It is currently Tue Jun 19, 2018 7:31 am

Readings from a lamp limiter

 
Posts: 2853
Joined: Wed Jul 27, 2011 7:13 pm
Location: Croydon

Re: Readings from a lamp limiter

Post by sideband » Mon Feb 09, 2015 8:39 pm

The trouble is that not all meters say the same when reading open circuit. An old one I had read OL. I was never sure if it meant 'overload' or 'Off limit'....The one I have now reads INF for infinity.

 

Re: Readings from a lamp limiter

Post by unclereggie » Mon Feb 09, 2015 8:58 pm

Connecting the mains voltage directly to the transformer did nothing other than give me a nice bright glowing lightbulb.

 
Posts: 1218
Joined: Thu Jul 28, 2011 10:28 pm
Location: Sunderland

Re: Readings from a lamp limiter

Post by Red_to_Black » Mon Feb 09, 2015 9:19 pm

unclereggie wrote:Connecting the mains voltage directly to the transformer did nothing other than give me a nice bright glowing lightbulb.


Did you disconnect the existing mains connections from the transformer first ?

If not that would be my next move, I still think you probably have something amiss between the switch and the transformer, possibly a miswire, at least by doing what I suggest above you can determine if it is the transformer itself, or something prior.

Can you post a snippet of the diagram around the mains input area ?

 

Re: Readings from a lamp limiter

Post by unclereggie » Mon Feb 09, 2015 9:29 pm

Yes I did. I took the wire that connects the switch to the transformer, desoldered it from the switch contacts and connected it to the mains wires which I had also disconnected from the switch. In the instance the switch played no part and the voltage was going direct to the transformer, as there was an average reading from the primary coil the other suspect might be the voltage selector at the top currently set to 250v

Diagram shortly

 
Posts: 1218
Joined: Thu Jul 28, 2011 10:28 pm
Location: Sunderland

Re: Readings from a lamp limiter

Post by Red_to_Black » Mon Feb 09, 2015 9:32 pm

unclereggie wrote:Yes I did. I took the wire that connects the switch to the transformer, desoldered it from the switch contacts and connected it to the mains wires which I had also disconnected from the switch. In the instance the switch played no part and the voltage was going direct to the transformer, as there was an average reading from the primary coil the other suspect might be the voltage selector at the top currently set to 250v

Diagram shortly

No, I meant disconnect the existing mains wires from the transformer itself first, then apply your mains to just the transformer, this will eliminate everything prior to the transformer, including any miswires. :bba

Edit:
Ah! I just noticed you mentioned a voltage selector, so you may not be able to do what I was suggesting easily.
Last edited by Red_to_Black on Mon Feb 09, 2015 9:56 pm, edited 2 times in total.

 
Posts: 3712
Joined: Sun Feb 12, 2012 7:43 pm
Location: North Hykeham, Lincolnshire and Ilford, Essex (but not for much longer ...!)

Re: Readings from a lamp limiter

Post by Terrykc » Mon Feb 09, 2015 9:33 pm

sideband wrote:The trouble is that not all meters say the same when reading open circuit. An old one I had read OL. I was never sure if it meant 'overload' or 'Off limit'....The one I have now reads INF for infinity.

My Wavetek reads 1.OL and some el cheapo meters just read 1 on the extreme left hand end of the display.

Of course, it is all explained in the instructions ...


Image

 

Re: Readings from a lamp limiter

Post by unclereggie » Mon Feb 09, 2015 9:58 pm

2015-02-09 at 20.jpg


"disconnect the existing mains wires from the transformer itself first, then apply your mains to just the transformer,"

This is what I did. I'm not being very clear am I? my apologies. I also tried moving the voltage selector down to 230 V with no effect.

 
Posts: 1218
Joined: Thu Jul 28, 2011 10:28 pm
Location: Sunderland

Re: Readings from a lamp limiter

Post by Red_to_Black » Mon Feb 09, 2015 10:09 pm

Judging by that drawing you would be able to do what I suggested after all :bba

I would disconnect temporarily everything from the primary side of the transformer, either photograph it or take notes of what went where.

Then supply it via your lamp limiter to the points marked as per the drawing, maybe using the 250V tap for your L, terminal 1 for your N.

Do this with a temporary lead made up, so you are using nothing else in the set from the mains input point of view, if your lamp still lights up brightly then it would suggest that the transformer is perhaps faulty after all.

