UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Audio (record players, hi-fi etc)

Notices

Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

Reply
 
Thread Tools
Old 2nd Aug 2020, 6:17 am   #1
magician
Diode
 
Join Date: Dec 2019
Location: Darwin, Northern Territory, Australia
Posts: 5
Default Capacitor and Output Transformer question for valve amplifier. Philips EV4437a

I recently purchased a Philips EV4437a tube amplifier. I have a couple of questions.

I want to replace the capacitors however I want to make sure I get the correct types.
There is a 16uF/450vdc capacitor however it has 3 connections at the bottom so would this be a dual 16uF/450vdc capacitor?

There are also some smaller metal can type capacitors and I'm not sure if they are electrolytic or not and what style of modern capacitor would be a good replacement?

In regards to the output transformer, I have tested it with just my multi-meter and it looks to be good however, I did get continuity between 2 of the secondary wires and ground. I believe it is the secondary that shows a direct connection to ground on the schematic so this should be normal for both wires right?

Thanks in advance (pictures attached)
Attached Thumbnails
Click image for larger version

Name:	20200802_085930.jpg
Views:	113
Size:	34.5 KB
ID:	212435   Click image for larger version

Name:	20200802_131309.jpg
Views:	111
Size:	51.9 KB
ID:	212436   Click image for larger version

Name:	20200801_132144.jpg
Views:	111
Size:	64.5 KB
ID:	212437   Click image for larger version

Name:	20200702_120334.jpg
Views:	112
Size:	65.2 KB
ID:	212438  
magician is offline   Reply With Quote
Old 2nd Aug 2020, 1:22 pm   #2
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 16,570
Default Re: Capacitor and Output Transformer question for valve amplifier

Hello and welcome to the forums.

As a general rule, in an amp of this age, any capacitor with a capacitance of 1uF or more will be an electrolytic type.

In the case of can capacitors writing on the can will show whether it is a single, twin or triple type and identify the connections. Is there writing on the can which is not visible in your picture? This amp uses two triple capacitors with the sections connected in parallel and the cap could be one of those.

If you are testing the transformer in circuit you'll need to allow for any connections to chassis when interpreting your readings.

A better circuit diagram along with under chassis pictures is available here:-

https://www.radiomuseum.org/r/philip...a_ev4437a.html
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 2nd Aug 2020, 1:25 pm   #3
snowman_al
Heptode
 
snowman_al's Avatar
 
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 502
Default Re: Capacitor and Output Transformer question for valve amplifier

As no one else has jumped in here is my 2 pence worth.

Quote:
Originally Posted by magician View Post
... I want to replace the capacitors however I want to make sure I get the correct types.
There is a 16uF/450vdc capacitor however it has 3 connections at the bottom so would this be a dual 16uF/450vdc capacitor?
That looks to be a single 16uF cap. Highlighted in red on the schematic. I suspect the two out side terminals are joined and are -ve, with the centre being +ve.

Quote:
Originally Posted by magician View Post
... There are also some smaller metal can type capacitors and I'm not sure if they are electrolytic or not and what style of modern capacitor would be a good replacement?
That does not look like an electrolytic, better picture of the underside would help tell which are what types. Critical are the ones in green circles. The ubiquitous yellow poly types are fine 0.1uF (10nF) and 0.22uF (22nF) at 630 volts.

Quote:
Originally Posted by magician View Post
... In regards to the output transformer, I have tested it with just my multi-meter and it looks to be good however, I did get continuity between 2 of the secondary wires and ground. I believe it is the secondary that shows a direct connection to ground on the schematic so this should be normal for both wires right?
Correct, that is a feedback winding.

Look at this site for more info maybe? https://www.guitargear.net.au/discus...?topic=38959.0
Attached Thumbnails
Click image for larger version

Name:	EV4437A schematic.jpg
Views:	74
Size:	70.8 KB
ID:	212448  
__________________
Never Leave Well Enough Alone...
snowman_al is offline   Reply With Quote
Old 3rd Aug 2020, 3:07 am   #4
magician
Diode
 
Join Date: Dec 2019
Location: Darwin, Northern Territory, Australia
Posts: 5
Default Re: Capacitor and Output Transformer question for valve amplifier. Philips EV4437a

Thank you for the replies.

The small metal can type capacitors are 0.2uF, 0.3uF, and the 3rd is unreadable so I'll assume they are non-electrolytic.

In regards to the 16uf/450vdc, I have attached a close up with one of the outside leads is obvious negative and the other outside lead connects to the negative of another capacitor so safe to assume you are correct? Any special way to connect the new cap since it will only have 1 negative lead?

I'm planning on replacing the wax paper caps and small metal caps with polyesters. One of the wax paper caps is 0.056 uF, is it okay to replace with a 0.05 polyester?

