Correct polarity for capacitor in audio amp? - UK Vintage Radio Repair and Restoration Discussion Forum

Marky P · 26th Jul 2008, 9:34 am

At this very moment in time, I have a hot soldering iron andreplacing caps in my Wurlitzer jukebox amp. All is going swimmingly at the mo, but I've found what could be an error on the schemetic or the board. The board has + symbols on it to denote the cap polarity, but the schematic shows one of the caps with opposite polarity to the board. It's a stereo amp and there are two caps going to the 'Aux Amp' output. According to the board, the 'minus' of the cap goes to the 'aux amp'output, but the schematic shows one of these caps with the 'plus' going to the output. Surely both caps should be the same way round (one's left channel & one's right) so I'm assuming the schematic is wrong.

TrevorM6TSE · 26th Jul 2008, 11:04 am

I reckon you must be right. They'd have to be the same way round logic would say. But which way is right I'm not sure! I would say the signal should go from + to - but I may well be wrong.

mikelect · 26th Jul 2008, 11:12 am

Common sense dictates it should be fitted the same way as the original

Mike

Marky P · 26th Jul 2008, 11:53 am

Quote:

Originally Posted by mikelect

Common sense dictates it should be fitted the same way as the original

Mike

Unfortunately I took the old one out before checking

. But I've decided to go with the board markings and have the minus going to the output, which basically makes sense. Anyway, I will know in a few minutes as I am abou to power it up

.

Nickthedentist · 26th Jul 2008, 11:57 am

Quote:

Originally Posted by Marky P

Unfortunately I took the old one out before checking

.

I know it's easy to be wise after the evnt but... Next time, take some really good digital photos before you start. Would have helped with the valves too, maybe

Sideband · 26th Jul 2008, 2:12 pm

How about showing us the circuit? We can probably deduce from that which way the capacitors should go. It is possible for PCB's to be incorrectly marked.

Rich.

Marky P · 26th Jul 2008, 2:30 pm

Quote:

Originally Posted by Richard_Newman

How about showing us the circuit? We can probably deduce from that which way the capacitors should go. It is possible for PCB's to be incorrectly marked.

Rich.

Posted diagram in 'powered up wurlitzer' thread

.

Station X · 26th Jul 2008, 3:30 pm

Sorry Marky, but the quality of the diagram isn't good enough for me to identify component designations. I've tried "blowing it up", but to no avail. Members with beter eyesight than me may be able to assist.

Kat Manton · 26th Jul 2008, 3:34 pm

Hi,

Nope, it's far too low-resolution to be of any use.

If you have a restriction on size/resolution on your photo hosting (most do), zip a higher-res scan then use "Manage Attachments" to add the .zip file to your post and upload it to the forum. (The forum has a larger file-size limit for .zip files than images.) Ensure that it's possible to clearly read all component designations and values when zoomed in.

Cheers, Kat

Marky P · 26th Jul 2008, 4:50 pm

Posted zip file of schematic over at 'powered up my wurlitzer' thread

.

Kat Manton · 26th Jul 2008, 5:06 pm

Hi,

Thanks for uploading a good copy of the schematic

Correct polarity for both caps is with the +ve end connected to the PCB track leading to the cathode pin of the valve, the -ve end connected to the PCB track leading to the off-board wiring.

The reasoning behind this? The cathodes are shown as being at 10.5V and it's a reasonable to assume that anything connected to the 'aux' output may have a DC path to ground.

Regards, Kat

Marky P · 26th Jul 2008, 5:51 pm

Quote:

Originally Posted by Kat Manton

Hi,

Thanks for uploading a good copy of the schematic

Correct polarity for both caps is with the +ve end connected to the PCB track leading to the cathode pin of the valve, the -ve end connected to the PCB track leading to the off-board wiring.

The reasoning behind this? The cathodes are shown as being at 10.5V and it's a reasonable to assume that anything connected to the 'aux' output may have a DC path to ground.

Regards, Kat

So it looks like the markings on the board were right and the diagram (of the board, not the schematic) in the service manual is wrong. The manual shows four caps with the wrong polarity (+ going to ground) but the actual bourd is labelled correctly, so the caps I've installed are the right way round

.

