7th Dec 2009, 12:28 am | #21 |
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Re: Roberts R77
Thanks for the info. I have the service sheet, but I'm not sure how to measure the LT and HT current drawn. With the pics I've uploaded, could someone talk me through this please.
Many thanks. |
7th Dec 2009, 2:02 am | #22 |
Dekatron
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Re: Roberts R77
Set your meter to DC current(maybe milliamps?)-which sometimes uses a different socket to that for volts and ohms.The meter then goes in SERIES with the HT or battery.
Remember to switch back again before taking voltage readings! I would expect the HT current to be in the region of 10mA
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7th Dec 2009, 10:20 am | #23 |
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Re: Roberts R77
Thanks. But I don't know where to put the meter prods and what to look for, thats why I've posted the valve info and the circuit diagram. I need detailed info as to where I put the meter prods and what values I should be getting. I haven't done these types of checks before, so I need an idiot guide if someone could guide me through the process. Regards, John.
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7th Dec 2009, 12:57 pm | #24 | |
Heptode
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Re: Roberts R77
Quote:
Regards Last edited by Robert Darwent; 7th Dec 2009 at 1:04 pm. |
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7th Dec 2009, 4:17 pm | #25 |
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Re: Roberts R77
Thanks. I have done the reading and the theory, but like everything else the jump from theory to practice is, well, just that, a jump. If this was a cheap radio then perhaps I'd have a go and not worry too much if I made a mistke along the way. But this is a Roberts R77, a very nice one and still quite pricey, even for one that doesn't work. All I'm looking for is a little advice to take me through the steps. Once I've done this radio then the experience I'd gain from this project would give me more confidence for the next radio.
john. |
7th Dec 2009, 4:37 pm | #26 |
Heptode
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Re: Roberts R77
Hi John,
We all have to start somewhere and its very easy for an expert to take basics for granted. I'm still very much a chassis novice but am happy to spend a bit of time to get you started so please don't be afraid to pester me via e-mail; we can both learn together? Once you get used to using a multimeter you do it automatically and the basics are easy enough to pick up. I'll be in touch shortly. Regards, Col. |
7th Dec 2009, 6:43 pm | #27 | |
Heptode
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Re: Roberts R77
John, Col, I hope my previous comments were not taken as flippant and a put-down, that was not my intention at all.
I hope the 'expert' bit was not directed at me Col? (Nothing could be further from the truth! ) And taking the basics for granted is the exact opposite of the message I was trying to get over to John. The basics are the foundation of every aspect of this hobby and I was trying to impress the importance of not just reading about them but understanding them. Otherwise, as you have found out, trying to follow the advice offered to you already by members is always going to be very difficult. Quote:
I'm not trying to deter you at all, just hopefully giving you friendly advice to help you go about learning and progressing the right way. It really is a case of learning to walk before you can run, there are no real shortcuts to be had I'm afraid. Regards Last edited by Robert Darwent; 7th Dec 2009 at 6:49 pm. |
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7th Dec 2009, 7:03 pm | #28 |
Heptode
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Re: Roberts R77
Hi Robert,
I'm very sorry as I could have been more tactful and certainly no offence was meant to anyone as I was thinking in general terms. All the advice given to John is top class and forum members are brilliant with help; I know this first hand. No; I certainly didn't mean you Robert and sincerely apologise if it appeared so; I was thinking about people in general who are used to using a multimeter and take them for granted; I know I do as I use the multimeter automatically without thinking about it. I hope I can be of assistance to John and have just sent him a lengthy e-mail covering taking voltage readings. I'm doing this in stages and am sure John will soon pick it up. Regards, Col. |
7th Dec 2009, 9:10 pm | #29 | |
Heptode
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Re: Roberts R77
Quote:
No need for apologies, I certainly didn't take any sort of offence from your comments. I was only making sure that my reply to John wasn't misunderstood and was only took as I intended it to be, genuinely helpful. Kind regards |
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7th Dec 2009, 11:11 pm | #30 |
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Re: Roberts R77
Blimey, I didn't take any offence either, all the advice I've ever had from users of this site has been very helpful. I'm a complete novice with electronics, but users on this site have helped me repair a bakelite telephone, build a nixie clock, and now I have a working Roberts R77 . I took your advice Colin on checking voltage through the resistors whilst leaving power on. I was onto my 9th resistor (R9) and as soon as I put the multi-meter prods to either end of R9 the radio just burst into life! I have no idea why it did this, though another chap on this site has said that capacitors need to be 'formed' if the radio has been off for a while. I had power on for 10-15 minutes, though as I say, nothing happened until I tested voltage on R9. The only real work I've done to the radio is change C13, which was one of those nasty wax types and was open circuit. I've sprayed Servisol-10 on some of the switches, and used said stuff to clean the plastic facia. It looks almost new. Have wiped leather case with leather wipes. Will get suitable polish for it in due course.
The zips on these cases are prone to tearing, luckily this ones ok. However it was pretty stiff. Obviously one can't use oil on the zip as this may tend to rot the cotton in the long term. So a bit of baby talk carefully rubbed into the zip has loosend the zip considerably. I must say, I'm very pleased with this Roberts. My thanks to everyone on this site who gave their advice I will post a pic of the Roberts tomorrow morning. |
7th Dec 2009, 11:29 pm | #31 |
Nonode
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Re: Roberts R77
R9 is a 10M resistor and has probably gone high. Putting the meter across it uses the resistance of the meter to effectively "replace" this resistor. It is also possible that C20 is leaky and this is causing the DAF96 screen grid voltage to be too low
Check the value of R9 and replace if greater than 12M. It's probably worth changing C20 especially if it's a waxed paper type. Keith |
8th Dec 2009, 1:57 pm | #32 |
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Re: Roberts R77
This is the Roberts R77. Left it on for 20 minutes and no problems. Its still operating with the old valves that came with the set, so I have the NOS duplicates as spares. I will get on and check the resistors again, and the caps at some stage. All I'm waiting on now is a B126 battery, currently being made up by another forum user, and it can get an outing for the first time in probably over 40 years.
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8th Dec 2009, 2:21 pm | #33 |
Heptode
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Re: Roberts R77
Gonna send out the B126 harness today!
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20th Dec 2009, 12:39 am | #34 |
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Re: Roberts R77
Thanks Batterymaker, harness received. Radio got an outing today, works well, a nice success this!
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20th Dec 2009, 2:01 am | #35 |
Heptode
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Re: Roberts R77
Good to hear.
As the old Simon and Garfunkel tune goes... "Just trying to keep my customer satisfied..."
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