Philco 97 - RF problem... HELP! - Printable Version
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RE: Philco 97 - HOTWIRE - 05-09-2016
HOLD the horses.
Mine is not the same as yours Steve. See that cap block up there in the very corner beside the 85 tube in mine.
Well it aint in yours.
I am now thinking mine is an American model 98 chassis after all. Which would mean I have a Philco 98 chassis in a Philco 98 Cabinat. WOW.
I am off to get a 98 service sheet. Chow.
RE: Philco 97 - kiwi_steve - 05-09-2016
(05-09-2016, 05:01 PM)HOTWIRE Wrote: Hi Steve. Typo on my post. The dial number should be 27-5094.
If you can engage the other members to work with you on the rf problem they are top end when it comes to these philcos. I have only done one of em before but I would say this.
I think you really should be fitting Electrolitics where it says Electrolitics and stay with the Cap values as stated on the service sheets. The philco engineers determined these values for a reason. I would also check the routing of the wiring.
It is important to keep the original routing intact. A simple thing like moving a wire away from the chassis can cause problems. Check all the voltages you have on the service sheets and check that 78 RF tube.
I think you should complete the resistor and cap replacement including the mica. I dont buy in to the notion that mica seldom goes gaga. Any radio I have ever fiddled with has had dodgy mica's.
Finally, I have a spare wave trap (again thanks Ron) Maybe I can email it to you or drop it into your local pub.
Kind Regards Steve.
Will.
I have a spare wave trap
Thanks Will, I'm pretty sure the radio never had the wave trap from factory so unless I can be convinced it needs it I'll just leave that part of the circuit alone... but feel free to drop into the local pub and we can discuss it over a beer or two
(or just email me a beer instead)The cap values are as near to correct as I can get - and I already went through last night and replaced the remaining resistors with modern 1W carbons. I also replaced the 2 x 110pF caps that are (electrically) beside the volume control because they were a little leaky. I'd originally left them alone because of their values. I have no new mica caps in stock, and very rarely change them... only once in fact, and that was because of SMD. I've put 2 new 3kv 100pF ceramics in there. I went through my 100pF caps and found 2 that were reading high so they're 107 and 109pF respectively (I don't believe this point in the circuit really needs micas because it doesn't appear to be a critical tuned circuit - again, I am open to advice). I'm using what I've got there... micas are expensive and my budget is... well, I don't have one because that would imply I have money spare to spend on this
Regarding the polarised / non-polarised nature of the caps in the small can - I did ask about that, but got no feedback. Unless using electrolytics will provide some important advantage I'll leave that. I've used 1uF and 2.2uF... better than the 16uF someone had strung up over there in there in the past (not to mention the 40uF they'd wired across the 1uF!)
The voltages are about right everywhere I have checked and the RF 78 got replaced with a spare I had... no change. I don't have any more, nor does my usual valve guy.
Re the routing, I have changed very little of that - only around the power supply where I've moved the reservoir cap and smoothing cap on to tag strip just below the originals - otherwise everything is as-was. I'm aware that certain parts of the circuit need to be kept as they were designed and I've done that pretty much everywhere.
Interestingly, the one band (SW) that I would expect to be the most finicky and potentially the biggest problem is fine, and the ones I would expect to be easier to sort and giving me the biggest headache. I'm sure I will solve it eventually, and I'm sure it will be something simple, and probably something I did
RE: Philco 97 - kiwi_steve - 05-09-2016
(05-09-2016, 05:28 PM)HOTWIRE Wrote: HOLD the horses.
Mine is not the same as yours Steve. See that cap block up there in the very corner beside the 85 tube in mine.
Well it aint in yours.
I am now thinking mine is an American model 98 chassis after all. Which would mean I have a Philco 98 chassis in a Philco 98 Cabinat. WOW.
I am off to get a 98 service sheet. Chow.
What is the block there for? I have the mounting hole - but not the block. That looks like a resistor on the side of it - is it decoupling the cathode of the 85? I can't quite see in the photo... The 97 circuit shows the 85 cathode straight to the chassis which is how mine is.
The service info for the 97 doesn't show everything in exactly the right place. There is a cap block with two 110pF caps (mentioned above) on the side wall of the chassis - the service info shows it on the bottom of the chassis the way all the others are between the 85 and the ANT coil. Yours is in the same place as mine.
Interesting... they look very similar, I wonder what the actual differences between yours and mine are - seems more like a code change difference than another actual model...
RE: Philco 97 - HOTWIRE - 05-09-2016
Steve. That hole you refer on yours to looks a bit suspicious to me. See the staining on it. I wonder was there a block there at one time. By any chance did you take any photos of it before you worked on it although I cant imagine you somehow lost a block along the way. Maybe. Just maybe the famous ghost repair person was at it back when. That black wire running from the tone control to ground next to the audio transformer looks a bit suspicious too.
Thing is though yours is clearly stamped as a 97 and no block is shown in that position. on the service sheet. Can you have a close up look at that hole stain.
RE: Philco 97 - kiwi_steve - 05-09-2016
Yep, I'll check the hole for threading tonight. Definitely was nothing there when I started, yes I do have a before photo...
