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1959 KB QV30/1

 
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Re: 1959 KB QV30/1

Post by Marcus 3500 » Tue Jun 14, 2016 2:16 am

Hello,

I did one of these sets back in 2008 / 2009 I think. I used to watch the Z cars episodes I have on it, but got bored with it's boring (to me appearance) And went back to using my 1400 / 1500 sets.

Good luck with it.
Cross 1.JPG


Regards,
Marcus.

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Tue Jun 14, 2016 11:14 pm

All references are taken from the Trader sheet linked to on Photobucket.

As such there is no "V13", at least on my set, the frame output in the diagram supplied by Chris is V12.

So in answer to the voltage questions:

V12 pin 7 is at 208V instead of 190V
V12 pin 1 is -23V as opposed to -43V

When the focus circuit is disconnected, the boost HT comes up slightly to 610V from 590V but still nowhere near what it should be.

Many thanks,
AidanLunn

 
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Re: 1959 KB QV30/1

Post by freya » Wed Jun 15, 2016 7:35 am

Thanks for clearing up the service sheet info, you are using the ERT service sheet.
The only other component I can see that may cause the issue is C86, if this were leaking it would drag the boost down being linked to the HT rail.

 
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Re: 1959 KB QV30/1

Post by Cathovisor » Wed Jun 15, 2016 3:16 pm

Can I just add for the avoidance of future doubt - when referring to "Trader" sheets, we are referring solely to those produced by the Wireless and Electrical Trader.

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Sat Jun 18, 2016 2:40 am

Further updates:

Using the ERT sheets in Photobucket.

I have checked C86 and this is a polypropylene cap that I had previously replaced that is working fine.

While taking measurements, I noticed that R71 (820K) had risen to 1M. Replaced, not much difference, but now the height as the control is advanced meets a maximum then reduces as the control is further advanced.

I also noticed that R102 I had accidentally put in a 220K as opposed to 820K. In the early stages of this restoration, the only service literature I had to go off before I obtained the ERT sheet was the RTVS 1959-60 book. In this it has the original QV30 but it acknowledges the QV30/1 in a footnote as having "a number of minor variations". In fact, this is somewhat misleading as most of the frame stage is different!! I only ordered the ERT sheet once it became clear that the circuit in the RTVS book had more than just "minor" differences and resembled very little the frame circuit of the set I had in front of me. So that is another possibility I will need to look up, any components changed to the wrong values because of Newnes' reluctance to include a separate entry for the QV30/1 in that year's book!



As for the low boost HT I have had a suspicion all along that it is a problem with *generating* the boost HT in the first place as opposed to something loading it down. The boost HT with all loads present and correct is now about 610V. The confirmation it is a problem with generating the boost HT came when I cut off the boost line from C62 and C63 and then measured at that point - just 640V. The boost capacitor is working fine, this I had also replaced recently (1000V 100nF polyprop).

My NOS/new PY83s and PL81s still haven't arrived so I still can't test if this is tired valves or not (I only have used examples of both types, unfortunately) so it could be those, or does this low boost sound like something much more sinister?

 
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Re: 1959 KB QV30/1

Post by sideband » Sat Jun 18, 2016 7:39 am

AidanLunn wrote:I also noticed that R102 I had accidentally put in a 220K as opposed to 820K. In the early stages of this restoration, the only service literature I had to go off before I obtained the ERT sheet was the RTVS 1959-60 book. In this it has the original QV30 but it acknowledges the QV30/1 in a footnote as having "a number of minor variations". In fact, this is somewhat misleading as most of the frame stage is different!! I only ordered the ERT sheet once it became clear that the circuit in the RTVS book had more than just "minor" differences and resembled very little the frame circuit of the set I had in front of me. So that is another possibility I will need to look up, any components changed to the wrong values because of Newnes' reluctance to include a separate entry for the QV30/1 in that year's book!


Question: Why do you not change 'like for like'? Surely if you find an 820K (which is obviously original) in the set and the circuit you have (which is known to be different) says 220K, you change it for an 820K anyway! Suppose you didn't have a circuit at all and you were tracing through the frame stage and found an 820K had gone high. With no other reference you would replace it with another 820K wouldn't you? Or would you say....'Haven't got one of those so I'll stick a 220K in as that's the highest I've got'......no I don't think you would.....or would you?

Same with any other components. Your comment above saying 'any other component changed to the wrong value because of Newnes reluctance to include a separate entry...' is NOT down to Newnes. They already said that there were differences so you should have been aware of that.

Circuits are not always 100% correct. When you consider production changes during the life of any set and frequent 'manufacturer modifications' it's a wonder some circuits bare any resemblance to the later production runs. Remember also that Newnes (and Trader and all the other companies producing circuits) were not the manufacturers and some manufacturers were reluctant to give anything other than basic information. Typical example the well-known KB 'Toaster' radio....I have three circuits for that set and none of them quite match the radio I have. I didn't 'modify' any of the radio circuitry to match the available circuits when I restored it though!

On rare occasions, there can be production errors where a wrong value is fitted but that generally results in the set not working properly and it's either found in final testing or very soon after the set is sold.

So basically try to replace 'Like for like' as far as possible especially when there are doubts about the information you have. Only modify component value when there is a known change. Remember that the set has worked for probably 10 or more years in its first lease of life.

