Voltage drop on Philips 730A - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

jonnybear · 22nd Sep 2020, 12:41 pm

Quote:

Originally Posted by Dick Glennon

Hi again, The voltage on the heater/ dial bulb winding is 4.6 volts but when I put a 6 volt 300ma bulb across the winding it lit for a few seconds and blew the bulb. Is the winding doing this. Thanks again, Dick.

If you are blowing 6 volt bulbs on a 4 volt supply which is in parallel with the 4 volt valves their heaters would be damaged as well, what meter are you using?
John

Dick Glennon · 22nd Sep 2020, 3:16 pm

Hi Johnny, I have just powered up the radio with no valves or dial bulb installed and I measured 4.45 volts on the heater/dial bulb winding. I left the red lead attached with the power supply switched off and the voltage started creeping up on the multimeter. It went up to almost 9volts . This to me might be the reason why the bulb is blowing but I do not know for sure. I now think that I may have to get a new transformer. Would one from a Cossor 484 in anyway suit . It is in a working chassis but the cabinet is long gone. Thanks again , Dick.

Herald1360 · 22nd Sep 2020, 3:24 pm

4.45V doesn't sound unreasonable for an unloaded 4V heater supply. It won't hurt a heater short term either- try plugging in all valves except rectifier and measure it again.

Station X · 22nd Sep 2020, 3:28 pm

With no valves plugged in the LT voltage from the transformer will be high. A load ie the valve heaters is needed to drop the voltage. As explained several times if the voltage was high the heaters would blow as well as the dial lamps.

Have you verified that your meter is accurate and that you have the correct lamps?

crackle · 22nd Sep 2020, 5:28 pm

Quote:

Originally Posted by Dick Glennon

I left the red lead attached with the power supply switched off and the voltage started creeping up on the multimeter. It went up to almost 9volts .

The above makes no sense to me.
What power supply was switched off?
How can the voltage increase with it switched off.
What is this red lead?

Mike

22nd Sep 2020, 3:16 pm	#22
Dick Glennon Hexode Join Date: Oct 2006 Location: Edenderry, Republic of Ireland. Posts: 428	Re: Voltage drop on Philips 730A Hi Johnny, I have just powered up the radio with no valves or dial bulb installed and I measured 4.45 volts on the heater/dial bulb winding. I left the red lead attached with the power supply switched off and the voltage started creeping up on the multimeter. It went up to almost 9volts . This to me might be the reason why the bulb is blowing but I do not know for sure. I now think that I may have to get a new transformer. Would one from a Cossor 484 in anyway suit . It is in a working chassis but the cabinet is long gone. Thanks again , Dick.

22nd Sep 2020, 3:24 pm	#23
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Voltage drop on Philips 730A 4.45V doesn't sound unreasonable for an unloaded 4V heater supply. It won't hurt a heater short term either- try plugging in all valves except rectifier and measure it again. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

22nd Sep 2020, 3:28 pm	#24
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Voltage drop on Philips 730A With no valves plugged in the LT voltage from the transformer will be high. A load ie the valve heaters is needed to drop the voltage. As explained several times if the voltage was high the heaters would blow as well as the dial lamps. Have you verified that your meter is accurate and that you have the correct lamps? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.