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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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26th Jul 2021, 8:37 pm | #1 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
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Radford amp; parts queries
1. Can anyone please confirm the make-up of these grey RS capacitors? They show measurable leakage and a loss tangent much inferior to polycarbonate, which might suggest they are paper based?
2. This STA 12 amp has not been messed with too much, and it's very likely that the 'resistor' mounted on the socket of the GZ34 rectifier is original. Is this a brimistor? If, so, based on its dimensions, it's an STC CZ1? John |
26th Jul 2021, 8:47 pm | #2 |
Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,823
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Re: Radford amp; parts queries
ISTR that these are Mixed Dielectric types.
See this page. https://www.vintage-radio.com/repair...apacitors.html Cheers Mike T
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Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk |
26th Jul 2021, 9:03 pm | #3 |
Octode
Join Date: Sep 2004
Location: St. Albans, Hertfordshire, UK.
Posts: 1,477
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Re: Radford amp; parts queries
This thread suggests it may be a CZ6? (roundabout post 10, as fitted to the MA15)
https://www.vintage-radio.net/forum/...d.php?t=164829
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26th Jul 2021, 9:11 pm | #4 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Radford amp; parts queries
I've had those grey RS capacitors fail in the past - the innards swell and crack the plastic outer-casing.
Personally I'd be installing some nice shiny new LCR or Kemet yellows in their place - then you know things will be good-to-go for another couple of decades. |
26th Jul 2021, 9:57 pm | #5 | |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
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Re: Radford amp; parts queries
Quote:
Mike: thanks for that. Having read the capacitor page above, it could perhaps do with an update! John |
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26th Jul 2021, 10:04 pm | #6 | |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
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Re: Radford amp; parts queries
Quote:
Richard: you could well be right. Both the CZ1 and CZ6 are 1.25" long, but I was trying to guess the type from the cold resistance: this sample measures 8k2 at room temp, which is higher than either. So I susepct it's cooked at some point and changed characteristics. It measures 250 ohms at 100mA, again with normal room ambient As this amp uses 20uF main smoothing caps, it may not be necessary to employ the brimistor at all? I may try using a fixed R to keep the HT voltage about right? John |
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27th Jul 2021, 8:58 pm | #7 |
Heptode
Join Date: Jan 2009
Location: West Lothian, UK.
Posts: 760
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Re: Radford amp; parts queries
Yes - think these are they - monochrome cat but look like they could be the grey ones.
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George |
27th Jul 2021, 9:19 pm | #8 | ||
Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,823
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Re: Radford amp; parts queries
Quote:
Cheers Mike T
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Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk |
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27th Jul 2021, 9:47 pm | #9 | |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
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Re: Radford amp; parts queries
Quote:
Yes, I quite agree. Those mixed dielectric capacitors often test leaky and many have swollen up cracking the case. Shades of Rifas here! I suppose the paper part of the dielectric has absorbed moisture over a long period which would cause the innards to expand and rupture the case. I've come across various colour mixed dielectric caps. I've seen grey, white, blue and white, blue and grey, and blue and yellow cases. I don't know if there's any significance relating to the case colour. I recall the blue and yellow case versions were often used by BRC/Thorn. I think their 1400 chassis used them. Regards, Symon |
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