Different capacitors in the chassis and different values in the schematic ! - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Lef de art · 9th Nov 2019, 7:45 pm

Thanks Uncle Bulgaria but i know my level

Well i have tested them and in generally they don't have big differences

Uncle Bulgaria · 11th Nov 2019, 6:33 pm

I suppose it's time to go over all the voltages and bias settings then! Have you got a service manual with voltages on and maintenance instructions? I had a look and found one picture of a circuit diagram but no manual for the Geloso.

Lef de art · 12th Nov 2019, 12:40 am

Yes i have found the service Manual with some voltages. I will test them but i think the problem is in some capacitors because has appeared after i have changed the papper capacitors.
The problem with low frequencys is only in the new recordings.
So it must be a capacitor who is involved only in recording process. Not in amplifier.
Perhaps close to microphone input.

Maarten · 12th Nov 2019, 1:27 am

Maybe one of the new capacitors is too low a vaue? Maybe you missed a decimal point position, e.g. used a 22n instead of a 220n or a 4n7 instead of a 47n?

Lef de art · 12th Nov 2019, 6:44 pm

Trying to configure what can be happen, and to exclude the possibility to have read wrong any capacitor inscription i decide to compare the removed capacitors with the inscription in schematic.
Comparing them i have found 3 big difference.

In the schematic in the chassis
2K/600v 0.02uf/150V
2K/400V 0.05uf/350V
5K/400V 0.005uf/50V

The inscription on them is very clear. You can see in the pictures.

Change them with the schematic values maybe will bring me more bass in recording mode ?

All the other removed capacitors correspod with the schematic.
I really can't configure what i made wrong.
I haven't mess them, i have changed them carefully one by one and everything is in correct position.

'LIVEWIRE?' · 12th Nov 2019, 10:29 pm

I would take 5k/400v to be the same capacitance as 0.005uf, so, other than the lower working voltage, there is no difference there. The 0.05uf however, is 25 times the capacitance of the 2k (which I assume to be 2nf or 0.002uf) Depending upon it's circuit position-and I cannot read the small diagram in your picture- this much higher value could make a considerable difference. The first capacitor in your list is 2nf (0.002uf) 600v, whilst your replacement is Ten Times the value, and, perhaps more importantly, too low a working voltage. My 'golden rule' is to replace with a capacitor of the same, or higher, working voltage, but never with one of a lower working voltage. The manufacturer had good reason to use a cap. of the working voltage specified, so, unless the circuit has been further modified, one of a lower voltage should not have been fitted.

Lef de art · 12th Nov 2019, 11:27 pm

The strange thing here is that 3 capacitors have different value in the schematic from the capacitors in the chassis. I mean the geloso capacitors in chassis. This values are not the replacing values but the Geloso chassis values.

Mine replacement are through what i have found in chassis . Not in schematic.
In schematic is written 2k and in Geloso i have found 0.05uf.
And the machine was never opened !

Oldcodger · 12th Nov 2019, 11:29 pm

Lef- as a rule of thumb, any decoupling capacitors ( i.e. cathode resistor decouplers) , should be at least 1/10 the impedance of the cathode resistor at th lowest design frequency.
i.e. if the cathode resistor is 200 ohm, then the decoupler (capacitor) should be impedance wise 20 ohm at the lowest frequency. Then apply the capacitance formula
Z= 1/(2*PI*F*C)
And use the nearest high value capacitor in the series( with the capacitor having a voltage above the measured volts across the resistor).

9th Nov 2019, 7:45 pm	#21
Lef de art Pentode Join Date: Oct 2019 Location: Nicosia, Cyprus. Posts: 165	Re: Different capacitors in the chassis and different values in the schematic ! Thanks Uncle Bulgaria but i know my level Well i have tested them and in generally they don't have big differences

11th Nov 2019, 6:33 pm	#22
Uncle Bulgaria Nonode Join Date: May 2016 Location: Cornwall, UK. Posts: 2,329	Re: Different capacitors in the chassis and different values in the schematic ! I suppose it's time to go over all the voltages and bias settings then! Have you got a service manual with voltages on and maintenance instructions? I had a look and found one picture of a circuit diagram but no manual for the Geloso.

