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Author Topic: ts 520 new driver or and finals  (Read 17168 times)
KC9ZNC
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Posts: 13




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« on: July 19, 2014, 12:50:58 AM »

recently acquired 520 seems to load up mostly fine but lower output but then drops after transmitting a few times to nothing thinking it's the driver but should I change finals too?
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W8AAZ
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« Reply #1 on: July 19, 2014, 06:32:40 AM »

Does it drop power down into a dummy load, too? Bet the finals are getting tired by now.  But it would be nice to put them on a tube tester and see what is going on for sure.  I suppose HV power supply issues could affect power out, also.  Probably good idea to have a set of spare tubes for it, even if not immediately needed.  Have to say, the prices are not going down any.
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AC2EU
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« Reply #2 on: July 19, 2014, 06:33:21 AM »

The finals do the "heavy lifting" for the power, so those would be the first suspects to cause low power. However, you say the power drops after a while. Are you able to verify the Final B+ and screen supply is OK? Generally, if a tube has low emissions, it stays that way ( you can't get blood from a stone), so I wonder if there might be something other than the tubes causing the problem.
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K8AXW
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« Reply #3 on: July 19, 2014, 09:10:31 AM »

Not quite enough info OM.  I've never seen soft tubes "drop to nothing" as another poster mentioned. 

My question is, what do you have to do to get the power back up?  I can understand the power dropping off to zero, but what happens to the drive current and the plate current?  One other thing.  Not to insult your intelligence, but is the power actually dropping off or to phrase this another way....what are you using to measure to the power output?

I think you have something else going south.....something heating up and dropping a critical voltage.
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A Pessimist is Never Disappointed!
AC5UP
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« Reply #4 on: July 19, 2014, 10:15:53 AM »

Assuming the finals haven't been abused by years of improper and/or clumsy tune-up cycles the driver will tend to fail at least as often if not more, so don't rule out that possibility.

With that said, in the case of a used rig assume nothing. First thing I'd do is pop the covers including the HV cage. Look closely at the getter (silver spot inside the glass) on all three tubes. Shiny & clean inside? No red, brown or white discoloration around the edges? This is what a pristine example looks like...


If the getter is noticeably discolored (especially white) that's a gassy tube. If the inside of the glass is visibly darkened that's a tube with a buttload of hours on the clock (some small signal tubes like a 6BZ6 normally have a well defined grey band inside the glass but that's an exception).


If all looks good the next observation is with power on and modest room lighting. Apply HV to the plates. A slight purplish glow against the inside of the glass is OK. A visible purplish glow inside the plate & screen grid assembly is not. That's a common indication of gas. With a dummy load tune the TX. Do the plates of the finals show any color, like a dull red to orange glow? If so, they're drawing too much current. Double check the grid bias current adjustment as described in the owner's manual. Key the radio in a constant carrier mode like CW and observe the power output as well as the plates on all tubes. If any start to glow a dull red they're drawing too much current. Troubleshoot as appropriate with attention to the HV condensers and bias resistors.



Mandatory Disclaimer:  If you are not familiar with HV safety precautions Google for web sites that explain why you want to routinely pull the power cord and bleed down the HV before you smoke your Joules. It's also poor form to work on the radio when you're the only one home. Check the maximum DC voltage spec on your meter. Some are 600 VDC, others are a kV or better. 800 VDC on the final plates is typical of a 100 watt hybrid like yours but that's a nominal value... Your mileage may vary.
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AC5UP
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« Reply #5 on: July 19, 2014, 10:35:49 AM »

FYI:  I have never seen one this bad, but this is a no-brainer gassy tube:

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KH2G
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« Reply #6 on: July 19, 2014, 10:57:06 AM »

Have you confirmed that your power supply is not dropping voltage?
regards,
Dick KH2G
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N8CBX
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« Reply #7 on: July 20, 2014, 08:54:40 AM »

then drops after transmitting a few times to nothing thinking it's the driver but should I change finals too?
Watch the ALC on transmit; If it peaks then starts to drop down, then yes the driver tube is bad.
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
KC9ZNC
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Posts: 13




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« Reply #8 on: July 22, 2014, 02:23:47 AM »

