New member with 37-650 Questions - Printable Version
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RE: New member with 37-650 Questions - Chinook47 - 03-24-2021
Thank you for the diagram. Looking at the provided diagram then checking my chassis it appears to follow the print. I'm reading 115 ohms on r58 instead of the 109 ohms. I didnt think I was too far off. When I installed c59 they were new and both times sent positive to ground. Also today I was measuring the voltage on the plates of the output 6f6g and the 1st stage audio 6k5g. When I power up the plates jump little over 300v then drop below around 120 volts. Sporadically it climbs back up to 200v then drops. The first 6f6g baffles me, starts at 150v then drops around 30v. Seems like it cant maintain the required voltage. I'm trying to see if this somehow connects to the exploding c59 cap. Im wondering if my transformer is defective with the fluctuation in voltage.
Yesterday with my meter I was testing the grounding connections which checked out fine. When I bought this radio the seller told me he couldn't get the chassis working and sent it to a friend to work on. I'm guess he had no luck either. I will keep looking.
Also, thank you to the person that moved my thread to this forum.
To someone else's question, I have been on a Chinook but not in flight. Hopefully some day. I'm just associated to the a manufacturing of the aircraft. The Chinook prints seems easier to read than this chassis at times.
RE: New member with 37-650 Questions - OZ4 - 03-24-2021
I think the voltage at the 6f6s should be above 200v or even 270v when operating normal. Check the voltage at the center tap of the output xformer it should be a little higher than the plates. And check if any of it is shorted to ground.
RE: New member with 37-650 Questions - OZ4 - 03-24-2021
That output xformer could easily have bad windings (open). Or things could be arcing inside making the voltage wander around. Oh and you know these are lethal voltages right?
RE: New member with 37-650 Questions - Chinook47 - 03-24-2021
Thanks. Yeah I had the same thought on the windings. I will either just replace the transformer if I can find one or cut my losses and send it to a local shop for further testing. I am limited with my multi meter. I will double check again on the grounding connections as well.
RE: New member with 37-650 Questions - Radioroslyn - 03-24-2021
You could unhook one side of 59 so you don't have it ready blowup in your face at any moment while your troubleshooting. It may get you a little hum but not much most of the filtering is done by the other two caps.
Take a close look at both of the 6F6 socket between pins 2 and 3. What you are looking for are carbon traces. They look like black lines that are burned into the wafer material. If you see them, some sign of arcing I would replace the socket. Both pins 3 and 4 have hv on them but pin 2 is at gnd so 3 would be more likely to arc to it. Any black marks are over there worth have a look at. Pinched speaker wires are common. They have hv too.
If not you may want to pull the 5y4 and watch the hv going to the plates. Just to be sure the transformer isn't bad. You'll want to watch it for 5 or 10min. Should be steady unless the washer or dryer are on.
Happy Hunting!
RE: New member with 37-650 Questions - Chinook47 - 03-30-2021
I was able to get all tubes lighting. Does anyone know how many ohms I should be reading on the connection point of c59? I read 128 ohm. My meter is measuring 3M ohms. Also could anyone tell me where this information would be available? I'm curious where the data is coming from when I dont see it on the print. I guess I like to look at the source rather than keep asking questions.
RE: New member with 37-650 Questions - OZ4 - 03-30-2021
Connection point of C59. What to chassis ground? C59 is in parallel to the resistor 58.
It should read about 128 ohms across it and C59. Much more and something is wrong.
RE: New member with 37-650 Questions - morzh - 03-30-2021
>> I read 128 ohm. My meter is measuring 3M ohms.
Not sure I understood.
But if it is 3M your R58 is open.
RE: New member with 37-650 Questions - Chinook47 - 03-30-2021
Thank you, I'll look into replacing the bias resistor r58. Just strange that I'm reading 115 ohms at r58. I'll search the forum to see if this process has been covered.
RE: New member with 37-650 Questions - OZ4 - 03-31-2021
I must be missing something. You say you are reading 115 ohms at R58 and the meter is measuring 3meg ohms? What are you reading from?
Is there voltage across R58 while tubes are lit? I would think there should be something in the range of 20 volts.
RE: New member with 37-650 Questions - Chinook47 - 03-31-2021
On R58 power on I'm getting 120v. When I ohm R58 I'm getting 115 ohms, the print says it should be at 109 ohms. Where I was getting 3 meg ohms was at the connection point of C59. I'm wondering if I'm placing the probes at the right point. I took a picture but doesnt look like I can attach it to the thread.
I have one probe going to chassis ground and the other probe at the point where the negative side of C59A, C57, and CT coming of R58 come together. I was going to ask if this was the correct connection point that others are referencing stating 128ohms.
RE: New member with 37-650 Questions - Chinook47 - 03-31-2021
Here's a picture
RE: New member with 37-650 Questions - Chinook47 - 03-31-2021
Picture of the 115 ohms on R58
RE: New member with 37-650 Questions - OZ4 - 04-01-2021
I would reflow some of those solder joints, they look a little flakey.
115 ohms sounds OK.
Your are measuring one half of R58.
What is the reading across both halves together of R58?
120 volts sounds way too high for R58. That would make some 900+ MA That would make way too much current. 120v would pop C59.
It sounds like it's intermittent open.
Even if it's 100 MA would be only 12.8v
I am not familiar with this radio. With push pull output the current will be on the high side.
Stick some making tape on the components with there circuit numbers. It helps me. Again I am not familiar with this radio.
Oh and it's helpful when soldering to turn the caps so you can read the values on them.
RE: New member with 37-650 Questions - mikethedruid - 04-01-2021
Also, what's with the safety caps on the outside of the bakelite block? To replace the caps in that bakelite block you have to REMOVE the old ones inside it. That is done by heating the block in an oven at about 250F until the resin inside melts out, then pulling out the guts, then replacing the guts INSIDE with the two safety caps. If you don't remove the old ones inside they can still short and form a shock hazard to the chassis.