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Author Topic: 1947 Zenith TransOceanic 8G005YT only static after recapping  (Read 27609 times)
KC5AQO
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Posts: 32




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« on: September 02, 2013, 02:28:42 PM »

Hello Gents,

     Sorry to have another problem. I completely re-capped the radio including the two paper cans, and even got the polarity right on all 5 electrolytics. Cleaned all antenna connections. Checked all the tubes on my little B&K 606 emissions tester (can't believe I sold the TV-7) and had to replace 2 of them. Can't find out how to test the 117Z6 GT rectifier as B&K didn't list it. It lights up well when on. De-oxed the band tower sliding connections and all the tube pins and put them in wet so as to clean the holders hopefully. Anywhoo, all I can get now is low static on any of the 3 antennas, and all bands. I recapped a NC-183D and a WS-19 Mk2 and they sprang to life and worked beautifully, but not this 8G005YT 1947 job. NOT an electronic tech here, but I do have a Tenma cap, resistor, diode checker & VOM. Any and all help appreciated. Yes, I know it has a hot chassis. Mack KC5AQO
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AC5UP
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« Reply #1 on: September 02, 2013, 04:03:50 PM »

Betcha' one of the new condensers isn't soldered to the same two places as the old one was............
Easy mistake to make, difficult to catch, as you'll need to confirm every new condenser is exactly where it needs to be per the squidmatic.

BTW: If the B+ voltage is good the 117Z6 is working.
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W1BR
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« Reply #2 on: September 02, 2013, 06:55:08 PM »

check the filament voltages on the battery tubes. is the B plus okay?
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KC5AQO
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Posts: 32




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« Reply #3 on: September 03, 2013, 05:48:58 PM »

THANKS for the advice Gents,
      I've got a pretty failsafe way of changing out caps. I only do one at a time, and I always leave about 1/4" of wire on each terminal I cut the cap off from. I then carefully wrap each end of the cap wire around a tiny swiss screwdriver, about 2 and 1/2 turns. Slid screwdriver out. Nip off any excess and slid each circular formed wire over the 1/4" stub sticking out. Of course you have to make measurements and some good guesses. I then solder each joint using a heat sink on the wire. Ugly, I guess, but simple and  seemingly stout.
     I am not a tech, but will remove the chasis and try to find the B+ (hopefully on schematic) and see what voltage it has. THANKS again.   Mack
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W1BR
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« Reply #4 on: September 03, 2013, 09:34:15 PM »

Verify B+ at the rectifier cathode... if it is there, then make sure the filament voltage for the battery tubes is present. There are some dropping resistors that could have failed.

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N4NYY
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« Reply #5 on: September 04, 2013, 05:30:05 AM »

Verify B+ at the rectifier cathode... if it is there, then make sure the filament voltage for the battery tubes is present. There are some dropping resistors that could have failed.



I am going to lean on this. Recapping is fairly easy with the method he uses. I use the same method of one at a time. But it sounds like one of the resistors is open. Likely very close to being open before the recap. I would measure the resistors in that chain and see if they are out or way out. If so, he might need the whole thing done.
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K1CJS
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« Reply #6 on: September 05, 2013, 05:32:09 AM »

Could be too that even though you were careful on replacing and resoldering, that another wire connection got disconnected when you applied heat to one of the solder joints.  Most of the time, techs were good and made sure that the connection was mechanically solid, but sometimes some of them just soldered a wire to the connection without doing a good mechanical connection first.  Check to see if there are any wire stubs next to the cap solder connections you disturbed.  If so, that could be your problem.

Added--I see in another thread that you have re-capped around the old can caps that were in the radio.  Are you sure that you connected the new caps correctly and didn't miss a connection?  Sometimes, the way those canned caps were, the connections weren't too obvious. 

