AC/DC radios' electrolytic filter can caps. - UK Vintage Radio Repair and Restoration Discussion Forum

lin3coln · 23rd Aug 2015, 11:42 pm

When a 60 year old AC/DC valve radio will ONLY be used with batteries, is there any need to replace the electrolytics in the filter cans?

paulsherwin · 24th Aug 2015, 12:08 am

You don't need to replace them, but you do need to disconnect them.

Refugee · 24th Aug 2015, 12:39 am

Surely would the audio amplifier oscillate if there is no filter at all.
The value could possibly be reduced for use on batteries only though.

ms660 · 24th Aug 2015, 9:00 am

Most DC only battery valved radios have an electrolytic decoupling the HT rail.

Lawrence.

lin3coln · 24th Aug 2015, 11:24 am

The first can has 3 filter caps and appear to be disconnected when the power supply switch is set to DC. The second can has: a 200ohm, connects with output amp valve filament pin, the 40ohm connects to the B+ bus, so perhaps these must be in working fettle!

Francois

G6Tanuki · 24th Aug 2015, 11:53 am

Some of these radios used a resistor in the negative HT line [between chassis/the filaments and the HT supply -ve] to provide bias - this resistor needs to be bypassed by a suitable-value electrolytic (25uF 25V was popular) or some very strange things can happen (motor-boating, audio getting superimposed on the AGC line, local-oscillator changing frequency with audio volume).

paulsherwin · 24th Aug 2015, 11:55 am

I was referring to the reservoir and smoothing electrolytics in the mains power supply. If these are disconnected by the battery/mains switching then there is no need to disconnect them.

Other electrolytics should be reformed or replaced as appropriate, but they may still be in good working condition.

ms660 · 24th Aug 2015, 11:56 am

A make, model/schematic might help.

Lawrence.

lin3coln · 24th Aug 2015, 2:16 pm

1948 Zenith 8G005TZ1 Transoceanic. Shall be replacing most/all paper caps and reform or replace 2nd cans' caps first, and see what happens then!

Thanks for all comments so far.

ms660 · 24th Aug 2015, 4:21 pm

Can't find the 8G005TZ1 schematic at the moment but found the 8G005YT, it might be similar?

In that one, one of the filter capacitors appears to be connected when used on batteries (C34...40uf)

http://www.staff.science.uu.nl/~tel0...cu/8g005z1.pdf

Lawrence.

ms660 · 24th Aug 2015, 5:18 pm

A link to the Riders schematics/data for the 8G005 series for anyone that's interested:

http://www.nostalgiaair.org/pagesbym...1/M0025421.pdf

Lawrence.

lin3coln · 25th Aug 2015, 5:28 am

Thank you for the links, shall be useful as soon as the ordered caps arrive and C34 is essential for the set to work on either power source as all mention.

Francois.

23rd Aug 2015, 11:42 pm	#1
lin3coln Retired Dormant Member Join Date: Feb 2015 Location: Mahebourg, Mauritius Posts: 4	AC/DC radios' electrolytic filter can caps. When a 60 year old AC/DC valve radio will ONLY be used with batteries, is there any need to replace the electrolytics in the filter cans?

24th Aug 2015, 12:08 am	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,970	Re: AC/DC radios' electrolytic filter can caps. You don't need to replace them, but you do need to disconnect them.

24th Aug 2015, 12:39 am	#3
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: AC/DC radios' electrolytic filter can caps. Surely would the audio amplifier oscillate if there is no filter at all. The value could possibly be reduced for use on batteries only though.

24th Aug 2015, 9:00 am	#4
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: AC/DC radios' electrolytic filter can caps. Most DC only battery valved radios have an electrolytic decoupling the HT rail. Lawrence.

24th Aug 2015, 11:24 am	#5
lin3coln Retired Dormant Member Join Date: Feb 2015 Location: Mahebourg, Mauritius Posts: 4	Re: AC/DC radios' electrolytic filter can caps. The first can has 3 filter caps and appear to be disconnected when the power supply switch is set to DC. The second can has: a 200ohm, connects with output amp valve filament pin, the 40ohm connects to the B+ bus, so perhaps these must be in working fettle! Francois

24th Aug 2015, 11:53 am	#6
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: AC/DC radios' electrolytic filter can caps. Some of these radios used a resistor in the negative HT line [between chassis/the filaments and the HT supply -ve] to provide bias - this resistor needs to be bypassed by a suitable-value electrolytic (25uF 25V was popular) or some very strange things can happen (motor-boating, audio getting superimposed on the AGC line, local-oscillator changing frequency with audio volume).

24th Aug 2015, 11:55 am	#7
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,970	Re: AC/DC radios' electrolytic filter can caps. I was referring to the reservoir and smoothing electrolytics in the mains power supply. If these are disconnected by the battery/mains switching then there is no need to disconnect them. Other electrolytics should be reformed or replaced as appropriate, but they may still be in good working condition.

24th Aug 2015, 11:56 am	#8
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: AC/DC radios' electrolytic filter can caps. A make, model/schematic might help. Lawrence.

24th Aug 2015, 2:16 pm	#9
lin3coln Retired Dormant Member Join Date: Feb 2015 Location: Mahebourg, Mauritius Posts: 4	Re: AC/DC radios' electrolytic filter can caps. 1948 Zenith 8G005TZ1 Transoceanic. Shall be replacing most/all paper caps and reform or replace 2nd cans' caps first, and see what happens then! Thanks for all comments so far.

24th Aug 2015, 4:21 pm	#10
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: AC/DC radios' electrolytic filter can caps. Can't find the 8G005TZ1 schematic at the moment but found the 8G005YT, it might be similar? In that one, one of the filter capacitors appears to be connected when used on batteries (C34...40uf) http://www.staff.science.uu.nl/~tel0...cu/8g005z1.pdf Lawrence.

24th Aug 2015, 5:18 pm	#11
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: AC/DC radios' electrolytic filter can caps. A link to the Riders schematics/data for the 8G005 series for anyone that's interested: http://www.nostalgiaair.org/pagesbym...1/M0025421.pdf Lawrence.

25th Aug 2015, 5:28 am	#12
lin3coln Retired Dormant Member Join Date: Feb 2015 Location: Mahebourg, Mauritius Posts: 4	Re: AC/DC radios' electrolytic filter can caps. Thank you for the links, shall be useful as soon as the ordered caps arrive and C34 is essential for the set to work on either power source as all mention. Francois.