First Project in Radio = Philips 838HU Advice /Guidance

[Dunc100]

Hi everyone, I have introduced myself over in the intro thread so I will crack on with the Radio talk.

I love the style of these old radios and when I saw this old girl at an auction I had to have her. Now initially I thought that it would be shot through and would have valves missing etc. If this were to be the case I might (dont shoot me yet) have turned it into a guitar amp.

Put the guns down. I opened the back and as the set is complete I was not going to wreck this beauty.

Now I don't know a great deal about radio. Circuit diagrams, components and basic testing I am fine with. Specific knowledge on radio I do not have, this is where I hope the good members here will help me out.

I've hopefully attached some photos, they wont be great as our camera is old and struggling. Don't tell the wife but she is getting a new one for Christmas!

As you can see things were dirty, with thick felt like substance covering everything. Pretty gross but nothing a paint brush and hoover didn't solve.

I didn't struggle too much removing the chassis from the cabinet and was surprised that all the screws moved relatively easily. Once cleaned I was astonished at the build quality of this radio. They certainly built things to last back then!

Things I have noticed so far:

1) the set does not earth in the modern way (through the mains plug) but instead there is a amusing diagram showing that the owner should earth it to a water pipe. As I have no intention of placing the set anywhere near my kitchen sink I will have to modernise this part of the set. I am obviously replacing the power chord. Should I affix the earth wire from the mains lead to the chassis? Would this do the job and what do members here do?

2) Having said that I am OK with components, perhaps I should have said "Post War" components. Some of these capacitors and resistors look very different. Advice on these is welcome.

3) Is that a metal tuning cord? Weird. What is the purpose of the semi circular metal plate attached to the tuning capacitor(?)

4) "setting a radio up" is not something I am familiar with. With a tape recorder and test tapes one would set your machine up for Frequency response, bias etc. Will this set need "setting up" after it is made safe and ancient capacitors are replaced? If so is there a sticky thread on this that I haven't spotted?

5) the cabinet is in great condition for its age. I don't see many scratches or dings, its just got 70 years worth of grime on it. I have tentatively used a turps and linseed oil mix in warm water on a small section and it looks great. Am I ok to continue in this way or do members have a definitive "way" to do it?

I hope you can see that I am in no way going to butcher this set and I hope you will give me advice on my way through getting her singing again.
Will she sound good?

PS I have the service manual downloaded. It says "confidential for Philips service engineers only". I guess I can call myself a trainee!! The schematic is in this document and I hope to get it printed out today (cant bear working off a schematic on screen!)


Many thanks in advance.

Duncan

[GeoffK]

This set has a 'live' chassis as denoted by the U suffix, not sure what the H is for, and is a TRF or tuned radio frequency. Not the ideal first set to work on. The live side of the mains should go via the barretter to the anode of V4 the rectifier. The capacitor between V2 anode and V3 control grid is the one that needs checking for leakage. It may be labelled C22 depending on the schematic you have. Any attempt to bring the radio back on should be done with a variac slowly winding it up. The older black Philips capacitors can be quite reliable contrary to some options. The main electrolytics C1 and C2 may not reform though.

[TonyDuell]

I've just looked at the Trader Sheet for this set. I agree with Hetrodyne that this would not be my choice as a first set to restore, but as I said in a thread last week, the ideal set is the one you can get, and you have this one.

It's what's called a 'Universal' or 'AC/DC' receiver. It does not have a mains transformer. The valve heaters (there are 4 valves along the back edge of the chassis) and the dial lamp are connected in series. A thing called a 'Barretter', basically a special type of light bulb, is conneted in series with that, and the whole lot connected across the mains. The purpose of the barretter is to pass the right current (here 200mA) for any mains voltage in the range the radio will work off so the valves get the correct heater current. The barretter is the glass thing nearer the front of the chassis.

To get the high voltage needed for the valve anodes, the mains is half-wave rectified and smoothed. The rectifier is the valve on the far right looking at the back of the set, type CY1.

Now this means that the radio circuits are directly connected to the mains. In fact the metal chassis that the radio is built on is connected to one side of the mains when the set is switched on. This should be the neutral mains wire, it is worth checking this. With the set unplugged, turn the switch on the set on, and measure the resistance from each of the mains wires to the chassis. One should read 0 Ohms (or very close to it), the other rather more resistance. If the second one seems to be open-circuit then one of the valves, the dial light, the barretter or the mains swtch is open-circuit. Or there's a bad connection somewhere.

