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#135955 - 02/24/03 03:14 AM Old Radio's  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,217
SI,New Zealand
I have an elderly radio that has a number of
Octal valves, the sockets are all worn out,as well as the Capacitors are all shot.
I do not know what type of set this is.
It has one Rectifier valve, from what I can see, it has 4 stages to it, I think that it may be a Superhet, I have to fix it before the 18th of March, it's a birthday present.
Could anyone please help?????.


Let's face it, these days if you're not young, you're old - Red Green grin

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#135956 - 02/24/03 09:17 AM Re: Old Radio's  
SvenNYC  Offline
Member
Joined: Aug 2002
Posts: 1,691
New York City
Trumpy, an excellent place to ask for information and help is the UseNet newsgroup rec.antiques.radio+phono.

If you have a picture of the radio and tube linup it would help a lot. However if you're going to post a picture for that newsgroup, don't do it on the newsgroup itself - they have a separate "binaries" group set up for that.

Tube sockets and capacitors are pretty much standard items that can usually be clipped out and replaced with no problem. If the set has been mangled up terribly by previous repair efforts you will certainly need a schematic or wiring diagram.

Good luck. Those old radios can become addictive!! [Linked Image]


#135957 - 02/25/03 08:06 PM Re: Old Radio's  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
"Four-plus-rectifier" was a fairly common lineup in a typical domestic valve/tube radio.

The first stage is most likely a triode-heptode converter, also known as a frequency changer (the triode section is the oscillator, the heptode the mixer). Second stage will be a pentode IF amplifier, third stage is most often a double-diode-triode used as audio amplifier, detector, and AGC. The fourth stage will be a pentode or beam tetrode audio output.

Can you still read the valve numbers? That would be a start at identifying the basic stage lineup.


#135958 - 02/26/03 02:30 AM Re: Old Radio's  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,217
SI,New Zealand
Paul,
I'll have a look, for the valve codes.
This is a beautiful set, mate,
just doesn't go.
But I think you may be right, about the 4+Rectifier, this seems to ring a bell, for some odd reason. [Linked Image]


Let's face it, these days if you're not young, you're old - Red Green grin

#135959 - 02/27/03 02:18 AM Re: Old Radio's  
SvenNYC  Offline
Member
Joined: Aug 2002
Posts: 1,691
New York City
Is it an AC/DC set? That's probably one way to tell. Look for a mains transformer (don't confuse it with the output one - that's connected to the speaker).

If it lacks one, it's an AC/DC set -- the tube filaments are all connected in series.

The usual American combination of these (in the 1960s-70s at least) was usually a 12AV6, 12BE6, 12BA6, 35W4 and 50C5 - these are the radios I'm most familiar with and have a few of.

Add up the first numbers in the tube codes and you'll get the line voltage the set is supposed to work on - 121 volts in this case.

It was called an All-American 5 and the idea was to eliminate the high cost of the transformer.

The ones designed to work on 220 volts would also have a dropper resistor (big fat ceramic thing) in series with the heater string.

Warning: when working on one of those, use an isolation transformer!!!!

Usually you will find the big electrolytic mains filter cap to be leaky and all these paper and bakelite-encased "black beauties" capacitors to be shot. Replace them all with comparable values.

Then check the resistors and the tube sockets. On rare occasions you'll find a bad tube.


#135960 - 02/27/03 07:34 PM Re: Old Radio's  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
One thing to watch is that some of these sets actually had the dropper incorporated in the line cord (nichrome resistance wire protected by an asbestos coating). The 1940s saw some American "midget" sets imported into Britain, and to drop our 200 to 250V supply down the line cord was often 9 ft. long! The problems arose if somebody decided to shorten the cord.

Sven mentioned replacing the capacitors. Just one thing to watch closely is the voltage ratings. In some points in the circuit a quite high rating is needed -- Any top-cut capacitor across the audio output transformer primary for example. The voltage swing when driven loud meant that manufacturers often needed 500 or even 750V types in that position, even though the HT (B+) line is of much more moderate voltage.


#135961 - 03/04/03 01:00 AM Re: Old Radio's  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,217
SI,New Zealand
Hi Guys,
Sorry I haven't got back to you about this,
today is the first day I have been able to access any sites, outside of NZ, still can't use Emailfast, don't know why!?.
But, back to the matter at hand, I checked the valves, the unfortunate thing is, if you rub the accumulated dust off them, you can also take the codes off too!.
The only two codes are 12AT7 and 6LB6?,
there are 2 12AT7 valves, in this set.
Hope that this helps. [Linked Image]


Let's face it, these days if you're not young, you're old - Red Green grin

#135962 - 03/04/03 12:00 PM Re: Old Radio's  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
The numbers do tend to rub off a little too easily in some cases!

A 6LB6 is a pentode output tube which could be used as an audio output, although I've never seen one used in a typical domestic receiver. The 6LB6's usual application was as a TV sweep output amplifier. Anyway, the pin-out and specs. are here:
http://hereford.ampr.org/cgi-bin/tube?tube=6LB6

The mystery deepens with two 12AT7 valves. The 12AT7 (directly equivalent to Mullard/British ECC81) is a double-triode. They were a very common device in many applications, but not in your average 5-tube domestic radio, and certainly not two of them!

I suspect somebody may have been swapping valves and left you with the wrong ones.

By the way, these aren't actually octal tubes. Count the pins! [Linked Image]

[This message has been edited by pauluk (edited 03-04-2003).]


#135963 - 03/11/03 01:48 AM Re: Old Radio's  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,217
SI,New Zealand
Don't worry guys.
The transformer (Mains), is shot!.
Don't know how, I overlooked this one, this is normally bread and butter to me at work!.
The client said don't worry, if that was the problem.
Shame to see a good radio like this, be junked, I offered to re-wind the transfomer, but no, he didn't want that either.
Paul, I have a sneaking suspicion, that the wrong valves have been fitted to this set, hence the Xformer failure, what do you think?. [Linked Image]


Let's face it, these days if you're not young, you're old - Red Green grin

#135964 - 03/11/03 09:30 AM Re: Old Radio's  
SvenNYC  Offline
Member
Joined: Aug 2002
Posts: 1,691
New York City
Trumpy, you could always offer to buy the carcass or if he lets you have it....keep it....and fix it up for yourself at your own pace.

That way it's one more nice radio that gets saved from the dump. [Linked Image]


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