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Old 26th Nov 2021, 8:08 pm   #1
poppydog
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Default Philips B3G75U voltages

I am having a bit of trouble with voltages on this Philips.

The rectifier valve uy85 and output valve ul84 voltages are fine, the troublesome voltages are on all the rest. The voltages that are of concern are listed below.
V1 UF80 - PIN7=173.4V PIN8=162.2V
V2 UF80 – PIN7=171.2V PIN8=128.4V
V3 UCH81- PIN1=62.5V (AM) 58.8V (FM) PIN6=182V (AM) 171.4V (FM)
V4 UF89- PIN7=155.3V (AM) 154.6V (FM) PIN8= 88.2V (AM) 65V (FM)
Voltages were taken with a dmm

I have replaced all the non elec black sticky caps bar c51, 1 elec cap c46 has been replaced and 1 resistor c15, other resistors have been checked and are in tolerance,
I am using the Philips service manual.

The radio itself works very well on all bands with no hum etc so I didn’t really have any reason to suspect anything was wrong, but checking voltages before putting chassis back in cabinet I found some weren’t good.
I have tried good replacement valves from working radios and some NOS valves but voltages are still more or less the same.

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Old 26th Nov 2021, 10:35 pm   #2
Restoration73
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Default Re: Philips B3G75U voltages

What meter are you using ?In this era, these stated voltages are as measured on an Avo 8
(20k ohm per volt DC) and may be somewhat higher on a modern DMM.
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Old 27th Nov 2021, 9:52 am   #3
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Default Re: Philips B3G75U voltages

I have stated that I used a DMM in the post??,.
If I took voltages with a avo 8 then wouldn't the voltages that i think are ok, be too low?
I give up.
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Old 27th Nov 2021, 9:55 am   #4
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Default Re: Philips B3G75U voltages

In any case, most published voltages given should be used a guide only rather than treated as 'gospel'. 10% variation is quite normal and as stated above, the voltages were measured on either a meter with 10 or 20,000 ohms per volt or even only 1000 ohms per volt. A modern DVM will behave quite differently and may give voltages that are higher than published. Some DVM's will respond incorrectly if there is RF imposed on the DC voltage and give wildly wrong readings.

I don't think you have a problem at all. You've already said the radio is working well....
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Old 27th Nov 2021, 11:55 am   #5
poppydog
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Default Re: Philips B3G75U voltages

The sheet states that voltages were taken with a valve voltmeter, out of curiosity, how does that differ from a Dmm?
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Old 27th Nov 2021, 2:01 pm   #6
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Default Re: Philips B3G75U voltages

Your DMM has the same 10M ohm input impedance as the meter used for the service sheet data, however, the mains for the tests was only 220V AC using the 220-250V setting so you should expect your measurements to be higher.
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