Hi All;
Before I start to build a Breadboard Oscillator circuit.. I though I would ask --
What steps would Everyone suggest I take in finding and or eliminating where the problem might be ??
By having a checklist I can go thru it and "say" I've done that or I need to do that, or I didn't think of that..
I just want to make sure I have done or tried everything that would logically be done to find the problem..
I have sound going thru the Audio stages and IF going thru the IF stages, and get the output on the speaker from it.. I can pass IF (460KC) thru from the antenna.. And some but not regularly I could get a station to come in.. But, not at present.. When looking at the Oscillator I can get a variable frequency, not necessary the correct one.. But, it did oscillate..
My next step would be to build the front end: Antenna to RF to Oscillator to Mixer circuit on a seperate wooden board.. And subb it in..
What suggestions does everyone have ???
THANK YOU Marty
Marty,
A lot of unnecessary effort there, unless you just want to use it as a teaching tool.
First thing you want to do is to check all the resistors in the LO circuit and replace any that are out of tolerance. This is assuming that you have already replaced all the paper caps in the radio.
Next, remove the oscillator coil and inspect it for broken wires, corrosion, etc. Oscillator coils generally go open due to corrosion on the feedback side of the coil. This is pretty easy to rewind, as a rule. Or you can have someone else rewind it for you.
Also, try subbing in a new tube, as a weak or gassy tube my fail to oscillate while still being able to pass some RF through it.
Another fun thing you can do to test whether the circuit is working as a first detector is to feed in a signal from a generator into the oscillator section (chassis ground and the LO section of the tuner is a good injection point). Choose a strong local station, add 460 KHz to their frequency, and inject that. Tune the tuner to their frequency on the dial, you should hear the station.
Hi All;
Thank You, BrendaAnn for Your response..
I would like sort of build the circuit for a teaching aid for myself..
I had checked and replaced all the Caps and what resistors that needed to be.. But, I will check them and try again..
The coils were in fine shape no corrosion at all on any of them.. And they all measured fine.. But, if a turn or two had become shorted, I would not have known.. So, I will re look and re measure them again..
I think I tried the alternate oscillator with the generator and got nothing, But, I will try that again.. I know I could pick up a squeel on another radio, but since it was a cheap transistor radio without a fine detail of where I was on the dial, I couldn't tell if it was on the correct spot or not..
Two other things.. Part of building a Breadboard circuit is so that I can build the same circuit, with out the Band Switch and with out Short Wave Reception.. Just BroadCast band.. Eliminating those two possible problems..
Secondly, I found from checking, after cleaning the Trim Caps on the Tuning Capacitors, That (it has a four Cap gang) the upper two and the lower two set of caps are shorted together on Switched Band 1 and 2 and 3, But are not shorted on Band 4.. I don't know and can't tell yet IF this is correct or IF I have a problem in my Band Switch.. The Diagram in the Documentation Shows the Switch settings for Band 4.. And I have trouble figuring out what should be connected together when the Band Switch is in any of the other positions.. I am thinking I will need to take the Band Switch and all of the coils Out again and orinate it like the drawing measuring all connections and drawing it out on paper then turn it one position and see what changes, and redraw it.. So, I have four sheets of Paper with four parts of the Band switch on each sheet..
THANK YOU Marty
If this is a battery radio two other things to look at are dirty tube sockets and poor solder joints on the grid caps themselves and the grid leads in the mixer-oscillator section.
Regards
Arran
Hi All;
Thank You Arran for Your response.. And yes this is a Battery set.. With a Battery type of Eliminator for its power.. All of the voltages are correct and have been capped to cure any 60 cycle Hum..
I will re check the Grid Caps.. ALL of the Sockets have been replaced with new sockets..
But, (sort of) per Your suggestion I will check all of the Grid connections and make sure that they are wired correctly..
THANK YOU Marty
Hi All;
I think I have found two problems, one major.. The minor problem was a possible short on the Lead from the Grid Cap of the 1C6 to the top of the tuner may have been shorted to the base of the tuning Capacitor.. Or it was some of the time..
The other major problem was I had on the 1C6 G1 and G2 switched, Thank You Arran.. I might not have found it otherwise.. I went to a Philco 623 and found the Pinout for the 1C6, from the bottom view , with voltages, and that is what led to me finding the problem.. My soldering Iron is warming up while I write this, and after I close this, I will fix it..
THANK YOU Marty
Hi All;
No, that didn't fix it to working condition.. And a Resistor got hot, so I am going to trace things out again, as a friend says "until I find not mistakes". Get out the Yellow marker and figure out what and where each wire is suppossed to go.. Put it in Band four, which is the position that the schematic shows the switch connector is in, and start from there..
THANK YOU Marty
Hi All;
I just took out the Band Switch, along with the four coils and the four trimmer (Compensating) Caps.. It is easier to take it all out at once and less leads to disconnect..
