Roberts R200 Lockdown 3 Project 2

[Andy 1964]

Postman came today with a nice green box and some shiny things, AF125s & AF127s. I have ordered from Russia bag of GT322B, but there is no airmail at the moment.

It works, but not very loud, compared to my R500.
AF117 next to aerial is dodgey, crackle, pop and on/off just with a finger tip tap.
Middle knob brass insert missing.
Strap missing green rexine.

I will work through this page https://www.vintage-radio.com/recent...erts-r200.html
Looks like those red top caps have been replaced.
I have this on order so I can test components properly https://uk.banggood.com/BSIDE-ESR02P...r_warehouse=CN

I have spent hours watching Mr. radiocruncher on YouTube, a great way to learn, but I do wish he would not have his 3Dprinter running.

[Graham G3ZVT]

I'm a great believer in zapping the tin-whiskers.

The mix/osc in my TR82 went intermittent about 10 years ago, disconnecting the screen restored normal operation but of course in the fullness of time the whiskers engulfed more than one electrode so I removed it from the set, shorted the C-B-E and applied 50v from a charged-up 470uF WRT the case. Re-installed it into the set, including the screen lead, and it's been trouble free.

Now there are some who don't like doing this, because it doesn't stop the original problem, and they are quite right of course, but it gives me satisfaction to "repair" something that rightfully should be unrepairable.

[paulsherwin]

As you suggest, it's a matter of personal preference, and there's no right or wrong way to do it. The drawback with zapping the tin whiskers is you don't know how long the repair will last. If you're lucky the transistors will be fine for decades, but if you're unlucky there will be lots of whiskers just fractions of a millimeter away from causing a short, and those won't be cleared by the zap.

[Andy 1964]

First AF127 fitted, which took a lot longer than expected. 2 of the pins are crossed, sussed it out now. I took the precaution of applying coloured sleeves, so I could keep track of orientation, and they are much smaller and fiddly to fit. I always wondered what the little holes were for in my multimeter labelled NPN, PNP. The old one gave a reading of 0072 somethings, new one 0082. Does that mean anything? Will do other two tommorrow, one is now crackling.

[Vintage_RC]

The meter is showing the hfe or current gain of the transistor, a measure of how much it can amplify by.

[paulsherwin]

The readings will only make sense if the transistor isn't shorting internally.

[Andy 1964]

The dial was turned to hfe, had no idea what it meant, other than identifying the pins. So the new 82 is better than the old 72. If there are tin wiskers does the number go up or down? I can now test the transistors before installing. Just waiting for the other meter from China so I can test the capacitors.

[paulsherwin]

An hfe of 82 isn't 'better' than 72, it just means the transistor has a bit more gain. It's normal for transistor gain to vary between batches, and even between individual components.

A reading of 72 is normal and suggests there was no shorting at the time of the test. Tin whisker shorts are often intermittent.

[Andy 1964]

Thanks for the explanation Paul

[Andy 1964]

All 3 AF127s installed, and working.
Looking at those red top Caps next.
First one is C16 10uF 50v, is this the right replacement? https://uk.rs-online.com/web/p/alumi...itors/7111425/
As I understand it a 16v can replace a 12v! But not a lesser voltage.

Perspex dial cover, scratches polished out.
Case cleaned and 2 coats of shoe cream applied.

[paulsherwin]

Higher voltages are fine.

Are you sure you need to replace them though? Those Plessey electrolytics have a bad reputation, but I have several radios where the originals are soldiering on without problems. Is there an ongoing fault?

[Andy 1964]

I am figuring out what I need to order if they are faulty.

[paulsherwin]

Anything with a similar value and the same or a higher voltage rating will work equally well. Buy either on price or cosmetic appearance, depending on your priorities.

[Andy 1964]

Onto alignment, this has definately been fiddled with, I can see marks on the screw heads, probably happened when the transistors became faulty. It is louder now, but does seem over sensitive. The only measurement tool I have is a multimeter, at the moment, and after reading various pages I am just confused. How to do it?

[paulsherwin]

You can align a simple radio like this without instruments, though a signal generator makes things easier. See https://www.vintage-radio.info/download.php?id=374

That document describes aligning a valve set, but transistor designs are broadly similar. Use in conjuction with the R200 alignment instructions.

[Andy 1964]

With the chassis and speaker on my desk, I disconnected the red wire from the volume pot, and reconnected the end of a 3.5mm lead + resistors and the ground to the chassis from my iPod, to simulate a bluetooth connection. I will be using the simple self powered type. Wow, a simple radio sounds that good! I wont even have to use my phone. "Alexa, play Absolute radio" Now that's what I call wireless.

[Radiocruncher]

I have spent hours watching Mr. radiocruncher on YouTube, a great way to learn, but I do wish he would not have his 3Dprinter running.[/QUOTE]

Apologies for the 3D printer running in the background. I try to record things as I’m going and sometimes I need to be printing customer orders at the same time.

Regards

Graham

[Andy 1964]

RF signal generator, is this what I am looking for? https://uk.banggood.com/DDS-Function...r_warehouse=CN