Cossor Melody maker model 501 help - UK Vintage Radio Repair and Restoration Discussion Forum

marcus 3500 · 3rd Sep 2007, 4:28 pm

Hi all

Cossor Melody maker model 501 serial number SY-46989

The fault with this set is the sound is low the volume control is fine i do have some info on the set (R&T vol 1)

After removing the back the only visible fault i can find is the 7B7 and 7C6 valve heaters are a bit feeble to say the least is that normal on this set? the set was on for over an hour yesterday and both valves felt cold the rest are nice and hot with a healthy glow.

I found a scrap 501 yesterday serial number ?-43316 and swapped over the 7B7 and 7C6 valves and the results are the same any help woud be much appreciated.

Regards

Marcus........

Steve_P · 3rd Sep 2007, 4:37 pm

OK - First of all: Read and Learn:

http://www.vintage-radio.com/repair-...lves-work.html

However, I can advise you to change C25. The circuit for this set (and many others) is available from our esteemed webmaster, the Rt Hon. Mr Stenning, on the panel top right!

Cheers,

Steve P

marcus 3500 · 3rd Sep 2007, 5:18 pm

Sorry i should have put ive already changed C25, C26, C30 this afternoon

The most likely fault Steve is all 4 valves are kaput then ? i was hopeing the 2from the spare 501 would be ok and the fault was with the radio

Regards

Marcus.......

Steve_P · 3rd Sep 2007, 6:01 pm

I assume you've tried it with a large aerial. Most sets of this era needed it. Is it quiet Audio wise or quiet as in weak stations. Also, measure the HT and see make sure that's OK.

Go for a changing the waxies session and make sure none of the Resistors have gone high. This will quieten it.

Check the RF end as well - for small cap problems.

Cheers,

Steve P.

marcus 3500 · 3rd Sep 2007, 7:32 pm

Hi Steve

The only aerial ive tried on this set is the one thats attached to the rear cover on the inside, the set picks up quite a fair few stations on MW but only 1 on SW and 2 on LW, the problem with the set is the volume is not very loud if i read this im typing to my self out load in a normal voice im louder than the radio, is it normal for the Cossor 7B7 and 7C6 to run cool ? the radio as been on for the last 2 hours and those 2 valves are just warm sorry for my stupidity this is the first valve radio ive ever tried to fix.

The resistors are all ok Steve just a few of them have changed value R12 100ohm in my set it reads 108 ohm, R13 470k in mine R13 reads 466k etc

I dont have many of the caps this set uses Steve ive just swapped the 32UF cap C26, c25 0.1UF and c30 25UF.

Ive just tried to take a pic of the febble glow of the 7C6 but you cant see it

you can see the healthy glow from the 7C5 in the picture only.

Thanks for the help Steve with this set i think ill box it up for now untill i can get them 2 valves and take it from there Steve.

Regards

Marcus......

Sideband · 3rd Sep 2007, 8:53 pm

One problem with these valves was corrosion of the pins...admittedly more of a problem on the rectifier and output valves because they run hotter. The pins are rather short and thin so not much contact area. Pull out the valves and thoroughly clean the pins on all of them. Afterwards put a drop of switch cleaner on them. This should take care of any problems in this area but you may need to do it again in a few years.

Measure the voltage across the heater pins if you have any doubt (pins 1 and 8 on these valves, either side of the locating 'pip' (remember it's AC)!

HT should be in the region of around 230v on the cathode of the reccy. If it's low, replace the reccy (probably a 7Y4 or equiv).

Rich.

PaulR · 3rd Sep 2007, 9:33 pm

I have one of these and the reception using the inbuilt aerial is very poor. Try a good long aerial, maybe upstairs (assuming you don't live in a bungalow!) and see what happens then. Valves are actually very reliable and don't really glow very much. In any case the amount of light they emit has no relationship to their condition.

As Richard says the pins on these valves can cause problems as can the valve holders themselves as the sockets are thin bits of bent brass sandwiched between two paxolin circles. I had to replace two in mine and had to repair the one holding the rectifier.

Follow Richard's advice about the voltages, and if you really want to replace any valve try the rectifier.

Finally, mine oscillated at high volume settings. I traced this to the earth connection on the main tag strip.

Just another thought - the set will have an pickup input. Try a CD player or something connected to that to see how well the amp works.
Paul

kalee20 · 4th Sep 2007, 12:51 pm

Hi, just a comment - I have a Cossor 500 (same chassis, wooden cabinet). On radio, volume is quite good, but the sensitivity from the pick-up input is not high. A CD playerhardy gives enough output to fully drive the amplifier, even at full volume setting.

