Philips B3G75U

[Wage Slave]

So at last a valve project to work on. A collector gave me one of these on my last trip back to the UK and I will be back in Japan with it looking forward to starting work by the weekend. I am told it isn't working and the suspect is one of the valves. I don't think anyone has looked at it carefully though.

I have a set of service sheets including a diagram and a table of valve voltages.

What I would appreciate is some advice on where to start on this set and any advice from anyone who has worked on one. I'll post pictures when I get back to Japan.

[Alistair D]

Hi Wage slave

Sorry to be the harbinger of doom but that model will not work on your 110V mains supply.

Al

[Wage Slave]

Hi Alistair - Great to hear from you.

I have a 300 Watt transformer which will give me 200V and there is a also a 200V mains supply for the air conditioners which I could use. That goes up to 2.5 Kw I believe.

Hopefully that should do it or .............

[Alistair D]

That sounds as though you have a solution already sorted out. Sort this one and you will be the envy of all your friends. "That radio was made when?" Yes it was 1952.

I will have a look for some websites that cover basic valve theory and basic superheterodyne theory. Superheterodyne is the method that this radio uses to turn radio signals into audio from the loudspeaker.

Al

[stitch1]

Hi Wage Slave,
I have just started a B3G97U which has the same chassis.
Like this one .. http://www.thevalvepage.com/radios/p...7u/b3gu97u.htm

I picked it up for £5, it's very dirty inside and out but is intact.

I've done very little so far but I noticed that the cap accross the mains had exploded so I've removed that (you may want to do the same before powering up) there was also a visably open circuit resistor which I've replaced and I've replaced 'THAT' capacitor.

I powered it up on a lamp limiter and all seemed OK, and with full power its working.
Now I'm going to change the larger capacitors (although the smoothing caps seem ok so I'll probably leave them) and check the resistors, then lots of cleaning!

You don't say how much you know about restoring radios but this is an AC/DC set so watch out for the live chassis.
This site is excellent for a beginner.

http://www.vintage-radio.com/repair-...ion/index.html

Enjoy!

[Alistair D]

Does your 300W transformer have an isolated 200V secondary? Even if it does it might be worth picking up a 240V mains test screwdriver so you can easily test to see if the chassis is live. They only cost a pound or two.

Your radio is built using live chassis techniques. One side of the mains is connected directly to the chassis. Much has been said on here before regarding this. It would be worth doing a search to ensure you know about safe practices.

Al

[stitch1]

Originally Posted by alistair d

your radio is built using live chassis techniques. One side of the mains is connected directly to the chassis. Much has been said on here before regarding this. It would be worth doing a search to ensure you know about safe practices.

Al

Snap!

[Alistair D]

Sorry Stitch1. I didnt see your post. I really should not keep jumping to the last post.

Wage slave; It might be worth taking a couple of 240V 40 or 60 watt bulbs back as well for the lamp limiter.

Al

[Herald1360]

Also..... isn't ground (neutral) half way between the legs of the 200V supply (actually 100-0-100V) in Japan, so either way chassis would be at 100V to ground if the radio is directly connected. Not necessarily a problem for normal operation, but interesting for servicing.

[Alistair D]

Herald1360, yes I remember that from a previous post. That should be OK if Wage slave uses his 110/240 transformer since one side of the 110 will be ground. Even if the transformer is not an isolation type He can still have the chassis at ground potential. So long as he does the safety tests all should be well.

Al

[Tim]

Sorry to be the harbinger of doom but that model will not work on your 110V mains supply.

True, but it might be possible to modify as it's an AC/DC model.

[Alistair D]

Tim,
convert the heater chain to 110V and convert the HT supply to a half wave voltage doubler. Nice one. That sounds like a good possibilty after the set is working.

Al

[Wage Slave]

Excellent - even better than I thought. Many thanks, everyone. Lots of terrific information here already.

I have a couple of 240V test screwdrivers which went to Japan with my tool kit when I moved over. I'll pick up a couple of bulbs tomorrow. I have a couple of 60's somewhere but not a 40 or so I believe. I have an anglepoise and a standard lamp with bayonet fittings.

The 200v aircon supply is 100V-0-100V I believe so that's something to watch but I will likely run it off the transformer anyway.

"Does your 300W transformer have an isolated 200V secondary?"

Not sure. I believe it is just a a straightforward step up transformer in a heavy duty plastic case.

Anyway, I will read the links carefully and be very careful to test the chassis before doing anything. I won't be back until Sunday and then will need a week or two before even considering starting work.

"convert the heater chain to 110V and convert the HT supply to a half wave voltage doubler. Nice one. That sounds like a good possibilty after the set is working."

I like this project more and more. Really looking forward to it.

[Wage Slave]

So as promised a few pictures. I have had a chance to have a poke around and give it a quick clean.

