BC-348-0 Help Please - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

ms660 · 17th Dec 2016, 1:45 pm

Yes, tag 12 on board 271 so far as I can make out.

EL84? Thought it was a 41 now or haven't you fitted it yet?

Lawrence.

wlindsay1984 · 17th Dec 2016, 1:53 pm

Thanks Lawrence, I had retrofitted the 41 to the EL84 socket with wires, after soldering them lightly to the 41 valve. Just a matter of pulling them out and placing the EL84 back in. Fingers crossed, will try and fire it up within the next hour and update. Here is a pic of the rewiring of the unit so far, I have just added the cap and resistor. Will

wlindsay1984 · 17th Dec 2016, 2:00 pm

I also forgot to add, before starting from scratch, this 0.1 mfd 350vdc capacitor was somewhere within the "tube shelf" in the pic above. Any ideas? Pic attached. Thanks

ms660 · 17th Dec 2016, 2:06 pm

Don't understand what you mean by "tube shelf" ?

Lawrence.

wlindsay1984 · 17th Dec 2016, 2:25 pm

Sorry Lawrence, the location below the resistor boards, where vt48, vt 70 are mounted etc.. It was somewhere in there but I can't remember where.

WB6NVH-GEOFF · 18th Dec 2016, 8:02 pm

All of the BC-348 manuals have "practical wiring diagrams" which show the physical wiring and component layout, it should be easy to find what goes where by referring to them. And I believe there are some excellent scans of these manuals on the web.

We call the "tube shelf" the subchassis behind the front panel on the right side that has the tubes [valves] mounted on it and which has the underside accessible by removing that plate on the front panel.

Which made me think of a trivia question - - how many other communications receivers made in the USA or UK had part of the front panel removable to access components? I can't immediately think of any. Notice I said USA and UK as I think some Axis and maybe Russian sets did.

ms660 · 18th Dec 2016, 8:08 pm

Cheers for the explanation.

Can't think off hand of any more receivers with a small removable front panel for access, only the T1154 transmitter (companion to the R1155 receiver)

Lawrence.

ms660 · 18th Dec 2016, 8:23 pm

Whoops...Forgot the R1082, made by STC, front sub panel removable for tube/valve replacement:

https://www.pa3esy.nl/military/gb/ai.../r1082-set.htm

Lawrence

M0SOE_Bruce · 19th Dec 2016, 8:14 am

Looking at the parts list there is no listing for a 0.1@350V capacitor. It must be part of the mods that were done.

The best manual I found was here: http://www.jamminpower.com/main/bc348.html

The manual AN 1-40BC224-3 gives very good pictorials. If you are going to use the 41 valve as was original you'll need a bias circuit for it.

wlindsay1984 · 2nd Jan 2017, 1:46 pm

Hello Folks

Still working on the radio, I tried to use the original transformer that was with the radio, it appears to be from the 1950's, as are some of the other components, one of the capacitors were dated 1955. It was assembled in the manner that was specified in one of the early conversion magazines, with a 5Z4 rectifier. The transformer appears to have seen better days, and is blackened/damaged. So I am starting from scratch, using the HP Friedrichs schematic, as mentioned by another user. I have all of the components except the transformer and filter choke, which I am going to purchase today, the only thing I am having issues with is the Filter Choke. HP Friedrichs mentions that he used one that measured almost 2H, the schematic specifies a 2H Choke, but does not specify what DC current it puts out. There are a number of 2H Filter Chokes, with differing DC outputs, any help for what you think I need would be much appreciated. Many Thanks.

http://www.hpfriedrichs.com/radioroo.../pwrscheme.jpg

The Attached Link shows the Schematic

ms660 · 2nd Jan 2017, 2:04 pm

50 or 60mA or greater should be no problem, wouldn't go below 50mA.

EDIT: But if you're running it with an EL84 output valve then go for 100mA.

Lawrence.

wlindsay1984 · 2nd Jan 2017, 3:24 pm

Many Thanks Lawrence for all of your help. I have just placed the order. Should be able to get working on it this coming weekend. There has been plenty of times where I have just felt like giving up on it, but I keep going back to it, I feel like I am almost there. I think the old transformer was not putting out its full voltage, the voltage regulator bulb, on the "tube shelf", which is accessed from the front, would half light up, dim, and then die off, along with the transformer bubbling etc and over heating at that point, the windings were charred, the longer it was on, the less power it seemed to give out. Fingers crossed for the new equipment.

ms660 · 2nd Jan 2017, 3:37 pm

Before you power up, with the PSU connected to the receiver check for HT shorts in the receiver, test meter set to measure high value resistance, one probe to chassis and the other to the HT in from your new power supply, it should read very high or infinity.

