I have a T-600 that needs some help.
When I first got it both 1U4 tubes had open filiments.
I got replacements and recapped the radio. When it is turned on stations come it loud and clear for about two seconds then fade out. This happens on all the bands. After that there is just a background hiss. All the filiments are still lit. The voltages seem about right and I've triple checked my recapping. Unfortunately I don't have a tube tester yet.

Two things I've noticed. The 50A1 checks ok for resistance but the two vertical wires inside the tube glow a nice orange. Is this normal? Also, I checked the local oscillator with a scope and it is not running.

Any ideas would be greatly appreciated.

Thanks.

Mike M

I haven't encountered an oscillator that will immediately poop out once it starts. I would try to confirm your 'scope finding by tuning the Zenith back and forth while listening on another AM set for the oscillator at the Zenith's tuned freq + IF.

Oscillator problems can be caused by a weak oscillator tube.

:I haven't encountered an oscillator that will immediately poop out once it starts. I would try to confirm your 'scope finding by tuning the Zenith back and forth while listening on another AM set for the oscillator at the Zenith's tuned freq + IF.
:
:Oscillator problems can be caused by a weak oscillator tube.

Thanks Doug.

What I need to get is a tube tester. I hope the 1L6 isn't bad, very expensive. I've used your method for checking the oscillator before but had forgotten about it. Thanks for the reminder.

Mike M.

Interesting. I am working on an H500 with the same problem. I narrowed it down to the 1L6 and the oscillator. The tube tests weak. I was wondering whether others had seen this. Now I know!

This radio has the large hole in the chassis for an oversized wafer socket on the 1L6. Rumored to be for a 1LA6 loktal. I have read about the conversion to 1LA6 and I am considering it.

In my experience with portables (mostly Zenith, but no Transoceanics), your oscillator tube must be good. If you have an Eico 625 tester, you can try turning the selector to #4 for a brief moment. This will put an excessive load through the tube, which shakes crap off of the filament or something, or perhaps it burns off gas. Anyway, any oscillator tube I had with the popping out trouble usually was cured for a week or so by doing this to the tube. Depending on your tester, overloading the tube may or may not solve the problem, and if your tester is powerful enough, it might fry the tube.

Another problem I had with one of my radios was a leaky filament ballast resistor. I think your 50A1 takes the place of this resistor, but I thought I'd mention it just the same. It's a wire wound unit with three terminals, and is encased in sheet metal. There is a varnished paper insulator and some asbestos between the wire and the metal case. This started to break down, allowing leakage to the chassis, which is isolated from everything through a condenser. It puzzled me why there was suddenly 60 volts DC on the chassis, since the chassis is isolated by a condenser. For some odd reason this voltage presence threw off some things through shielding, etc. Both the audio and the oscillator section would drop out from time to time. Momentarily shorting out the chassis condenser solved the problem. ......So I disassembled the resistor and put in some new insulation. Surely a simpler route would have been to prop the resistor up on a slice of ceramic with sleeves around screws for insulation, but my brain doesn't always think like that.

Anyway, the second problem isn't likely your's, but I thought I'd mention it. Be absolutely sure that you replaced all condensers with the freshest and newest condensers which are leak free. With these portables, I cannot stress enough how important it is for condensers to be leak free. They cannot have leakage even in the millions of ohms. If you pulled some condensers from another radio, this is unacceptable. www.tubesandmore.com sells metalized film condensers which are quite small and yellow in color. They fit nicely inside of the paper tubes of the old Zenith condensers. With portable radios, any leakage of DC current through a condenser is enough to severely throw off grid biasing, which will cause the audio to distort and the oscillator to operate irratically. Remember to disconnect a condenser before you test it. Leaving the condenser in the circuit will throw off your readings due to other current paths in the circuit. When you test a condenser, you use the most sensitive resistance check scale your meter has (usually X10,000). Without touching the leads of your meter with your fingers, touch them to the condenser in question. If your meter needle swings up at all, it should fall back to EXACTLY where it started. WATCH CLOSELY. Condensers smaller than .001 MFD won't likely move the needle up at all unless they have leakage. Larger condensers in good condition will swing the needle up just a bit, and then the needle will fall back down after the condenser has charged. The larger the value, the larger the swing. For any condenser, though, if the needle swings up, it must fall back down to where it started. Even the smallest value condensers will swing the needle up if they are leaky. The needle just won't fall back down if they are indeed leaky.

Thomas

Hi

Try a 1R5 in place of the 1L6. It should oscillate on broadcast band but not very well on short wave. Radios with B+ tied directly to pin #5 require this pin to be removed on a 1R5.

Increasing voltage slightly on you 1L6 should cause the tube to oscillate. Sometimes reducing the value of a series filament resistor will get a radio going. Maybe someone already has done this? Your ballast tube was glowing. Measure voltage between pin #1 and #7 on your tubes. All should have around 1.4 except output tube which will be twice that.

