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 Philips Mod 172 - Interesting!
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 Return to top of page · Post #: 1 · Written at 1:45:09 PM on 24 April 2010.
Flakes's avatar
 Location: Adelaide, SA
 Member since 27 February 2010
 Member #: 630
 Postcount: 392

Hi there

Just found an interesting (to me anyway) Philips set. I have decided to work on this while I wait for parts for my Solonola/Aristocrat.

WHat makes this set interesting is its tuning gang. It is a mechanical drive that winds up and down a former inside a box. (Well having never seen this before that how I will describe it until someone out there can correct me)

I have gorn through all the normal steps of replacing all the caps, Even restuffed the old chassis mount ones.

The only problem is now that I have done this I cant get anything to work. I assume that there was a problem when I started due to a few resistors being changed.

I hooked up to the Phono input my port cd player just to check the audio but only got a very low volume distortion. (Ihave used this on my other radios and normally works well.

I dont even get a whistle from my other radio as I tune across the band.

OK Details are
Philips Aust. Mod 172 AM only with Phono I/P
Valve Line up - 6AN7, 6BH5, 6BD7, 6M5, 6V4

Does anyone have a cct for this or info about it.

Stuff I have done
1. Change all Caps
2. Test transformers
3. Test Speaker
4. Fit 3 cored power cable and Earth
5. Powered up and got Nothin!

Stuff done before me.
Resistors changed across the main filter caps, Output valve and one going to the phono select switch.



Click on image for larger resolution


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Valve radios, They just don't make them like they used to

 
 Return to top of page · Post #: 2 · Written at 2:32:25 PM on 24 April 2010.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 396

Hi Flakes, from your description it could be variable inductance tuning rather than variable capacitance tuning. A Google search on Permeability tuning may help. Ian


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Cheers, Ian

 
 Return to top of page · Post #: 3 · Written at 2:54:11 PM on 24 April 2010.
Flakes's avatar
 Location: Adelaide, SA
 Member since 27 February 2010
 Member #: 630
 Postcount: 392

Thats it. After googling it it makes sense now. The cap is the fixed part and you vary the inductance to tune the cct.

Well that helps me understand how the tuning works.... Now I need to know why the set dosnt work!!!
Smoke Sad Smoke


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Valve radios, They just don't make them like they used to

 
 Return to top of page · Post #: 4 · Written at 7:10:05 PM on 24 April 2010.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4178

No.......... Fixed part is an inductor. Frequency is changed by moving the slug in or out changeing its resonant frequency.

Very common in car radios.

Marc


 
 Return to top of page · Post #: 5 · Written at 7:32:50 PM on 24 April 2010.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6174

I dare say also in push-button consoles like the AWA R283.


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A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 6 · Written at 6:08:35 AM on 25 April 2010.
Flakes's avatar
 Location: Adelaide, SA
 Member since 27 February 2010
 Member #: 630
 Postcount: 392

Sorry I stand corrected. I meant to imply that. Of course you can’t change inductance. Just the resonant frequency!

Long Day!

I have had a bit more of a look at the set and it is confusing me. I have a tasma with the same set of audio and power valves but the circuit is completly different. There is alot more componentry in this set than the Tasma and cant clearly make my own diagram to see where I am going wrong.

I know that I am new to Valves but with my electrical background this set just dosnt make sense....

Sad


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Valve radios, They just don't make them like they used to

 
 Return to top of page · Post #: 7 · Written at 1:12:16 PM on 25 April 2010.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 760

The frequency is changed by moving a slug into or out of a coil of wire. The change of position of the slug changes the inductance of the coil of wire, the cap is kept constant, and that is how the radio is tuned. Same thing is done with slug tuned IF transformers, the inductance is varied a bit during set alignment at the factory to get it on the IF frequency.


 
 Return to top of page · Post #: 8 · Written at 3:07:07 PM on 25 April 2010.
Flakes's avatar
 Location: Adelaide, SA
 Member since 27 February 2010
 Member #: 630
 Postcount: 392

Thanks for that....

I need to know (If anyone has info) what value of resistor is used as the HT dropper across the 2 electros. Also what value resistors go to the grid of the 6M6.

Both of them have been replaced and I think maby this is my problem.

Thanks
Smile


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Valve radios, They just don't make them like they used to

 
 Return to top of page · Post #: 9 · Written at 4:01:17 PM on 26 April 2010.
Flakes's avatar
 Location: Adelaide, SA
 Member since 27 February 2010
 Member #: 630
 Postcount: 392

I have checked the OP tx and seems ok. anyone know why the volume would be very low and distorted?


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Valve radios, They just don't make them like they used to

 
 Return to top of page · Post #: 10 · Written at 12:40:12 AM on 27 April 2010.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4178

Explain resistors "across" main filter caps. The only time you see them across the cap is as a voltage divider if they are in series and too small for the HT. eg CRO has 2 x 470K as it has 450V caps and can get to 800+ volts.

You may have a screen divider, HMV used to decouple them? I would expect about 2-6K from the cathode of the rectifier, taking the place of a choke and having an electro either side?

We need to see a circuit or we are speculating. Philips often ran feedback from the secondary of the output transformer, that can cause havok if it's reverse phased.

What voltage is the HT, distortion and / or can be caused by low voltage, the filter cap reversed draging down the voltage, failure to put in the PU coupling if its's meant to have one. Filter cap on the wrong side of back bias. burned back bias. cooked cathode resistors. wiring errors. Incorrect or failed plate bypass cap.Dud valve.

