Radiomobile 4200 help - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Steve_P · 9th Jul 2010, 1:59 am

Hmmm - put another signal in at the volume control and let's see if this also comes out distorted.

Cheers,

Steve P.

Station X · 9th Jul 2010, 11:27 am

Is it possible to unplug the vibrator, leaving the battery connected to supply LT, and provide HT from a bench supply connected to the smoothing capacitors? This will help you to determine if there are vibrator problems.

Station X · 9th Jul 2010, 11:29 am

Looking back I see you don't have a bench power supply. What about some PP3s in series?

PaulR · 9th Jul 2010, 7:08 pm

Well, mystery solved.

It sounded and felt so much like a "that cap" fault that I decided to test the voltages at the ends of them. I found that the brand new poly cap connected to the cathode of the splitter valve was a dead short and had 50 or so volts on the other end of it. Replacing the cap has brought the HT up to spec (more or less) and there is now a healthy negative voltage on the grids of the o/p valves. The sound is much better although I haven't had time to try it with a CD input or with a really suitable speaker.

Who would have thought it?

Thanks for the help, all.

Paul

9th Jul 2010, 1:59 am	#41
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Radiomobile 4200 help Hmmm - put another signal in at the volume control and let's see if this also comes out distorted. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

9th Jul 2010, 11:27 am	#42
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,286	Re: Radiomobile 4200 help Is it possible to unplug the vibrator, leaving the battery connected to supply LT, and provide HT from a bench supply connected to the smoothing capacitors? This will help you to determine if there are vibrator problems. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

9th Jul 2010, 11:29 am	#43
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,286	Re: Radiomobile 4200 help Looking back I see you don't have a bench power supply. What about some PP3s in series? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

9th Jul 2010, 7:08 pm	#44
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Re: Radiomobile 4200 help Well, mystery solved. It sounded and felt so much like a "that cap" fault that I decided to test the voltages at the ends of them. I found that the brand new poly cap connected to the cathode of the splitter valve was a dead short and had 50 or so volts on the other end of it. Replacing the cap has brought the HT up to spec (more or less) and there is now a healthy negative voltage on the grids of the o/p valves. The sound is much better although I haven't had time to try it with a CD input or with a really suitable speaker. Who would have thought it? Thanks for the help, all. Paul