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Post by John on Jul 5, 2019 11:57:37 GMT 12
Hi All
Just after a bit advice if possible - I am a total newby, and have been doing up my Granddad's old Ultimate FA (https://www.vintageradio.co.nz/model/ultimate/fa). I am basically done now (have replaced caps and faulty valves), but just have a question about the aerial/ground connections. There is a loose wire coming out the back, which i initially assumed was the aerial, but does not seem to affect the reception. I just noticed there are also two input plugs at the rear, so am now wondering whether they the aerial and the loose wire is an earth? On some of the other photos I have seen, the loose wire appears to be connected to something on top of the chassis. I still can't read the schematic, but there is one in the link above. Is anyone able to shed some light? I am sure it is easy if you are used to looking at those schematics.
Cheers
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Post by Philconut on Jul 5, 2019 20:05:14 GMT 12
From memory, all the coil sets are under the chassis but these wires could be the aerial, which appears to be missing in your case, and the earth. I suspect the two input plugs are a mod for a pickup input.
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Steve
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Post by Steve on Jul 6, 2019 3:38:04 GMT 12
Hi John, I do have other examples to upload to vintageradio.co.nz for the FA and FJ (same as the FA, but one less valve)... and I've restored an FJ some time back so I do have some photos to go on as to the aerial location that might help. This is the aerial wire. Factory wiring was rubber on a lot of these, so its often wrecked and needing replaced. it enters at the base near the middle of the back And this shows where it attaches to the back of the band selection switch (click the images for larger views). The input plugs are for gramophone input. There is probably a spring clip on the top of the chassis which is for attaching an earth, but if you've used a three-wire mains cord and connected the earth to the chassis then you won't probably need one. One last photo that shows both the aerial wire and the earth wire clip - sorry about the poor quality, its all I have. These sets have incredibly nice sound when running properly, very impressive bass and tone, good sensitivity, and they look great when cleaned up... I'll show some before and after cabinet photos shortly... You might possibly have an open aerial coil if the aerial isn't doing anything... If you look at the schematic in the top left corner, the aerial comes in and goes through a coil, then through another one and to ground. Lightning strikes, or corrosion, or something else could have taken out the coil... so if you can, trace to that coil and check it with a meter... On the FJ, the coil is behind the tuning gang on the top of the chassis under the box shield, I assume the FA is the same but you'll need to trace the wires from the aerial through the band switch and follow them... Cheers, Steve
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Steve
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Post by Steve on Jul 6, 2019 3:40:34 GMT 12
Before After - just scraped clean, washed in acetone, then a couple of coats of shellac to seal the grain... what a difference... very nice veneers used on these cabinets.
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bang
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Post by bang on Jul 6, 2019 13:11:43 GMT 12
Hi guys
Thanks heaps for your replies. I tested again and touching the aerial wire does affect the reception slightly - last time I tested I had just connected a coat hanger to the wire, and was wondering why I could only pick up a few scratchy stations on AM. So it would appear that the coil is still ok, and the wire is the aerial. Good to clear up what the other input plugs are for too, thanks very much for that. I do have the clip, and a 3-wire plug, so assume it is earthed through that as you say. The aerial wire does not connect directly to the band selector though, it goes through what looks like a tube base, but isnt - so assume this is the coil? and then on to the band selector. I havent figured out how to add photos yet, but will try and add some below this comment. I am still trying to source a replacement 6Q7-G valve (which I understand is part of the signal rectification), so have been testing with the old one in, which may have contributed to the poor reception. And further research also suggests I need a much longer aerial than a coat hanger to pick up more stations too.
The photos of your completed cabinet are very nice. I did a similar thing - sanded lightly to remove old finish, cleaned with meths and then a bunch of coats with automotive lacquer. looks great - ill try and add a photo below.
thanks again for your help, it is much appreciated.
John
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bang
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Post by bang on Jul 6, 2019 13:17:55 GMT 12
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Post by Philconut on Jul 6, 2019 13:32:17 GMT 12
I have a 6Q7GT if you want it. Postage only. Yes, it is the detector & first audio valve. John
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Post by Philconut on Jul 6, 2019 13:34:29 GMT 12
Your wireless could probably well do with a re-alignment too which will help immensely with the performance.
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bang
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Post by bang on Jul 6, 2019 15:37:30 GMT 12
Thanks very much for the offer. I actually have a 6Q7-GT as well as a replacement, but there is a raised ring around the base which he cover slips onto, and the GT valve has a slightly wider diameter base than the G valve, so doenst fit.
In terms of realignment, I had come across that and was wondering whether I would need to, particularly with having replaced all the capacitors. It seems pretty complicated though, and easy to stuff up. I am hoping the new valve will make all the difference... otherwise ive probably reached the end of what i should be attempting by myself.
