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 Restoring a Kriesler 3K15 receiver
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 Return to top of page · Post #: 1 · Written at 8:42:07 AM on 28 August 2016.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 883

Hi All, here is my story about restoring this set.
While the chassis turned out very good I did not do so well with the cabinet mainly from a lack of talent!
There are some questions about the set that puzzle me and any comment would be welcome.
1/ the dial plate markings are just weird I just cant see any logic in the way they are distributed randomly and not in horizontal lines state by state. Why is this so?
2/ The IF response has a normal skirt slope below the nominal 458Kc and starts to slope down past nominal but then peaks up partially at about 50% again at around 480Kc before dropping off. Thus the response has an extra lower "Hump" on that side. Shifting the core positions just moved the nominal response around but did not remove the basic double hump shape. The set is very sensitive and very selective hauling in dozens of BC and SW stations and generates plenty of AGC so has plenty of controlled gain indicating nothing is badly wrong, so why the double hump response?
3/ I don't think the set was designed to have a short wave set of coils as the change switch is stuck on the side like an afterthought and not front panel mounted. Are there any other sets like this?

I call this work I have done a "restoration" and I have tried to use as much of the original material as possible and did not re-design anything!
I give my self about 80/100 for the chassis/speaker and 30/100 for the cabinet, that item should have been binned and remade completely.

Restoring a Kriesler 3K15 Valve Radio

Cheers, Fred.


 
 Return to top of page · Post #: 2 · Written at 9:13:05 AM on 28 August 2016.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1381


 
 Return to top of page · Post #: 3 · Written at 11:23:11 AM on 28 August 2016.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 411

Hi Fred,

It is awhile since I went through this theory and practice, but a few ideas ........ the double hump is usually associated with coupled resonance circuits ie 2 identical parallel resonance circuits, tuned to the same frequency, slightly decoupled to give a double hump ..... used for broadening the bandwidth of IF's. The hump is close to symmetrical. I've always assumed that the degree of coupling of L's in the IF can is set by the manufacturer and alignment of the IF is by adjustment of the cores ... so that both circuits are resonating at the same frequency.

I am wondering if both circuits at the same frequency? Are both caps good? Do both cores shift the passband similarly?

Cheers,
Ian


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Cheers, Ian

 
 Return to top of page · Post #: 4 · Written at 9:18:57 AM on 29 August 2016.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 883

Hi Ian, re the IF response, yes, I was wondering if it is an attempt as you say to broaden the response , but has gone wrong, OR, there is a subtle fault in one of the coils. The total band width ignoring the second bump is about 20Kc and the skirts are very steep making the set very selective. I can hear soft hetrodynes when you tune slightly up scale from a station that don't appear when you tune down scale indicating the assymetric nature of the IF response. Each core did peak up as expected, the first 3 ( plate , grid, plate ) have a sharp peak and the 4th that is loaded by the detector diode has a flatter peak, or, maybe its the odd one? I could move the whole double hump response up and down a centre frequency by moving all cores the same direction. The cores by the way were sealed with goop as received and my final settings are very close to original.
I'm developing my "wobbulator" test oscillator now using octal valves and once that is functional and tested on some coils and sets i'll pull the Kriesler off the shelf and have another look at the response this time on the CRO screen!
Now that the PDF is up on this thread you can see the IF's in photo and just look like normal double coils with ceramic caps.
Also you can see the crazy dial markings, any clue on that?
Cheers, Fred.


 
 Return to top of page · Post #: 5 · Written at 9:49:07 AM on 29 August 2016.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 411

Hi Fred,

Just found your 'link' to the refurb of this radio. Haven't read it in detail as yet, but I am already smiling at some of your comments ....

* page 5 ...... regarding bulk replacement of capacitors ....... "all that would have done was demonstrate that replacing all the capacitors fixes most ills but then I would have learnt NOTHING. I like to get into trouble and then reason my way out and learning something,
not just be a parts jockey." That is usually my approach also .... I hasten to add that I do understand the commercial need, or sometimes a safety need, to do bulk replacement.