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Sat Jun 18, 2016 2:18 pm

sideband wrote:
Question: Why do you not change 'like for like'? Surely if you find an 820K (which is obviously original) in the set and the circuit you have (which is known to be different) says 220K, you change it for an 820K anyway! Suppose you didn't have a circuit at all and you were tracing through the frame stage and found an 820K had gone high. With no other reference you would replace it with another 820K wouldn't you? Or would you say....'Haven't got one of those so I'll stick a 220K in as that's the highest I've got'......no I don't think you would.....or would you?


I do as a rule.

However in this case when I was replacing R102 I only had the RTVS servicing book at that point. The "original" R102 was so mucky that I couldn't make out the coloured bands and when I attempted to clean it the paint came off with the muck. The "original" is in speech marks because the soldering on this as I got it was not original anyway (it was significantly poorer than the manufacturer's and even mine!), so even then there is the possibility of there being a bodge.

 
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Re: 1959 KB QV30/1

Post by Spot-Wobble » Sat Jun 18, 2016 3:29 pm

Short of using a valve voltmeter or modern equivalent you will not get a true boost HT voltage reading due to the high impedance of the circuit.
So your boost HT is probably higher than you have actually measured it.....

Andy

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Tue Jun 21, 2016 11:58 pm

So, with the advice of all of you still ringing in my ears and a few days break while I cleared my head, I came back to the set today and after replacing R116, R144 & R148 (again, using ERT diagram as a reference sheet), the image you see is the result.

R116 & R148 had both gone high (116 to 1.1M from 820K and 148 to 16M from 1M) and 144 had gone completely o/c.

A huge step forward and this *almost* confirms if there is a boost HT problem. I called it a night (and tidied up my workspace!) before I could test a trio of new line osc, LOP and boost rectifier valves on it. Once done, taking note of Andy's point re: meters and boost HT voltages above, this should absolutely confirm if it's a boost HT problem or not, as the boost rail still measures 595V on my meter now that all loads on that rail are present.

Earlier in the restoration those who read the first post will remember that I had to take the tube out. Of course to do this necessitates removing the scanning coils and the width sleeve. After checking the valves, this will be my next port of call - I have already confirmed that the width sleeve works to an extent because the width sleeve adjusted to both its extremities gives or takes about an inch either side of the raster.
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KB10.jpg

 
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Re: 1959 KB QV30/1

Post by Katie Bush » Wed Jun 22, 2016 12:36 am

Hi Aidan,

Be careful when adjusting the "shorted turn device" that's the euphemistically called 'width sleeve' - it must never be adjusted to its extremities since this will cause overheating.. This device is there primarily to trim the line linearity.. If it has 'tell-tale' marks as to where it has been originally set, this is where it should be set to again, then the lack of width investigated more thoroughly, if it still exists.

Marion

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Wed Jun 22, 2016 12:46 am

Thank you Marion, this is the first time I have ever attended to a line linearity/width sleeve.

There are no "tell tale" marks but I took photos and either the ERT sheet or the RTVS book for the original QV30 states that the patch to make contact on the width sleeve should be in line with the "anode button" (rubber anode cap?).

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Mon Jun 27, 2016 6:37 am

Well I replaced the line output, line oscillator and boost diode valves and moved the sleeve to how I had it from a photo I took and only a slight increase in width was the result.

I began checking the windings on the LOPT. I have a suspicion that these readings may be down to my meter instead of the one the ERT sheet uses for references, but decreased width is a symptom of LOPT failre. Most of the other windings measured OK, however winding 49 measured 12.3Ohm instead of 15Ohm that the manual assumes. Winding 50 measures 210Ohm instead of 150Ohm. This is with the tuning cap disconnected. I will, of course, measure the other coils in the circuit, but as the LOPT primary is very warm - touch becomes unbearable after a few seconds.

When I got this set there were signs it hadn't bee used too much. Thick layer of white dust and it had the original two-pin round pin mains plug. So I'm thinking that LOPT failure happened and the set was used for some time with decreased width before being pensioned off?

Bu as I'm new to what could possibly be primary winding failure on an LOPT, I can't think of any other cause than some of the other chokes associated with the width.
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Re: 1959 KB QV30/1

Post by Duke Nukem » Mon Jun 27, 2016 12:51 pm

There's a whiff of lack-of-line-drive about this; what is the voltage on the grid of the line output bottle, is it about right ? Check R54 - I'm assuming C48 already replaced. I'm also assuming C51 (grid coupling cap) will have been changed, so next triple check the screen resistor R61.

TTFN,
Jon

(PS: Apologies if I missed above points in previous responses).

 
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Re: 1959 KB QV30/1

Post by AidanLunn » Tue Jul 05, 2016 1:34 pm

I'm using the ERT sheet, not the other "Trader" sheet (I thought, because of what "ERT" stood for, that ERT was "Trader", since corrected by Catho).

I have replaced C59 in the ERT sheets I linked to on Photobucket on the first page of the thread. I have also replaced R62 and R66 as they had both gone out of spec.

Replacing all these has resulted in only a very minimal increase of the width.

The voltage at the screen of V6 is 148V, close enough to the 152V that the ERT diagram specifies, but when the set is warmed up, both R56 and R57 begin "sweating" they get that hot. V6 doesn't have an internal short as I've replaced it with another PCF80 and it's exactly the same. I doubt it's a short in C53 or C54 as the 148V would be much lower and there would be a low voltage at the cathode - that's at 4V, close enough to the ERT's guidance of 4.2V

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