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Old 25th Aug 2019, 7:38 pm   #21
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Arrow Re: Philips 170A restoration

Paul: reference your post 17. It is not my intention to ignore that post, but I feel that the OP could benefit from a brief remark about 'regulation' - albeit in addition to yours.

A regulator: the basic idea. The fundamental principal of any type of regulator is that it regulates - that is to say it maintains a constant output irrespective of the demands place on that output. This 'regulation' is achieved by feedback: a sample of the output is compared to some unvarying reference and the output is thus adjusted to compensate for changes in that output.
HTH,

Al.
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Old 25th Aug 2019, 9:06 pm   #22
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Default Re: Philips 170A restoration

Well I'll leave the valves alone as they work fine although I do have some conductive paint but its grey ew. If need be I can always use that if the valves start playing up cheap alternative.
Tin foil so you just wrap a sheet of it around the valve loosely? Or do you need to push it down onto the conductive wire then just wrap?

Well thanks for the feedback on a regulator did not realise it would cause such a stir. Kinda took the original questions in another direction I'll choose my words carefully from now on me thinks.

Another question are those caps the 0.047uf ones coated in tar? As its definitely not wax. As I still have the original wax electrolytic in there which tested fine and no signs of degrading. Just curious? Not come across these types before.

Plus these what people call dog bone resistors are they just a smaller version of a wire wound? And what wattage are they? normally looking at size 5mm length by about 2/3mm diameter would they be around 0.5 watt?
Cheers Chris
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Old 25th Aug 2019, 9:17 pm   #23
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Default Re: Philips 170A restoration

Hi Chris, nice work. Once you get a decent aerial connected you should be pleasantly surprised how strong and clear the reception can be even on Short Wave. A good aerial can also improve the signal to noise ratio if you have LED lights, routers and switch mode power supplies within the house. Before I get shot down it might not help of course if you are surrounded by neighbours with lots of similar appliances! Thanks for the photo of the cabinet interior showing the speaker mounting point. I've searched everywhere for a decent pic like that. On my set as I mentioned elsewhere I am transplanting a chassis from a Mullard MAS281/15 wooden cased set into an empty bakelite cabinet and so I have made a baffle board on which to mount the speaker - hence the need to get a clear idea of where to cut the speaker hole. Cheers, Jerry

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Old 25th Aug 2019, 9:23 pm   #24
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Default Re: Philips 170A restoration

The caps are coated in what is known as bitumen or pitch. Philips used a lot of them but they are just as susceptible to moisture ingress over the years which degrades them I.e. makes them leak dc. The foil wrap on the EF39 needs to be tight round the bottom and electrically connected to the chassis wire. You can put a turn or 2 of wire over the foil to do this. Dog bone resistors are usually carbon types and come in different sizes and ratings. The size you mention is probably 0.5W. Cheers, J
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Old 25th Aug 2019, 11:15 pm   #25
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Default Re: Philips 170A restoration

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Originally Posted by cdm1christopher View Post
Well I'll leave the valves alone as they work fine although I do have some conductive paint but its grey.
Yes, I've used that grey conductive paint a few times to redo the screening - and it always worked well. Just make sure that you have a bare wire, electrically connected to that paint and to pin 1 of the valve base: that maintains the screening, since pin 1 is - or should be - connected to chassis at the valve socket.
Although red is the most usual colour for the screening of an EF39 (and ECH35), occasionally I have seen some EF39 that were grey. From memory, they were probably ex-military versions with a 'VR' number: same valve, though.

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Old 25th Aug 2019, 11:25 pm   #26
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Arrow Re: Philips 170A restoration

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Well thanks for the feedback on a regulator. Did not realise it would cause such a stir.
Chris
It didn't cause a 'stir' at all Chris. I, for one, was simply trying to help you, since you seemed to have misunderstood just what a 'regulator' is and what it does.

One of the great things about this Forum is the tremendous help that various members provide to others - and sometimes that 'other' is a member whose been 'doing electronics' for years and years. It's such a vast subject that no-one can be totally knowledgeable about all of it. And, of course, 'electronics' is changing all the time - sometimes very fast too - or so it seems to me.

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Old 27th Aug 2019, 11:03 am   #27
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Default Re: Philips 170A restoration

I'm glad the pics helped Jerry bit of a coincidence. Think the baffle on mine is 1/4 pitch pine. Whether that makes a sonic difference than normal ply I do not know only ever repaired speakers not built any.
Not sure what ya mean about router LEDs as an aerial!
Switced her on yesterday everything at okay even on that little Ali plate was picking up stations all over the world nice one.
The EM34 is a bit dull but all of the coating has worn off so the panel lights are reflecting through the valve so will re spray that. Have not touched the caps underneath yet 0.047uf but think I will change along with some of the resistors. The wire used is horrendous stuff not sure why they used it must have been a better quality available at the time.

Good luck with your project I'll have nose on your thread.

Cheers for info Al I'll coat them EF39 valves as pointless buying new if their working okay just paint over the wire wrapped around the bases.

