Hi All;
Now that the Philco 45 has been working for several days..
I am wondering, on alot of the Broadcast Band, I get mostly squeels especially in the upper part of the band, where Stations are so close to each other ?? I do get Both Weak and Strong stations..
I have done some adjustments on it, But my thinking is that the IF Transformers are too Broadly Coupled and so let more than one station thru, especially on the outside fringes of its coupling.. Am I anyway near correct in my Thinking or is it that I need to do a real Full Blown Alignment..
My thinking, is I need a Wobbulator or a Signal Generator that can swing 10 to 20 KC on either side of my set frequency and can see what actually my IF Transformers are doing..
Or would an Alignment do what I need ?? I think the Radio is receiving well and is more than able to pull in stations, so I am not sure what is the problem.. I have seen the article about building an IC wobbulator..
THANK YOU marty
Sounds more like a bad bypass capacitor or poor shielding.
Maybe a missing tube shield.
Agreed with previous posts. And if you've dittled with the IF trimmers that will do it too. Always use a generator to adjust the IF stages. You don't need wobbulator. You been reading some old dusty books again. Most of us would know it as a sweep generator. The sets you have been working on only have a single IF amp. You are unable to change the coupling between the coils in side the IF cans( physical spacing) so the bandwidth general is going to stay same. What you can change is the frequency that the IF amp operates. Both IF transformers must be tuned to the same frequency for best performance. The Philco 37-116 and several of the top of the line sets have a knob that moves the coils in the IF cans that change the actual selectivity. Also it has a pot to control the gain of the IF stages so the volume doesn't change as the change the selectivity. Gosh they think of everything!!!!
Terry
Hi All;
Thank You all for Your responses..
Brenda Ann, and Vinzer, I have all of the Tube Shields in place.. I don't know If they are all Grounded.. But, they are all there..
How would I know If I have a Bad Bypass Cap, with out re-placing all of the Caps again ??
The One set of Caps that have Not been Replaced are C22, a pair of .09's in a Block, and the Caps in the Tone Control..
I have a Signal Generator, But not a low enough frequency Sweep Generator, the one Sweep Generator I have is for TV's, an Eico 369..
Radioroslyn, I know what a Sweep Generator is, I just don't have anything in the Radio Frequency Range.. And If needed be I could build the circuit using Ic's for almost nothing, hence Why I mentioned it..
THANK YOU Marty
That dual .09 cap could very well be your problem, since one half is the cathode bypass for your 1st IF amp, while the other half is the screen bypass for the 2nd IF. Replace those with .1's and you should be OK.
Hi All;
THANK YOU Brenda Ann for you response and information..
Would I be better off with .1's or with two .047's on each side ??
THANK YOU Marty
Do you have the grid wire of the 75 tube routed inside the tube shield?
Steve
Do you have the grid wire of the 75 tube routed in side the tube shield?
Steve
Hi All;
Thank You Steve, Yes, I have..
It looks like I will be using the .047's as I have plenty of those.. I am heating up the Iron right now to put them in.. I will let Everyone know of the results..
THANK YOU Marty
Hi All;
I put in the twin .047's in place of the .09's and I took out the Tone control wire and wired in a .01, in its place..
I is alot better, the squeeling is gone except for a little below 700KC.. And I think that an alignment would help there..
I have tweeked the IF transformers by sound and put them closer to where they need to be, I had offset them a little to help get rid of the squeel.. But, since it is not there now, I could put them closer to where they need to be..
The Radio is playing more like it should be..
I can now do a real Alignment, since I think the Radio is ready for One..
THANK YOU to EveryOne Marty
Hi All;
Doing the Alignment took care of the rest of the squeels, Thank You to EveryOne.. It seems alot more sensitive now..
THANK YOU Marty
Hi All;
I got some of my Tubes in, so I put in the 42, the 75, and the 6A7.. Its even better now..
THANK YOU Marty