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 HMV Little Nipper Super Five
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 Return to top of page · Post #: 1 · Written at 8:32:49 PM on 30 June 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1576

I have started work on this little baby and am quite surprised at the quality of the components in it. 90% of the caps are the Philips ceramic types of which I am told hardly ever give any grief. I changed the power cord and two ducon electros plus two Ducon .0100μF caps. It does work and is very sensitive but very low volume and slightly distorted. My next trick is to test all the resistors . What I found very strange was there was two 10k resistors wound together to make a 5k resistor and this was actually illustrated in the service manual "why would this be so". why not just have a larger 5k resistor. Also can any of you tell me in plain English how to test the high tension voltage and heater voltage ie where to put the probe that's not on the valve. I am using this little baby to help myself to learn these basics and if all else fails I will take it to my buddy that lives around the corner. I will be gifting this one to my brother inlaw in the Philippines at Christmas time.

HMV Little Nipper Super 5 Mantel Radio
HMV Little Nipper Super 5 Mantel Radio


 
 Return to top of page · Post #: 2 · Written at 9:00:36 PM on 30 June 2016.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1381

I'm assuming the two 10k resistors are in the filter circuit, between the 2 main filter electros.

I think it was probably cheaper to use 2 lower-wattage resistors rather than the extra expense of a high-wattage 5k.


 
 Return to top of page · Post #: 3 · Written at 9:05:14 PM on 30 June 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1576

That's exactly where they are.


 
 Return to top of page · Post #: 4 · Written at 10:38:49 PM on 30 June 2016.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4348

I tend to behave as a commercial fixer as I often do that. There is far less risk of damage & considerable stress to be avoided, when the set fails to fire up, if you check the resistors & replace them as you change the caps.

HMV must have bought a semi trailer full of 10k resistors to abuse. The popular 61-51 had parallel 22k resistors (R5 R6) on the screens. With others with same valves they used a single 10k and it often failed as the screen current added up to more than one watt.

HMV normally had all of its socket voltages listed for all valves.

Distortion can be the product of failing to change resistors and the thing should be re-aligned. HMV did not use 455kHz in many of there sets many like 61-51 used 475.5kHz, which is no problem if you calibrate the generator with a counter (Tone off). I calibrate the set using the CRO as the measuring device, as, if there is distortion, I can use it to ping the source.

Grid resistors of around 10M on 6AV6, plate resistors on most det audio valves & grid resistors on 6V6 & similar seem to have an attrition rate. All electrolytics should be replaced & if they back biased it, it may well have an electrolytic across that resistor and it will be positive to chassis & the first filter cap then goes to Neg Centre tap. Mess that configuration up & hum & distortion will normally happen.


 
 Return to top of page · Post #: 5 · Written at 1:06:18 AM on 1 July 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1576

Ok so its sounds like I am on the right track checking the resistors then.


 
 Return to top of page · Post #: 6 · Written at 1:11:30 AM on 1 July 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1576

My Main question is this. Knowing where to put the probe on the valve where do I put the other probe to check the voltage is it the chassis or somewhere else. Ie to check the HT and heater voltage.
Marcc I have been deciphering your advice and I am very thankful for your input. I will certainly go hunting down those ten meg resistors and test them.


 
 Return to top of page · Post #: 7 · Written at 8:40:16 AM on 1 July 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1576

I did get to replace the 10 meg resistor this morning and there has been noticeable improvement. I will endeavour to test all resistors especially the high value ones.


 
 Return to top of page · Post #: 8 · Written at 9:39:33 AM on 1 July 2016.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4348

In finding just one dud resistor, you reinforce my comment. Rework is undesirable, time wasting, and presents additional risk. The general rule of thumb, bearing in mind that some resistors cannot be accurately tested "in circuit", is that if it is high in circuit it is more than probable that it is a dud.

Meters can get you into trouble and like the circuit, you need to understand them and how they work to interpret what they are telling you. The Analogue meter is not dead, nor is the Digital suitable for some applications.