When I was trying to follow where all the leads went, I found a connection that looked like it was wrong.. But I could not be sure without taking the whole thing out..
Plus I get to document the other two coils.. The connection looks as old as the rest of the set.. But, since I already know, that it went in for repair about a year after it was made, based on Transformer Dates.. All bets are off as to whether it worked after it went in for repair..
UPDATE, the connection is Wrong..
THANK YOU Marty
Hi All;
I realize I made a wiring error which is what caused the Resistor to get Hot..
But the mistake on the Bank Switch is either origional or maybe a Year later, when it was repaired, Can't tell..
All of the other Bank Switch connections seem to be OK..
I have take pictures of the Switch and the coils.. Next I need to document the coils..
So, once I get things back together, I will see if either of these errors will make a difference in its ability to work..
THANK YOU Marty
Hi All;
I found that the Hot resistor was a differnt issue, with making an oscillator circuit, as described in my other posting..
Today I just observed a funny to me thing.. I just came back and Had turned on my scope and my Signal Generator.. I had NOT turned on the Radio, nor is it plugged in..
The Signal Generator is connected to the Antenna clip.. The scope was connected to the grid 2 and It was displaying the frequency that the generator was putting out.. So, I checked all of the tube connections and to some varying degree they all displayed the generators frequency.. Of course it was strongest on the Grid Cap and would vary its strength with me moving Dial..
So would this be helpful in tuning the RF/Antenna Coupling (tuning cap and coil) and doing the Same with a different Frequency on the Oscillator coil and caps ??
I can put in the 460KC and the 550Kc added together in other words feed in a 1010KC to the Oscillator coils, and correct me If I am wrong, I should be able to tune with the Caps for a Strongest signal on one or the other of the coils.. With the Tuner set for 550KC, then use the compensating Capacitors to peak the signal..
If nothing else I now know that the RF/Antenna Coil/transformer is working.. The signal has to pass thru it to get to the rest of the radio..
THANK YOU Marty
Hi All;
Latest update, I have found that a wire that I didn't notice since putting everything back in that was broken.. one of the oscillator wires.. I need to find where this wire broke its connection and wire it back together, then I can check if I can get coupling between the two coils..
THANK YOU marty
Hi All;
No good on the 34.. But I have made significant progress on the Breadboard.. Since, switching the wiring arround on the 1C6 so that the dropping resistor has the correct voltages on it.. And taking the Cap out of the circuit that was in parallel with the Coil, it Now will Oscillate.. It is not at the correct frequency, but it oscillates..
I decided to Re-Count the number of turns I had on the secondary coil.. It seems that I had lost count more than I thought.. I re-counted by marking with a black marker every ten turns, and found that instead of 110 turns I had 162 turns..
I took off two turns and measured the resistance for a base measurement and then took off 10 more turns measuring each time with my VTVM.. After getting the VTVM going again.. (Another posting).. when I got down to my goal of 100 turns I tapped it to a terminal and wrapped 10 more turns and put it to another terminal..
When I tried the oscillator at the 100 turn mark the Frequency was a little high.. I tried it at the 110 mark and it was Higher yet..
So, I took off the extra 10 turns and then took off 5 more turns tapped it to a terminal and put the remaining 5 back on just in case, and terminated it..
I tried it at the origional 100 turn mark, still too high, tried it at the 95 turn mark it was almost correct, and with a little tweaking on the grid leak Variable Cap I got it to Oscillate at about 1010KC..
Which led me to my Tuning question, (another posting)..
THANK YOU Marty
Hi All;
I got it hooked up and the voltages look right, on the Breadboard..
I found that ALL I had to switch was the Plate (Pin 2) and Grids 3,5 (Pin 5).. So that at least answers the question of why the Oscillator worked..
THANK YOU Marty
Hi All;
I have put the wires as they belong on the Philco 34 and I have hooked up my signal generator to the Grid Cap of the 1C6 and while tuning the Tuning capacitor, I get Squeels out of the speaker, I have not had that before, from this Grid input, I have had the IF (460KC) go thru from here.. I have not tried to set anything or do any alignment on the set, just trying to see If any signal can get thru..
THANK YOU marty
Hi All;
I have it receiving signals from the Generator at 600KC, 700KC, 1100KC and 1400KC on the Broadcast Band..
BUT, I found out that the Oscillator works on these frequencies ONLY when I have my O'scope probe attached to pin 4 of the 1C6..
Go figure ???
IF, I attach my probe at the 2nd Detector then the signal comes in but a few points lower of the scale..
Attaching the probe at the 1st AF it moves down another point or so..
So, do I need to put a Capacitor on pin 4 of the 1C6 to compensate for something that the scope is doing to the oscillator circuit ??
Would possibly a Gimmic wire make the difference that I need ??
THANK YOU Marty