Norm

:In my experience with portables (mostly Zenith, but no Transoceanics), your oscillator tube must be good. If you have an Eico 625 tester, you can try turning the selector to #4 for a brief moment. This will put an excessive load through the tube, which shakes crap off of the filament or something, or perhaps it burns off gas. Anyway, any oscillator tube I had with the popping out trouble usually was cured for a week or so by doing this to the tube. Depending on your tester, overloading the tube may or may not solve the problem, and if your tester is powerful enough, it might fry the tube.
:
:Another problem I had with one of my radios was a leaky filament ballast resistor. I think your 50A1 takes the place of this resistor, but I thought I'd mention it just the same. It's a wire wound unit with three terminals, and is encased in sheet metal. There is a varnished paper insulator and some asbestos between the wire and the metal case. This started to break down, allowing leakage to the chassis, which is isolated from everything through a condenser. It puzzled me why there was suddenly 60 volts DC on the chassis, since the chassis is isolated by a condenser. For some odd reason this voltage presence threw off some things through shielding, etc. Both the audio and the oscillator section would drop out from time to time. Momentarily shorting out the chassis condenser solved the problem. ......So I disassembled the resistor and put in some new insulation. Surely a simpler route would have been to prop the resistor up on a slice of ceramic with sleeves around screws for insulation, but my brain doesn't always think like that.
:
:Anyway, the second problem isn't likely your's, but I thought I'd mention it. Be absolutely sure that you replaced all condensers with the freshest and newest condensers which are leak free. With these portables, I cannot stress enough how important it is for condensers to be leak free. They cannot have leakage even in the millions of ohms. If you pulled some condensers from another radio, this is unacceptable. www.tubesandmore.com sells metalized film condensers which are quite small and yellow in color. They fit nicely inside of the paper tubes of the old Zenith condensers. With portable radios, any leakage of DC current through a condenser is enough to severely throw off grid biasing, which will cause the audio to distort and the oscillator to operate irratically. Remember to disconnect a condenser before you test it. Leaving the condenser in the circuit will throw off your readings due to other current paths in the circuit. When you test a condenser, you use the most sensitive resistance check scale your meter has (usually X10,000). Without touching the leads of your meter with your fingers, touch them to the condenser in question. If your meter needle swings up at all, it should fall back to EXACTLY where it started. WATCH CLOSELY. Condensers smaller than .001 MFD won't likely move the needle up at all unless they have leakage. Larger condensers in good condition will swing the needle up just a bit, and then the needle will fall back down after the condenser has charged. The larger the value, the larger the swing. For any condenser, though, if the needle swings up, it must fall back down to where it started. Even the smallest value condensers will swing the needle up if they are leaky. The needle just won't fall back down if they are indeed leaky.
:
:Thomas

My problem was indeed the 1L6. I picked up a Y600 today for 35 bucks. Putting the 1L6 from that radio into the H600 restored normal operation.

:My problem was indeed the 1L6. I picked up a Y600 today for 35 bucks. Putting the 1L6 from that radio into the H600 restored normal operation.
:
:

Hi Everyone,

Thanks for all the info. The caps are all new metalized film units and I went back and checked all of them for leakage. I also rebuilt the electrolytic cap can with new ones and verified the correct polarity.

The glowing 50A1 has me worried. I never worked with one before so I don't know if this is normal. I calculated the current draw in the filiment circuit from the voltage drop across the 700 ohm series resistor. I got 49Ma which should be ok for the tube complement in this radio. I also double checked the electrolytic on the filiment side of the 50A1.

I'm going to try to get the 1L6 to oscillate by changing the resistance a little.

Again, thanks everyone.

Mike M

Make sure, too, that the electrolytic on the filament side of the 50A1, if you replaced it, is connected with respect to proper polarity. If you connected a new one backwards, or if the original one is at all leaky (or low in capacitance), your filament voltage will be low at all tubes, which will cause the oscillator to not work. It is normal for most ballast tubes to glow, but if you suspect trouble, it is wise to check all filament voltages. They can be .1 or .2 over what they are supposed to be, but on AC operation, they should never be below what they are supposed to be. Often with my radios, on AC operation I find the filament voltages slightly over, as mentioned above. Anything greater than this is also not acceptable, as these tubes have very fragile filaments.

Anyway, check filament voltages. If they are low, then there might actaully be some trouble related to your 50A1 glowing (especially if it's glowing abnormally bright).

I do not have access to a schematic of this radio. Does it use a tube type rectifier or does it use a solid state rectifier? If solid state, and if you replaced it, are you sure that you connected the new one properly?

Thomas

:Make sure, too, that the electrolytic on the filament side of the 50A1, if you replaced it, is connected with respect to proper polarity. If you connected a new one backwards, or if the original one is at all leaky (or low in capacitance), your filament voltage will be low at all tubes, which will cause the oscillator to not work. It is normal for most ballast tubes to glow, but if you suspect trouble, it is wise to check all filament voltages. They can be .1 or .2 over what they are supposed to be, but on AC operation, they should never be below what they are supposed to be. Often with my radios, on AC operation I find the filament voltages slightly over, as mentioned above. Anything greater than this is also not acceptable, as these tubes have very fragile filaments.
:
:Anyway, check filament voltages. If they are low, then there might actaully be some trouble related to your 50A1 glowing (especially if it's glowing abnormally bright).
:
:I do not have access to a schematic of this radio. Does it use a tube type rectifier or does it use a solid state rectifier? If solid state, and if you replaced it, are you sure that you connected the new one properly?
:
:Thomas

Thomas,

It has a selenium rectifier that I've substituted with a solid state diode. All the filiment voltages are correct and the replacement electrolytic is installed correctly and not leaky.

It's good to know the ballast tube glows normally. I hate to say this but I'm leaning toward the 1L6 as the problem.

The schematic is available at http://transoceanic.nostalgiaair.org

Thanks for your help.

Mike M.

How does the 1L6 test? Be sure to set the "line" adjustment properly on your tester (don't cheat). If it is borderline, then it may be faulty.

Thomas