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Post by elorens on Aug 26, 2020 17:23:24 GMT 12
This nice little 1959 mantel is now working as it should, after correction of a number of faults, including an incorrectly wired output transformer. It was intriguing to find a frequency-changer valve where the detector/first audio should be, and doing the job, after a fashion. But the back is missing! Does anyone have a spare, by chance? Failing that, can anyone let me have an image of the back so I can fabricate one?
The 1959 circuit shows B8A valves such as the ECH 42, but mine has been converted to B9A throughout, I assume by the makers. Does anyone know when and why this happened?
Thanks,
Lawrence
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Post by davidballantynezl1tfg on Aug 28, 2020 9:55:11 GMT 12
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6A8G.
Society Members
Hard working kiwi soundmixer.
Posts: 10 
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Post by 6A8G. on Sept 20, 2020 9:04:38 GMT 12
Around four years ago I repaired one of these for a colleague. The NZVRS came to the rescue with a circuit diagram & I had to do a whole lot of learning about the circuit around the output transformer... then I looked more carefully & found that someone had replaced it with an ordinary type, replaced C26 with a 150 uF cap & C25 was nowhere to be found. Like yours though, the valve lineup was B9A's. I did replace the 150 uF cap - according to the data I had to hand, even 50 uF is pushing it..... Best, John:)
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Post by elorens on Sept 20, 2020 22:34:37 GMT 12
Thanks, John. Yes, 150 uF would give a big surge at switch-on. In my case R17 was missing. Replacing it and changing the electrolytics brought the hum down quite nicely. It looks as if someone had misunderstood the functions of T3. Not sure why they changed to B9A or when, but I’m guessing it was about availability. The circuit I have is dated 1959 so presumably the change was made in 1960 or later. Would be good to know how long they were made for, but that is often a difficult figure to find.
Cheers
Lawrence
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Steve
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vintageradio.co.nz
Posts: 303
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Post by Steve on Sept 27, 2020 18:39:16 GMT 12
Hi Lawrence... it seems like the 40-series valves were what was commonly available in NZ in 1959, and it also seems like most manufacturers here that were using the 40-series switched over to 80-series in around 1960/61. So my best guess (because it was a long time before me) is that the MD54 ran for several years, and it got an update. I'd love to know what the later valve lineup is so I can add that into the site. Is there a label inside your cabinet? I note from the pictures I have that there was a label, at least on some. The speaker also looks a little "Akrad-y"... if it is it might have a date on it... or the electrolytic can may be dated?   These are the best 'back' pics I have, which were taken from a Trade Me advert a long time ago... hopefully they will help recreate something. If I could get that material and a cad drawing I could laser cut the vent slots - otherwise I suspect it will be difficult to recreate them neatly. The label could probably be recreated easily on a laser printer. Cheers, Steve |
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Steve
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vintageradio.co.nz
Posts: 303
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Post by Steve on Sept 27, 2020 18:44:54 GMT 12
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Post by elorens on Sept 30, 2020 16:06:51 GMT 12
Hi Lawrence... it seems like the 40-series valves were what was commonly available in NZ in 1959, and it also seems like most manufacturers here that were using the 40-series switched over to 80-series in around 1960/61. So my best guess (because it was a long time before me) is that the MD54 ran for several years, and it got an update. I'd love to know what the later valve lineup is so I can add that into the site. Is there a label inside your cabinet? I note from the pictures I have that there was a label, at least on some. The speaker also looks a little "Akrad-y"... if it is it might have a date on it... or the electrolytic can may be dated? These are the best 'back' pics I have, which were taken from a Trade Me advert a long time ago... hopefully they will help recreate something. If I could get that material and a cad drawing I could laser cut the vent slots - otherwise I suspect it will be difficult to recreate them neatly. The label could probably be recreated easily on a laser printer. Cheers, Steve Thanks, Steve. The valve lineup in mine, almost certainly not original, was ECH81, 6F18, 6C12, EL86, EZ80. I replaced the miscast 6C12 by a 6LD13, but it’s possible the original could have been EBC81. The Rola speaker model 5F has a code 28J5 on the rim, but not sure if that is a date code. Cheers, Lawrence |
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Post by elorens on Sept 30, 2020 16:13:51 GMT 12
Steve, thanks too for those images. There was a label inside the cabinet, but most of it has been torn away. There is a reference to an ECH81, which suggests that the change to B9A types was ‘official’.
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