A little help if you please. Looking at the schematic of the Philco 42-PT-7, #9 is the oscillator transformer, what is the unmarked capacitor also indicated by #9? And, is the connection point above the unmarked cap pin #1 on the osc transformer? And to return to my original chassis ground question; looking at for example #5 the 1.5 pf capacitor; where should its physical connection to ground be made? Is the ground connection symbol a shorthand indicator for B- or what? I understand that the little three line ground symbol indicates that all are tied together but how is the mechanical connection made? Where is it made if not to the B- common ground?
>what is the unmarked capacitor also indicated by #9?
It's the grid leak capacitor which is incorporated with the osc coil.
> And, is the connection point above the unmarked cap pin #1 on the osc transformer?
Yes.
> #5 the 1.5 pf capacitor
Not seeing a 1.5 pf. #5 is 1500pf or .0015mf I don't do nF.
>where should its physical connection to ground be made?
According to the diagram to the chassis.
< Is the ground connection symbol a shorthand indicator for B-
No.
> I understand that the little three line ground symbol indicates that all are tied together but how is the mechanical connection made?
Solder to the chassis.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Thanks again Terry.
By the way, is it common practice to use the center tap on tube sockets as a chassis grounding point? Notes I took when I disassembled the pt-7 indicate all the center taps were connected (not the rectifier), not sure why.
< center tap on tube sockets as a chassis grounding point?
Not sure what you are referring to? If you mean the ground connection at the center of the local tube socket yes typically they are connected to the chassis.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Will you please verify for me:
Looking at sch of 42-PT-7, on the 7A8:
Grid 4, pin6 connects to the aerial compensator, also to a 10uuf mica cap, also to the variable (tuning) cap
Grid 1, pin4 connects to pin 1 on osc trans, also to 47K resistor, also to the osc comp, also to the variable (tuning) cap, also
to pin 2 on the osc trans.
TIA Larry
>Grid 4, pin6 connects to the aerial compensator, also to a 10uuf mica cap, also to the variable (tuning) cap
Close but no cigar! There's no 10 uuf cap there as it's only used in the PT4. #1 and 1A are the rf side of the tuning cap and it's trimmer (1A)
>Grid 1, pin4 connects to pin 1 on osc trans, also to 47K resistor
So far so good.
>also to the osc comp, also to the variable (tuning) cap, also to pin 2 on the osc trans.
Not directly but thru are mystery cap.
Having an oscillator problem??
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Thought the used only cap said 7, tough to read. I have no sound from speaker. Field coil and OT seem to function though output is very faint. Using the AO from a EICO 324 vintage sig gen. I'm in the process of determining the correct connections of aerial and front end components. Obviously not getting a clear point to point from the schematic.
Larry
By the way, in the parts list, the 10uuf cap is designated for use on the PT7. So at this point I have negative voltages, <1V and reading negative at the plate, G2 and G3,5 on the 7A8 and high voltage,> 100V on the plate of the 50L6 output tube. Ant and osc coils show continuity and resistance as well as first IF but signal does not pass from 7A8 to 7B7 or forward from 7B7.
How best to test the primary of the 2nd IF without disassembly? Signal forward from 7C6, 50L6, on/off forward test good.
>How best to test the primary of the 2nd IF without disassembly?
You can measure the resistance from the + side of # 26 to the plate pin of the IF amp tube. Likewise you measure the resistance from 26 to the plate pin of the mixer too to check the 1st IF pri. Should be very low like 30 ohms or so. Would also check #12 it supplies the screen voltage to the mixer and IF tubes. Best guess is that you got a bad connection or broken wire from 26 over to the IF and mixer stages. I little odd to have more that one thing missing the HV when it's all fed from the same source.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 03-07-2018, 11:16 AM by Radioroslyn.)
Terry what are the proper connection points for the #12, 27K ohm resister ? The schematic is confusing and my interpretive skills are weak. Looks to me like pin 5 on #9 and pin #3 on the 7B7. Then a connect from pin #3 on 7B7 to pin #5 G3,5 on the 7A8.
I have nothing between 26+ and the plate of the mixer !
>I have nothing between 26+ and the plate of the mixer !
I'm not completely sure of your answer. Do you mean you have no voltage? Or no resistance?
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Hi Terry sorry for the confusion. After a few wiring changes, I have between the positive side #26 and plate of 7A8 29.2 ohms. And from positive side of #26 to plate of 7B7 20.3 ohms.
Watching B+ on powerup and looking for around 95V, shut down when voltage climbed above 105V.
May have done some damage as on 2nd attempt B+ only climbed to around 30V.
> After a few wiring changes, I have between the positive side #26 and plate of 7A8 29.2 ohms. And from positive side of #26 to plate of 7B7 20.3 ohms.
Ok so that's good.
>Watching B+ on power up and looking for around 95V, shut down when voltage climbed above 105V.
105v is not much of a big deal, filter caps are rated @ 150 or 160v. Typically the dc output voltage isn't
going to rise above the ac input to the rectifier if there is some load on the p/s.
>May have done some damage as on 2nd attempt B+ only climbed to around 30V.
Seems like you have short somewhere on the hv rail or a weak 35Z3.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
