Hey all, I got me another radio that I'm familiar with instead of them pesky tubeless ones heh, The symptom this Zenith T.O has is after a few minutes on all bands die off and it seems the radio just dies. before I tear into it and dig my tester out to test the 1u5 I just wanted to ask if ya dealt with this.

Well it could be many things but you might want to test your 1L6 it is likely weak. A 1R5 can be substituted with good results for am reception.

You should be able to do a search to find out more about this.Some times ir is recommended to cut a pin off the 1R5 but it's late and I don't remember which. I have had good results even with shortwave using the 1R5.
Good luck.
Henry

The selenium rectifier can cause this issue. Check your B+ voltage to see if it falls off as the radio dies. What model of ZTO do you have?

Model is g500

Here's another vote for a failing selenium rectifier. The "dies after a few minutes of operation" is a classic symptom. What happens is that the rectifier heats up internally and starts dropping a large amount of voltage across itself, resulting in lowered DC voltage output. At first this manifests itself as "deafness" on the higher frequency ranges but eventually progresses to being inop across the board.

Lets look at why the rectifier heats up, this is usually caused by defective filter capacitors. Replacing the filters will usually correct the situation if the selenium has not been damaged. Replacing the selenium with silicon will usuall give you a tempory repair as the 1 amp silicon can overcome the capacitor leakage which caused the 30ma selenium to heat. This is like using a 1 amp fuse where a 30ma fuse is required. The first step on any repair is to replace the filters. All my TO's have the original seleniun installed and they work great. What gave seleniums a bad rap was their use in TV's where they we pushed to their limits and run hot until they failed. Bad seleniums were never a problem in radios but I have replaced tons of them in TV's. The choice is yours.

DM

great ideas I have gotten in many ZTO radios with the diode inline with the selenium rectifier which should be one or the other not both.
I had some old pc power supplys that I take the large caps from and use them to test filter caps in the radios, the radio has a hum when volume is all the way down so at least part of it is dried up, tonight I'll jump these large caps in and see what goes on and like the other suggestion about watching in the voltage drops.
I did get rid of all them black beauties as I never seen one that wasn't dried up junk.

Not a good choice unless the capacitors are close in value to the original ones. Just replace them with the proper value capacitors and be done with that part of your repair.

DM

Oh I do I just use the higher value ones I clip lead in just for testing then I do order the right ones.

ok here's what the dealeo is, a few tubes tested weak so I swapped them out but the 1l6 tube is leaky it tests in the green then the needle slowly falls below green, and the SR gets hot not hot enough too not touch but very warm and the sand resister gets warmer so I figure it is a combination of the leaky 1l6 and filter caps.
I'm out of them tubes and the 2 in my stash tested dead but them always were **deleted** tubes, I have some 1r5 tubes I can use I believe pin 5 I cut.

A bad selenium was the main problem with my G500 along with an extremely tired 1L6.A rare problem it seems,but they do go bad.

I have a G500-you don't have to cut any pins to make it work in place of the 1L6.I must have had a hot one as the BCB and the first two shortwaves band would work perfectly with the 1R5 sub.

Depends who you talk to on cutting pin 5. I have a test 1U5 with pin 5 cut off. It's always worked for testing. I've also gotten burnt by testing a 1L6 which shows good until I started holding the test button down for a while and watch the meter go half way down in the red. A 1LA6 and my adapter took care of that.

Freeman

I borrowed a 1l6 from my 600 that tests good but the bands do die out but now I still get static meaning it doesn't go silent so the next thing I can try is ordering the right filter caps for it but I'm thinking the rectifier may be bad as clipping in larger caps does really nothing and I know they are good I use the same ones for other radio filter tests maybe I should jump in a diode and a 100k resister I don't know I found in the past that Zeniths either work or they don't, 1 out or 6 zto's that came in were worth working on.

I wouldn't trust your tube tester to determine whether your 1L6 tube is bad, unless the filament is blown or its shorted. I have had several tubes that test exactly as you describe yet function perfectly in a radio. I have had 1L6 tubes that test good, yet drop out after playing for a while. The best tester is in a radio. I would take your suspected bad 1L6 and put it in the 600 radio you mentioned to test its performance.

ZTOs are well built radios that I have found to be readily restorable. I have given up on only a few due to "mouse house" or previous hack restoration. The power supply always needs work, filter caps should be replaced and the selenium rectifier removed. With the space freed up by removing the selenium rectifier, you can easily fit new filter caps under the chassis. I no longer restuff the multi section capacitor, I disconnect it electrically and leave it in place.

Getting the filament voltage correct is important and one thing that I do is replace the shunt resistors in the filament string with modern 5% resistors. This helps to keep tube filament voltages correct and even from tube to tube.

Dear Sir-PM sent:)-Gearhead222

Happy news I fixed it the problem was a crappy output tube and the selenium rectifier got real weak so I rigged up a diode and some resisters and it has been playing for 20 minutes with all bands working, thanks for the ideas it does help trouble shoot quicker

Did you replace the filter capacitors?

DM

yes I did, even though it wasn't that bad it had a hum to it so it's good to just change it now and I replaced all the bumblebees too as them are never good.