Lawrence.

TrevorG3VLF · 2nd Jan 2017, 8:53 pm

The transformer may not be quite dead.
Did the reservoir and smoother capacitors get warm?

wlindsay1984 · 3rd Jan 2017, 1:36 pm

Pic of transformer, I made the mounting board to the chassis, using tufnal, a sort of insulation board, it was from a usaaf dump site here, along with many other wartime components that I regularly find, so it has an additional wartime component.

wlindsay1984 · 6th Jan 2017, 5:04 pm

Hello folks, if anyone would like the original power supply components for The price of the postage you can have them, maybe you could do something with them?. There is the transformer as pictured, a choke, a dubilier drillitic capacitor 16 + 8mfd, and a 5z4 rectifier. The transformer seems to be damaged but maybe someone might have the patience and skill to rewind it.

FrankB · 26th Jan 2017, 10:32 am

If you decide to go back to the 41 tube, I have a number of used, good ones. I will be happy to send you one.
Yours for the postage from the USA
FrankB.

17th Dec 2016, 1:45 pm	#41
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: BC-348-0 Help Please Yes, tag 12 on board 271 so far as I can make out. EL84? Thought it was a 41 now or haven't you fitted it yet? Lawrence.

17th Dec 2016, 1:53 pm	#42
wlindsay1984 Retired Dormant Member Join Date: Nov 2016 Location: Antrim, Co. Antrim, Northern Ireland, UK. Posts: 19	Re: BC-348-0 Help Please Thanks Lawrence, I had retrofitted the 41 to the EL84 socket with wires, after soldering them lightly to the 41 valve. Just a matter of pulling them out and placing the EL84 back in. Fingers crossed, will try and fire it up within the next hour and update. Here is a pic of the rewiring of the unit so far, I have just added the cap and resistor. Will Attached Thumbnails

17th Dec 2016, 2:00 pm	#43
wlindsay1984 Retired Dormant Member Join Date: Nov 2016 Location: Antrim, Co. Antrim, Northern Ireland, UK. Posts: 19	Re: BC-348-0 Help Please I also forgot to add, before starting from scratch, this 0.1 mfd 350vdc capacitor was somewhere within the "tube shelf" in the pic above. Any ideas? Pic attached. Thanks Attached Thumbnails

17th Dec 2016, 2:06 pm	#44
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: BC-348-0 Help Please Don't understand what you mean by "tube shelf" ? Lawrence.

17th Dec 2016, 2:25 pm	#45
wlindsay1984 Retired Dormant Member Join Date: Nov 2016 Location: Antrim, Co. Antrim, Northern Ireland, UK. Posts: 19	Re: BC-348-0 Help Please Sorry Lawrence, the location below the resistor boards, where vt48, vt 70 are mounted etc.. It was somewhere in there but I can't remember where.

18th Dec 2016, 8:02 pm	#46
WB6NVH-GEOFF Tetrode Join Date: Aug 2013 Location: Monterey, California USA Posts: 51	Re: BC-348-0 Help Please All of the BC-348 manuals have "practical wiring diagrams" which show the physical wiring and component layout, it should be easy to find what goes where by referring to them. And I believe there are some excellent scans of these manuals on the web. We call the "tube shelf" the subchassis behind the front panel on the right side that has the tubes [valves] mounted on it and which has the underside accessible by removing that plate on the front panel. Which made me think of a trivia question - - how many other communications receivers made in the USA or UK had part of the front panel removable to access components? I can't immediately think of any. Notice I said USA and UK as I think some Axis and maybe Russian sets did.

18th Dec 2016, 8:08 pm	#47
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: BC-348-0 Help Please Cheers for the explanation. Can't think off hand of any more receivers with a small removable front panel for access, only the T1154 transmitter (companion to the R1155 receiver) Lawrence.

18th Dec 2016, 8:23 pm	#48
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: BC-348-0 Help Please Whoops...Forgot the R1082, made by STC, front sub panel removable for tube/valve replacement: https://www.pa3esy.nl/military/gb/ai.../r1082-set.htm Lawrence

19th Dec 2016, 8:14 am	#49
M0SOE_Bruce Pentode Join Date: May 2013 Location: Deal, Kent, UK. Posts: 139	Re: BC-348-0 Help Please Looking at the parts list there is no listing for a 0.1@350V capacitor. It must be part of the mods that were done. The best manual I found was here: http://www.jamminpower.com/main/bc348.html The manual AN 1-40BC224-3 gives very good pictorials. If you are going to use the 41 valve as was original you'll need a bias circuit for it.

