Mullard MAS15-34
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Location: Hobart, TAS
Member since 31 July 2016
Member #: 1959
Postcount: 563
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Have you measured any voltages around it. And let us know.
Have you had a look at it in a darkened room.
Have you checked any resistors connected to the base. Megohm resistors are renoun to go high.
JJ
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Location: Latham, ACT
Member since 21 February 2015
Member #: 1705
Postcount: 2174
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Johny I have had it in a darkened room and checked the resistors . I havent checked voltages yet but Ray Pfister ( ex reliance radio service tech ( how lucky am I ) ) has tested the valve and found very low emission.
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Location: Belrose, NSW
Member since 31 December 2015
Member #: 1844
Postcount: 2476
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Like I said, the check voltages.
If a valve is run for a long period with no anode voltage you can get cathode poisoning. Since it's dead anyway, try doing a cathode re-activation with 12V on the heater for a day. Try it again after that - but check the voltages! Data sheet says the target needs 250 volts, lees that 200 and it won't work.
All accounts I've read say that the target material itself is the main reason for failure to glow green. It just gets dimmer and fades away to nothing. Ion burn no doubt.
Oh - what does the getter flash look like? Can you see it? The bottle may have shipped some gas.
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Location: Latham, ACT
Member since 21 February 2015
Member #: 1705
Postcount: 2174
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The EM1 turned up this week and I found time today to check things out. It worked straight up. I have to keep saying " The reason why I was able to get this item at such a reasonable price is solely because I like to treat everyone in this hobby with respect and dignity " the gentleman whom sent this to me is one that I helped with some hard to get spares some time ago and well my good deed was paid back. This is how any hobby should be treated.
I will now complete this set and have some pics up very soon of this fine old set.
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Location: Latham, ACT
Member since 21 February 2015
Member #: 1705
Postcount: 2174
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Well I finally got to complete this beautiful set. Replaced the speaker cloth and modified the power socket to take 3 core instead of 2 core and it looks and performs really good.
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Location: Latham, ACT
Member since 21 February 2015
Member #: 1705
Postcount: 2174
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Ok advice please. The phono switch on the back is playing up. It may just need a good clean. But if need be can I replace it with a toggle switch. Not worried about authenticity , just want it to work. I take it that it would be a two way switch ie 3 contacts with the middle being common.
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Location: Hill Top, NSW
Member since 18 September 2015
Member #: 1801
Postcount: 2078
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Yes, every other setup I've seen essentially does that. Common will be the one going to the volume control.
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Administrator
Location: Naremburn, NSW
Member since 15 November 2005
Member #: 1
Postcount: 7395
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Images uploaded to Post 36.
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A valve a day keeps the transistor away...
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Location: Sydney, NSW
Member since 28 January 2011
Member #: 823
Postcount: 6761
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Location: Wangaratta, VIC
Member since 21 February 2009
Member #: 438
Postcount: 5389
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If the switch is not carrying screen voltage (One needs a switch that can handle DC, rather than AC) then it would be a case of getting a multi pole switch & getting rid of it, even that you may have to buy new.
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Location: Latham, ACT
Member since 21 February 2015
Member #: 1705
Postcount: 2174
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Yeah I wont muck around. I think the original may be redeemable but wont hesitate to replace it.
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Location: Wangaratta, VIC
Member since 21 February 2009
Member #: 438
Postcount: 5389
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I note that in a Roberts I repaired that whilst they used a wafer switch switching mains & battery; to reduce the possibility of flashover N to A, Neutral was on a separate switching bank to Active.
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