Definitely change the waxies, ESPECIALLY the one coupling to the output valve grid. Then, measure the reisistance from 7C5 pin 7 to chassis (to check the cathode resistor) with the set off (270 ohms), then switch on and measure 7C5 cathode voltage - the service sheet (from Paul Stenning's CD-ROM) indicates 9V. Mine shows 6.5V indicating a tired 7C5, yet changing to a new one doesn't increase volume noticeably!

I'm really interested as to whether yours works on short wave. I'm having a lot of fun with mine - see separate thread.

marcus 3500 · 4th Sep 2007, 5:16 pm

Hi all

Thank you for all your replys.

Steve, Richard, Paul i measured the HT at cap c31 and the voltage was 173v
ive removed the 7Y4 from the spare chassis and cleaned the pins the HT is now at 278v is that ok ? the valve heater voltages are 6.3v AC rectifier valve and the rest of the valves heater voltage comes from another winding on the transformer that is only 5.7v AC is that correct.

Ive replaced c26,c31 from the scrap chassis rather than use 2 caps

The radio is much louder now so thanks all but could you get back to me regarding the voltages cheers guys.

kalee on SW my set picks up now 2 stations near 16 (on the dial)1 near 12
a fast beeb at 8 and 1 station at 0 hope that helps

Regards

Marcus.......

Steve_P · 4th Sep 2007, 5:43 pm

Use new caps Marcus!

Cheers,

Steve P

marcus 3500 · 4th Sep 2007, 6:07 pm

Hi Steve

This is a pick of the duff cap c26,c31 it reads 3UF on the 16UF section and 11UF on the 32UF section the one ive fitted from the scrap cossor reads 15UF on the 16UF section and 30UF on the 32UF section, i guess i could fit 2 new caps in the old can or do you think the one from the scrap Cossor that ive fitted will be ok it is dated 1955.

Regards

Marcus.........

Steve_P · 4th Sep 2007, 6:10 pm

Yes that'll be fine. Chuck the other one in the bin. I should have checked what they were on the diagram first. Sorry about that.

Cheers,

Steve P

Sideband · 4th Sep 2007, 9:51 pm

Quote:

Originally Posted by marcus 3500

ive removed the 7Y4 from the spare chassis and cleaned the pins the HT is now at 278v is that ok.

That's fine

. the trader sheet quotes 280v on the cathode so you have a very good reccy valve there!

Anode volts on the 7C5 output valve should be around 268 so a bit higher than I suggested. These sets work well but you'll need an external aerial for SW.

I hope no-one has twiddled the alignment. I'd be inclined to check that next.

Rich.

marcus 3500 · 5th Sep 2007, 4:19 pm

Hi All

Thank you everyone for all the fantastic help ive been given with the Cossor, the radio is back together and sounds quite good.

Here are the end results and a pic of the donor Cossor Thanks again Guys

Regards

Marcus.......

PaulR · 5th Sep 2007, 7:06 pm

You will, of course now be restoring the "donor"!!

Steve_P · 5th Sep 2007, 9:57 pm

Easily done too. Valves can be got, Capacitors can be changed, Cabinets can be cleaned, etc.

Cheers,

Steve P

Mike Phelan · 6th Sep 2007, 8:12 am

Well done, Marcus - it looks good.
The donor looks quite reasonable as well; heed Paul's and Steve's advice.

marcus 3500 · 6th Sep 2007, 8:21 pm

Hi all

Thanks Paul, Steve, Mike

For now the donor Cossor can join the to do pile. I'm keeping it that way just in case anything goes wrong with the working one.

Thanks again all for all your kind help, without it I would still be scratching my head.

Regards

Marcus.........

3rd Sep 2007, 4:28 pm	#1
marcus 3500 Retired Dormant Member Join Date: May 2006 Location: South Yorkshire, UK. Posts: 351	Cossor Melody maker model 501 help Hi all Cossor Melody maker model 501 serial number SY-46989 The fault with this set is the sound is low the volume control is fine i do have some info on the set (R&T vol 1) After removing the back the only visible fault i can find is the 7B7 and 7C6 valve heaters are a bit feeble to say the least is that normal on this set? the set was on for over an hour yesterday and both valves felt cold the rest are nice and hot with a healthy glow. I found a scrap 501 yesterday serial number ?-43316 and swapped over the 7B7 and 7C6 valves and the results are the same any help woud be much appreciated. Regards Marcus........ Attached Thumbnails Last edited by Darren-UK; 21st Mar 2008 at 8:09 pm. Reason: Excessive use of emoticons.