Impedance mismatch, or overloading by the CD or both.

6M5 is notorious for silver tracking. Grid resistor is speculation as it could have a 47K grid stopper then 500K to 1M which could also be involved in the feed back circuit.
Philips did that sort of thing.

Unfortunately, we really do need more info.That number is not in AORSM and most of that number series had PP output.

Philips would likely have more parts to do things better as it was likely aimed at the higher end market.

Marc


 
 Return to top of page · Post #: 11 · Written at 2:01:07 AM on 27 April 2010.
Flakes's avatar
 Location: Adelaide, SA
 Member since 27 February 2010
 Member #: 630
 Postcount: 392

When I said across I meant between.

I have obtained a rough copy of the cct now so I should be able to try and find where I have gone wrong (Or the person before me).

One thing that is interesting, the switch on the front, when turned to phono it cuts off the voltage and grounds the grid of V1 and V2 (Turning then off to reduce interference). I suspect that the resistor in this line is open (I have tested it in cct a suspect it was faulty as it read open) But was not rushing to change it until I got audio happening.

The value of the resistor I was talking about across (Between) the 2 filter caps is a 1K. I have used a 1.2K 5w as it was all I had at the time. I knew it would be close but I guess that it could be a little large if you say that the HT voltage being low can cause distorted O/P. The CD player has been used on 2 other sets that I have restored one was the Astor that you helped on and another Kriesler.

I plan to thoroughly test all resistors in the audio stage and then check all my caps that I have changed.

The cct has made things clear now that I see the way that they have arranged things. My drawing was way off to the point it went in loops and back on its self in a few places.

I guess I still have a bit to learn.....


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Valve radios, They just don't make them like they used to

 
 Return to top of page · Post #: 12 · Written at 3:25:03 PM on 27 April 2010.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4178

My general plan with radio's that I am forced to, or consider it advisable to, draw a circuit is based on a bit of experience.
After 40 years one generally has a fair idea of the likely plot.

I got wise some time ago & bought a simple AutoCad program that had an add on electrical symbol library as one package module. This decision I have never regreted.

With the aid of a valve data manual or "Frank's Electron Tube pages", you draw the valves and their pinouts and the transformers, roughly as they sit in the radio.

Allow spacing for tuning coils and switches if they are SW,
You may need to do some shuffling.

Then you gradually add wires & the caps & resistors.

I always advocate tacking photo's before attack, for the benefit of interuptions & senior moments.

Coloured pencils are handy.

Some early sets used magnet pickups in them others crystal in them. Often the magnetic one was in the cathode circuit.

1K2 will cause some drop but not massive. As I have said countless times; I always check resistors as I change caps. The Astor football (Brown version of the one in the May Silicon Chip) had several replaced, whilst doing this.

This actually led to the realisation that the back bias was open, a dead set clue of a HV short. The set would not have run.

Apart from the Filter caps being seriously leaky (For some reason I checked them, I knew one was gone) I checked the valves in a tester (set not run) and the 6V6 was shorted.

It is the correct order to start at the power supply & work backwards. I am always ammused when six people looked perplexed at a radio, not making radio noise, only to realise that it is on PU or the essential (to that radio) link is out.

Marcc


 
 Return to top of page · Post #: 13 · Written at 4:09:47 PM on 27 April 2010.
Flakes's avatar
 Location: Adelaide, SA
 Member since 27 February 2010
 Member #: 630
 Postcount: 392

I havent had time to work on the radio today but I will post up the photos of the cct that I obtained from Mr Richard Begbie. Its not real clear but I have now something to work from. I am seeming to get muddled up when it comes to feedback lines and the tone control when I drew my version.

I used the website you mentioned as well for info on Valves. that was my starting point.

I checked most of the resistors when replacing caps and from the badly faded and cracked off colour codes worked out that most were within 10% toll.

This set should have been thrown out but I am trying to get as much experience with Valves before getting into my other sets. Hence all the questions in my other posts for the 2 other sets. I just should have started with the simple ones but the old wooden and bakerlite sets look great and are of more attraction to me.

What Autocad program do you use? I am currently messing around with things the very hard way of MS Paint, cutting and cropping other images to piece a cct together. Its time consuming but I have plenty of time when not at work.


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Valve radios, They just don't make them like they used to

 
 Return to top of page · Post #: 14 · Written at 10:28:08 PM on 27 April 2010.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4178

The original with the symbol library dates back to Windows 3.1. I did have hassles with the last Epson Inkjet printer which caused a conflict and you could not print from it. The 360 column matrix however could.

I also bought TurboCAD 12 which was handy for odd jobs & I could send the other files to it. Since the Epson tossed in the towel, I bought a Canon Pixma that actually has no trouble with anything so far.

I would suggest while paint will get there, you will be flat out getting it all in, yet alone seeing the big picture. The old fashioned 2B (or not 2B) & graph paper would actually give a better result and be faster (been there done that).

Might be an idea to send circuit & I can compare with that which I have. Sometimes (eg some HMV nippers ) circuits did not vary much between several models.

Marc


 
 Return to top of page · Post #: 15 · Written at 11:22:02 PM on 27 April 2010.
Flakes's avatar
 Location: Adelaide, SA
 Member since 27 February 2010
 Member #: 630
 Postcount: 392

I sent Brad an email from my work account with the cct I obtained. I dont have your email here but I am sure if Brad has time he will send the files to you.

At least with the proper cct you might be able to give me a few clues on where to start


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Valve radios, They just don't make them like they used to

 
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