[Image: http://i241.photobucket.com/albums/ff222/4wdstuff/Philco%2097/20160430_224511_zpsnkpgvnzp.jpg]
The black wire that appears under the volume control and runs down to the back is one of the shadow meter wires - because I'm working on the shadow meter at the moment and will need to take it out again the wire is above where it normally sits in the layers of rats nest
RE: Philco 97 - kiwi_steve - 05-10-2016
Ok, I experimentally fed the RF coil primary with my sig gen, and put my digital scope on the secondary. With the radio tuned to around 600 on the dial (power off, unplugged) I had to detune the sig gen to around 485kHz to get a peak on the scope... this seems an awfully long way off... is this experiment valid?
RE: Philco 97 - HOTWIRE - 05-10-2016
Got the sheets for 98 and yes mine is 98 yours is 97. That corner block is same as in yours just moved into the corner and an additional cap and resistor added in its original location. So there was no other block in yours. This does not help you any with your RF problem.
My suggestion for what it is worth is to go through your schematic and check all the circuit for any error. Then look at components including if there are mica's in the RF can. Please dont do a Hakka on me over these Mica's steve its just my way of trying to crack the problem. Other suggestions are The pub. The top of a mountain and scream or finally bring the chassis to a field with a pound of those explosives .................
RE: Philco 97 - kiwi_steve - 05-10-2016
No hakkas from me... problem is, there are just no silver mica's in this circuit that can be changed. The only one is the 110pF cap to ground from the primary side... there's nothing on the secondary - which is the tuned side. Just the trimmers, but those work fine.
I will go over the wiring again tomorrow, its got to be something... probably something I did.
RE: Philco 97 - RF problem... HELP! - kiwi_steve - 05-11-2016
I'm stumped.
Anyone?
RE: Philco 97 - RF problem... HELP! - Radioroslyn - 05-11-2016
> hakkas
??
I'm a bit of a primitive guy so I would connect an outdoor antenna to the Philco and loose couple the output of the RF amp (grid cap of the 6A7) to the antenna post of a BC set. This can be accomplished by a a small cap (100pf or so or 2 pieces of hookup wire twisted together a bunch of times). Tune both sets to a station on the same frequency and see if the station as you tune the Philco.
By connecting the generator and scope to the coil it may detune it from added capacity from each device.
Terry
RE: Philco 97 - RF problem... HELP! - kiwi_steve - 05-11-2016
Cheers Terry...
Haka
https://www.youtube.com/watch?v=yiKFYTFJ_kw
Something fairly unique to NZ and its surrounding pacific islands. Often considered a 'war dance' of sorts.
Thanks for the advice... I will give that a go. What are you expecting I would see as a positive result on this?
Cheers
Steve
RE: Philco 97 - RF problem... HELP! - HOTWIRE - 05-12-2016
AND do you have the radio to ground. Separate from house ground. IE uncouple the house ground from the plug (no ground to house.) I have a Rebar thumped down into DAMP earth outside the house with a cable running to my radio room which I hook up to Radio. For Safety I have a Knife switch isolating the ground AND separately the External Arial as protection in the event of lightning. I shut down everything from a master switch and drop the knife switch as a habit.
So
1. Good external Arial check.
2. External ground check.
3. Check the nica on the inside to of the can.
3 follow Terry,s suggestion above to de-tune or re-tune the rf.
Wow. Great Hakka.
Will.
RE: Philco 97 - RF problem... HELP! - Radioroslyn - 05-12-2016
(05-11-2016, 10:04 PM)kiwi_steve Wrote: Cheers Terry...If all is well the output from the Philco's rf amp will increase the volume on the bc set as it is tuned to the same frequency. If not there will not be any increase.
Haka
https://www.youtube.com/watch?v=yiKFYTFJ_kw
Something fairly unique to NZ and its surrounding pacific islands. Often considered a 'war dance' of sorts.
Thanks for the advice... I will give that a go. What are you expecting I would see as a positive result on this?
Cheers
Steve
Or if you have at your disposal a signal and a tracer you could feed a modulated rf signal into the ant post and use the rf probe on the tracer to listen to it at the grid cap of the 6A7. Should hear an increase in the volume in the tracer as you tune the Philco to the same frequency as the generator.
At first I googled Hakka and came up with folks from a certain part of China. My daughter is from one of the regions listed. Didn't quite understand. Tnx for the clarification. Amazing what grown men will do!
GL
Terry
RE: Philco 97 - RF problem... HELP! - morzh - 05-12-2016
Haka is a maori people (Polynesia) war dance.
Today it is a part of sports ritual in those places.
Like Rugby etc.
RE: Philco 97 - RF problem... HELP! - HOTWIRE - 05-12-2016
Yep Hakka Chinese speak the Hakka dialect. . Not sure if it has two k,s I was doing a project in Malaysia many years ago close to a chinese Hakka village there called jeram. They ran from china during the mao tsi tung time. I made friends with the headman and stayed in his "house" for weeks. They traded with the Aslie a pigmy jungle people apparently geneticaly descended from LUCY I think. Never did see any Philco's in that village though.