1950's valve Blaupunkt Frankfurt, barely audible FM - UK Vintage Radio Repair and Restoration Discussion Forum

aturner · 15th Nov 2008, 2:38 am

I have a Blaupunkt Frankfurt valve car radio circa 1954/55 that (I'm told) works but FM is barely audible. I bought it earlier this year with a view to installing it in my 1955 VW Beetle once it's repaired.

I have 30 odd years experience in electronic repair but the past 25 years of that is confined to digital equipment. I'd like to have a go at repairing this myself so I'm here asking for help.

Firstly, I need a schematic since I'm not 100% certain where to shove the power in! I know this radio works on 6v but it may also work on 12v so there's the first costly mistake I want to avoid! Any ideas where I can get a schematic, please?

From spending some time reading the great radio servicing guides on here, I'm going to start by testing "high value" (>0.5uF) capacitors and replacing with new where appropriate. With the aid of a schematic I'll check the PSU rails etc. too. I guess it can't hurt to re-seat the valves as well, or are they best left undisturbed?

This radio employs an external 'vibrator'; can I readily test that before connecting it to the rest of the set or am I being unnecessarily paranoid?

Here are a few pics of the set and the vibrator:

Also, is that a bad capacitor on the top row of the tag-board?

howard · 15th Nov 2008, 1:48 pm

Hello,

I should check the output from the power supply and then replace all the wax capacitors (0.001 - 0.05uF), get some Servisol 10 switch cleaner and use it to clean the valve pins, potentiometers and switches and then see how the radio performs.

This car radio was released in 1954/5, and it was tailored for different brands of German cars including Mercedes and Porsche-VW. Quite a find that, an FM car radio from 1954 !

Howard

Ed_Dinning · 15th Nov 2008, 7:32 pm

Hi, the vibrators do appear to suffer with dirty contacts with age and they are not easy to clean; even when cleaned it may not last.
I think there was a thread here some time ago that showed how to convert a vibrator to drive MOSFETs, which in turn switched the transformer. This reduced the load on the contacts and allowed good performance.

Ed

'LIVEWIRE?' · 15th Nov 2008, 8:50 pm

About 10 months ago I repaired/overhauled one of these Frankfurts, and(as Howard says) I replaced all the waxed paper capacitors, but also the main reservoir/smoothing capacitor and the selenium rectifier(located in the power pack) plus other electrolytics. I don't recall any specific FM/VHF problems, though. If memory serves right the FM front end is built around an ECC 85(to the left of the upper IF Transformer in photo 1), and it may be worth sustituting this valve and/or checking it's associated circuitry. I have circuit diagrams somewhere, which I obtained from www.radiomuseum.org

15th Nov 2008, 2:38 am	#1
aturner Retired Dormant Member Join Date: Apr 2008 Location: Oxford Posts: 3	1950's valve Blaupunkt Frankfurt, barely audible FM I have a Blaupunkt Frankfurt valve car radio circa 1954/55 that (I'm told) works but FM is barely audible. I bought it earlier this year with a view to installing it in my 1955 VW Beetle once it's repaired. I have 30 odd years experience in electronic repair but the past 25 years of that is confined to digital equipment. I'd like to have a go at repairing this myself so I'm here asking for help. Firstly, I need a schematic since I'm not 100% certain where to shove the power in! I know this radio works on 6v but it may also work on 12v so there's the first costly mistake I want to avoid! Any ideas where I can get a schematic, please? From spending some time reading the great radio servicing guides on here, I'm going to start by testing "high value" (>0.5uF) capacitors and replacing with new where appropriate. With the aid of a schematic I'll check the PSU rails etc. too. I guess it can't hurt to re-seat the valves as well, or are they best left undisturbed? This radio employs an external 'vibrator'; can I readily test that before connecting it to the rest of the set or am I being unnecessarily paranoid? Here are a few pics of the set and the vibrator: Also, is that a bad capacitor on the top row of the tag-board? Attached Thumbnails Last edited by Darren-UK; 15th Nov 2008 at 9:40 am. Reason: Embedded images removed as unnecessary.

15th Nov 2008, 1:48 pm	#2
howard Nonode Join Date: May 2005 Location: Godalming, Surrey, UK. Posts: 2,593	Re: 1950's valve Blaupunkt Frankfurt, barely audible FM Hello, I should check the output from the power supply and then replace all the wax capacitors (0.001 - 0.05uF), get some Servisol 10 switch cleaner and use it to clean the valve pins, potentiometers and switches and then see how the radio performs. This car radio was released in 1954/5, and it was tailored for different brands of German cars including Mercedes and Porsche-VW. Quite a find that, an FM car radio from 1954 ! Howard Last edited by howard; 15th Nov 2008 at 1:59 pm.

15th Nov 2008, 7:32 pm	#3
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,195	Re: 1950's valve Blaupunkt Frankfurt, barely audible FM Hi, the vibrators do appear to suffer with dirty contacts with age and they are not easy to clean; even when cleaned it may not last. I think there was a thread here some time ago that showed how to convert a vibrator to drive MOSFETs, which in turn switched the transformer. This reduced the load on the contacts and allowed good performance. Ed

15th Nov 2008, 8:50 pm	#4
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: 1950's valve Blaupunkt Frankfurt, barely audible FM About 10 months ago I repaired/overhauled one of these Frankfurts, and(as Howard says) I replaced all the waxed paper capacitors, but also the main reservoir/smoothing capacitor and the selenium rectifier(located in the power pack) plus other electrolytics. I don't recall any specific FM/VHF problems, though. If memory serves right the FM front end is built around an ECC 85(to the left of the upper IF Transformer in photo 1), and it may be worth sustituting this valve and/or checking it's associated circuitry. I have circuit diagrams somewhere, which I obtained from www.radiomuseum.org