East German Ilmenau 675/55 tuning problem - UK Vintage Radio Repair and Restoration Discussion Forum

petervk2mlg · 25th Jan 2018, 9:40 am

Hi
I’m having some trouble with my Ilmenau 675/55 GWU.
The radio works but on the MW my local radio station broadcasting on 1404 KHz comes in on the tuning scale at around 1200KHz. Also therefore I cannot tune in my other local station on 549KHz. The radio will not tune down far enough.

With a regular conventional radio I would adjust the oscillator trimmer capacitor to correct this and then peak the low frequency 549 KHz station with the padder. As it is, the 549 station does not appear at all as the radio will not tune down that far.
With the 675/55 which uses permeability tuning – with the aerial and oscillator slugs moving in and out of the aerial and oscillator coils – the procedure to fix the fault is not so clear to me.
From looking at the circuit, can someone tell me what adjustment I must make to get the 1404 KHz station in the right place and also allow me to tune in the 549KHz station.

Many thanks,
Peter

Herald1360 · 25th Jan 2018, 10:36 am

You would normally adjust trimmer caps near HF end of band and padder caps/inductor cores at the LF end. There seem to be trimmer inductors in the front end circuit so start by tweaking the capacitors as usual.

ms660 · 25th Jan 2018, 11:54 am

So far as I can make out, using this schematic:

http://www.gfgf.org/GFGF-Schaltpland...555GWU_sch.pdf

On the schematic the wave change switch is shown in the VHF position.

Next switch position = LW, next = MW.

Osc: L15 = MW, L16 = LW, L15 & L16 are connected in series for LW, L16 is shorted out on MW, both are adjustable, for MW adjust L15 for LF end of the band and C24 for HF end of the band, there's no osc trimmer for LW.

RF: L11 = MW, L10 = LW, L11 & L10 are connected in series for LW, L10 is shorted out on MW, both are adjustable, for MW adjust L11 for the LF end of the band and C14 for the HF end of the band, there's no RF trimmer for LW.

Hope I've got that right

If not then guilty as charged.

Lawrence.

crackle · 25th Jan 2018, 1:36 pm

Quote:

Originally Posted by petervk2mlg

Hi
I’m having some trouble with my Ilmenau 675/55 GWU.
The radio works but on the MW my local radio station broadcasting on 1404 KHz comes in on the tuning scale at around 1200KHz. Also therefore I cannot tune in my other local station on 549KHz. The radio will not tune down far enough.

The problems I normally get are the reverse, with the tuning cap and oscillator trimmer fully open I often cant get the tuning to go high enough on MW. So if all else fails then adding a little extra capacitance to the MW trimmer may help.

Mike

petervk2mlg · 26th Jan 2018, 6:22 am

Quote:

Originally Posted by ms660

Osc: L15 = MW, L16 = LW, L15 & L16 are connected in series for LW, L16 is shorted out on MW, both are adjustable, for MW adjust L15 for LF end of the band and C24 for HF end of the band, there's no osc trimmer for LW.

RF: L11 = MW, L10 = LW, L11 & L10 are connected in series for LW, L10 is shorted out on MW, both are adjustable, for MW adjust L11 for the LF end of the band and C14 for the HF end of the band, there's no RF trimmer for LW.

Many thanks Lawrence. C24 was either open circuit or very out of tolerance. A new trimmer across there with proper capacitance enabled me to bring stations in at the correct spots on the MW band.
Peter

ms660 · 26th Jan 2018, 9:44 am

A really eco FM circuit (slope) how well does it work on FM?

Lawrence.

petervk2mlg · 26th Jan 2018, 9:51 am

No FM reception at all yet. All I get is hiss which increases towards the low frequency end.

25th Jan 2018, 9:40 am	#1
petervk2mlg Heptode Join Date: Jan 2007 Location: Parkes, NSW Australia Posts: 877	East German Ilmenau 675/55 tuning problem Hi I’m having some trouble with my Ilmenau 675/55 GWU. The radio works but on the MW my local radio station broadcasting on 1404 KHz comes in on the tuning scale at around 1200KHz. Also therefore I cannot tune in my other local station on 549KHz. The radio will not tune down far enough. With a regular conventional radio I would adjust the oscillator trimmer capacitor to correct this and then peak the low frequency 549 KHz station with the padder. As it is, the 549 station does not appear at all as the radio will not tune down that far. With the 675/55 which uses permeability tuning – with the aerial and oscillator slugs moving in and out of the aerial and oscillator coils – the procedure to fix the fault is not so clear to me. From looking at the circuit, can someone tell me what adjustment I must make to get the 1404 KHz station in the right place and also allow me to tune in the 549KHz station. Many thanks, Peter Attached Thumbnails

25th Jan 2018, 10:36 am	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: East German Ilmenau 675/55 tuning problem You would normally adjust trimmer caps near HF end of band and padder caps/inductor cores at the LF end. There seem to be trimmer inductors in the front end circuit so start by tweaking the capacitors as usual. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

25th Jan 2018, 11:54 am	#3
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: East German Ilmenau 675/55 tuning problem So far as I can make out, using this schematic: http://www.gfgf.org/GFGF-Schaltpland...555GWU_sch.pdf On the schematic the wave change switch is shown in the VHF position. Next switch position = LW, next = MW. Osc: L15 = MW, L16 = LW, L15 & L16 are connected in series for LW, L16 is shorted out on MW, both are adjustable, for MW adjust L15 for LF end of the band and C24 for HF end of the band, there's no osc trimmer for LW. RF: L11 = MW, L10 = LW, L11 & L10 are connected in series for LW, L10 is shorted out on MW, both are adjustable, for MW adjust L11 for the LF end of the band and C14 for the HF end of the band, there's no RF trimmer for LW. Hope I've got that right If not then guilty as charged. Lawrence.

26th Jan 2018, 9:44 am	#6
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: East German Ilmenau 675/55 tuning problem A really eco FM circuit (slope) how well does it work on FM? Lawrence.

26th Jan 2018, 9:51 am	#7
petervk2mlg Heptode Join Date: Jan 2007 Location: Parkes, NSW Australia Posts: 877	Re: East German Ilmenau 675/55 tuning problem No FM reception at all yet. All I get is hiss which increases towards the low frequency end.