13th Jan 2021, 7:47 pm | #61 | |
Hexode
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Re: My newly found Marconi 707
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Cheers Mark. I’ve actually bought most of the RF Mica caps from justradios. Brilliant quality stuff. |
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13th Jan 2021, 10:09 pm | #62 | |||
Dekatron
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Re: My newly found Marconi 707
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Hey Ed, this sounds like the wood veneers getting unstuck, very common with age, heat and dessication. Quote:
Good move. I have HER608's here yours FOC. Pop a few in series for good measure They're 6A 1000 PIV rated IIRC. Please acknowledge here and then PM me if interested. Quote:
I'd just go softly softly and get some Servisol in there. Sometimes it can help to soften up solidified grease/gunk with topical application of heat with a hair dryer. This isn't a specific to your set, just in general.
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13th Jan 2021, 11:13 pm | #63 |
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Re: My newly found Marconi 707
Use the original U52/5U4G H.T. rectifier. J.
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13th Jan 2021, 11:37 pm | #64 |
Hexode
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Re: My newly found Marconi 707
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14th Jan 2021, 12:44 am | #65 |
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Re: My newly found Marconi 707
How many of these were you intending to replace Ed?
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14th Jan 2021, 12:51 am | #66 | |
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Re: My newly found Marconi 707
Quote:
I’ve ordered a few different values but only the two Domino type ones which are leaky. I’ve carefully checked the others and they actually appear OK. So for now I will leave them be. |
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14th Jan 2021, 11:43 am | #67 |
Dekatron
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Re: My newly found Marconi 707
Mica capacitors are very rarely faulty.
Peter |
14th Jan 2021, 11:55 am | #68 |
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Re: My newly found Marconi 707
I know this has probably been asked before but is there any import duty when ordering from Just Radio?
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14th Jan 2021, 1:15 pm | #69 | |
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Re: My newly found Marconi 707
Quote:
Mark |
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14th Jan 2021, 1:45 pm | #70 |
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Re: My newly found Marconi 707
Thank you Mark.
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G8JET BVWS Archivist and Member V.M.A.R.S |
14th Jan 2021, 2:17 pm | #71 |
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Re: My newly found Marconi 707
The 5U4/U52 are directly heated valves with a filament, although the surge is less than using a silicon or selenium rectifier, the voltage across the HT Line rises very quickly and doesn't stabilise to its running voltage until the load increases with the other valves warmed up.
On a set that is only used rarely I'd advocate using the likes of a GZ33 or GZ37 , being an indirectly heated valve the warm up time is much longer so its kinder to smoothing capacitors and other components, the peak surge voltage will never reach what it was with the 5U4 or silicon etc.
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Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member Last edited by murphyv310; 14th Jan 2021 at 2:23 pm. |
14th Jan 2021, 2:46 pm | #72 |
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Re: My newly found Marconi 707
Great, so would you like me to pop some in the post to you?
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Al |
14th Jan 2021, 6:18 pm | #73 |
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Re: My newly found Marconi 707
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14th Jan 2021, 6:20 pm | #74 |
Hexode
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Re: My newly found Marconi 707
Hi everyone.
All replacement capacitors are now finally here, so will get started and post some updates soon. I’ll see if I can link some YouTube videos as well, as a visual aid. Thanks, Ed |
14th Jan 2021, 8:40 pm | #75 |
Tetrode
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Re: My newly found Marconi 707
BTW, I notice from your pictures that you have the tuning dial glass in place. This is pretty much irreplaceable and can easily be accidently broken shifting the heavy chassis around. When working on my pre-war TVs for any length of time I always remove it, putting it in a safe place until the work is complete.
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20th Jan 2021, 1:37 pm | #76 |
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Re: My newly found Marconi 707
Does anyone know where I could find a C clip suitable for one of the dual pot controls?
The little C clip holding the outer shaft in place was already loose on the control, a failed attempt at putting it back on sent it flying across the room... |
20th Jan 2021, 1:44 pm | #77 | |
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Re: My newly found Marconi 707
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21st Jan 2021, 1:53 am | #78 |
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Re: My newly found Marconi 707
Thanks for the tip.
I’ve now thankfully found the C clip but having trouble re attaching. Originally the control was actually bent when I got the set, but thought nothing of it until a slight touch pinged the C clip off. I’ve attached some photos of it. Is the shaft broken? It moves back and forth freely but is firmly screwed in place. I’m a little stuck here as id like to sort this before I continue. I’d hate to remove the pot for a closer inspection as it’s hidden under a spiderweb of wires, and the EHT bleed chain - but I’m sure I’ll have to!
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21st Jan 2021, 2:46 am | #79 |
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Re: My newly found Marconi 707
Hi Ed,
have a look here:- https://www.vintage-radio.net/forum/...=hmv905&page=5 Look at post 97 to see what is on the inside of these pots. If the C clip is removed and the shaft is allowed to slip backwards, the track wiper washer (for want of a better name) will fall off, which results in more play in the shaft and scoring of the track if the control shaft is rotated. The key to putting them back together is to remove the retaining nut at the front of the pot (you have to remove the pot from the chassis to get to this). I do have some spare morganite pots for spare parts. I might have a spare timebase control for your set from the scrap 709, but it would need some sort of repair I expect as the chassis was very rusty. I'll have to have a look in my spares box. Cheers Andy
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21st Jan 2021, 3:06 am | #80 | |
Hexode
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Re: My newly found Marconi 707
Quote:
Please let me know if you find something suitable spare! In the meantime I’ll dismantle this one and try to repair it. Wish me luck!
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With regards, Ed |
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