Good luck and 73!
« Last Edit: September 05, 2013, 05:39:40 AM by K1CJS » Logged
G3RZP
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Posts: 1217




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« Reply #7 on: September 05, 2013, 01:13:18 PM »

Did it work at all before you recapped it? If not, you could have added to the original problems....Check the B+ line, and the filament voltages as a start.
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KC5AQO
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Posts: 32




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« Reply #8 on: September 05, 2013, 01:52:00 PM »

Men,
     I was careful to make sure I had the correct mfd electrolytic to the correct wires (squares 40mfd and triangles 20mfd) that went to the old ones, and the negative wires were to the chasis. All original can wire connectors were twisted off.
     NOW, I've decided to check the resistances through the tube socket pin holders to look for bad resistors. Sams says to go to broadcast position, check. Problem, using the chasis as ground, I can't get any pin holder resistance readings on my VOM. Nothing even wiggles the needle, volume switch on or off. BTW, last night I turned it on in a dark room, with the back open. 117Z6 lit up but none of the other tubes even had a glimmer. Any suggestions will need to be made in cave man talk. Sri. abt that. THANKS in advance. Pulled out some of my 1940's radio handbooks, so i can read up on vacuum tube technology.
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G3RZP
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« Reply #9 on: September 05, 2013, 02:17:29 PM »

But have you measured the B+ from the 117Z6 and have you measured the filament voltages?
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N4NYY
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Posts: 5206




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« Reply #10 on: September 05, 2013, 03:08:36 PM »

Men,
     I was careful to make sure I had the correct mfd electrolytic to the correct wires (squares 40mfd and triangles 20mfd) that went to the old ones, and the negative wires were to the chasis. All original can wire connectors were twisted off.
     NOW, I've decided to check the resistances through the tube socket pin holders to look for bad resistors. Sams says to go to broadcast position, check. Problem, using the chasis as ground, I can't get any pin holder resistance readings on my VOM. Nothing even wiggles the needle, volume switch on or off. BTW, last night I turned it on in a dark room, with the back open. 117Z6 lit up but none of the other tubes even had a glimmer. Any suggestions will need to be made in cave man talk. Sri. abt that. THANKS in advance. Pulled out some of my 1940's radio handbooks, so i can read up on vacuum tube technology.

I measure the resistors in circuit. Most will be able to be read. The ones that you cannot read in circuit, I usually pull a leg and then measure.
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KC5AQO
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Posts: 32




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« Reply #11 on: September 05, 2013, 07:03:09 PM »

Put in the 117Z6 and checked voltages on the tube sockets. 155 volts which I assume is B+ went to the 2 watt power resistor. Checked several tube sockets 4.5 volts 16 volts,150 volts, and so on but no 1 or 1 1/2 volt readings so the filiment string must be out HuhHuhHuh I will check the resistors tomorrow. Maybe then I can find a problem part. THANKS for putting up with a non-tech w/16 brain cells. Your EXPERT help is really appreciated.   Mack Lester     ps. After this I've got to figure why my Drake TR-4 is only putting out 90 watts max on 80 and 40. It never ends, does it ? Roll Eyes
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N4NYY
Member

Posts: 5206




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« Reply #12 on: September 05, 2013, 07:17:05 PM »

Put in the 117Z6 and checked voltages on the tube sockets. 155 volts which I assume is B+ went to the 2 watt power resistor. Checked several tube sockets 4.5 volts 16 volts,150 volts, and so on but no 1 or 1 1/2 volt readings so the filiment string must be out HuhHuhHuh I will check the resistors tomorrow. Maybe then I can find a problem part. THANKS for putting up with a non-tech w/16 brain cells. Your EXPERT help is really appreciated.   Mack Lester     ps. After this I've got to figure why my Drake TR-4 is only putting out 90 watts max on 80 and 40. It never ends, does it ? Roll Eyes

What is the the Drake supposed to put out?
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G3RZP
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Posts: 1217




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« Reply #13 on: September 06, 2013, 01:16:55 AM »

It has three 6JB6 sweep tubes, so it should do pushing 200 watts on 80, although that is stressing the tubes a bit - the total dissipation available is 52.5 watts.

The tubes may well be a bit tired, though, explaining the low output. Because of the difficulty of getting 6JB6s, I'd keep it to about 100 watts anyway.
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N4NYY
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Posts: 5206




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« Reply #14 on: September 06, 2013, 04:54:36 AM »

It has three 6JB6 sweep tubes, so it should do pushing 200 watts on 80, although that is stressing the tubes a bit - the total dissipation available is 52.5 watts.

The tubes may well be a bit tired, though, explaining the low output. Because of the difficulty of getting 6JB6s, I'd keep it to about 100 watts anyway.

OK. I do not see a big deal at 90W. When I did google it, I found 300 input power. No output power specs. WTH is that?
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