Because the chassis is connected to the mains, it cannot be earthed. At best connecting an earth wire to the chassis will trip an RCD. At worst it will be spectacular.

[Edward Huggins]

Not only have you chosen a Philips (never straightforward) but a Philips like this one. Ouch!
What an oddball set to work on? Be aware that even when fully restored, the choice of stations will be limited as it's a broadly tuned TRF set and maybe not like the more typical Superhet you may be thinking of. The "Earth" socket is meant for a signal earth, nothing to do with a mains earth.
And don't even think about using it as an Amp!

[Dunc100]

Thanks for the response chaps.

Chassis is what? Attached to Neutral!!
This actually makes the schematic make some more sense, I thought I was looking for the Holy Grail or something when I had a brief look over it earlier. No mains transformer, never touched anything like that before.

So it seems this radio has chosen me to lose hair and sleep over then. Never mind I love learning so this is going to throw some opportunities my way.

So, its a no flipping way do I attach an earth to the chassis. I will do the test that TonyDuell suggested to check the chassis is hooked to Neutral correctly, seems a good place to start.
I should thatnk Tony for that simple description of a Barretter. The first thing I did was look on r-type.org to find out what the (to me) unusual valves were. The C1 datasheet on there has a detailed description but Tony's took less time to read and is probably all I needed to know!

Hetrodynes suggestion of a variac is solid advice but i don't own one
Would the old lightbulb trick with my hand on the off switch do at a push?

I had no idea that U in the name denoted this style of power supply. Does anyone know what the H stands for? The back of the set describes the model as a 838HU but the chassis just 838U. It also has the model number 5021. Yep it seems this is an oddball.

As far as I can tell the only thing missing from this set is the little round Philips badge on the front. The only thing broken is one side of the leather strap that holds the cover on the back. I might try to "sew" the edges together when I have the set working.

Talking of working and picking up stations, less of a worry as long as I can get Radio 4! To be honest its more about getting a thrill from getting a working set of this age than listening to the radio for lengthy periods with it.

I think all paper and electrolytics will get replaced before I put power to the set, especially without a variac. I may even try to follow a method of putting them back in the can / paper. Or not thoughts?

Thanks again and I'll update on progress. Off to stick printer ink in the printer and get familiar with the circuit.

Duncan

[60 oldjohn]

Once restored, this set along with most MW receivers will be nearly unusable. There is just too much interference in today's world, from fridges to computers, in fact most devices that are plugged in to the mains, especially SMPS. For a first restoration I would advise you try and get a Hacker Mayflower 2 the 1 version is better but expensive. The Mayflower 2 is easy to work on VHF only, has a mains transformer and has none of the complicated Bowden cables and wire ropes found in Philips set.

John.

[Ed_Dinning]

Hi Duncan, it is however a nice looking set and if taken carefully with the assistrance of the people here you should be successful.
These Philips TRF's were known for well designed coils so it should be capable of something. A frame aerial should help a lot to reduce interference.

Good luck, Ed

[Boater Sam]

My best piece of advice is, as always, don't go mad changing parts until you get it working, only change what has to be changed to achieve this.

Then you can get it back to full performance by changing pieces ONE AT a TIME, ensuring it works after every part changed, then you make no connection mistakes.

There is one exception, temporarily replace the output valve grid coupling cap With something suitable ( keep the old one for restuffing) first off before powering up. A lamp limiter is a good idea.

Yes, please restuff as much as you can, it preserves an old set looking original and the practice is good for you. Many would not agree but we are all individuals.

Is that the weird Philips tuning cap I can see? Or just a boxed ordinary one?

[Sideband]

Originally Posted by 60 oldjohn

Once restored, this set along with most MW receivers will be nearly unusable. There is just too much interference in today's world, from fridges to computers, in fact most devices that are plugged in to the mains, especially SMPS.

I don't entirely agree with that statement, especially with one of these sets. These Superinductance TRFs seem to cope very well....at least my 274A does. In fact I recently stood it next to a PC and monitor and there was no interference from either. Not so with a later superhet that whistled and buzzed and made all sorts of noises.

[Maarten]

5021 is probably the serial number. Could you take a picture of the type plate? It may be possible to determine whether it was imported and if so, where it was made.

The H in HU is most likely for "high", so a high mains voltage range, for example 210-250V. Is the mains voltage mentioned anywhere?

The earthing arrangement as depicted on the back, is meant for the receiving earth, not the mains earth. It can usually be left open, but if it is used make VERY sure to replace the coupling capacitor to the earth connector. Also replace the coupling capacitor to the antenna connector as a matter of course. Use Y2 or Y1 class ceramic capacitors for safety reasons. Actually, any connection to the outside world, such as the pick up connection if present, should be mains separated by using such capacitors. Originally they were either not present (for insulated pick ups, very dangerous) or now leaky (also dangerous).