The capacitor across the mains appears to have had an incident, like stich1's set, at some point. You can just about make it out in the 4th picture. There's a bit of what may be scorching there too on the mains leads. Judging from what he said this capacitor can just be safely removed.

In the last picture you can perhaps just see a dark mark on the coil across the aerial posts. At first I thought it was scorch but on closer inspection I think it is epoxy or something. Other than that I couldn't spot anything obviously wrong.

The output transistor winding resistances are OK. The valve heaters are all OK and there are no plate/heater shorts. The electrolytics all seem good on the ESR meter except for the biggish yellow one at the front of picture 3 which is a bit high. I'll change that and "that capacitor" which is a black "waxy" .022uf 300V.

What do people think about the other black waxies? Change them all or attempt to test them for short circuit and use them if they seem OK?

Still quite a long way away from attempting to power up but I am wondering about procedure given that I don't have a variac and am using a 100V to 200V transformer. I have heeded the warnings about potentially live chassis and am wondering if I should ensure that the chassis is connected to neutral rather than the active? Or does it not matter? In any case, I suppose the golden rule is to make sure that I don't touch anything, including the chassis, while the power is on and until the caps have discharged?

Edit to add: Reading through Paul's excellent guide linked earlier by Stitch1 I see that there is a comprehensive and highly practical guide on preparing to power up and actually doing so.

[stitch1]

Hi,
Yes the mains cap has gone the same way as mine, I've left it out but you could replace it with a X2 class if you want.

I just use a lamp limiter to power up radios.

Yes neutral to chassis.

I would change all the black ones, I had a problem with R18 over heating and smoking I changed the black caps one by one (always change components one at a time and power up after each change) and C58 cured the problem although I'm not sure why.

Here's a couple of before and after pics, I haven't spent much time restoring the chassis but it works well and will get regular use.

[Alistair D]

Hi there

It is certainly a good looking set.

A couple of points.

Lets start with your transformer. It will be one of 2 types, an auto transformer has only 1 winding with a tap in the middle for the 110V input. This type does not give mains isolation. The second type has fully isolated windings for primary and secondary and does give isolation. It would be worth making a few resistance measurements to see which type you have.

It is always safer to ensure the chassis is connected to the neutral. This is where your mains test screwdriver comes in handy.

Those black caps will almost certainly be leaky and need to be changed. The one drawback of an ESR meter is that will not detect leakage, infact, the leakier the cap the lower the ESR will read. Disconnect one end of one of them and connect your meter on its highest ohms range across the cap. Anything other than an open circuit reading and the cap is faulty. Some of these caps will have around 200 Volts across them so even the slightest leakage will be multiplied when in service.

Al

[Wage Slave]

This is the transformer:

http://www.tlc-direct.co.uk/Products/SC5467W.html

I see it is 500VA (not 300) and has toroidal windings if that helps. Primary winding measures 2.6 ohms, secondary 4.5 ohms.

[Herald1360]

The info on the transformer tells you everything but whether it's isolating or autowound. Probably it's auto, since that's cheaper to make and perfectly good for its intended use. Even if it's double wound, for its end use, the input and output neutrals could still be connected, otherwise you would lose any RCD protection that may otherwise be available.

Check whether there is a (much) lower resistance between neutral in / neutral out and line in / line out. For safest operation there should be, other wise the output "neutral" could end up at 100V from ground with the set effectively on the same 100-0-100 as if it were on the aircon supply!

If by any chance the input and output sides are isolated, so much the better for your particular application.....

[Wage Slave]

Ah yes of course. Slaps head and gives thanks for the patience. The old meter battery has just clapped out so I will have to check later. In the meantime, off to pay respects to/remember the dead today as is the custom here once a year.

Sounds like all those black waxies will have to be replaced soon, if not now as I plan to use this set a reasonable amount. Cue a delay while I see what parts are available locally and/or order them from the UK.

What would people do? Cut out the mains cap, replace that cap and the high ESR electrolytic and then look to changing them one by one while checking on a lamp limiter? Or change them all in one go?

[Neil Purling]

Capacitors with a waxed paper insulator have such a poor reputation, as I am sure you are aware from looking at the Forum they are changed en-masse without any test whatsoever.
If 'that' capacitor is leaking DC it can ruin the output transformer, if there is one.
Even if everything else looks good it is the first to be changed.
In your case sort out the power supply so it will give HT safely & change 'that' capacitor.
The power supply will have a two or three section 'can' electrolytic to smooth the DC from the rectifier. This will have to be re-formed or replaced it it won't re-form.
So the set should be safe to try a cautious test with the lamp limiter.
From there you may prefer to change just one or two of those wax capacitors at a time, trying the set afterwards. Don't be disappointed that your first ever switch on did not yield any signals. Some of those malignant capacitors my prevent the local oscillator from running. You can get a buzzing sound by touching a screwdriver blade to the wiper contact of the volume control and prove the audio stage is working.
I have never had a Phillips radio, so I cannot give any information beyond general points.