Smoothing cap value suggestions.. - UK Vintage Radio Repair and Restoration Discussion Forum

kentplums · 23rd Aug 2018, 3:42 pm

Hi
This is off a Mikson "Regence" about which there is little info.
Valve line up is EZ80 6BM5 6AV6 6BA6 ECH81 and EM3 magic eye.
Having replaced audio coupling cap I fired it up with a dim bulb tester, which showed a very dull glow indicating nothing horrendous, but also an aggressive buzz/hum started as soon as the set warmed up.
The nearest schematic I can find is this

https://www.doctsf.com/documents/aff...4642&num_fic=1

although the Mikson has a normal wavechanger.
The smoothing caps on the schematic show 32µf each, although the double can pictured has something illegible then +16µf . Maybe 24 is visible?

The cap has 3 wires: dark red going to pin 3 EZ80
blue going to TX then chassis
brown going to TX then pin 6 6BM5

Any suggestions please,
Thanks
R

HamishBoxer · 23rd Aug 2018, 4:02 pm

It looks like 24uF, certainly try a 22uF 400V though if the EZ80 is meant to have 32uF then perhaps as per the circuit (32 x32).

Station X · 23rd Aug 2018, 4:13 pm

Max value reservoir cap for an EZ80 is specified as 50uF.

kentplums · 23rd Aug 2018, 4:18 pm

This is identical apart from the badge.

https://www.doctsf.com/grandlivre/fi...f=13506&ori=ps

Apparently schematics are available but I can't find them!

R

kentplums · 23rd Aug 2018, 4:21 pm

Thanks for the replies.
50µf max does give some leeway!
If replacing with two separate electrolytics, the negatives would go to where?

Nuvistor · 23rd Aug 2018, 4:25 pm

Quote:

Originally Posted by Station X

Max value reservoir cap for an EZ80 is specified as 50uF.

With a 300 ohm surge limiter, usually the transformer winding resistance.

Station X · 23rd Aug 2018, 4:55 pm

Quote:

Originally Posted by kentplums

If replacing with two separate electrolytics, the negatives would go to where?

Chassis.

The other two wires go to the cathode of the EZ80 and Grid 2 of the 6BM5.

kentplums · 23rd Aug 2018, 5:03 pm

Thanks
I have two 33µf s which should fit the bill
R

Sideband · 23rd Aug 2018, 5:53 pm

Quote:

Originally Posted by kentplums

If replacing with two separate electrolytics, the negatives would go to where?

The blue lead on the original is obviously the common negative, so the negative of both caps should connect where the blue wire goes. The positives as stated above.

kentplums · 23rd Aug 2018, 5:57 pm

Thanks!
R

kentplums · 24th Aug 2018, 4:10 pm

Well, changing the two electrolytics certainly cleared up that buzz, in fact it appears to be quite a powerful little radio.
Two things bother me slightly. Firstly the chassis, the wave changer and the volume all seem to have some voltage present as does the antenna wire. *
Secondly the wave changer changes in the wrong order ie PU is in the middle rather than at one end.
Anything to worry about?

*Actually I just rechecked to measure any voltage and it appears to have disappeared. Something breaking down perhaps? The big red resistor (marked 1800, 2.2kOhm on the schematic) between 6BM5 and the EZ80 appears to get warm, and is a bit discoloured incidentaly

R

23rd Aug 2018, 3:42 pm	#1
kentplums Hexode Join Date: Nov 2012 Location: Limoges, Haute-Vienne, France. Posts: 280	Smoothing cap value suggestions.. Hi This is off a Mikson "Regence" about which there is little info. Valve line up is EZ80 6BM5 6AV6 6BA6 ECH81 and EM3 magic eye. Having replaced audio coupling cap I fired it up with a dim bulb tester, which showed a very dull glow indicating nothing horrendous, but also an aggressive buzz/hum started as soon as the set warmed up. The nearest schematic I can find is this https://www.doctsf.com/documents/aff...4642&num_fic=1 although the Mikson has a normal wavechanger. The smoothing caps on the schematic show 32µf each, although the double can pictured has something illegible then +16µf . Maybe 24 is visible? The cap has 3 wires: dark red going to pin 3 EZ80 blue going to TX then chassis brown going to TX then pin 6 6BM5 Any suggestions please, Thanks R Attached Thumbnails Last edited by kentplums; 23rd Aug 2018 at 3:44 pm. Reason: spelling

23rd Aug 2018, 4:02 pm	#2
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: Smoothing cap value suggestions.. It looks like 24uF, certainly try a 22uF 400V though if the EZ80 is meant to have 32uF then perhaps as per the circuit (32 x32). __________________ G8JET BVWS Archivist and Member V.M.A.R.S

23rd Aug 2018, 4:13 pm	#3
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Smoothing cap value suggestions.. Max value reservoir cap for an EZ80 is specified as 50uF. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

23rd Aug 2018, 4:18 pm	#4
kentplums Hexode Join Date: Nov 2012 Location: Limoges, Haute-Vienne, France. Posts: 280	Re: Smoothing cap value suggestions.. This is identical apart from the badge. https://www.doctsf.com/grandlivre/fi...f=13506&ori=ps Apparently schematics are available but I can't find them! R

23rd Aug 2018, 4:21 pm	#5
kentplums Hexode Join Date: Nov 2012 Location: Limoges, Haute-Vienne, France. Posts: 280	Re: Smoothing cap value suggestions.. Thanks for the replies. 50µf max does give some leeway! If replacing with two separate electrolytics, the negatives would go to where?

23rd Aug 2018, 5:03 pm	#8
kentplums Hexode Join Date: Nov 2012 Location: Limoges, Haute-Vienne, France. Posts: 280	Re: Smoothing cap value suggestions.. Thanks I have two 33µf s which should fit the bill R

23rd Aug 2018, 5:57 pm	#10
kentplums Hexode Join Date: Nov 2012 Location: Limoges, Haute-Vienne, France. Posts: 280	Re: Smoothing cap value suggestions.. Thanks! R

24th Aug 2018, 4:10 pm	#11
kentplums Hexode Join Date: Nov 2012 Location: Limoges, Haute-Vienne, France. Posts: 280	Re: Smoothing cap value suggestions.. Well, changing the two electrolytics certainly cleared up that buzz, in fact it appears to be quite a powerful little radio. Two things bother me slightly. Firstly the chassis, the wave changer and the volume all seem to have some voltage present as does the antenna wire. * Secondly the wave changer changes in the wrong order ie PU is in the middle rather than at one end. Anything to worry about? *Actually I just rechecked to measure any voltage and it appears to have disappeared. Something breaking down perhaps? The big red resistor (marked 1800, 2.2kOhm on the schematic) between 6BM5 and the EZ80 appears to get warm, and is a bit discoloured incidentaly R