Most decent (and we do not have a lot) data sheets will tell you the Ohms per volt of the meter used, perhaps the type and what it is referenced to, which is in most cases the chassis (even if the chassis is back biased).

Meter (& instrument) quality & designed purpose are a factor. Many modern instruments cannot handle the Voltages, RF and short, or get into strife with e.g. reflexed circuits where you can have RF, AF, & DC wizzing around in the same valve. Because they read & then write, you will not often get a good reading from dirty DC or any fluctuating voltage with a digital. An analogue meter on DC will not see RF.

The difference is it draws current from the circuit; The DVM is a constant load of around 10Meg & will not draw as much & read higher. The larger, is say a Plate resistor, the more will be the discrepancy as the analogue will load it down.

Heaters may "float" above the chassis (often a twisted pair) but more commonly one heater pin of the socket is grounded to the chassis. The common octals & miniature valve pin outs are referenced to the "Base or wiring side" and are read clockwise: Other sockets may not.

So if you get one off HMV's sheets with the valves with the page with ideograms with voltages on them, that should show you where to measure.

Some times it pays to indicate what the model number, or valve line up is. 61-51 has a whole family called "Little Nipper" and many are the same internally Kriesler Beehive is one with about 26 variants and I have seen three at a Radio Club where none were internally the same.


 
 Return to top of page · Post #: 9 · Written at 6:13:24 PM on 1 July 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1576

As a rule I never test resistors in circuit. On Monday night I will seek out all the high value resistors and change them out. Then we may be looking to test the valves.


 
 Return to top of page · Post #: 10 · Written at 11:41:50 PM on 1 July 2016.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4348

You can test quite a few in circuit, but you need to understand it relative to where it is and the device you use. A common LV ohm meter be it digital, or analogue, has insufficient voltage to be able to see a cold valve as anything other than an open circuit.

If you study Plate, control grids and cathodes (without electrolytic caps across the resistor) the ohm meter sees those elements as an open circuit & will only measure the resistor.

I see no need to change resistors that are within 10% (in my book) of assigned value and having to go back & change them now is, from my way of doing things, a methodology fail. As I have said apart from the added damage risk, in a commercial refurbish brutal efficiency is king.

As far as I am concerned I do not want to see that radio again for a long time if ever & rapid fails are not good for repeat business. So nothing gets treated as a hobby fix.

A good guide to a valves behaviour is to stick it in a radio with the same valve (if available) & was working perfectly until you put the unknown valve in it.


 
 Return to top of page · Post #: 11 · Written at 3:16:11 AM on 26 July 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1576

Well I found what the problem was with this little baby. Its speaker transformer was open circuit. What threw me was that there was still sound but low volume . Well I bought a speaker transformer from Jaycar and converted it to operate on valve radio and hey presto I have a very strong little performer. I could always remember this one as a child was a very strong performer and its back to its former glory.


 
 Return to top of page · Post #: 12 · Written at 12:54:40 PM on 26 July 2016.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6014

A re-cap of that model here (he doesn't attend to performance issues): https://www.youtube.com/watch?v=Zv0eSZSXp-k


 
 Return to top of page · Post #: 13 · Written at 10:04:42 PM on 26 July 2016.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6354

Photos uploaded.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 14 · Written at 12:56:13 AM on 28 July 2016.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1576

Managed to find time to watch the above youtube clip and when it showed the two electros it confirmed in my mind that one of the originals in mine was actually reversed. I would be asking how this happened because they were the original caps. how did this radio ever work unless it was reversed later by someone that had no idea.


 
 Return to top of page · Post #: 15 · Written at 1:37:30 AM on 28 July 2016.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6014

how did this radio ever work unless it was reversed later by someone that had no idea.

Reverse the polarity of an electro and it will usually explode. If yours was still intact, and the radio was operational, then I guess there's the chance that it was polarity-mislabeled by the manufacturer -- though I have never come across an example of that myself, and where they are axials the polarity is deal easy to determine because the case (negative) is usually exposed.

Otherwise we have to assume that it's been monkeyed with, as Marc would say.


 
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