12th Nov 2019, 12:40 am	#23
Lef de art Pentode Join Date: Oct 2019 Location: Nicosia, Cyprus. Posts: 165	Re: Different capacitors in the chassis and different values in the schematic ! Yes i have found the service Manual with some voltages. I will test them but i think the problem is in some capacitors because has appeared after i have changed the papper capacitors. The problem with low frequencys is only in the new recordings. So it must be a capacitor who is involved only in recording process. Not in amplifier. Perhaps close to microphone input.

12th Nov 2019, 1:27 am	#24
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: Different capacitors in the chassis and different values in the schematic ! Maybe one of the new capacitors is too low a vaue? Maybe you missed a decimal point position, e.g. used a 22n instead of a 220n or a 4n7 instead of a 47n?

12th Nov 2019, 6:44 pm	#25
Lef de art Pentode Join Date: Oct 2019 Location: Nicosia, Cyprus. Posts: 165	Re: Different capacitors in the chassis and different values in the schematic ! Trying to configure what can be happen, and to exclude the possibility to have read wrong any capacitor inscription i decide to compare the removed capacitors with the inscription in schematic. Comparing them i have found 3 big difference. In the schematic in the chassis 2K/600v 0.02uf/150V 2K/400V 0.05uf/350V 5K/400V 0.005uf/50V The inscription on them is very clear. You can see in the pictures. Change them with the schematic values maybe will bring me more bass in recording mode ? All the other removed capacitors correspod with the schematic. I really can't configure what i made wrong. I haven't mess them, i have changed them carefully one by one and everything is in correct position. Attached Thumbnails

12th Nov 2019, 10:29 pm	#26
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Different capacitors in the chassis and different values in the schematic ! I would take 5k/400v to be the same capacitance as 0.005uf, so, other than the lower working voltage, there is no difference there. The 0.05uf however, is 25 times the capacitance of the 2k (which I assume to be 2nf or 0.002uf) Depending upon it's circuit position-and I cannot read the small diagram in your picture- this much higher value could make a considerable difference. The first capacitor in your list is 2nf (0.002uf) 600v, whilst your replacement is Ten Times the value, and, perhaps more importantly, too low a working voltage. My 'golden rule' is to replace with a capacitor of the same, or higher, working voltage, but never with one of a lower working voltage. The manufacturer had good reason to use a cap. of the working voltage specified, so, unless the circuit has been further modified, one of a lower voltage should not have been fitted. Last edited by 'LIVEWIRE?'; 12th Nov 2019 at 10:35 pm.

12th Nov 2019, 11:27 pm	#27
Lef de art Pentode Join Date: Oct 2019 Location: Nicosia, Cyprus. Posts: 165	Re: Different capacitors in the chassis and different values in the schematic ! The strange thing here is that 3 capacitors have different value in the schematic from the capacitors in the chassis. I mean the geloso capacitors in chassis. This values are not the replacing values but the Geloso chassis values. Mine replacement are through what i have found in chassis . Not in schematic. In schematic is written 2k and in Geloso i have found 0.05uf. And the machine was never opened !

12th Nov 2019, 11:29 pm	#28
Oldcodger Nonode Join Date: Oct 2014 Location: West Midlands, UK. Posts: 2,181	Re: Different capacitors in the chassis and different values in the schematic ! Lef- as a rule of thumb, any decoupling capacitors ( i.e. cathode resistor decouplers) , should be at least 1/10 the impedance of the cathode resistor at th lowest design frequency. i.e. if the cathode resistor is 200 ohm, then the decoupler (capacitor) should be impedance wise 20 ohm at the lowest frequency. Then apply the capacitance formula Z= 1/(2PIF*C) And use the nearest high value capacitor in the series( with the capacitor having a voltage above the measured volts across the resistor).