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Adding scale lamps

Hints and tips for vintage technology repair and restoration
 

Adding scale lamps

Post by unclereggie » Sat Mar 16, 2013 12:18 pm

Not for a moment would I suggest that anyone would want to change the authenticity of a particular set :wink: but if they did (and for experimentation purposes) ...where is the safest/best place to add in a wire to run two bulbs to this set as a 'mod' - Ekco U245 - to illuminate the tuning scale?

 
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Re: Adding scale lamps

Post by Jamie » Sat Mar 16, 2013 12:20 pm

A conversion I have thought about too on this set... However you cannot simply run it from the Valve Heater chains.. As this would cause all sorts of problems... I think the easiest way could be to mount a small transformer from mains to 6.5V and do it that way? (Or a dropper resistor).. But of course this set gives off a large amount of heat anyway! So I decided against the mod as I didn't want even more heat. :O

My restoration can be found here.. viewtopic.php?f=3&t=1240&p=9464&hilit=ekco+u245#p9464

 

Re: Adding scale lamps

Post by unclereggie » Sat Mar 16, 2013 12:27 pm

OOh. I shall study that thread closely. Mine was a fairly simple job but (once again... :( I am plagued with a moderate buzzing. I left that alone while I worked on the other two sets I've got going.

 
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Re: Adding scale lamps

Post by Jamie » Sat Mar 16, 2013 12:31 pm

Odd? My set has no buzz whatsoever? You sure it's not local interference? Could be anything these days.. Strip lights.. WIFI routers.. Microwaves.. Computers.. Even Flat Screen TVs *yuck* bhbg

 
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Re: Adding scale lamps

Post by Michael Watterson » Sat Mar 16, 2013 12:53 pm

Moderate buzzing:

Switch EVERYTHING else off one at a time.

Interference sources:
Soldering Iron (I scrapped a controller as it was just a Triac based like lighting dimmer switch)
LED, CFL, Florescent lights
Low voltage Halogen (may use 12V SMPSU)
Any light on a dimmer switch
Mobile phone / Tablet / Laptop
LED displays (the multiplexing) like on Alarm clock or old frequency counter
PC PSU, even if "off" unless it has a physical on/off switch.
Chargers, PSUs
Fridges, freezer motors when running.
CPU in Dishwasher, Cooker, Microwave even when doing nothing.
TV set sometimes even in standby, a CRT can be better or worse than an LCD.
Set top box. Sky boxes have a fake standby that only kills the modulator and AV on Scart /HDMI as they need to get updates (or content if a plus model).
Anything with a Standby mode rather than a real disconnecting the mains can produce interference.

Use a portable radio on batteries on LW to identify source and verify it's via mains (if it has a mains PSU does it get noisier on mains?). When you put the portable right beside the offending article you will hear the exact same flavour of interference. It may be worst every 45kHz (or some other multiple between 18kHz and 90kHz) etc rather than the same all over the LW.

Extreme test for an AC/DC Radio ... 134 off D Cells :)

 
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Re: Adding scale lamps

Post by Michael Watterson » Sat Mar 16, 2013 1:01 pm

For an AC/DC set one lamp option is a low power mains lamp. My 1955 Ekco actually has this as original feature.

But really I wouldn't add extra scale lighting except on a DIY or new model. Thin end of a wedge.

 

Re: Adding scale lamps

Post by unclereggie » Sat Mar 16, 2013 2:41 pm

The odd thing is (and the reason I keep banging on about this issue) is that I have a PYE Piper from about that same era which is totally silent - when the vol is down, as you turn it up the sound is clear and hissy (as you'd expect). This set sits on the window ledge with all these others so (presumably) is vulnerable to the same influx. Unless the PYE workings are somehow superior. From this 'anomaly' I have drawn the conclusion that the hummy-buzzy ones are not working correctly. Possibly wrongly. And yes, I have all of the above electrical items in and around, as do we all. I shall have a full 'power down' (when 'she who must be obeyed has gone out) and see what happens. :thumbr:

(Note - Perhaps migrate this bit of the discussion to the other Ekco U245 thread? as it's not really about lamps anymore.

 
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Re: Adding scale lamps

Post by GlowingAnode » Sat Mar 16, 2013 3:15 pm

Jamie wrote:A conversion I have thought about too on this set... However you cannot simply run it from the Valve Heater chains.. As this would cause all sorts of problems...


Care to expand Jamie?
Cheers,
Rob.

 
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Re: Adding scale lamps

Post by Michael Watterson » Sat Mar 16, 2013 3:17 pm

Pye workings are good.

Also AC/DC sets are more vulnerable to interference on mains and mains hum than parallel filaments and transformer :
There is some capacitive heater / cathode coupling, so with 0V to 12V DC on Cathode and maybe 60V and 80V on heater, more hum and interference buzz on AC/DC vs 6.3V heaters.

The Mains Transformer is rubbish at passing high frequency AC. On an AC/DC set there are low impedance paths to chassis and HT for Interference. The Electrolytic HT caps are poor at higher frequencies, hence often a 10nF to 100nF across the AC mains in and often on HT rail too.

