failing that, scanned it so I could make a copy. I was a bit rattled at the time having discovered my mistake with the adjustment. I wasted hours trying to find out what was wrong. What is still a mystery is: why is there another hole in the bottom of the can opposite the mounting screw? It's not necessary at all as far as I can tell.

[@davidsheedy5793]

Another great job!

[@Donno308]

Thank you! Cheers!

[@erikdenhouter]

About that zener diode, you saw that the voltage did not perform to expectations, 0.2 to high. A the voltage of a zener is reached when the current is high enough, that is when you use the full given power rating. Any current less and the voltage is higher. In your case you cannot choose the current, so you will have to accept what it does. And at the end, about the voltage drop of that diode that made the radio stop working, that is a silicium diode with a 0.7 V drop. You can try a Schottky diode, these have only 0.2 - 0.3 V drop. A downside of them is that they do not come in high voltage ratings, but that is no problem here.

[@erikdenhouter]

Ai, I made a very fundamental error in that writing.... I found out while in bed already 😰The zener voltage is LOWER when the current is less than the rated power 🥴 So that could suggest that the current is to high for that zener. Cannot see exactly what it is, but at the look of it it is 0.5Watt, at 6.2V. Sorry for my really stupid comment.

[@Donno308]

Hi Erik Sorry for the delayed reply - for some reason your comment didn't come up in my notifications. Anyway there are no stupid comments and you obviously know more about it than me. I'm pretty new to semiconductors. The zener I used was a 1 watt but I do think it might be a bit under rated for the current. I haven't measured the current but I will when I get back to this radio, hopefully next week. In any case I have bought some 5W zeners on ebay so I'll swap them out. I'm also wondering if the 6V supply would support a bluetooth board...

[@GeorgeChristofi]

I've had my fingers in some tight spaces before but that looked like a complete nightmare to work on.

[@Donno308]

It sure is tight but I've had my fingers in worse places!

[@radio-ged4626]

Great work, especially with that tricky soldering. Maybe I would put a diode in series with that zener to stop any reverse current and drop another 0.5 volt. Not that it seems a problem as it is. The battery charge and current leakage while on mains is an interesting problem. I will study the circuit to see if I can think of anything.

[@Donno308]

I'm currently thinking that rechargeable batteries would be the way to go, that way I wouldn't have to worry about the current back into the batteries. What are your thoughts about adding bluetooth?

[@radio-ged4626]

@@Donno308 Hi Don, why not try with bluetooth? Gonna be difficult because of component density and shielding the RF from the module but interrupting the IF with a switch and also powering off the bluetooth when on radio would negate that. What's life without challenges? ( Besides a lot easier - but who wants that!)

[@electrosoundaust]

Hi Don, I think you voided the warranty when you tried to remove that sticker! I generally dislike working on portables. I have a very small Tasma that I started on a few years ago and I've finally bought the valves, so I guess I have to bite the bullet. Nice work though and a real challenge overcome. Autumn was in the air in Canberra, so hopefully things will begin to cool down.

[@Donno308]

Hi Andrew. Yes I'm afraid I now have little chance of making a warranty claim. I was thinking of asking them to replace the missing centre button on the tuning dial. Obviously a case of faulty manufacture as it's missing. It's such a relief when I've published a video. Now I can have my life back and catch up on watching other peoples videos among other things. I see you've posted some interesting looking ones so I'll watch some tonight. There will be more to come on this little Grundig. I do quite like it and I would like to get the battery charging section working. Odd that on a battery portable they have not provided any means of storing the mains cord when not in use. I might also add bluetooth if I can wrangle the power supply without upsetting the rest of the radio. Cheers

[@brucepickess8097]

Hi Don, just a comment about that zener diode. You said that it was getting a bit hot, do you know the power rating for the device that you fitted ? and what sort of current is being passed through it ?. Could be underrated for the demand placed upon it, and in addition there will be some variation on the zener regulation voltage dependant on the current through it and temperature variation. Interesting upgrade and refurbish of an old radio.👍😏🇬🇧

[@Donno308]

Hi Bruce, The zener I used was a 1 watt. I thought that would be ok but as it's getting warm I've ordered some 5W zeners so I'll change it when they arrive. I didn't realize that the voltage across a zener could change with current but I guess that would account for the missing 0.2V. Cheers

[@xsc1000]

@@Donno308Why dont you put zener diod just parallel to selenium stabilizer ?

[@Donno308]

@@xsc1000 I wasn't sure how the selenium would behave. I thought it might just act as a parallel resistor and reduce the voltage across the zener.

[@xsc1000]

@@Donno308Even if it acts like resistor, voltage should be OK. Without zener there is 7,5V, so with zener it should go to the zener voltage but not lower. Because in that case zener diode stops to be conductive.

[@coltronex]

What a nightmare Don!

[@Donno308]

Yep, this is a tricky one for sure. Kind of fun though!

[@retro_tech]

Great job, Don! I actually quite enjoy working on those cramped radios. The trick is to take your time and stay calm. And if you notice you're getting frustrated: stop and come back to it the next day. And what a nice looking (and sounding) radio! I hope you figure out the batteries and post an update some time. It would be nice to actually use this radio for its intended purpose as a travel radio. Really glad I could help with the restoration of this nice and interesting radio.

[@SeekingTheLoveThatGodMeans7648]

man it's hawt in that shack. is it possible to install a window air conditioner in there?

[@Donno308]

Sure is! Yes I could install an air con. Summer's over now so maybe next summer. Soon I'll need a heater lol.

[@tubeDude48]

WOW! Don't know how you work in that heat. Hear in Norther California, along the Pacific Coast during Summer, when we hit 68° F we complain. I don't know why people J-Hook. It looks sloppy! Probably should go with a higher watched Zener. --- Since you don't show an email for you, I can't give you the page on my web site that has nothing but manual's.

[@Donno308]

Hi. I don’t know why my email isn’t showing but you can email me at: [e-mail] I’d be very interested in a link to your web page with the manuals. I couldn’t get a higher wattage Zener at that voltage from the local electronics shop. I’ll try eBay & see what’s available. I agree - a higher wattage Zener would be better. Cheers

[@Donno308]

Update: I just got some 5W zeners on eBay so when they arrive I’ll swap it out. Cheers

[@tubeDude48]

@@Donno308 - Got it. You've got mail!

[@Donno308]

@@tubeDude48 Thanks Ted. Got it.