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 > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Reply
 
Thread Tools
Old 11th Apr 2019, 8:16 am   #1
Levente
Pentode
 
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 176
Default DC filament / capacitor

Hey Guys,

Just a quick question...please enlighten me for learning purposes...

on the attachment am I seeing correctly that the filament is AC ? I am confused...isn't suppose to be DC with some filter cap's?

Please help as I am getting confused here...

Thank you !
Attached Thumbnails
Click image for larger version

Name:	filament dc.JPG
Views:	190
Size:	98.4 KB
ID:	181197  
Levente is offline   Reply With Quote
Old 11th Apr 2019, 8:36 am   #2
Cobaltblue
Dekatron
 
Cobaltblue's Avatar
 
Join Date: Dec 2010
Location: Exeter and Poole, UK.
Posts: 3,070
Default Re: Dc filament / capacitor

Hi

The filaments are AC that capacitor arrowed is part of the HT (DC) circuit.

The snip shows the filament supply

Cheers

Mike T
Attached Thumbnails
Click image for larger version

Name:	Fils.JPG
Views:	46
Size:	24.5 KB
ID:	181198  
__________________
Don't care if it was a bargain why's it in my kitchen
Mike T BVWS member.
www.cossor.co.uk
Cobaltblue is online now   Reply With Quote
Old 11th Apr 2019, 8:39 am   #3
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 4,841
Default Re: Dc filament / capacitor

It's a voltage doubler rectifier creating DC for HT, with the heaters powered directly from the transformer (so yes, running on AC).

These valves are indirectly heated, so are designed to run on AC. Directly heated valves are often restricted to DC only on the filaments (as for battery valve receivers) but can also be AC (eg 2A3 output triode; DY81 rectifier).
kalee20 is offline   Reply With Quote
Old 11th Apr 2019, 8:40 am   #4
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 5,152
Default Re: Dc filament / capacitor

The arrow on your diagram is pointing to a filter capacitor in a voltage doubler circuit. The voltage doubler is in turn supplying 272V DC to the rest of the set.

The filaments (heaters) of the valves (6AL5, 6CG7, 6BC8) and the pilot lamp (PL 1) are being fed from a separate AC supply as normal.
__________________
On Spike Milligan's headstone......I told you I was ill...
Sideband is online now   Reply With Quote
Old 11th Apr 2019, 8:44 am   #5
Levente
Pentode
 
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 176
Default Re: Dc filament / capacitor

whooo thanks guys!

So this is the power stage of an Altec schematic where someone advised to put a 4700uf 16V or better capacitor for DC filament supply....that's where my confusion came from looking at the schematic's...
Levente is offline   Reply With Quote
Old 11th Apr 2019, 10:32 am   #6
AC/HL
Moderator
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 7,012
Default Re: DC filament / capacitor

At a glance it does look like there is a connection between the heater supply and the HT supply, but it's just the way the circuit has been drawn.
__________________
Bill, BVWS member
AC/HL is offline   Reply With Quote
Old 11th Apr 2019, 10:56 am   #7
Levente
Pentode
 
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 176
Default Re: DC filament / capacitor

...thanks guys...in the meantime reading through the modification suggestion, found out where the 4700uf DC filter cap was recommended to go together with a diode...

not sure why or what this will do...i am getting way confused on that

attached it....point number 10.
Attached Thumbnails
Click image for larger version

Name:	diode.jpg
Views:	72
Size:	32.4 KB
ID:	181200  
Levente is offline   Reply With Quote
Old 11th Apr 2019, 10:59 am   #8
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 12,983
Default Re: DC filament / capacitor

There is a connection, but since it's to chassis/ground/0V for HT- and heater CT it has no effect on the way the circuit works. That's not to say it isn't an unusual circuit- I wonder why a suitable voltage winding wasn't specified on the transformer and a conventional circuit used? It would have been cheaper.

The capacitor and dc heater suggestion sounds incomplete and misleading. Dc heaters in the front end of an amp can reduce hum but there will need to be a suitable rectifier and attention paid to getting the right dc voltage as well as just a capacitor.

