Roberts R77 - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

wheresthetubes · 7th Dec 2009, 12:28 am

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.

Tim · 7th Dec 2009, 2:02 am

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

wheresthetubes · 7th Dec 2009, 10:20 am

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.

Robert Darwent · 7th Dec 2009, 12:57 pm

Quote:

Originally Posted by wheresthetubes

I haven't done these types of checks before, so I need an idiot guide

John, You need to do some reading up on basic electrical theory first (how to take readings with a multimeter, connecting resistors/capacitors in series and parallel, etc) before attempting to restore any radio. Otherwise its highly likely you are going to cause more problems to the set than repair it. I suggest you do an internet search for the required information and only proceed with your R77 when you are confident of how to use your multimeter safely. Good luck with it.

Regards

wheresthetubes · 7th Dec 2009, 4:17 pm

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.

Retired · 7th Dec 2009, 4:37 pm

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.

Robert Darwent · 7th Dec 2009, 6:43 pm

John, Col, I hope my previous comments were not taken as flippant and a put-down, that was not my intention at all.

Quote:

Originally Posted by Retired

...its very easy for an expert to take basics for granted.

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.

Quote:

Originally Posted by wheresthetubes

I have done the reading and the theory...

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:

Originally Posted by wheresthetubes

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...

Exactly the reason for gaining a sound understanding of the principles involved and learning how to connect and use your multimeter correctly before finding out the hard way and irreparably damaging your R77 and perhaps injure yourself too in the process! (Hopefully not!

)

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

Retired · 7th Dec 2009, 7:03 pm

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.

Robert Darwent · 7th Dec 2009, 9:10 pm

Quote:

Originally Posted by Retired

I'm very sorry as I could have been more tactful and certainly no offence was meant...

Hello Col,

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

wheresthetubes · 7th Dec 2009, 11:11 pm

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.

KeithsTV · 7th Dec 2009, 11:29 pm

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

wheresthetubes · 8th Dec 2009, 1:57 pm

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.

batterymaker1 · 8th Dec 2009, 2:21 pm

Gonna send out the B126 harness today!

wheresthetubes · 20th Dec 2009, 12:39 am

Thanks Batterymaker, harness received. Radio got an outing today, works well, a nice success this!

batterymaker1 · 20th Dec 2009, 2:01 am

Good to hear.

As the old Simon and Garfunkel tune goes...

"Just trying to keep my customer satisfied..."

7th Dec 2009, 12:28 am	#21
wheresthetubes Retired Dormant Member Join Date: Jul 2009 Location: Reading, Berkshire, UK. Posts: 135	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. Attached Thumbnails

7th Dec 2009, 2:02 am	#22
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	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 __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

7th Dec 2009, 10:20 am	#23
wheresthetubes Retired Dormant Member Join Date: Jul 2009 Location: Reading, Berkshire, UK. Posts: 135	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.

7th Dec 2009, 4:17 pm	#25
wheresthetubes Retired Dormant Member Join Date: Jul 2009 Location: Reading, Berkshire, UK. Posts: 135	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
Retired Heptode Join Date: Mar 2009 Location: Fenay Bridge, Huddersfield. UK. Posts: 673	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, 7:03 pm	#28
Retired Heptode Join Date: Mar 2009 Location: Fenay Bridge, Huddersfield. UK. Posts: 673	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, 11:11 pm	#30
wheresthetubes Retired Dormant Member Join Date: Jul 2009 Location: Reading, Berkshire, UK. Posts: 135	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
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,573	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
wheresthetubes Retired Dormant Member Join Date: Jul 2009 Location: Reading, Berkshire, UK. Posts: 135	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. Attached Thumbnails

8th Dec 2009, 2:21 pm	#33
batterymaker1 Heptode Join Date: Apr 2006 Location: Indianapolis, Indiana, USA. Posts: 674	Re: Roberts R77 Gonna send out the B126 harness today! __________________ Just playing with high voltage....

20th Dec 2009, 12:39 am	#34
wheresthetubes Retired Dormant Member Join Date: Jul 2009 Location: Reading, Berkshire, UK. Posts: 135	Re: Roberts R77 Thanks Batterymaker, harness received. Radio got an outing today, works well, a nice success this!

20th Dec 2009, 2:01 am	#35
batterymaker1 Heptode Join Date: Apr 2006 Location: Indianapolis, Indiana, USA. Posts: 674	Re: Roberts R77 Good to hear. As the old Simon and Garfunkel tune goes... "Just trying to keep my customer satisfied..." __________________ Just playing with high voltage....