3rd Sep 2007, 4:37 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Cossor Melody maker model 501 help OK - First of all: Read and Learn: http://www.vintage-radio.com/repair-...lves-work.html However, I can advise you to change C25. The circuit for this set (and many others) is available from our esteemed webmaster, the Rt Hon. Mr Stenning, on the panel top right! Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

3rd Sep 2007, 5:18 pm	#3
marcus 3500 Retired Dormant Member Join Date: May 2006 Location: South Yorkshire, UK. Posts: 351	Re: Cossor Melody maker model 501 help Sorry i should have put ive already changed C25, C26, C30 this afternoon The most likely fault Steve is all 4 valves are kaput then ? i was hopeing the 2from the spare 501 would be ok and the fault was with the radio Regards Marcus.......

3rd Sep 2007, 6:01 pm	#4
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Cossor Melody maker model 501 help I assume you've tried it with a large aerial. Most sets of this era needed it. Is it quiet Audio wise or quiet as in weak stations. Also, measure the HT and see make sure that's OK. Go for a changing the waxies session and make sure none of the Resistors have gone high. This will quieten it. Check the RF end as well - for small cap problems. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

3rd Sep 2007, 7:32 pm	#5
marcus 3500 Retired Dormant Member Join Date: May 2006 Location: South Yorkshire, UK. Posts: 351	Re: Cossor Melody maker model 501 help Hi Steve The only aerial ive tried on this set is the one thats attached to the rear cover on the inside, the set picks up quite a fair few stations on MW but only 1 on SW and 2 on LW, the problem with the set is the volume is not very loud if i read this im typing to my self out load in a normal voice im louder than the radio, is it normal for the Cossor 7B7 and 7C6 to run cool ? the radio as been on for the last 2 hours and those 2 valves are just warm sorry for my stupidity this is the first valve radio ive ever tried to fix. The resistors are all ok Steve just a few of them have changed value R12 100ohm in my set it reads 108 ohm, R13 470k in mine R13 reads 466k etc I dont have many of the caps this set uses Steve ive just swapped the 32UF cap C26, c25 0.1UF and c30 25UF. Ive just tried to take a pic of the febble glow of the 7C6 but you cant see it you can see the healthy glow from the 7C5 in the picture only. Thanks for the help Steve with this set i think ill box it up for now untill i can get them 2 valves and take it from there Steve. Regards Marcus...... Attached Thumbnails Last edited by Darren-UK; 21st Mar 2008 at 8:10 pm. Reason: Excessive use of emoticons.

3rd Sep 2007, 8:53 pm	#6
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Cossor Melody maker model 501 help One problem with these valves was corrosion of the pins...admittedly more of a problem on the rectifier and output valves because they run hotter. The pins are rather short and thin so not much contact area. Pull out the valves and thoroughly clean the pins on all of them. Afterwards put a drop of switch cleaner on them. This should take care of any problems in this area but you may need to do it again in a few years. Measure the voltage across the heater pins if you have any doubt (pins 1 and 8 on these valves, either side of the locating 'pip' (remember it's AC)! HT should be in the region of around 230v on the cathode of the reccy. If it's low, replace the reccy (probably a 7Y4 or equiv). Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

3rd Sep 2007, 9:33 pm	#7
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Cossor Melody maker model 501 help I have one of these and the reception using the inbuilt aerial is very poor. Try a good long aerial, maybe upstairs (assuming you don't live in a bungalow!) and see what happens then. Valves are actually very reliable and don't really glow very much. In any case the amount of light they emit has no relationship to their condition. As Richard says the pins on these valves can cause problems as can the valve holders themselves as the sockets are thin bits of bent brass sandwiched between two paxolin circles. I had to replace two in mine and had to repair the one holding the rectifier. Follow Richard's advice about the voltages, and if you really want to replace any valve try the rectifier. Finally, mine oscillated at high volume settings. I traced this to the earth connection on the main tag strip. Just another thought - the set will have an pickup input. Try a CD player or something connected to that to see how well the amp works. Paul Last edited by PaulR; 3rd Sep 2007 at 9:40 pm. Reason: Another thought

