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Philco 19H weak/no reception - Printable Version

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Philco 19H weak/no reception - jeffb - 01-13-2015

Hello folks, I rewound this oscillator transformer "tickler" coil and the radio is now alive! BUT, there is a very weak signal. I only have a piece of wire hanging off the thing for an antenna, but I was only able to get one station in, barely, with my volume cranked up to max, lots of static otherwise. I did an alignment and was able to peak the IF, antenna, detector, and high and low frequency trimmers. I only get a weak station on the uppermost band, around 1500KC. Any suggestions? All tubes check correct, but maybe there is a weak one? All caps have been changed, all resistors checked and changed so they are right on tolerance as per the schematic, all coils check good as well. Cold solder joint? Suggestions? Thanks!

PS- I'm still studying the shadowgraph- When I turn it on, there is a fine slit, and when it warms up, a wide, black rectangle that doesn't change, even with my weak station.

RE: Philco 19H weak/no reception - morzh - 01-13-2015

Good news. your shadograph is working, so don't touch it unless needed.

RE: Philco 19H weak/no reception - morzh - 01-13-2015

How are voltages on your 44 tube?
Check intergrity of transformer 8.

I am looking at this sch

http://www.nostalgiaair.org/PagesByModel/153/M0013153.pdf

If not this, give the link.

RE: Philco 19H weak/no reception - jeffb - 01-13-2015

(01-13-2015, 10:23 PM)morzh Wrote:  Good news. your shadograph is working, so don't touch it unless needed.

Great, thanks for the advice, I'm glad I didn't mess with it, I think I will reflow some solder joints.

RE: Philco 19H weak/no reception - jeffb - 01-13-2015

Hi, the voltages on the 44 tube are close to the chart on the schematic you and I are looking at- 200vdc plate to kathode; 104 Vdc s. Grid to kathode; .3 control grid, 5 vdc k to filament. However, I am getting -22vdc on the output tube- cg to kathode, where the voltage chart states 2.2 vdc?

RE: Philco 19H weak/no reception - morzh - 01-13-2015

Check 263 and 21 ohm sections on your 52 resistive divider.

RE: Philco 19H weak/no reception - jeffb - 01-14-2015

Hello morzh- I did that, mine is 255 ohms and 22 ohms; in circuit, though. I am still questioning the control grid to kathode volts on the output # 42 tube. Mine is -20 volts dc, the chart in Riders volume, page 4-19 says it should be 2.2vdc. I agree with Ron where he said in one of my posts that the old vtvm's really loaded down the circuits, but I just don't know. Thanks.

RE: Philco 19H weak/no reception - morzh - 01-14-2015

In circuit is fine, these are low values and do not depend much on stuff around them.

The voltage should by itself be negative as you measure from the Chassis to the centertap (where the bias comes from) which is negative. If you draw 30mA you have roughly -10 V. Then the tube will develop its own internal bias which will detract from that value but it can be still negative.
Or you cold change the tube and see if it improves performance: in circuit check is alwys the ultimate proof.

Same goes for other tubes.

RE: Philco 19H weak/no reception - jeffb - 01-14-2015

Hi, thanks. And a wierd note: When putting the 1400Kc modulated signal from my signal generator into the detector/oscillator grid (tube # 36), I have my attenuation on the signal generator output barely off zero, and the volume pot barely on; otherwise the sound will be deafening coming out of the speaker, so that proves that the radio is able to pass a signal???

RE: Philco 19H weak/no reception - morzh - 01-15-2015

Is your waveband switch good?
What and are you at?

Also: why put signal in 36 and not 44 RF stage?

RE: Philco 19H weak/no reception - jeffb - 01-15-2015

Hello, I assume the switch is good. To be sure, when you turn the radio on, is the first selection the AM selection and the second position the police? Well, with the waveband switch in the first position- Here's what's new to me: I put a modulated signal of 1400 kc from my signal generator right to the antenna post, tune radio to 1400kc also, and it "kicks" into oscillation and the radio works great! Sometimes! Sometimes if I tune it below 1000 kc it will die. Put the 1400 kc modulated signal back to antenna, tune back to 1400 on radio, it works great. I think I have a weak RF or oscillator tube. Again, my RF and oscillator coils check out with an ohm meter. It gets a jolt from my generator, works good! Turn off radio, turn it back on, static, until I apply the modulated signal again. Any suggestions? Thanks!

RE: Philco 19H weak/no reception - Ron Ramirez - 01-15-2015

Yes. Change resistor (10), 15000 ohms which is in parallel with mica cap (11), 700 pF, to 8200 or 7500 ohms.

If that doesn't work, replace the 36 tube with a known good one.

It was found during production that 15K was too high a value to allow for reliable oscillation, so the factory recommended changing to 10K. As many of us have been restoring these sets, we have found that a change to 8.2K or even 7.5K is necessary to make the oscillator run reliably.

The autodyne circuit employed in the 89 and 19 is known to be flawed, but when it does work, it is usually OK.

RE: Philco 19H weak/no reception - jeffb - 01-15-2015

Thanks again Ron. So should I increase the value of the cap to 1500pF also, as it states in your tech section? Again, it is clear and has lots of volume once it works, but otherwise?? Thanks.

RE: Philco 19H weak/no reception - Ron Ramirez - 01-15-2015

No, leave it 700 pF. 1500 pF is used if you replaced the 36 tube with a 77 tube. That would involve changing the 5-pin socket to a 6-pin. A lot of trouble. Let's try to get the original design functional first before even considering modifications.

Just thought of something else - when you rewound the coil, did you also bake it before rewinding?

RE: Philco 19H weak/no reception - jeffb - 01-15-2015

Thanks, yes I did. Also, the other coils in item # 12 were ok, they checked ok, so I did not rewind them, only the small one. Thanks and I will get a few tubes from my friend to try!