Thanks everyone for the help,  have at200 tuner watt meter chking output  been good lst day and half 100 on 20 meters went to 40 and tuned up only 25 out back to 20 same thing leave it ten min tunes up fine
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KD0REQ
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« Reply #9 on: July 25, 2014, 03:20:32 PM »

first impression is a creepy tube that is operated out of bias and emitting gas.  solder some nicely insulated wires (like test lead) and run them out of vent holes to DVMs, and watch them.  could be the B++ drooping, but it could also be the bias supply drifting away.  if the voltages stay up for 20 minutes, then it's only tubes.  if they don't then it's time to redo the power supply from A to Z with new caps and maybe bleeders, too.  the suspect tube for me is the driver.  but if operating off the curve is what's happening, why kill a good one before fixing the other issue?

second impression is since it went to noplace fast after band switching, make the first step a bottle of De-Ox-It and gently put a half drop on each bandswitch contact, then rotate them through ten times.  don't glop up the wafers, just make a little red spot on each contact and that is cleaning enough.  if that fixes your problem, you just saved a ton of effort and a nice pile of change on tubes.

it has also been known that tinplate tube socket pins oxidize just like switch contacts, clean them too with De-Ox-It on the tube pins.
« Last Edit: July 25, 2014, 03:25:12 PM by KD0REQ » Logged
KC9ZNC
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Posts: 13




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« Reply #10 on: July 31, 2014, 08:29:27 AM »

Thanks everyone for ideas voltages were good so replaced driver and seems good now
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KE4DRN
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« Reply #11 on: August 01, 2014, 05:25:24 PM »

hi,

You can get new old stock USA Made GE JAN military driver and final tubes here

http://www.surplussales.com/Tubes-Sock-Acc/TubeSpecials.html

73 james
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G3RZP
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Posts: 1319




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« Reply #12 on: August 02, 2014, 02:53:47 AM »

Remember that the 6146B is a different animal to the 6146/6146A/6146W. The 6146B is a 35 watt plate dissipation as opposed to the 25 watts of the others. The 6146W is a mechanically ruggedized 6146A.

Plus all the 6146 family have, for a given set of screen, bias and plate voltages, an allowable plate current difference between tubes  in the ratio of 2:1.
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AF6AU
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Posts: 69




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« Reply #13 on: August 05, 2014, 10:12:23 AM »

I have a TS-820S, and did have a FT-101ZD, and when it came time to replace the 6146B's that were in them, I found NOS G.E. 12 volt filament 6883B's (same as a 6146B) at a marine supply store that has been in business for 60+ years. These rigs actually use 12 volts on the filaments, as the sockets are wired for the filaments to run in series. If you look at the socket bases it's easy to run them in parallel for 12 volt filaments.

6883B's were used a lot in Motorola VHF mobile radios as a single tube final, also in many Marine radios. My NOS 6883's came from a Marine supply store in Wilmington Calif., for $40 the quad, and the store owner was pleased to see the new shelf space. 4, 6883 tube boxes take as much space as a new micro uniden VHF radio today. There are a few other tube numbers that will work as well, search 6146 tube types and you will find a list. Old ARRL handbooks show a few. Forget finding 6293's these were top shelf pulse 6146 variants and were highly sought after.

Be resourceful searching and calling around, as the 6883B's are near drop-in, and they work the same as  6 volt filament 6146B's. They are much better than the Chinese 6146's. It's also easy to change back the sockets to 6 volts again.

Lets call the sockets A and B. 12 volt power comes in at socket A pin 2, exits at pin 7. Socket A pin 7 is connected to socket B pin 2. Sometimes you find a capacitor here to ground as well. The other side of the 12 volt line is at socket B pin 7. So move the 12 volt feed from socket A pin 2, over to the A socket to B socket jumper or interconnect. Add a new wire from Socket B pin 7 to Socket A pin 2. Now you have 12 volts at each socket. Install the 6883's and fire it up. BE SURE TO NEUTRALIZE ANY NEW FINALS.

To restore, remove the jumper, and move back the 1 wire. Easy stuff, and you get to use easier to find USA made tubes. There are also 25 volt filament versions available (6159B) that would also work, but you don't have 25 volts in the chassis. You could add a small 1 ampere 26 volt filament transformer if you find room.

JML AF6AU
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