2nd Jan 2017, 1:46 pm	#50
wlindsay1984 Retired Dormant Member Join Date: Nov 2016 Location: Antrim, Co. Antrim, Northern Ireland, UK. Posts: 19	Re: BC-348-0 Help Please Hello Folks Still working on the radio, I tried to use the original transformer that was with the radio, it appears to be from the 1950's, as are some of the other components, one of the capacitors were dated 1955. It was assembled in the manner that was specified in one of the early conversion magazines, with a 5Z4 rectifier. The transformer appears to have seen better days, and is blackened/damaged. So I am starting from scratch, using the HP Friedrichs schematic, as mentioned by another user. I have all of the components except the transformer and filter choke, which I am going to purchase today, the only thing I am having issues with is the Filter Choke. HP Friedrichs mentions that he used one that measured almost 2H, the schematic specifies a 2H Choke, but does not specify what DC current it puts out. There are a number of 2H Filter Chokes, with differing DC outputs, any help for what you think I need would be much appreciated. Many Thanks. http://www.hpfriedrichs.com/radioroo.../pwrscheme.jpg The Attached Link shows the Schematic Last edited by wlindsay1984; 2nd Jan 2017 at 1:51 pm. Reason: Inclusion of Link

2nd Jan 2017, 2:04 pm	#51
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: BC-348-0 Help Please 50 or 60mA or greater should be no problem, wouldn't go below 50mA. EDIT: But if you're running it with an EL84 output valve then go for 100mA. Lawrence. Last edited by ms660; 2nd Jan 2017 at 2:29 pm.

2nd Jan 2017, 3:24 pm	#52
wlindsay1984 Retired Dormant Member Join Date: Nov 2016 Location: Antrim, Co. Antrim, Northern Ireland, UK. Posts: 19	Re: BC-348-0 Help Please Many Thanks Lawrence for all of your help. I have just placed the order. Should be able to get working on it this coming weekend. There has been plenty of times where I have just felt like giving up on it, but I keep going back to it, I feel like I am almost there. I think the old transformer was not putting out its full voltage, the voltage regulator bulb, on the "tube shelf", which is accessed from the front, would half light up, dim, and then die off, along with the transformer bubbling etc and over heating at that point, the windings were charred, the longer it was on, the less power it seemed to give out. Fingers crossed for the new equipment.

2nd Jan 2017, 3:37 pm	#53
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: BC-348-0 Help Please Before you power up, with the PSU connected to the receiver check for HT shorts in the receiver, test meter set to measure high value resistance, one probe to chassis and the other to the HT in from your new power supply, it should read very high or infinity. Lawrence.

2nd Jan 2017, 8:53 pm	#54
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: BC-348-0 Help Please The transformer may not be quite dead. Did the reservoir and smoother capacitors get warm?

3rd Jan 2017, 1:36 pm	#55
wlindsay1984 Retired Dormant Member Join Date: Nov 2016 Location: Antrim, Co. Antrim, Northern Ireland, UK. Posts: 19	Re: BC-348-0 Help Please Pic of transformer, I made the mounting board to the chassis, using tufnal, a sort of insulation board, it was from a usaaf dump site here, along with many other wartime components that I regularly find, so it has an additional wartime component. Attached Thumbnails

6th Jan 2017, 5:04 pm	#56
wlindsay1984 Retired Dormant Member Join Date: Nov 2016 Location: Antrim, Co. Antrim, Northern Ireland, UK. Posts: 19	Re: BC-348-0 Help Please Hello folks, if anyone would like the original power supply components for The price of the postage you can have them, maybe you could do something with them?. There is the transformer as pictured, a choke, a dubilier drillitic capacitor 16 + 8mfd, and a 5z4 rectifier. The transformer seems to be damaged but maybe someone might have the patience and skill to rewind it.

26th Jan 2017, 10:32 am	#57
FrankB Heptode Join Date: Oct 2005 Location: Olympia, Washington, USA. Posts: 664	Re: BC-348-0 Help Please If you decide to go back to the 41 tube, I have a number of used, good ones. I will be happy to send you one. Yours for the postage from the USA FrankB.