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Tube question - Eric - 08-27-2012

Working on an Emerson CS-270 and I think I have a bad tube and have a question on a 6K8GT. The tube tester says it's good but when I check the filament voltage.
I only get 3 volts not the 6 volts I should and the others show 7 volts. Replace the tube ?



Eric

RE: Tube question - rghines1 - 08-27-2012

What are the filament voltages on the 25V tubes and the ballast tube?

http://www.nostalgiaair.org/Resources/967/M0004967.htm

RE: Tube question - Eric - 08-27-2012

I believe I had 26 across them but will recheck in the morning as I didn't write them down but I did across the ballast and across 3&7 it called for 42v and I get 44v and across the pilot 8&7 it calls for 4v and I get 4.2

Eric

RE: Tube question - Arran - 08-28-2012

If the tester says it's good keep the tube, the low filament voltage reading is unrelated to the tube. There can only be two causes for low filament voltage across a tube heater: (1) you are measuring from the wrong reference points (2) the rest of the tubes and ballast are dropping too much voltage from the string. However if something were dropping too much voltage across the string then the heater voltages would be lower on all tubes not just the 6K8 tube.
Regards
Arran

RE: Tube question - Eric - 08-28-2012

I measured the Voltage across the pins on the tubes Is this wrong?
pins V
6k8 2&7 3.0
6k7 2&7 7.2
6sq7 8&7 7.2
6ae5 2&7 7.6
25ac5 2&7 25.6
25z6 8&7 27.9

RE: Tube question - codefox1 - 08-28-2012

Quite rare, but I think you have a heater to cathode short on the 6K8. Sub another one and tell me I am a fool.

RE: Tube question - Eric - 08-28-2012

Wish I could but right now I don't have another and I don't see a sub so far but will get one and post the results

RE: Tube question - Arran - 08-29-2012

I would think that a heater to cathode short would show on most testers, but you could try with an ohm meter between the cathode pin and either of the heater pins to see if they is a low resistance reading. Heater to cathode shorts are usually something you see in a power output tube but anything is possible. I still find the voltage distribution strange.
Regards
Arran

RE: Tube question - Eric - 09-01-2012

New 6K8 came today and I changed it out. Still no stations just static but Volume seems much better. Here are the voltages that I took per the print.
Tube Plate Screen Cathode Osc plate Fil
6K8 96 96 0 72 6.5
6k7 92 96 0 7.0
6sq7 51 -- 0 7.3
6ae5 96 -- 13.6 7.3
25ac6 89 -- 0 24.2
25x6 133 26.5

L42 3&7 42.6
pilot 7&8 4.9
Across Speaker 36 taken on the + side of C27&C28
Do I have a ant coil problem?

RE: Tube question - Steve Davis - 09-02-2012

Eric, here is quick and dirty troubleshooting procedure. First, holding a capacitor (value not critical .01 or so would be good) in your fingers by one lead, touch the other lead to the center terminal (the wiper) of the volume control. You should hear a hum in the speaker. If so, the audio section is working, at least in some fashion. Next, tune the radio to mid band, say 800kc. Now take a portable radio tuned to 1255 (800 + 455) and place it near your Emerson. Now rock the tuning slightly on either one of the radios. The portable should pick up the local oscillator of the radio under test. By doing these two test, you will prove (or disprove) about 2/3 of the radio circuit.

Steve

RE: Tube question - Eric - 09-03-2012

Great info I will keep for future.

Thanks Terry for all the help last night!
I removed T4 and sure enough one of the coils is open, The side that goes to 6sq7 & Vol Control is open the other side reads 2.6K ohms.
I'm going to see if I can find the break and repair. Thanks again for all the help everyone!!!

RE: Tube question - Radioroslyn - 09-03-2012

Glad to help out!
Terry

RE: Tube question - Eric - 09-04-2012

Terry



Took T4 off the chasse and tried to unwind and count turns but it kept breaking so I cut one side through and took it off the insulating tube and I was able to separate and count the turns. I came up with 350 turns of .004" wire and I lucked out and actually a spool of #38 magnet wire which is 004" so I made two collars and hand wound the coil. It measures 27 ohms when I was done.

Now the strange part. I powered it up and got nothing but static so I tapped the cap of the 6k8 and got some pops where before it was dead. Then went to 6k7 and did the same but what I got was sound so I clipped a jumper to the cap and a station 680 came in very strongly with good volume I went to try and tune another station but no matter where I put the gang cap all I get is the 680 station. changed to SW and the same thing only the 680 station! I'm glad the radio played I was questioning that everything was bad on the set.

So what should I do to get the gang caps working like there supposed to.



Eric

RE: Tube question - Radioroslyn - 09-04-2012

Well what's happening is the coil you wound for the IF transformer is resonant at 680 or so when it needs to be at 455kc. If you hook the ant to the cap of the 6K7 the tuning cap is not in the circuit. SO the 680 kc signal comes down the ant and goes into the grid (input) of the 6K7 gets amplified and then get detected and on to the audio stages.
Two things to try. Hook up your generator at the tv input and adj it for 455kc w/modulation. Peak the 4 trimmers on the IF transformers. Then try the main tuning to see if you get any BC stations.
If that doesn't help add another 100turns to your coil and see if you can get a sharp peak when adjusting the last trimmer.
Short of those two things find yourself a 455kc IF transformer.
Terry

RE: Tube question - Eric - 09-06-2012

I can now get 750 or 680 but it has to be tuned to the freq not through the tunner. I added the 100' you suggested. I'm concerned about the other coil the first number I gave for resistance (2.6k ohms) which was wrong the coil measures 850ohms which I think is wrong. Let me explain. The coils were the same physical size and the wire size is the same #37 or .0045" looks like a dog bone (coil on each end) mounted on a ceramic plate which as the trimmers on the other side. well the coil I wound is only about 30ohms using the data I took # of turns and wire size, well by my wire chart for #37 the resistance is 512ohms per 1000' which is a H**l of a lot of wire. so I'm thinking of rewinding that one too?