4th Sep 2007, 12:51 pm	#8
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: Cossor Melody maker model 501 help Hi, just a comment - I have a Cossor 500 (same chassis, wooden cabinet). On radio, volume is quite good, but the sensitivity from the pick-up input is not high. A CD playerhardy gives enough output to fully drive the amplifier, even at full volume setting. Definitely change the waxies, ESPECIALLY the one coupling to the output valve grid. Then, measure the reisistance from 7C5 pin 7 to chassis (to check the cathode resistor) with the set off (270 ohms), then switch on and measure 7C5 cathode voltage - the service sheet (from Paul Stenning's CD-ROM) indicates 9V. Mine shows 6.5V indicating a tired 7C5, yet changing to a new one doesn't increase volume noticeably! I'm really interested as to whether yours works on short wave. I'm having a lot of fun with mine - see separate thread.

4th Sep 2007, 5:16 pm	#9
marcus 3500 Retired Dormant Member Join Date: May 2006 Location: South Yorkshire, UK. Posts: 351	Re: Cossor Melody maker model 501 help Hi all Thank you for all your replys. Steve, Richard, Paul i measured the HT at cap c31 and the voltage was 173v ive removed the 7Y4 from the spare chassis and cleaned the pins the HT is now at 278v is that ok ? the valve heater voltages are 6.3v AC rectifier valve and the rest of the valves heater voltage comes from another winding on the transformer that is only 5.7v AC is that correct. Ive replaced c26,c31 from the scrap chassis rather than use 2 caps The radio is much louder now so thanks all but could you get back to me regarding the voltages cheers guys. kalee on SW my set picks up now 2 stations near 16 (on the dial)1 near 12 a fast beeb at 8 and 1 station at 0 hope that helps Regards Marcus....... Last edited by Darren-UK; 21st Mar 2008 at 8:08 pm. Reason: Excessive use of emoticons.

4th Sep 2007, 5:43 pm	#10
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Cossor Melody maker model 501 help Use new caps Marcus! Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

4th Sep 2007, 6:07 pm	#11
marcus 3500 Retired Dormant Member Join Date: May 2006 Location: South Yorkshire, UK. Posts: 351	Re: Cossor Melody maker model 501 help Hi Steve This is a pick of the duff cap c26,c31 it reads 3UF on the 16UF section and 11UF on the 32UF section the one ive fitted from the scrap cossor reads 15UF on the 16UF section and 30UF on the 32UF section, i guess i could fit 2 new caps in the old can or do you think the one from the scrap Cossor that ive fitted will be ok it is dated 1955. Regards Marcus......... Attached Thumbnails

4th Sep 2007, 6:10 pm	#12
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Cossor Melody maker model 501 help Yes that'll be fine. Chuck the other one in the bin. I should have checked what they were on the diagram first. Sorry about that. Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

5th Sep 2007, 4:19 pm	#14
marcus 3500 Retired Dormant Member Join Date: May 2006 Location: South Yorkshire, UK. Posts: 351	Re: Cossor Melody maker model 501 help Hi All Thank you everyone for all the fantastic help ive been given with the Cossor, the radio is back together and sounds quite good. Here are the end results and a pic of the donor Cossor Thanks again Guys Regards Marcus....... Attached Thumbnails Last edited by Darren-UK; 21st Mar 2008 at 8:07 pm. Reason: Excessive use of emoticons.

5th Sep 2007, 7:06 pm	#15
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Cossor Melody maker model 501 help You will, of course now be restoring the "donor"!!

5th Sep 2007, 9:57 pm	#16
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Cossor Melody maker model 501 help Easily done too. Valves can be got, Capacitors can be changed, Cabinets can be cleaned, etc. Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

6th Sep 2007, 8:12 am	#17
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: Cossor Melody maker model 501 help Well done, Marcus - it looks good. The donor looks quite reasonable as well; heed Paul's and Steve's advice. __________________ Mike.

6th Sep 2007, 8:21 pm	#18
marcus 3500 Retired Dormant Member Join Date: May 2006 Location: South Yorkshire, UK. Posts: 351	Re: Cossor Melody maker model 501 help Hi all Thanks Paul, Steve, Mike For now the donor Cossor can join the to do pile. I'm keeping it that way just in case anything goes wrong with the working one. Thanks again all for all your kind help, without it I would still be scratching my head. Regards Marcus......... Last edited by Darren-UK; 21st Mar 2008 at 8:06 pm. Reason: Excessive use of emoticons.