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Steve
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Post by Steve on Jul 6, 2019 16:03:36 GMT 12
Hi John, first of all where are you and where is the closest AM transmission to you? My FJ was ok with a 2m wire hanging out the back and at the time I was out in the country about half an hour from Christchurch - so I would expect an FA, which has the extra RF amplifier at the front end, to be very good with a simple short aerial - but typically these old beasts needed a decent long-line aerial for good reception - I use about 30m of wire strung from the garage to my barn (the birds love it). Of course, as mentioned, an alignment could help especially if any of the trimmers underneath have been tweaked, bumped or played with - but that is probably something you might want to get some help with as these are not the simplest beasts to align (although a rough BC alignment can be done by ear). The coil can that the aerial wire is connected to is the SW (1) aerial coil... the can beside it will be the BC (2) (broadcast band - this is what a lot of people call 'AM') aerial coil. Even with a break they might appear ok at first glance. You can see if you follow the yellow line that the two coils are connected to provide the aerial-to-earth path the radio needs to feed signal to the set. . Do you have a multimeter? You can check your aerial coil windings... see the image below 1 - 2 : this is the upper left coil on the schematic, the SW primary coil (the coil beside it is the SW secondary) 2 - 3 : if that brown rectangular package has something like 00025 on it then 2-3 is the other left-most coil (BC primary) with the BC secondary beside it These are going to probably be quite a low value - the SW primary could almost seem like a short circuit, the BC primary maybe 20-50 ohms. 4 is, I think from what I can see, the variable capacitor (the two parallel lines with the arrow through them) that is wired across the BC secondary winding. Check the resistance across this, it should probably be quite low, maybe around 5-10 ohms. This part of the radio works something like this: The aerial collects radio signals from the air, and these try to get to ground so pass through these coils. This causes an electromagnetic field around the coil (think of an electromagnet), and this EM field couples the signal to the coils beside it. At the same time these coils have a optimal frequency (known as the resonant frequency) - determined by a bunch of things, including the wire size, coil size, number of windings, and capacitors across them. That resonant frequency is also changed by the first of the three gangs on the gang condenser, so they stay optimised as you tuned across the BC band (as long as the set is aligned properly).Frequencies outside of the tuned frequency get rejected to a certain degree, so this section of the radio is designed to just allow the radio frequency you want to listen to through. The first 6SK7 then amplifies this and passes it to the next section. Thats an over-simplified view of it, but its generally whats happening. Hopefully it helps Cheers, Steve Attachments:
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Steve
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Post by Steve on Jul 6, 2019 17:26:12 GMT 12
Oh, two more quick things - thats a nicely refinished cabinet, with almost the same grill cloth I chose on my one... the veneer looks fantastic Secondly, did you have the valves tested or are you just changing them as a matter of course? I seldom find valves in these sets need replacing - capacitors do, but typically valves are ok. Why do you refer to it as faulty? I'll take a look in my valve stocks and see if I have a good 6Q7G I can send you... Cheers, Steve
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bang
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Post by bang on Jul 6, 2019 18:54:10 GMT 12
Hi Steve
Thanks heaps for the detailed reply. I do have a multimeter so will test as you recommend and let you know how it goes. I gave all the original valves to a guy here in christchurch (Geoff Edwards) who tested them all for me. There were a few he reckoned were no good so sold me replacements. The 6Q7 was one of them, and he gave me the GT one, and then i realised it didnt fit just the other day. he is still trying to source a G one as well, but apparently they are rare as they only made them for a short period?
yes i noticed we had the same grill cloth!
John
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Steve
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Post by Steve on Jul 6, 2019 22:18:00 GMT 12
Ah, good - yes Geoff has as good a valve collection as anyone I would think - I have no 6Q7G's in my stash unfortunately. Worst case you could put some masking tape over the socket pins and wrap some more around the base to stop metal going everywhere and use a dremel to widen the hole in the base to fit the GT valve in. Unfortunately these shortages are only going to get worse with nobody making these any more.
I've asked a friend who might have one... I'll let you know what he says.
Cheers, Steve
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Post by Philconut on Jul 7, 2019 8:32:42 GMT 12
If you're in Christchurch or can bring the set to me I am happy to help with an alignment check.
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bang
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Post by bang on Jul 7, 2019 11:35:21 GMT 12
Hi Steve
I tested the coils as you recommended, and got resistance close (but a little lower) to your estimated values. Thanks for the explanation too, I had to read it a few times to understand it and how it related to the tests, but I think I did in the end! I had read a few blogs about people testing primary and secondary windings around coils, but unless someone explains it and shows the points to test, its very hard to get your head around, so thanks for taking the time.
If I tested things correctly, I get:
SW Primary - 2.6-3 ohms SW Secondary - 0.5-1 ohms BC Primary - about 19 ohms BC Secondary - 2.4 ohms Variable capacitor - 2.2ohms.
And yes, the brown plastic capacitor has 0.00025MFD on it. Do those seem reasonable?
Philconut - that would be amazing if you were happy to help with an alignment check. I am in Christchurch. Probably best to wait till I have the other valve sorted, but will message you once I do and organise a time.
John
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