* page 6 ....... "the worst thing I ever did was a long while ago was to strip a car gearbox down and try and reassemble it from memory and the workshop handbook. Some gearboxes are dead simple to re build but this one was a British 4 speed box with hundreds of parts" An MG by any chance ? Sold my '67 recently .... never stripped down the gearbox, but had a lot of fun with everything alse including the SU carbies.

* re your double hump .... I had in mind that you were using a Sweep generator and viewing the resonance curve directly ... much easier to see and analyse the 'problem'.

Re your workmanship and refurb .... excellent.

Cheers,
Ian


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Cheers, Ian

 
 Return to top of page · Post #: 6 · Written at 3:49:10 PM on 29 August 2016.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 411

Hi Fred, a 'partial short' within a coil could lower its L and add resistance into the parallel resonance circuit, causing a lowering of its Q, hence lower peak and broader skirt ..... and shift frequency higher.
Good luck, and let us know the outcome when you get back to it.
Ian


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Cheers, Ian

 
 Return to top of page · Post #: 7 · Written at 2:18:13 PM on 30 August 2016.
Sirwin's avatar
 Location: QLD
 Member since 10 April 2009
 Member #: 465
 Postcount: 104

Hello Fred. I have an explanation about the dial. The pointer is supposed to be at an angle, so that is intersects the transparent strips adjacent to the station indicated. The angle should be such that when the top of the pointer intersects the top of one of the strips, the bottom part of the angled section of the pointer should be just about to intersect the bottom of the next strip. That way the effective dial scale length is much greater than the length of the dial cord traverse. I've seen this on a few radios, mostly British. I have a Kriesler, model unknown, which has the same cabinet and dial as yours, but I can't tell if the pointer is angled without pulling the chassis out. It is not the same as yours, having an R.F. stage.

As to the double hump issue, it could be a faulty resonating capacitor or capacitors in the I.F.T.s. If part of the capacitor has developed a high series resistance to one of its leads, then you will get two humps in the associated resonant circuit. You will get a broad hump when both parts of the capacitor are lumped in with the resonant circuit, and a sharper hump from the section which is good alone resonates with the coil. Just a theory, but I've seen all sorts of problems caused by faulty resonating capacitors in I.F.T.s recently. Nearly drove me around the bend some of them! By the way, your resonating capacitors are mica types, - very troublesome, not ceramic types, although they are housed in ceramic cases. Ceramic capacitors were not much used in Australia at the time, although AWA did use them ( N750 etc) as temperature compensating elements in some of their push-button sets, and in their 7-banders.

Hope that helps. Cheers, Stuart


 
 Return to top of page · Post #: 8 · Written at 9:10:04 AM on 1 September 2016.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 883

Hi All, and thank you Stuart!
I feel like a COMPLETE PRAT.
Of course the dial pointer should be at an angle. ( slaps side of face!).
That is WHY it has the funny bell crank at the bottom and why the thing was too long when pointing straight up!
I just now grabbed a pair of long nose pliers and from inside the cabinet (carefully) bent the thing over a bit and yes now I see it all, the pointer intersects with the stations...oooooo...durrrrr!
As well I think you are all correct in that one of the resonating caps or a coil is a bit leaky/shorty and that would be the one that had a very flat peak. I thought it was just the detector loading but now I am really suspicious.
So the next time I pull the chassis out I have 2 jobs to do.
1/ investigate the coil and repair/replace.
2/ complete the alinement now lining up with the stations!.
Thank you all for the clues.
Cheers, FredL.


 
 Return to top of page · Post #: 9 · Written at 1:17:56 PM on 29 September 2016.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1912

Hi Fred

Re the double hump in the IF response.

This is normally caused by overcoupling between the IFT windings. Assuming it was designed properly in the first place, the usual reason for this is tuning the IFT with the slugs in the INNER position. Try winding them right out and then tune for the FIRST peak on the way in.

Late post I know but hope it helps.


 
 Return to top of page · Post #: 10 · Written at 8:47:30 PM on 21 November 2016.
Jimb's Gravatar
 Location: Kanahooka, NSW
 Member since 18 November 2016
 Member #: 2012
 Postcount: 662

Hi Fred.
Had a look at your restoration.
Great job, I would not have your level of patience to have undertaken that.
Regards.
Jimb


 
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