Brian R Pateman · 26th Jul 2008, 6:00 pm

Now that the polarity of the capacitors has been sorted out it is probably time we closed this thread and continued discussion of this amplifier in this thread;

https://www.vintage-radio.net/forum/...ad.php?t=30699

which is where Marky has posted the relevant schematics.

Regards,

26th Jul 2008, 9:34 am	#1
Marky P Retired Dormant Member Join Date: Oct 2007 Location: St. Neots, Cambridgeshire, UK. Posts: 52	Correct polarity for capacitor in audio amp? At this very moment in time, I have a hot soldering iron andreplacing caps in my Wurlitzer jukebox amp. All is going swimmingly at the mo, but I've found what could be an error on the schemetic or the board. The board has + symbols on it to denote the cap polarity, but the schematic shows one of the caps with opposite polarity to the board. It's a stereo amp and there are two caps going to the 'Aux Amp' output. According to the board, the 'minus' of the cap goes to the 'aux amp'output, but the schematic shows one of these caps with the 'plus' going to the output. Surely both caps should be the same way round (one's left channel & one's right) so I'm assuming the schematic is wrong.

26th Jul 2008, 11:04 am	#2
TrevorM6TSE Heptode Join Date: May 2003 Location: Old Tupton, Derbyshire, UK. Posts: 539	Re: Correct polarity for capicitor in audio amp? I reckon you must be right. They'd have to be the same way round logic would say. But which way is right I'm not sure! I would say the signal should go from + to - but I may well be wrong. __________________ I'd just like to say "Good luck, we're all counting on you"

26th Jul 2008, 11:12 am	#3
mikelect Retired Dormant Member Join Date: Sep 2003 Location: Wrexham, North Wales, UK. Posts: 799	Re: Correct polarity for capicitor in audio amp? Common sense dictates it should be fitted the same way as the original Mike

26th Jul 2008, 2:12 pm	#6
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,567	Re: Correct polarity for capicitor in audio amp? How about showing us the circuit? We can probably deduce from that which way the capacitors should go. It is possible for PCB's to be incorrectly marked. Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

26th Jul 2008, 3:30 pm	#8
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Correct polarity for capicitor in audio amp? Sorry Marky, but the quality of the diagram isn't good enough for me to identify component designations. I've tried "blowing it up", but to no avail. Members with beter eyesight than me may be able to assist. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

26th Jul 2008, 3:34 pm	#9
Kat Manton Retired Dormant Member Join Date: Jul 2005 Location: West Yorkshire, UK. Posts: 1,700	Re: Correct polarity for capicitor in audio amp? Hi, Nope, it's far too low-resolution to be of any use. If you have a restriction on size/resolution on your photo hosting (most do), zip a higher-res scan then use "Manage Attachments" to add the .zip file to your post and upload it to the forum. (The forum has a larger file-size limit for .zip files than images.) Ensure that it's possible to clearly read all component designations and values when zoomed in. Cheers, Kat

26th Jul 2008, 4:50 pm	#10
Marky P Retired Dormant Member Join Date: Oct 2007 Location: St. Neots, Cambridgeshire, UK. Posts: 52	Re: Correct polarity for capicitor in audio amp? Posted zip file of schematic over at 'powered up my wurlitzer' thread.

26th Jul 2008, 5:06 pm	#11
Kat Manton Retired Dormant Member Join Date: Jul 2005 Location: West Yorkshire, UK. Posts: 1,700	Re: Correct polarity for capicitor in audio amp? Hi, Thanks for uploading a good copy of the schematic Correct polarity for both caps is with the +ve end connected to the PCB track leading to the cathode pin of the valve, the -ve end connected to the PCB track leading to the off-board wiring. The reasoning behind this? The cathodes are shown as being at 10.5V and it's a reasonable to assume that anything connected to the 'aux' output may have a DC path to ground. Regards, Kat

26th Jul 2008, 6:00 pm	#13
Brian R Pateman Nonode Join Date: Jun 2005 Location: Western Lake District, Cumbria (CA20) - UK Posts: 2,136	Re: Correct polarity for capicitor in audio amp? Now that the polarity of the capacitors has been sorted out it is probably time we closed this thread and continued discussion of this amplifier in this thread; https://www.vintage-radio.net/forum/...ad.php?t=30699 which is where Marky has posted the relevant schematics. Regards, __________________ Brian