[Dunc100]

Hi again everyone and thanks for your supportive comments and advice.

So, I have done the test outlined in post #3 regards to the live and neutral resistances to the chassis and initially I got nothing. after a few attempts in various positions on the chassis I feared the worst. Fortunately I reread post 3 and realised that during the clean up I had removed the bulb for the dial lamp, sometimes its the simple things isn't it? Anyway replacing the bulb and retesting gave me the following resistance readings which I presume are ok.

Live to chassis = no reading (I am having to use my cheapest, nastiest DMM as I leant my half decent one to a friend last week!) I think this is ok.

Neutral to chassis = 250 Ohms. About right?

I have printed the schematic along with the resister and capacitor values. Had a slight giggle when I realised they list the "condensers" values in uuf rather than the more familiar pf or nf. I guess in the '30s they hadn't thought of what to call something smaller than micro!

The service sheet is excellent as the expected voltage and current are noted for each valve, useful. This brings me to C22 and a suitable replacement. The grid voltages don't look too high on the grid, less than 100V. Am I correct in thinking a 100V to 200V cap would be fine? I.E no need for a 450V version?

Having read the schematic and squinted into the chassis i have located C22, I think. If I am right its a black paper cap. Correct? If a "guts" photo would be helpful I can provide one.

The volume control (R8) looks to me like a gain control rather than a traditional volume which I was expecting to see further down the signal path. Is this usual for this era radio?

As my OP said I am not familiar with radio and I will be having to ask loads of "simple" questions. There seems to be some discussion about the relative merits of this design VS "Super Het". Could someone point me in a good direction to better understanding how each of these designs works?

Regarding antenna (not sure if its plural has an S!). In my youth I would plug any old bit of wire in and get reception. This was in the 80's though and I was a lad who made do! This time around I would like to do it properly. Googling "frame antenna" offered load of pictures of a variety of shapes and sizes. Most seem to be DIY rather than off the shelf. Any thoughts on where to go for an easy description of making what I need?

@Maarten It would be interesting to learn the history of this particular set. I have tried to take photos of the type plate but just get flash rebound. I can tell you that the number I previously put as a model number is indeed the serial number it also has a capital M infront of it. The only other info on the plate is the model number 838U.
There are a couple of other markings on the chassis that might help.
Located on the rear of the chassis on the top is "10W"
Located on the front, top of the chassis and sort of between the On/Off volume knob and the tuning knob is "4915".

Once I get confirmation of the correct voltage for C22 I will source some. I take it the usual suspects would stock them, Farnell, Mouser etc. Personally I have used Rapid Electronics recently with reasonable shipping and quick turnaround.

I'm looking forward to restuffing as I think it will look best. If I do this I suppose a note on the inside of the machine explaining what I have done would help any future owners. I wouldn't want them ripping out my work presuming that they are originals!!

Thanks again, I'm really looking forward to hearing how she sounds.

[Station X]

Originally Posted by Dunc100

Live to chassis = no reading (I am having to use my cheapest, nastiest DMM as I leant my half decent one to a friend last week!) I think this is ok.

Neutral to chassis = 250 Ohms. About right?

Can you clarify what you mean by "no reading" please. Open circuit or short circuit?

[Dunc100]

Open Circuit. Too much to read on this Multmeter, I think.

Basically on all ranges the DMM does not read any resistance. Like I say its a cheap one which puts a vertical line / 1 on the screen if the meter range is too low or you have the probes not attached to anything. This stays like that when I test the live wire to chassis, throughout the ranges.

Can't wait to get my nicer one back it has a higher range than this thing.

Edit: tried again but this time used the continuity test between Neutral and chassis. Clear continuity here so thats good?

Still cant get the DMM to pick anything at all from live to chassis

[dave walsh]

Given it's your first set Duncan, you had no knowledge of live chassis techniques and confused the mains with receiving earth it's much better to be delayed and go slowly anyway. The Mains Transformer was usually the most expensive production item so it was left out for economy and an achievable price on the market. This half wave type of circuitry was used in many items right through to the sixties particularly TV's and the now very trendy record players into which some people appear to dive without any apparent awareness of risk. This is quite anxiety provoking.