It is important that you don't use anything already in the set on the primary side at this point, as we are trying to eliminate that part for the moment.

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Readings from a lamp limiter

Post by PYE625 » Mon Feb 09, 2015 10:19 pm

So lets recap.
The switch has now been eliminated from the list of problems.
The lamp limiter glows brightly when just the transformer is powered directly.

Are you finding that the primary is still measuring 26 ohms?
If it is, then a short in the secondry side is possible as it will tend to draw a lot of current through the lamp limiter.
A short in the heater wiring, for example, or on the AC side of the rectifier.

You mentioned a scrap set, you could use that as a reference as to resistance readings etc.

 
Posts: 377
Joined: Sat Jun 15, 2013 10:59 am
Location: Near Glasgow

Re: Readings from a lamp limiter

Post by niall » Mon Feb 09, 2015 10:21 pm

If as appears to be the case, the transformer primary resistance reads correct but excess current is being drawn when mains is connected, could there be a short on the secondary side, especially as there is also some evidence (wax) that the transformer gets hot?

Edit - I see Andrew beat me to it.
Last edited by niall on Mon Feb 09, 2015 10:22 pm, edited 1 time in total.

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Readings from a lamp limiter

Post by PYE625 » Mon Feb 09, 2015 10:21 pm

Sorry Red to Black, i'll remove my post if it adds to the confusion lol

I can't, so stuck with it i'm afraid. Ill shut-up now as the old saying "too many cooks" :bbc

 
Posts: 1218
Joined: Thu Jul 28, 2011 10:28 pm
Location: Sunderland

Re: Readings from a lamp limiter

Post by Red_to_Black » Mon Feb 09, 2015 10:34 pm

PYE625 wrote:Sorry Red to Black, i'll remove my post if it adds to the confusion lol

I can't, so stuck with it i'm afraid. Ill shut-up now as the old saying "too many cooks" :bbc


No, no need to :) it is a free forum, :cca

I would not have thought a heavy load on the secondary side would cause the lamp limiter to glow that bright, especially on the lower voltage rails, heaters and the like due to the winding ratios, a fully shorted turn might.

I am a bit suspicious of the voltage selector at the moment to be honest.

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Readings from a lamp limiter

Post by PYE625 » Mon Feb 09, 2015 10:43 pm

:thumb
I think the best way is perhaps to use the scrap set as a reference, at least a guide as to the primary and voltage selector wiring, and then perhaps some resistance checks too.
Fault-finding can lead to many merry dances and red herrings :ccb

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Readings from a lamp limiter

Post by PYE625 » Mon Feb 09, 2015 11:08 pm

unclereggie, if you want, I will get my VHF61 out and post some pictures of the transformer wiring layout and take some resistance measurements. If there is anything in particular you need reference to, it may help.

Will look in again tomorrow (Tuesday).

 
Posts: 2986
Joined: Thu Jun 28, 2012 12:20 pm
Location: The Vale Of York

Re: Readings from a lamp limiter

Post by Katie Bush » Tue Feb 10, 2015 12:40 am

sideband wrote:The trouble is that not all meters say the same when reading open circuit. An old one I had read OL. I was never sure if it meant 'overload' or 'Off limit'....The one I have now reads INF for infinity.


Hi Rich,

I always took OL to mean 'Off Line' - Or in other words, not connected to a readable source, be that Volts, Amps, Hz, uF/pF, or Ohms (etc.).

I have to confess, INF-inity would make more sense, though it's still saying the same thing - No readable source.

Marion

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Readings from a lamp limiter

Post by Refugee » Tue Feb 10, 2015 12:52 am

I always take OL to mean overload.
On a resistance range that is so as the resistance is above the maximum the meter can read when the probes are open circuit. It is a bit more obvious on a voltage range though.

 
Posts: 2986
Joined: Thu Jun 28, 2012 12:20 pm
Location: The Vale Of York

Re: Readings from a lamp limiter

Post by Katie Bush » Tue Feb 10, 2015 1:04 am

Refugee wrote:I always take OL to mean overload.
On a resistance range that is so as the resistance is above the maximum the meter can read when the probes are open circuit. It is a bit more obvious on a voltage range though.


