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Old 7th May 2017, 10:37 am   #1
Nukeybrown
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Default Beolit 600 component identity

Just sorting out this beolit 600 and came across this component , its marked on the circuit board as 72 which shows 4.7ohm , only thing thats confusing me is why its such a funny colour and size? Is there something special about it or is it just a wattage thing to why its so big and brown. All other resistors in the set look like, well, resistors lol. Anyone shed any light on this. ? I know it says vitraform and 4.7ohm so i know im looking at the right resistor as per the schematic.
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Old 7th May 2017, 10:39 am   #2
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Default Re: Beolit 600 component identity

And another
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Old 7th May 2017, 10:41 am   #3
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Default Re: Beolit 600 component identity

The top resistor is a carbon comp type, the bottom resistor looks like a wire wound type.

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Old 7th May 2017, 10:45 am   #4
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Default Re: Beolit 600 component identity

Only put the top one on the picture to show size lawrence. My question is why use this one and not just a standard resistor, is it to do with wattage etc or some other reason.
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Old 7th May 2017, 10:48 am   #5
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Default Re: Beolit 600 component identity

Power dissipation I would say, what's it's circuit function?

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Old 7th May 2017, 10:58 am   #6
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Default Re: Beolit 600 component identity

If your 600 is the early version with the AC128 output transistors it is will be the 4.7ohm (2.5 or 3 watt) emitter resistor and is a wire-wound type. I am not sure from your picture but if it has been stressed then the AC128s may be shot.
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Old 7th May 2017, 11:20 am   #7
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Default Re: Beolit 600 component identity

It's a wirewound resistor. Its size says it's a higher power rating than the little carbon composition one above it. Also it may be run to higher temperatures and that furter boosts the power rating.

The wirewound job will also have a higher peak current rating (more than just that due to difference in power rating) which is what makes it a good choice in output stages.

They don't drift much in value over time

They also make significantly less noise than carbon comps, though this doesn't matter in this application.

They are somewhat inductive, which is again OK here.

It's their expense which stops them being used in more places.

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Old 7th May 2017, 11:24 am   #8
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Default Re: Beolit 600 component identity

It is the one on the ac128s but the set is working so im guessing it hasnt yet fried them, it is however showing low resistance on the meter, 4.7ohm showing 3.2ohm. So what to replace it with , another wirewound resistor or a standard modern resistor rated 2w?
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Old 7th May 2017, 11:36 am   #9
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Default Re: Beolit 600 component identity

I'd be inclined to go for a 3 watt resistor. These should be available in 4R7 (4.7 ohms) resistance. The question is what made the original go low in value?
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Old 7th May 2017, 11:39 am   #10
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Default Re: Beolit 600 component identity

Maybe the meter's out?

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Old 7th May 2017, 12:29 pm   #11
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Default Re: Beolit 600 component identity

Since I have a set only useful for spares,I desoldered the resistor in question.
A Vitrohm 0.5W of the BW type.Exactly what several other B&O diagrams says.
Now what might BW mean?Today it's a wirewound resistor,but what was it then?

According to my old digital multimeter it measured about 5 ohms.

Did BW mean a bifilar wound resistor thereby reducing its maximum wattage?
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Old 7th May 2017, 1:15 pm   #12
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Default Re: Beolit 600 component identity

The plot thickens, i did see on the schematic next to it BW but what that means , who knows

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Old 7th May 2017, 4:35 pm   #13
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Default Re: Beolit 600 component identity

At that size and only half a watt I'd say it was carbon composition. In which case its value may well have drifted. I'd be surprised to see a 10% WW resistor get to 25% out!
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Old 7th May 2017, 4:50 pm   #14
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Default Re: Beolit 600 component identity

From the Vitrohm website:

1986 - The BW series production starts under the license of IRC, Philadelphia (USA) in Europe.

IRC is now part of TT Electronics and the BW type is not in their current product range.

This old advert for IRC states the BW type is an insulated, wire wound type:
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Old 7th May 2017, 7:57 pm   #15
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Default Re: Beolit 600 component identity

'Vitrohm' suggests to me that the resistor is a Vitreous Enamel type.
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Old 12th May 2017, 11:00 pm   #16
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Default Re: Beolit 600 component identity

Quote:
Originally Posted by Herald1360 View Post
At that size and only half a watt I'd say it was carbon composition. In which case its value may well have drifted. I'd be surprised to see a 10% WW resistor get to 25% out!
Exactly.
It's a Carbon resistor and they do drift when subject to overload.
Vitrohm was a Danish company founded before WW2.
Go here for the company history:
http://www.vitrohm.com/en/company/company_history.html
Their wirewound resistors last forever (like most anyone else's)
Carbon types should ALWAYS be suspected of having drifted when encountered in vintage equipment.
I've recently renovated a Danish made TO-R S-15 receiver from the early 60'ies.
Filled with Vitrohm carbon comp. resistors and not a single one in the entire receiver was within spec's.
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Old 12th May 2017, 11:23 pm   #17
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Default Re: Beolit 600 component identity

Assuming the OP's measurement really is accurate, such that replacement is definitely necessary, then surely a "destructive internal examination" will settle the question of type?

Who remembers the organ project in the classic Ladybird book "Simple Electronics"? That was tuned by filing chunks out of the resistors!

All that said, if the set draws the correct quiescent current, then I'd leave it alone.
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Old 12th May 2017, 11:41 pm   #18
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Default Re: Beolit 600 component identity

Because the 4.7 resistor was out of spec and looking at the diagram it looked like a likely place for bias current this is why i checked it. I can only assume it was put in as a wirewound as it was probably thought at the time to be more stable under load and hold it value better which is why i checked it also the fact that the colour of it looked odd compared to all other resistors in the set. The measurements on it are correct and it is showing 3.6ohm not 4.7 as it is printed up as. It has now been changed for a wirewound 4.7ohm which is why i wanted to check the current to ensure all is as it should be.
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Old 13th May 2017, 11:58 am   #19
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Default Re: Beolit 600 component identity

Well, it's only out of spec if we have confidence in your measurements. Resistance measurements in that region can be inaccurate, depending on the multimeter (though usually high rather than low, but anything is possible). Lawrence raised that point earlier in post #10, so it'll be really good to address that. If you can confirm that the new 4.7 ohm resistor reads OK with your meter, that'll be good enough for me

Secondly, unless I've missed it, you don't say if the quiescent current was actually wrong. From what you've said, it appears that you've been simply looking for out of spec components rather than logically chasing down a specific fault? However, many/all carbon-composition resistors will be out of spec. Honestly, literally every single resistor in a Hacker Sovereign I and II will read high by more than 10%. Does that cause problems? Rarely. Is changing every resistor a good plan? Absolutely not. So, before changing any component (not just resistors), we need a better reason than "out of spec", because "out of spec" does not always mean "faulty radio". In this specific case, if the quiescent current was too high, then yes, that absolutely was a good reason to change it. But as I say, you haven't told us that. And is it better/different now?

Finally, now that you've changed it, please could you cut the thing open to settle the question about what type it is? Just start by filing away at it - it'll be really obvious once you get into it, and there's a lot of people here who'd really like to know. Apart from that, it's good fun
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Old 15th May 2017, 9:03 am   #20
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Default Re: Beolit 600 component identity

It turned out to be a wirewound resistor.
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