Well good to know did not cause a stir.

What I was gonna ask and forgot from one of the cans with the yellow cases with large top cap attached going to one of the EF39s managed to have a look and it seems to be a shielded cable with what looks like ferrite ceramic beads running through the middle. What is this called and is it acting as signal component? Plus is it worth replacing?

Pics attached of valve and cabinet the yellow casing can be seen on my other pics.

Cheers Chris
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Old 27th Aug 2019, 1:23 pm   #28
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Default Re: Philips 170A restoration

Hi Chris, thanks for the info re: baffle board. I will post some pictures when I get the missing chassis bits from Sideband, who has helped me out no end on this - also Old John with speaker cloth. The issue with indoor aerials is pickup of interference radiated by routers, LED lights and assoc power supplies. They often produce lots of background A.M. noise across the bands sometimes sounding like a deep fat fryer or sometimes just a background buzz. I wasn't suggesting using them as an aerial, it's just that a length of wire plugged into the aerial socket (or your aluminium plate) will pick up this noise. An outside aerial sometimes can help as the incoming wanted signal should be (but not guaranteed to be) stronger than local interference. The cable to the top cap of the EF39 is a "special" and if you replace it you will likely affect the sensitivity/alignment of the set. It is a form of coaxial cable but if you replaced it with audio grade coax (or a plain wire) the capacitance between the centre core and ground will be markedly different and will upset the tuning of the IF coil to which it is connected. Don't go there! Cheers, Jerry
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Old 29th Aug 2019, 1:25 pm   #29
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Default Re: Philips 170A restoration

Cheers Jerry I'll leave that alone then don't have equipment to re align a radio ew.
Well I sprayed the EM34 valve made huge difference on eye can actually see it now so saved around 40 to 80 quid there. Decided to get two NOS EF39 valves at 6 quid each not gonna break the bank as the others although original pentone have just been salvaged but will keep them. The new AZ31 doing its job. I'll measure voltages later.
Changed all capacitors not the trimmers of course seems to have made reception exceptionally good with aerial earthed to the plumbing theres not much interference at all plus have been picking up a lot more stations. The main change is on the tone seems to be quite bassy now.

Changed the wax 25uf with good quality Vishay and the 0.1uf with a PIO cap.

But! changing these caps ****** nightmare as you cannot move the valve bases to get to the leads and then you move a wire out the way which decides to crumble on you. So I ended up cutting the leads and attaching that way. I was gonna drill out valve base rivets and bolt them done but I'll think on that one as some of the wiring definitely needs replacing which would make access much easier. These are definitely not the easiest of units to work on!
Plus also thinking of replacing the resistors at some stage might help with the tone.

I've kept the original capacitors as I'll melt the tar off them which will come in handy as I noticed that the solder points on the transformers where originally covered over with a light dob of tar.

Luckily the tuning dial cable is all brand new including the springs which was a bonus.

I'm running it in all day today just to make sure nothing is amiss.

But all in all very nice radio and does not seem to be many bakerlite ones around in good condition. I think it was a good buy at 25 quid seen a couple been refurbed go for over 250 and some in poor condition valued selling at 100 quid so quids in there.

Pic of magic eye working.

Cheers Chris
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Old 29th Aug 2019, 2:35 pm   #30
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Default Re: Philips 170A restoration

Don't change things for the sake of it! The resistors will be fine and changing them won't 'improve the tone'! No harm in checking some of the higher value ones as these tend to drift higher but remember most of these have a 20% tolerance so if a 680K resistor is reading as much as 816K....it's fine! Replacing it with a modern 5% won't make a scrap of difference. Even if any are out of the 20% don't bust a gut changing them......believe it or not most could be out by as much as 50% and wouldn't make any audible difference......there are exceptions to that depending on circuit position and function but in most cases you needn't bother. You are dealing with valve circuitry which is far less critical than modern solid-state stuff where a few ohms can mean something working or not working.

Up to you of course, just trying to save you a lot of unnecessary work. For the record, my 170a has all but one of it's original valves (I had to change the rectifier) and has all of it's original resistors. You don't have to use 'audio grade' (PIO) capacitors. Just ordinary polyester will do fine and last forever.
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Old 29th Aug 2019, 5:56 pm   #31
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Default Re: Philips 170A restoration

Thanks for info yeah I've used polys just have a few PIO laying around so whacked one in.

Think along the signal path the carbon resistors can become noisy when out of spec so worth checking them but if you say the rest will be fine out of spec then I'll leave them alone as you say quite a bit of work on these nothing that easy to get too and desoldering half the time seems you can do more damage than good. All those tags are pain lifting up the lips.

Things I keep noticing one of which the tunning dial on front end has a metal spindle on the shaft and on cleaning as it was covered in dried up oil/grease has spring clips attached and beneath them are what look like wipers! These go over the metal spindle. Now on this unit when tunning it's stiff but when you stop when picking up a channel it become loose and seems to allow you to fine tune. Is this an actual feature or just the spindle slightly loose? Plus what is that spindle with wipers on it for? Any ideas?

