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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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18th Aug 2020, 1:38 pm | #41 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,869
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Re: TF995A help please
Those silvery tubular capacitors are 'paper' ones, but the paper is soaked in oil and they rely on the rubbery end seals to keep the oil in.
Back in the era of this sig gen and these capacitors, the British motorbike industry was testament to the fact that the peoples of these islands couldn't design a good oil seal to save their souls. So it's oil that once was in the capacitors. Moisture will have leaked in to replace it, bringing the insulation resistance crashing down. THey need changing. Oily paper capacitors are rather fashionable in snobby hifi circles where they now get called PIO Paper In Oil. Back in the day, they were just 'Paper capacitors' The 'waxies' now known to be usually bad, were the same foil and paper structures, but the paper was wax-impregnated. They were rolled up, and then the manufacturer applied a label to stop 'em unwinding and to show the value etc, then they covered the whole thing with a slart of wax to seal them from the rigours of planet Earth. Electrolytes are conductive liquids and only used in electrolytic capacitors. David
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18th Aug 2020, 2:22 pm | #42 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,853
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Re: TF995A help please
Yep, as David has clarified, old ordinary metal tubular capacitors are impregnated with an "oil", which I recall can sometimes be of a phenolic nature - thought of these days as being hazardous. Then you get the older tubular cardboard capacitors where the cardboard & the internal paper are impregnated with wax - known as "Waxies". Then there is the polarised "electrolytic" capacitors which contain a corrosive chemical.
Just Google - Capacitors - heaps & heaps of info. Regards, David |
19th Aug 2020, 7:50 pm | #43 |
Pentode
Join Date: Jun 2016
Location: Kent, UK.
Posts: 190
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Re: TF995A help please
Hi all
I have taken the fine attenuator apart and my hunch was correct, the other leg of the resistor that goes into that recess that I could just see is actually soldered to a tag inside the rear of the fine attenuator, so you have to separate it by removing the circlip take it apart to get at it. As usual I have taken some pics as I go so if anyone else ever has this problem there is a point of reference, so I now need to desolder this leg and source a replacement part which is 'Resistor R99' a :- 37.5 ohm +/-1% High stability 1/8Watt resistor Also when I popped the back of the switch off i later found a single small ball bearing and a circular white plastic collar laying on the front panel, these had obviously come out the switch when i pushed the shaft through and freed it after removing the circlip. I think I can see where they go but will cross that bridge upon reassembly. Will order a replacement resistor and then report back with more progress but pleased with how it is going so far, not as straight forward as I thought it would be but I am really enjoying working on it! Thank you to everyone for the help and encouragement so far, it is really motivating me to get this sorted. Regards Mark |
24th Sep 2020, 11:12 am | #44 |
Pentode
Join Date: Jun 2016
Location: Kent, UK.
Posts: 190
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Re: TF995A help please
Hi all
Have any of you got a “go to” supplier in the UK you use for components who may have the :- 37.5 ohm +/-1% High stability 1/8Watt resistor I need as that is an odd value and i am struggling yo find one? Thanks! |
24th Sep 2020, 12:41 pm | #45 |
Octode
Join Date: Dec 2010
Location: St Ives, Cambridgeshire, UK.
Posts: 1,180
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Re: TF995A help please
You need to parallel a pair of 75R, like these maybe?
https://uk.farnell.com/vishay/mrs250...ilm/dp/9470000
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24th Sep 2020, 2:06 pm | #46 |
Octode
Join Date: Sep 2004
Location: St. Albans, Hertfordshire, UK.
Posts: 1,478
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Re: TF995A help please
There may not be room for parallel resistors in that assembly. You may be better off trying with 33R2 and 4R3 in series.
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27th Sep 2020, 2:25 pm | #47 |
Pentode
Join Date: Jun 2016
Location: Kent, UK.
Posts: 190
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Re: TF995A help please
Hi andrewausfa and dickie,
I will look athe internal dimension etc of the tube and see what my options are with the ideas suggested. Thank you!!! |
1st Oct 2020, 7:02 am | #48 |
Pentode
Join Date: Jun 2016
Location: Kent, UK.
Posts: 190
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Re: TF995A help please
Hi all
Managed to find 30R and 7R5 1% 1/4W resistors so have ordered these, they come in packs of ten (smallest order quantity). I will have to series them and cut leads very short to allow them both in the recess, i cant parallel as not the room. Will post a pic and some dimensions of the two i get to fit! |