Roberts R500 Missing Transistor

[sportiva62]

Hi have just purchased a Roberts R500,(not working), when it arrived to my dismay it had a missing transistor !(af 115) think its TR1(first on the left side of the pcb just above the speaker at about 10 am position, does anyone know the relative positions for collector ,base,emitter & screen when looking from the back of the set,think it might work better if it in there!


thanks Roger.

[Terry]

Welcome to the forum - but you should note that the Welcome thread is not the place for posts like this!

It rightly belongs in the Vintage Valve & Transistor Radios thread - but don't worry, I'm sure one of our friendly, helpful moderators will be along soon to move it for you!

[Yorkie]

Unfortunately only a two-page Trader Sheet is available for the 500 - not the more comprehensive Robert's data, and the component placement pic isn't detailed enough to show the connections.

However you should be able to easily trace which is which by reference to other components which connect to TR1. Namely:

The Base connects to R2, which is 8.5K
The Emitter connects to both C5 - 0.022uF & R3, 68K
The Collector goes to T1

Hope that helps a bit.

Expensive set in its day, but then all radios were. £15.6s.8d + PT - about £20 I guess - £360 at today's prices, accounting for inflation.

To put it another way, about the price of a 42" flat screen colour TV, a tablet computer/laptop, or half decent washing machine. Yikes!

[tiv48]

the leads are arranged in a square two on the right and two on the left.

from the bottom
right bottom= collector
right top screen
left bottom collector 
left top base.
Rob T

[ppppenguin]

Roger, you're probably aware that the AF11x series of transistors suffers from tin whiskers. These short out the electrodes. The subject has been covered many time both here and elsewhere. In summary:

Both old and NOS parts suffer from the whiskers
Cutting the screen lead will often give a rough and ready cure
It's sometimes possible to fix them by either blasting the whisker with a battery or by opening the case
You can replace the AF11x with AF124 or AF125 but these are starting to get more expensive now
Some people have reported successful replacement with low cost silicon devices such as the BC558 though the bias might need to be tweaked

[Mark Hennessy]

Welcome to the forum - but you should note that the Welcome thread is not the place for posts like this!

It rightly belongs in the Vintage Valve & Transistor Radios thread - but don't worry, I'm sure one of our friendly, helpful moderators will be along soon to move it for you!

Hi,

Yes, it can be confusing to navigate the forum structure. No problem - that's what the team are here to help with. As such, I've moved it into the correct forum. I've also changed the title so that it's not all capitals, as typing in capitals is considered to be "shouting".

When Terry says "thread", he means "forum". The terminology can be really confusing. I'm typing a post, and you're reading a collection of posts in a thread. This thread is located within the "Vintage Valve & Transistor Radios" forum. The site as a whole contains many forums, and is called a board. No matter - just do what others do, and you'll be just fine

Good luck with the R500. I've done a fair few of these over the years, and they are worth the effort

Mark

[Old Sparky]

It is also possible to replace AF11x series transistors with Russian germanium devices such as the GT322, which is TO-72 cased like an AF127 but the pin-outs are as the AF139, meaning that the base & emitter connections are reversed compared with the AF124, 125, 126 7 127. These are usually available from E-Bay sellers for around £1 each, though I haven't checked availability recently

[Nowhere-Man]

Hi have just purchased a Roberts R500,(not working), when it arrived to my dismay it had a missing transistor !(af 115) think its TR1(first on the left side of the pcb just above the speaker at about 10 am position, does anyone know the relative positions for collector ,base,emitter & screen when looking from the back of the set,think it might work better if it in there!


thanks Roger.

Maybe Mark will post a link to the article he did on fixing AF117's?

I'd say your best bet would be to contact Langrex who sell the AF117's (they are under a fiver). You could then test it or get them to test it before purchase (possibly follow Mark's AF117 voltage application).

Later, I'd be very interested to follow on from this topic with regard to these transistors as I sort of came a cropper over the AF117's. I have a Bush tranny that I plan to go back to work on in the future and I may buy a new AF117 as I feel these are a far hardier transistor than is appreciated. Sure, they can become defective but not all of them do and, besides, the problem can be fixed with care.

I have an early sixties car radio with all AF117's and it works fine. Not bad for a radio that's over 50 years old.

[Mark Hennessy]

I'll overcome my natural modesty

http://www.markhennessy.co.uk/articles/v....htm#treat

If using NOS, then definitely "treat" them before fitting.

If you scroll up slightly from where that link lands, you'll find a link to the NASA investigation into the AF11x. Actually, let's just paste it: http://nepp.nasa.gov/whisker/anecdote/af...index.html - it's quite well-known, but just in case anyone has missed it...

[Yorkie]

Is it just me, or has anyone else noticed how often new members pop up on the forum (and 'over the wall'), post a query seeking help and advice, which they're invariably given quite quickly, but havng made their initial post, the OP is never to be seen or heard of again? I often wonder what awful fate may have befallen them! 

 Here we are again, discussing a problem with a set, and the only person absent is the one who sought help in the first instance.

As often as not, these 'here today-gone tomorrow' posters start with something along the lines of: "Just bought a Dansette off ebay, told it worked but it doesn't - I'm not clued up on electrics - what could be wrong with it - are they simple to fix?"

Don't want to sound churlish or unwelcoming to newcomers, but this trait does seem to be commonplace, though it won't stop me trying to help as best I'm able, despite common courtesies seemingly now becoming a quaint relic of a bygone age. (Rather like me I guess!)