There will be much you can do without the mains, especially with the really knowledgeable members here as a guide. When you do apply power however, a light bulb in series with MAINS earth [ie in the plug] and with the other end clipped on the chassis is a further safeguard as it will always illuminate your mistake if the wiring is the wrong way round and the chassis is "live"-easily done! This has saved me a couple of times from a nasty "belt" if not full termination of my activities. Be carefull there

Dave W

[Dunc100]

Hi Dave and thanks for the advice.

I totally agree on not rushing but getting things right. I did say I had no knowledge of radio and that's the reason for joining here, to learn.

I get the idea of the "safety bulb" and will definitely use this when the time comes to apply power. I'm a way off doing that anyway as I need to (at least) make sure that the set is as safe as it can be and that C22 is replaced to prevent damage to the power valve and possibly OT.

The live chassis thing is totally knew to me, I'm not scared but yes I am going to be very careful. I've built my own valve guitar amp previously so am used to testing with one hand in my back pocket

Thanks for not telling me to give it to an expert, I appreciate everyones input!

[TonyDuell]

With a live-chassis set like this, if the set is unplugged from the mains and the on/off switch on the set turned on, there should be some non-infinite resistance between the live and neutral wires of the mains cable. There is a circuit through the switch, the barretter, the valve heaters (filaments) and back to the other side of the mains cable. The fact that you can get a resistance from the neutral wire to the chassis but not from the live wire to the chasiss suggests to me that this circuit is open Perhaps the switch has failed, or one of the filaments has burnt out. Anyway. that woold be the first thing I would vheck. Since you must do all these tests with the set unplugged from the mains it's relatively safe.

As regards geting round the live chassis, you can use something called an isolating transfomer. This is double-wound (2 separate windings) transformer that takes 230V (or whatever) mains in, and gives 230 (or whatever) out to the set. The point being that while one side of the mains input is earthed (the neutral wire of you house mains supply is connected to earth at some point), the output of the transformer is not. Touching any single point in a circuit connected to the output of the transformer should be safe, you would have to touch 2 points to have a complete circuit involving your body. Isolating transformers are not cheap, and are really only needed if you want to connected earthed equipment (like a 'scope) to the radio.

[dave walsh]

That's great Duncan-you are very reassuring. A lot of people come on, say they are going to do something doubtful... regardless of what's been advised and [to make it worse] are never heard off again. I can see that Live chassis designs must seem very counter-inuitive to someone of a later period. The upside is that [with good insulation techniques] there were very few bad outcomes and consumers could aquire items previously well out of reach-like record players..
great if you were a teenager then. It was never used for Guitar amps for obvious reasons though

Dave W

[ms660]

Originally Posted by dave walsh

There will be much you can do without the mains, especially with the really knowledgeable members here as a guide. When you do apply power however, a light bulb in series with MAINS earth [ie in the plug] and with the other end clipped on the chassis is a further safeguard as it will always illuminate your mistake if the wiring is the wrong way round and the chassis is "live"-easily done! This has saved me a couple of times from a nasty "belt" if not full termination of my activities. Be carefull there

Wouldn't that trip the RCD if fitted?

Lawrence.

[dave walsh]

Good point Lawrence-most of my experiences were pre-RCB and the Board here in Bexhill is quite sensitive but I think I could "live" with that happening. It's an additional precaution anyway and visually reassuring. I would always check with a meter first and make sure the bulb wasn't o/c otherwise it's no help at all. I think simply considering how to procede safely is a protection in itself though. It's a matter of choice and not everyone will use a bulb I'm sure. I still would as I'm even more likely to make a daft/dangerous mistake these days, unfortunately

As an aside, I spent a long time last week trying to sort the outside lights tripping a circuit breaker. Eventually I by-passed the outside wire to the lamp on the drive with some heavy duty arctic cable. The original wire half buried by the garden wall turned out to be only 1mm grey house flat T+E that had split or been chewed and was burnt out. Not the best installation I have come across. Every time I thought I'd Isolated a fitting and solved the problem the current built up and fifteen minutes later "pop". A resistance test showed it had to be the wire in the end. Ironically, that's the only time the RCD has not been so quick to trip but at least I can put the Xmas lights out now.

Dave

[ms660]

Yes, with an earth lamp and RCD supply the RCD would trip whichever way the chassis was connected to the mains once power was applied, could be confusing to a beginner.

Continuity test from plug neutral pin to chassis is what I used to do, having said that back in the mid 1960's when I was a bench engineer in the TV trade there was no RCD and no isolation transformers supplying the benches at one place I worked at, so back then it was a case of an earth lamp, it had a picture of an angel ascending to heaven placed above it.

Lawrence.