The only issue I would have with that interpretation, is that with the probes open circuit, there can't be an overload, likewise, if reading an excessively high value resistance, what is actually being overloaded?

The word "Overload" surely would infer a potentially damaging, or destructive, current passing through the instrument?

Marion

 
Posts: 5843
Joined: Sat Jul 23, 2011 8:19 pm

Re: Readings from a lamp limiter

Post by crustytv » Tue Feb 10, 2015 7:59 am

Ref is correct, see the extract from my Fluke manual. Basically a range that is too high to be measured

ol.jpg

 
Posts: 2513
Joined: Sun Jun 10, 2012 7:23 pm
Location: Basildon

Re: Readings from a lamp limiter

Post by crackle » Tue Feb 10, 2015 8:04 am

Reg
It may help if you check the operation of the transformer again with all the valves removed. Or if easy to do so, disconnect all the secondary wiring from the transformer to the radio circuit. That may help to determine if the fault is in the radio wiring.
Also can you please confirm what wattage lamp you use in your limiter.

Cheers
Mike

 
Posts: 3712
Joined: Sun Feb 12, 2012 7:43 pm
Location: North Hykeham, Lincolnshire and Ilford, Essex (but not for much longer ...!)

Re: Readings from a lamp limiter

Post by Terrykc » Tue Feb 10, 2015 12:26 pm

Here's a possibility that nobody has mentioned, if Reggie still has the earth connected, that is:

L_E_short.jpg


As for as the OL meter indication, as Chris points out it stands for OverLoad but the term may have been originally chosen for convenience. It is actually indicating Over Range but OR is difficult to display using seven segment displays whereas OL is easy!

(I know that modern LCD meter displays are customised but assume the practice is a hangover from the days of 7 segment LED displays.)

 
Posts: 1218
Joined: Thu Jul 28, 2011 10:28 pm
Location: Sunderland

Re: Readings from a lamp limiter

Post by Red_to_Black » Tue Feb 10, 2015 2:21 pm

I thought he was using 2-core cable, and the E was not shown on his circuit. :qq1

I saw the screen part of the transformer, but not where it was connected other than the parts of the secondary circuit as shown in the bit of the diagram. :bba

 

Re: Readings from a lamp limiter

Post by unclereggie » Sat Feb 21, 2015 12:12 pm

I think at this point it might be worth segmenting discussions about specific issues with this specific radio to a new thread. My intention was to highlight the value of a lamp limiter in diagnosing problems with circuits. I think this has been done to great effect and I'd be interested in other accounts of how they have been useful to others. The bulb in my limiter is 60W.

However, the problem raised with my radio should ideally follow a new thread, maybe? (which perhaps Admin could set up). The reason being that: after following various suggestions I have discovered a new symptom. By removing the transformer and comparing it to an identical one from my spare set, I connected the replacement in exactly the same configuration as the schematic (and also a third, working example of this set which I have) only to find that the original effect (i.e.- the lamp glows at full brightness with no effect on the radio) suggesting that the problem lies beyond the transformer. The chances of two transformers being the same (non functioning) is of course possible but this new evidence might point in another direction. I shall investigate further.

 
Posts: 4092
Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Readings from a lamp limiter

Post by Refugee » Sat Feb 21, 2015 1:26 pm

Have you tried the transformer on the bench without anything connected to the secondaries?
Does the lamp still glow full brightness?

 

Re: Readings from a lamp limiter

Post by unclereggie » Sat Feb 21, 2015 2:43 pm

Hi. Yes I did. The lamp did not glow at all with just a mains input to the primary and no other connections. (The transformer was out of the radio, connected to nothing on the secondary.) The mains input voltage was measured as 240V in on both terminals of the primary input. I also got a reading of 6V on the secondary for the scale lamp.

 
Posts: 763
Joined: Sun Aug 07, 2011 5:17 pm
Location: Edinburgh

Re: Readings from a lamp limiter

Post by Alistair D » Sat Feb 21, 2015 2:55 pm

According to the schematic snippet posted earlier, the set has 8 or more valves. I am wondering if 8 cold filaments, as opposed to 5, is too much for a 60W bulb. Try the lamp limiter on the set again with some of the valves removed. The rectifier and output valves probably have the highest current heaters.

Al

PreviousNext

Return to General Work Shop Discussion



Who is online

Users browsing this forum: No registered users and 3 guests