Thanks
Attached Thumbnails
Click image for larger version

Name:	20200803_105500.jpg
Views:	46
Size:	52.4 KB
ID:	212530  
magician is offline   Reply With Quote
Old 3rd Aug 2020, 7:18 am   #5
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 5,357
Default Re: Capacitor and Output Transformer question for valve amplifier. Philips EV4437a

Finding out what's what on vintage amps can be tricky as there's a good chance someone might have had a go at fixing it before you got it. They may have got things wrong or made connections not original to the circuit. Example, someones put bleeder resistors across some of those caps, so don't assume the caps that are in it are original or the right ones.

This is a challenging amp to recap for a relative beginner, changing a few caps might be more than is needed, you'll need to go through and check resistors too and lord knows what else.

To find what bits correspond to the schematic you'll have to patiently go through with a meter and figure things out, it can be very confusing until you have more experience. my advice is to go slowly with this amp, it's an excellent example of Philips design.

I'm making assumptions here about your experience, no disrespect intended, Andy.

PS a lot more good quality pics of the whole amp especially the underside wiring will help us, help you.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline   Reply With Quote
Old 3rd Aug 2020, 10:08 am   #6
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 16,570
Default Re: Capacitor and Output Transformer question for valve amplifier. Philips EV4437a

The capacitor shown in post #4 is C1 a single 16uF unit.

You can see the two 270k anode load resistors for V1, a double triode, connected to the centre tag, so that's obviously the positive connection.

You're going to have to trace the wiring to the other tags to show what the other connections are.

Is the other resistor I can see 1k? It's always difficult reading colour codes from pictures.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 3rd Aug 2020, 10:15 am   #7
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 16,570
Default Re: Capacitor and Output Transformer question for valve amplifier. Philips EV4437a

OK.

The bottom tag has C2 50uF and R2 1k connected to it, so it's a chassis or negative connection.

I can't help you with the top tag because I can't see where the wire connected to it goes to. However, given that the wire is bare, chances are it's connected to the chassis, making this a second negative tag. Don't take my word for it though, check it.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 5th Aug 2020, 2:58 pm   #8
magician
Diode
 
Join Date: Dec 2019
Location: Darwin, Northern Territory, Australia
Posts: 5
Default Re: Capacitor and Output Transformer question for valve amplifier. Philips EV4437a

Thanks for all the reply's/advice. I will go through it and test all capacitors/resistors.

Can anybody give me more information on what looks like a ceramic disc capacitor? It reads .015/2kvw.

I'm assuming the .015 is uF?

Thanks
Attached Thumbnails
Click image for larger version

Name:	20200805_224630.jpg
Views:	38
Size:	73.3 KB
ID:	212758  
magician is offline   Reply With Quote
Old 5th Aug 2020, 3:26 pm   #9
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 16,570
Default Re: Capacitor and Output Transformer question for valve amplifier. Philips EV4437a

0.015uF seems likely. At the time this amp was made only uF and pF were in common use and 0.015pF is a ridiculously small value.

Where's it connected to? Try to identify it on the circuit diagram.

BTW. It's highly unlikely to be faulty.

If you must replace caps concentrate on the cylindrical ones.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is offline   Reply With Quote
Old 5th Aug 2020, 6:52 pm   #10
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 5,357
Default Re: Capacitor and Output Transformer question for valve amplifier. Philips EV4437a

Rather than just change all capacitors on mass it's a good idea to change one at a time lest you introduce a fault. If you change the lot in one go it's could be difficult to then go back and find a fault as you have made numerous changes instead of one change.. With an amp of this age the only caps that will probably need replacing are the electrolytics - the big round ones, and the coupling capacitors. These last are important because if they're leaky, electrically speaking that is, they could put a positive voltage on valve grids, this means that damage could result.

Before powering it up for the first time it would be good idea to build yourself a simple lamp limiter, there is plenty of info on this forum if you put "lamp limiter" in the search box. Plans and instructions to make one here - http://www.vintage-radio.com/projects/lamp-limiter.html & here - file:///tmp/mozilla_andy0/Instructable%20-%20Assembling%20a%20series%20lamp%20limiter.pdf A lamp limiter will indicate if you have a fault and will prevent damage to the amp.

If you take it slowly and carefully and check the circuit beforehand it should save trouble later. Andy,.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline   Reply With Quote
Old 5th Aug 2020, 9:12 pm   #11
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 6,100
Default Re: Capacitor and Output Transformer question for valve amplifier. Philips EV4437a

Hi, it looks as if it is fitted from a fuseholder to the chassis. If so it is for suppression and should now be replaced with a Class Y capacitor of similar value for continued safety

Ed
Ed_Dinning is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 6:01 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.