Good afternoon,
Starting working on a pt 29. Recapped and nothing. Thought it might be a tube so I changed the first one in the series 35z3 and brought it up slowly on the variac. It started to light up one tube at a time then smoke. It was coming from part 33 3367 a line resistor. On the schematic it doesn't give a value?
Is this a common part? What is its value? It is connected straight to the ac line. Is this correct?
Please help
Thanks
Chris
Hi Chris and welcome,
I looked around for a PT-29 but didn't see one. Can you link a diagram to your post? There are a lot of PT sets and they are pretty similar but just wanted to be thorough
Oh you mean one of these
https://philcoradio.com/library/download...20Book.pdf The 1st section is abt 40 ohms and the 2nd is 200 ohms (+/-10%)@ a minimum of 7.5w. I suspect that the old one is shorted and that's why it's smoking. If so it needs to come out. Don't try to solder a new resistor across it.
GL
So is it two separate resistors? Where do I get them? How do I connect them? Sorry this type of resistor is new to me.
Thanks
Chris
It's two resistors in series. The 1st connects across the pilot lamp. The 2nd connects to the lamp and the heater string, schematic imply's that it's pin 1 of the 35Z3.
Where can I get the resistors? Any worry about heat generating?
Thanks Chris
Google is your friend. The heat that is generated is the same with the old vs the new resistors.
Chris,
The current through the heater circuit, which is in series with the resistors (also in series), is about 150ma. You should be able to calculate wattage of each resistor using this current and the resistance value of each resistor. Power (Wattage) = Current squared x Resistance. I would typically at least double the calculated value and round up to a standard available size.
The following link may help. They state slightly different values for the same part #, than what Terry mentioned above, but they are close.
https://philcoradio.com/phorum/archive/i...-2610.html
Bill
Chris
Before any further troubleshooting I would recommend cleaning up. It looks a bit unkempt. Gosh knows, a stray wire might touch something.
Keeping contacts and joints clean always helps.
Also long bare leads, especially the modern parts' ones, that are much thinner and softer than those used in the days of yore, should be insulated. Or they might touch things they were not intended to touch.
These resistors are commonly known as CANDOHM resistors. They are wire-wound high wattage resistors and cause several problems so we generally take them out as a proactive solution. I buy the white brick type and use two methods of replacing them. If I remove the rivets I use one of the rivet holes to mount a terminal strip for the new ones. I have also pulled the wire out of the metal case then use the existing terminals to mount the new resistors. Some restorers have tucked the new resistors inside after opening up the metal case and remove the guts. This makes the repair inconspicuous.
Ok waiting for resistor to come in. Which resistor to 40 or the 200 is connected to the Ac line?
My schematic is fuzzy and I can't tell.
Thanks
Chris
The 40 ohm section connects in parallel with the dial lamp.
So here is how I wired it.
One end of the Ac line, a o.o4 capand one end pilot lamp to one end of ,40 ohm 10 watt resistor. The other end of the 40 ohm resistor to one end of the resistor200 ohm which is connected to other end of pilot lamp and ground lug? of 35z3 tube. The other end of 200 ohm resistor to 35z3 tube lug.
When this was brought up in variac the pilot lamp glowed bright then went out.
The 35z3 tube got really bright.
No sound but end of 40 watt resistor started to smoke. Both resistors got really hot also.
I made sure no wires were touching .
Did I wire it wrong?
Thoughts?
Could you draw a sketch of what you did?