[dseverson]

Hello, everyone.

Has anyone restored a Gilfillan 5B8? I recently purchased one that someone hacked up. I found the schematics at http://www.nostalgiaair.org/PagesByModel...008581.pdf but I am having a heck of a time reading them. The print is horrible. I replaced the capacitors and resistors but I am unable to get any sound from it except when I touch the top of the 6Q7 tube. I get a hum from the speaker when I touch it. The tubes are all good. However, there is a 240k resistor soldered to the 6Q7 that runs through a hole in the 6F6 and is soldered to 5W4. I put some solder on the hole and now I get no sound whatsoever.

If anyone has restored one of these radios, I would appreciate knowing what you did and if anyone has photos of the underside of the chassis, I would like to see them.

Thanks for any assistance you can provide.

Dave

[Radioroslyn]

Hi Dave,
I'll take a stab at it. Need to know the dc voltages at pin 3 of 6V6, pin 4 of the 6V6, pin 5 of the 6V6 pin3 of 6Q7 And the grid cap of the 6Q7. Both pin 5 of the 6V6 and GC of the 6Q7 should have - voltage on them. All voltages are measured with - lead to the chassis.
Terry

[dseverson]

Hi Dave,
I'll take a stab at it. Need to know the dc voltages at pin 3 of 6V6, pin 4 of the 6V6, pin 5 of the 6V6 pin3 of 6Q7 And the grid cap of the 6Q7. Both pin 5 of the 6V6 and GC of the 6Q7 should have - voltage on them. All voltages are measured with - lead to the chassis.
Terry

Thanks, Terry, for the assistance.

I measured the voltages of the tubes and here is what I got (if I did it correctly):

6A8 - #3 is 293, #4 is 86, #5 is 13, #6 is 293
6K7 - #3 is 290, #4 is 90
6Q7 - #3 is 84, #5 is 0, grid cap is 0
6F6 - #3 is 290, #4 is 292, #5 is -128

This radio doesn't have a 6V6.

Hope this gives some clues and thanks again.

Dave

[dseverson]

Correction on 6A8 #5. It should be -13

[Radioroslyn]

Pin 5 of the 6F6 has -128vdc??? Not -12.8??
Terry

[dseverson]

Must have measured incorrectly.   I now get -20.8

[Radioroslyn]

Well -21v is a little high should be about -8 to- 12 v or so.  Is there a cap between pin 3 of the 6Q7 and pin 5 of the 6F6? Did you replace the resistors in bias divider? Looks like they are 350 and 50 ohms off of the choke or FC. Can you see the heater glow in the 6Q7 and the 6F6? -21 shouldn't stop it from working at all. All of the other voltages look good. Could have a bad connection between the tube and it's socket. Touch pin 5 of the 6F6 should get hum.
Terry

[dseverson]

Well -21v is a little high should be about -8 to- 12 v or so.  Is there a cap between pin 3 of the 6Q7 and pin 5 of the 6F6? Did you replace the resistors in bias divider? Looks like they are 350 and 50 ohms off of the choke or FC. Can you see the heater glow in the 6Q7 and the 6F6? -21 shouldn't stop it from working at all. All of the other voltages look good. Could have a bad connection between the tube and it's socket. Touch pin 5 of the 6F6 should get hum.
Terry

I've got a .015 between pin 3 of 6Q7 and pin 5 of 6F6 and the heater glows in both.  After that, I'm lost.  I don't know what  a bias divider or FC are.  Another problem arose.  I left the radio on for a while and now I don't hear the hum when I touch the top of 6Q7.

[Radioroslyn]

Ok the bias divider is the 2 resistors that are connected to center tap of the high voltage winding of the power transformer. The resistors are connected though a choke, it's drawn as a choke but it maybe the FC field coil part of the speaker. Looks like one is 350 ohms and the other is 50.

