Philips B3X81U Ground leak and small conversion

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Philips B3X81U Ground leak and small conversion

Post by Tom-Si on Mon Dec 25, 2017 9:14 am

I have a B3X81U and I'm trying to get it to work as a guitar amplifier it has a phono input and this input actually gives me great sounding amp. the only thing is when I touch anything else conductive while holding my guitar I get shocked. I have the schematics could it be something what a lot of people seem to call the death cap or is it something else? I can also measure the voltage with my multimeter but it only gives me 0,2 volts ac but its definitely a lot more than that. I hope i can get some help I have the schematics (in pdf but I don't know how to send a pdf but i found them on radiomuseum.org) and if it's the death cap could someone help me identifying the death cap?

Thanks and regards,

Tom

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Re: Philips B3X81U Ground leak and small conversion

Post by mr_ed01 on Mon Dec 25, 2017 11:22 am

No power transformer, appears to have one side of the line connected to the chassis. Not something to use as a guitar amplifier without an isolation transformer.

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Re: Philips B3X81U Ground leak and small conversion

Post by Chas on Mon Dec 25, 2017 2:05 pm

Schematic:

http://www.philipsradios.nl/Schemas/B3X81U.pdf

This is a line powered radio, no power transformer for line isolation.

An isolation transformer between the wall outlet and the radio would provide total protection.

"Death" cap?

It appears that C-65 and C-66 are to be used for phono input. One couples signal and one couples the return to the chassis. Do check the parts list and confirm the voltage value of the those two caps, should be better than 400 volts and a value of about .05 mf. or less. That would pass negligible AC current at that value.

If you still get a "tickle" reduce the mf. value to, say .022 or even .001mf. However expect bass tones to fall off and overall volume reduced.

Measuring leakage voltage with a high impedance meter will often resolve to line voltage. The leakage current must be measured or the leakage voltage across a known load for example 10k ohms then measure the leakage voltage across that resistance.

Check with electrical rules/laws for your jurisdiction in regard to measuring appliance AC leakage.

YMMV

Chas


Last edited by Chas on Mon Dec 25, 2017 2:08 pm; edited 1 time in total (Reason for editing : Typos)
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Re: Philips B3X81U Ground leak and small conversion

Post by Tom-Si on Fri Feb 02, 2018 12:45 pm

Chas wrote:Schematic:

http://www.philipsradios.nl/Schemas/B3X81U.pdf

This is a line powered radio, no power transformer for line isolation.

An isolation transformer between the wall outlet and the radio would provide total protection.

"Death" cap?

It appears that C-65 and C-66 are to be used for phono input. One couples signal and one couples the return to the chassis. Do check the parts list and confirm the voltage value of the those two caps, should be better than 400 volts and a value of about .05 mf. or less. That would pass negligible AC current at that value.

If you still get a "tickle" reduce the mf. value to, say .022 or even .001mf. However expect bass tones to fall off and overall volume reduced.

Measuring leakage voltage with a high impedance meter will often resolve to line voltage. The leakage current must be measured or the leakage voltage across a known load for example 10k ohms then measure the leakage voltage across that resistance.

Check with electrical rules/laws for your jurisdiction in regard to measuring appliance AC leakage.

YMMV

Chas

Hey thanks for the response! Sorry for my very late response. Since I'm still learning A LOT I had a couple of question what is the difference between a output/power/isolation transformer and a choke? Would this amp benefit from adding a ground and do you guys know a place where I can buy the right transformer for this amp in Europe? (a link would be greatly appreciated) How do you find out if a amplifier is a series filament or a paralel? Since I'm still learning a lot do you guys have any tips on things I should read or watch to teach me the basics? I'm watching the guitologist which helps but i sometimes feel like I'm missing some basic knowledge.

Thanks and regards,

Tom

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Re: Philips B3X81U Ground leak and small conversion

Post by Tom-Si on Sat Feb 03, 2018 10:18 am

mr_ed01 wrote:No power transformer, appears to have one side of the line connected to the chassis.  Not something to use as a guitar amplifier without an isolation transformer.

Is this a proper transformer? (sorry for the dutch text) https://www.conrad.nl/nl/block-st-632323-stuurtransformator-scheidingstransformator-veiligheidstransformator-1-x-230-v-1-x-230-vac-63-va-02-715887.html If this is the proper transformer should ground the chassis?

Thanks and regards,

Tom

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Re: Philips B3X81U Ground leak and small conversion

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