AC/DC sets existed by 1950s mainly as a cost reduction rather than for DC mains. A dropper resistor was much much cheaper than a mains transformer. Also AC/DC sets can be made a bit smaller (or a lot smaller if you don't care about the cabinet and back life!). AC/DC sets in general and especially smaller ones are a "cost reduction" effort, thus some are poorer performance and more sensitive to hum & Mains noise than transformer driven sets.

I noticed my Marconiphone Battery/Mains set (dropper resistor) was MUCH "buzzier" on mains than the Invicta 28 and Vidor Battery Mains sets. They both have transformers. Strangely with the "shaver" transformer (isolation) it was much worse till I added a pair of 2KV 2nF ceramic caps from the isolated socket to the earth wire on the mains lead. That made it almost as good as the other two.

My least affected by mains Interference Battery/Mains sets? The Pye PE94MBQ/LW and Pye P131MBQ. Both however at times on LW are noisier on mains than battery.

A VGA/SVGA/XVGA CRT monitor running at normal graphics modes was fine. But some game resolutions and in standby it's a disaster.

My LPR ethernet Server for parallel port laser printer was a huge source of interference (linear PSU plug top transformer) till I put it on ground beside PSU with DC cable all coiled up. Ferrite Clamps on the DC cable didn't cure it.

The round "bobble" at connector ends of many cables is a ferrite ring common mode choke to reduce radiated RF. USB cables are supposed to be balanced and screened and thus supposed to not need it. Some are just 4 core alarm wiring cable and don't meet USB specs and radiate RF.

 
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Re: Adding scale lamps

Post by Stitch » Sat Mar 16, 2013 5:22 pm

Michael Watterson wrote:.....

But really I wouldn't add extra scale lighting except on a DIY or new model. Thin end of a wedge.


I agree, but but everyone to their own its your radio.

My avatar is the pilot lamp on an Ultra U696 but there isn't a scale lamp so I think sometimes they're as much an indication the radio is on as to illuminate the whole dial.
I've seen people complaining about lamps being dim but its often normal operation e.g. the service date for the VHF90 says "glows dimly in operation".

John

 

Re: Adding scale lamps

Post by unclereggie » Sat Mar 16, 2013 5:39 pm

Oh, I know that this is another of those 'hot potatos' but I do tend to play 'devil's advocate' sometimes. Personally, I'd rather ask a question and appear a fool for a moment than never ask at all and remain a fool for life.

It also occurs to me that there may well be a huge number of readers of these threads who might also be thinking similar things and so I'm happy to be the one who chirps up and looks a berk. :oops: We're not all experts and that's why discussion groups are so useful.

 
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Re: Adding scale lamps

Post by Refugee » Sat Mar 16, 2013 7:03 pm

If i were to add LEDs to a radio dial I would first locate a faulty bulb and liberate the metal part.
Then i would solder in a jack plug and connect a couple of strings of LED on a thin bit of strip board and fit them to solder tags fitted under the scale fixing screws. This makes it quick to convert it to original again.
There is a bit of fiddling needed to get this to work and it can all be done through the metal base of an old bulb.

 
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Re: Adding scale lamps

Post by CTV » Sat Mar 16, 2013 7:16 pm

There's already been a top tip for LEDs as dial bulbs here

 
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Re: Adding scale lamps

Post by GlowingAnode » Sun Mar 17, 2013 1:59 am

Sorry, still don't understand why you can't add scale lamps to a heater chain and why it might cause a problem? :???:
Rob.

 
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Re: Adding scale lamps

Post by Michael Watterson » Sun Mar 17, 2013 10:23 am

On a "heater chain" the filaments are in series at a particular current (100mA, 150mA common on radios and 300mA on TV) You can only add same current rating (actually to avoid them "blowing" and stopping operation using say 150mA on a 100mA chain is common).

If you tried to have a brighter bulb by having a higher current rating, say 6.3V 300mA instead of 150mA, it will be much dimmer as the dropper and all the filaments are in series and two in series will only drop about 6V instead of 12V, thus filaments and dropper has an extra 6V. (closer to 4V to 5V and 8V to 10V actually)

On a DAC10 (like a DAC90A for bulbs) I couldn't get correct current 3.5V bulbs, so I put 2 x 6.3V 150mA bulbs (which is somewhat brighter than original). This is 12V, so the dropper needs to drop 6V less compared with 3.5V bulbs.

So on a series heater chain you need to adjust the bulb voltage and keep current rating and add bulbs in series and then reset dropper. On Parallel you must have the correct voltage (6.5 or 7V for 6.3V filament and a panel rated bulb not a torch bulb or life is short!).

Also while DAC10 & DAC90A have the lamps at the neutral end of the heater chain only, some sets have lamps across a dropper section or resistor in series with entire current (HT & Filament). These can be 12V, 17V, 20V or 24V etc at 100mA, the parallel resistor may have 50mA and if bulb fails is designed to cope with 150mA at x3 voltage. The Radio then runs on a lower voltage till lamp is replaced. The Portadyne U56 has such an arrangement with one end of bulbs direct to mains live. Naturally a brief short to chassis blows the bulb (easy given open construction).

