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16th Jun 2021, 10:56 am
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#1 |
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Triode
Join Date: Feb 2016
Location: Fife, Scotland, UK.
Posts: 30
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Bush VHF 81
I picked up on of these a wee while back on an auction site. It is missing the rectifier valve , and has had some replacement capacitors at some stage. The case, dial etc are good, and I have started going over it with a view to getting it up and running.
I have been over all the resistors, a few are 25-30% over their stated resistance and I have earmarked then to be replaced. I am curious about R28. On the service information it is stated to be 1M. The resistor looks original but I think it is a 1.6M, (brown blue green), and it reads about that. The wiring opposite looks a bit burnt- not sure if that is accidental by someone with a soldering iron at some stage. Should I be thinking about swapping out the resistor for a 1M ? |
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16th Jun 2021, 11:05 am
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#2 |
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Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Bush VHF 81
To me it looks like Brown, Black, Green....1meg.
Lawrence. |
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16th Jun 2021, 11:19 am
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#3 |
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Triode
Join Date: Feb 2016
Location: Fife, Scotland, UK.
Posts: 30
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Re: Bush VHF 81
It looks bluer in real life, but you could be right- colours tend to change / fade with time. It is reading almost 1.6M which may have influenced my assertion. Probably change then.
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16th Jun 2021, 12:06 pm
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#4 |
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Octode
Join Date: Mar 2011
Location: Sheffield, South Yorkshire, UK.
Posts: 1,453
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Re: Bush VHF 81
1.6MΩ isn't an E12 value anyway. From the photo it looks like 8.6MΩ (grey, blue, green) to my eyes.
As you say, colours fade with age and an old 1MΩ resistor going up to 1.6MΩ isn't very surprising as higher value ones seem to have the biggest proportional increases. |
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16th Jun 2021, 1:19 pm
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#5 |
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Triode
Join Date: Feb 2016
Location: Fife, Scotland, UK.
Posts: 30
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Re: Bush VHF 81
Ah, never spotted that. Thanks for all the help. Every day is a school day !
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16th Jun 2021, 1:54 pm
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#6 |
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Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,863
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Re: Bush VHF 81
Definitely a 1M that's drifted high, as said above.
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17th Jun 2021, 11:46 am
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#7 |
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Administrator
Join Date: Dec 2002
Location: Cardiff
Posts: 9,072
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Re: Bush VHF 81
Remember that these resistors are 20% tolerance anyway, so up to around 25% high should be fine. I would only replace those which are very high, not those that are just a bit out of tolerance.
The main thing to change with these sets and others of this era is all the little black and brown hunts capacitors and any wax-paper capacitors. These will be causing a lot more odd issues such as poor reception and instability. The VHF81 is a great sounding and performing set when fully sorted. |
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