Try touching pin 5 of the 6F6 should get hum. Try touching the grid cap on the 6Q7 and wiggle the tube at the same time to see of you have a bad connection. Check the resistance from pin8 of 6Q7 to the chassis. Should have 0 ohms. Pull off the grid cap and touch grid cap of the tube without the lead attached. Should hum.
Terry

[dseverson]

Touched pin 5 on 6F6 with the tip of a screwdriver but did not get a hum. Measured pin 8 on 6Q7 and got 0 ohms. Touched the grid cap of 6Q7 and wiggled it but there was no change. Pulled the grid cap off 6Q7 and touched the top of the tube but did not get a hum. This thing is making me nuts. I am thinking there is some problem with the 240k resistor that is soldered to 6Q7 and runs through a hole in a tab in 6F6 and is soldered to 5W4. Whenever the resistor's wire touches the tab in 6Q7, the hum goes away and I get a low volume pop when I touch the top of 6Q7. I don't think it will help but I'll insulate the wire.

I'm still trying to locate the 350 and 50 ohm resistors. Either I'm blind or they aren't there. Tomorrow, I'll post a picture of the underside of the chassis.

[Radioroslyn]

The 240K resistor supply's the high voltage to the 6Q7. You said that you have 78v on pin 3 of the 6Q7 that would indicate that the resistor is ok. If there was a short or bad connection you wouldn't have the 78v on pin 3.
I'm thinking that the 6Q7 is bad or there is a bad connection at the socket. Try Measuring the pin 3 voltage (78v) not at the solder lug but at the tube pin. Place the meter  probe into the center eyelet only touching the pin of the tube. Something else to try is reflowing the solder on the pins of the 6Q7. Also try injecting an audio signal (from audio generator , tuner, ipod, computer, ect) though a .01 cap and gnd to pin 5 of the 6F6.
Terry

[dseverson]

Touched pin 5 on 6F6 with the tip of a screwdriver but did not get a hum. Measured pin 8 on 6Q7 and got 0 ohms. Touched the grid cap of 6Q7 and wiggled it but there was no change. Pulled the grid cap off 6Q7 and touched the top of the tube but did not get a hum. This thing is making me nuts. I am thinking there is some problem with the 240k resistor that is soldered to 6Q7 and runs through a hole in a tab in 6F6 and is soldered to 5W4. Whenever the resistor's wire touches the tab in 6Q7, the hum goes away and I get a low volume pop when I touch the top of 6Q7. I don't think it will help but I'll insulate the wire.

I'm still trying to locate the 350 and 50 ohm resistors. Either I'm blind or they aren't there. Tomorrow, I'll post a picture of the underside of the chassis.

[dseverson]

I haven't given up yet on this radio, although I'm about to. I measured the tube pin 3 on 6Q7 and got 78v. I reflowed the solder on the solder lugs but when you say reflow the solder on the pins of 6Q7, are you talking the actual pins on the tube?

As soon as I get something I can use to inject an audio signal, I will try injecting a signal through a .01 cap and ground to pin 5 of 6F6. Don't laugh but would a home made audio signal injector found here work? http://www.instructables.com/id/Tic-Tac-...-Injector/

Dave

[Radioroslyn]

<when you say reflow the solder on the pins of 6Q7, are you talking the actual pins on the tube?
Yep.

Sigal injector should work fine. You may have a little trouble finding those BC xsistor as they are from the UK. They probably crossover to some generic easy to find ones. Not much on three wire fuse technology.
And the chassis pics are where??
Terry

[dseverson]

<when you say reflow the solder on the pins of 6Q7, are you talking the actual pins on the tube?
Yep.

Sigal injector should work fine. You may have a little trouble finding those BC xsistor as they are from the UK. They probably crossover to some generic easy to find ones. Not much on three wire fuse technology.
And the chassis pics are where??
Terry

OK.  I'll take a shot at reflowing the solder on the pins of 6Q7 and either building that signal injector or seeing if I can find a low price one somewhere.  

Still working on the chassis pics.  I have to upload them to my computer and resize them.