Apologies for all questions but good to learn what specific things do especially when you have not come across it before.

Many thanks to you all for your input much appreciated Chris

I think if an NOS EBL31 comes up be worth buying seem like gold dust.

Yeah I replaced rectifier the filament voltage exactly 4 volt was surprised by that spot on.

She's still running been on since 9am no problems encountered but as Jerry said need to sort out decent aerial. Got length wire in garden about 45ft long I'll hook it upto that see what receptions like.

It also looks like someone has retuned it as few of the tunning capacitors have had the covers removed and looks like the wire has been unwound and then cut and removed from the coils.
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Old 29th Aug 2019, 6:43 pm   #32
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Default Re: Philips 170A restoration

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Think along the signal path the carbon resistors can become noisy when out of spec so worth checking them but if you say the rest will be fine out of spec then I'll leave them alone

We are not talking anywhere near Hi Fi or low noise here.....it's a 1946 radio. once again modern Hi Fi solid state....yes of course resistors can cause noise in certain places. I doubt you will hear any change with something as low-fi as this radio....but again it's up to you.
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Old 29th Aug 2019, 7:37 pm   #33
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Default Re: Philips 170A restoration

My Philips 650A with the similar case and chassis, where the 170A design originated from, still has all its original components except that the electrolytics have been replaced, keeping the originals just for show. And the radio works just fine. No need to replace other components. If an FM source or good record deck output is fed to the gram input the dual cone (parasitic centre cone) 8 inch loudspeaker sounds very good.
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Old 29th Aug 2019, 8:38 pm   #34
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Default Re: Philips 170A restoration

Ah that sounds interesting I've got a dual 714q deck I'll plug that in and give it a go see if it works. I'll need to put in 2 rca inputs as the originals not designed to accept rca plugs. I've got some lying around so it's not gonna cost anything. Is that what you did with your unit?

Yes your right I'm thinking along the lines of valve amps and solid state as that's what I usually refurb mess around with. Keep forgetting it's a RADIO. I've just finished a quad 2 mono block amp and the mono QC2 pre amp so think my heads still in that mode.

Mind you does anyone know about the tunning dial as mentioned in my previous post. Forget about resistors leave them be.

Cheers Chris
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Old 29th Aug 2019, 10:52 pm   #35
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Default Re: Philips 170A restoration

I just fitted splitpin type connectors to wires that went into the two sockets on the gram input. The audio stage is all just the output valve.
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Old 30th Aug 2019, 8:26 am   #36
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Default Re: Philips 170A restoration

Hi Chris, yes you're spot on with the "slow motion" tuning drive - just a friction band round the outer pulley - allows faster sweep when going from one end of the dial to the other then picks up the geared-down motion for fine tuning for a few turns across each band. Simple but effective. Cheers, Jerry
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Old 30th Aug 2019, 10:37 am   #37
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Default Re: Philips 170A restoration

The 170A chassis utilises the EF39 IF amplifier as an audio preamplifier stage on "gram". The anode supply is disconnected and the screen grid of the EF39 is used, effectively as a triode anode. The screen grid decoupling capacitor is then used to couple the audio to the EBL31 control grid.

This arrangement gives rather limited gain on "gram", but should be sufficient if a large input signal is available, such as from a CD player or 'phone. It also explains why the "gram" switch is separate from the wavechange switch and has a number of contacts. Sets as supplied new had a tie-on label fixed to the "gram" switch, reminding users to select "radio" when needed.

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Old 30th Aug 2019, 11:38 am   #38
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Default Re: Philips 170A restoration

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The 170A chassis utilises the EF39 IF amplifier as an audio preamplifier stage on "gram". The anode supply is disconnected and the screen grid of the EF39 is used, effectively as a triode anode. The screen grid decoupling capacitor is then used to couple the audio to the EBL31 control grid.

Leon.
Yes not just the EBL1 output valve in the 650A. The same arrangement is used though using an EF9 Ct8 side lock base. The pickup is shunted by a 0.5 megOhm resistor and fed via the secondary coil of the first IF stage to the grid of the EF9. A switch in the HT feed via the first IF primary cuts the anode supply to the oscillator EK2 muting the radio (so worth checking this switch if the radio isn't working!).
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Old 30th Aug 2019, 1:09 pm   #39
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Question Re: Philips 170A restoration

Just a minor question which may be of interest.

Looking at the photos of the glass tuning scale shown in photos in this thread, it looks slightly different to the one fitted in a 170A that I remember from my childhood, which, yes, was many, many years ago. So, were there different tuning scales fitted or is my memory deceiving me? However, I must say that I have a strong feeling that it isn't. I spent many happy hours scanning SW with that set, watching the cursor as it traversed the scale and listening to all the sounds (and not necessarily speech) emanating from the speaker.

Just curious.

Al.
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Old 30th Aug 2019, 2:15 pm   #40
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Default Re: Philips 170A restoration

The only different scales I've seen are for the continental version.
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