The circuit shown here is already good in respect of heater hum since it has the heater ac supply balanced to HT-/ground by the centre tapped winding on the transformer.
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O

Last edited by Herald1360; 11th Apr 2019 at 11:07 am.
Herald1360 is online now   Reply With Quote
Old 11th Apr 2019, 11:20 am   #9
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 14,428
Default Re: DC filament / capacitor

Quote:
Originally Posted by Levente View Post
...thanks guys...in the meantime reading through the modification suggestion, found out where the 4700uf DC filter cap was recommended to go together with a diode...

not sure why or what this will do...i am getting way confused on that

attached it....point number 10.
This looks like a modification to run some or all of the heaters on DC. It depends on the way the set is physically wired. There may be more than one wire on pin 4 or the commoning point could be elsewhere.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now   Reply With Quote
Old 11th Apr 2019, 11:34 am   #10
Levente
Pentode
 
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 176
Default Re: DC filament / capacitor

Thanks Guys

yes it is definitely a modification and I was lost on that part at the DC and the diode on pin 4 at 6AL5.

Attached the full modification instruction...maybe you will get some good use to it...someone did write this up in 1991. The rest of mod's are really cool but still not getting the mod at the 6AL5...

have a look at the attachment...great stuff there !
Attached Thumbnails
Click image for larger version

Name:	0005.jpg
Views:	34
Size:	82.3 KB
ID:	181208   Click image for larger version

Name:	0006.jpg
Views:	25
Size:	72.9 KB
ID:	181209   Click image for larger version

Name:	0007.jpg
Views:	23
Size:	77.3 KB
ID:	181210   Click image for larger version

Name:	0008.jpg
Views:	22
Size:	65.0 KB
ID:	181211  

Last edited by Levente; 11th Apr 2019 at 11:43 am. Reason: no attachement
Levente is offline   Reply With Quote
Old 11th Apr 2019, 11:46 am   #11
Levente
Pentode
 
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 176
Default Re: DC filament / capacitor

following the previous post, the full schematic attached
Attached Thumbnails
Click image for larger version

Name:	0004.jpg
Views:	84
Size:	77.4 KB
ID:	181212  
Levente is offline   Reply With Quote
Old 11th Apr 2019, 12:32 pm   #12
G8HQP Dave
Dekatron
 
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,691
Default Re: DC filament / capacitor

That will provide a somewhat rough DC heater supply. About 1.2V pk-pk ripple, plus switching transients, and about 7.5V DC so overrunning the heater. The likely outcome is a slightly shorter life for the 6AL5/EB91 and replacement of some 50Hz hum by buzz.
G8HQP Dave is online now   Reply With Quote
Old 11th Apr 2019, 12:41 pm   #13
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 4,841
Default Re: DC filament / capacitor

Quote:
Originally Posted by Levente View Post
...thanks guys...in the meantime reading through the modification suggestion, found out where the 4700uf DC filter cap was recommended to go together with a diode...

not sure why or what this will do...i am getting way confused on that

attached it....point number 10.
This worries me, first, no indication of which way round to connect the diode and which way round to connect the (polarised) capacitor, the chance is 50:50 that wit will work or blow up; secondly the heaters are pins 3 and 4 of the 6AL5 not 4 and 5, with neither heater pin at chassis potential it is unlikely that pin 5 (a cathode) is commoned with a heater; and last, the heater will be a bit over-run, as others have already pointed out!
kalee20 is offline   Reply With Quote
Old 11th Apr 2019, 2:14 pm   #14
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 5,152
Default Re: DC filament / capacitor

Best advice is to forget the so-called 'mod'!!
__________________
On Spike Milligan's headstone......I told you I was ill...
Sideband is online now   Reply With Quote
Old 11th Apr 2019, 2:23 pm   #15
Levente
Pentode
 
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 176
Default Re: DC filament / capacitor

too right !!!

just wanted to understand the thinking of that person who decided to do this on this old unit...

Last edited by Levente; 11th Apr 2019 at 2:23 pm. Reason: missing
Levente is offline   Reply With Quote
Old 12th Apr 2019, 10:17 am   #16
G8HQP Dave
Dekatron
 
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,691
Default Re: DC filament / capacitor

I sometimes remind people that in order to genuinely improve a circuit you first have to understand it even better than the original designer. Sadly, many 'upgrades' found on the internet come from people whose understanding is significantly less than the original designer. What they lack in knowledge they make up for in misplaced confidence.
G8HQP Dave is online now   Reply With Quote
Old 13th Apr 2019, 8:36 pm   #17
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 12,983
Default Re: DC filament / capacitor

Not necessarily- though good understanding may explain perhaps what cost constraints may have been imposed on the original design that made it less than ideal. Unconstrained by these limits, a less competent designer may well "improve" a circuit or at least some aspect of its performance.
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is online now   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 11:05 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 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.