The DAC90A / DAC10 does have a "ballast" resistor across the lamps too, but filaments run very low if bulbs blow. Since they are at Chassis/Neutral end a short on bulb holder to chassis at worst increases filament & Dropper volts by 5 or 6 (or 10 to 12 on mine).

So Series fed bulbs are deliberately dim to give massive life as failure dramatically affects radio performance and any modification requires thought and care.

 

Re: Adding scale lamps

Post by unclereggie » Sun Mar 17, 2013 10:42 am

Thanks for a very specific answer Michael (and the 'hacks' about LEDs - pretty fascinating ideas there). It confirms my understanding that every single tiny step and detail of a layout contributes to the overall performance and how the seemingly simplest aspect can alter the overall performance. I'm sure I'm not alone in wondering about questions like this. It also goes to prove that harnessing and 'sculpting' with electricity is just not as simple as it might look.

I think the idea came from the allure that radios with inner lamps have - it's a very magical experience watching the thing 'wake up'. That little glow of warm light is almost reassuring in a strange kind of way. I'm sure that in many original designs it was little less than a 'feature' but it certainly is a very attractive one.

 
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Re: Adding scale lamps

Post by Michael Watterson » Sun Mar 17, 2013 11:12 am

In the early days people were encouraged to listen with the lights off to have a more immersive experience. Also often there was no mains socket and the radio plugged into the light socket. 2 and 3 adaptors for lamp sockets quickly appeared, some with a push switch for one socket (push in to set and push in at other side to reset).

Also a room might be lit by a single long life 40W bulb. Often bulbs were longer life than today and thus dimmer and slightly more orange.

The purpose of a Dial lamp isn't to illuminate the scale like a modern phone screen but to indicate the set is on and also to aid tuning in poorly lit evening / dusk conditions.

It's interesting that up to 1949 quite a few battery sets had scale lamp buttons and then very few (Transoceanic 600 from 1957 still had a lamp) though some some transistor transportables, especially high end German models had a scale lamp.

If the room is lit only by a standard lamp or hardly lit at all then much brighter than a DAC90A is annoying. Many modern Sound systems (and some set boxes) are very distracting, not only having an over bright power LED, over bright displays but bright dancing bargraphs (only appropriate on recording gear or mixer and a superfluous distraction for ordinary listening and TV viewing).

So given my comment, no surprise I have no bargraphs, scope displays or visualisation enabled on Winamp, Media Player or others. I use Audacity for recording, then the "metering" is valuable. For Test generation and Measurement I use www.sillanumsoft.org "Visual analyser" which has no shortage of fancy displays. BTW, replaces £1,000s of Audio Test gear if you have a 1/2 decent "Sound card/Chip", if you haven't you can by quality sound I/O in a box with USB less than price of one piece of test gear.

 

Re: Adding scale lamps

Post by unclereggie » Sun Mar 17, 2013 11:36 pm

Clearly so. However, my Philips Philetta has clearly got lamps in there to impress. They are as bright as you please and illuminate the front acrylic panel like a juke box. Quite the little charmer is the Philetta.

And, I completely agree about modern appliances having displays like a slot machine. I once had a cd player that insisted flashing a continuous display (even when on standby) of all its features and functions which after a while became annoying. I got rid of it for that reason alone!

 

Re: Adding scale lamps

Post by unclereggie » Sun Mar 17, 2013 11:43 pm

Michael Watterson wrote:In the early days people were encouraged to listen with the lights off to have a more immersive experience.


As a 'hard-core' fan (and collector) of vintage radio drama, science fiction and comedy I can completely understand this idea. Not only that, but I remember from the 60s that the BBC used to run 'public information' films about how to watch colour television which had very similar suggestions - i.e. watching in a darkened room.

 
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Re: Adding scale lamps

Post by Michael Watterson » Mon Mar 18, 2013 2:29 am

I found a back light unit today of an old transistor USA tuner/amp that had "negative blue" scale. i.e. Black but a travelling orange filtered bulb as scale pointer and blue frequency digits. Entire scale looks solid black when power is off.

This used FIVE 1.25" "fuse style" 6.3V long life lamps for a total current draw of 1.3A! Could be more power than the Push pull stereo amp and tuner would be taking at normal volume. I powered it up and they looked almost like 12V bulbs running at 6.3V (maybe they are!).

I've opened mice and snipped off spurious LEDs.

My son stuck a piece of black tape on the super bright blue LED of his TV when on, dim red in standby only to discover that the Power LED can be turned off by a menu setting so it only is dim red on standby!

 
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Re: Adding scale lamps

Post by davegsm82 » Wed Apr 17, 2013 4:26 pm

Some little bell is ringing in the back of my head about Blue light, something about the centre of your vision isn't as sensitive as the surrounding area, so when you look away the light will be very eye catching.

I used to have a Blue LED digital clock which was like this, I changed it for a green one of lower brightness and all is well now.

Dave.


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