[TV MAN]

One thing I forgot to mention is that the whole chassis seems microphonic. When I tap it, it sounds like a big reverb. Do you think the alignment will get this thing to pick up better? I still need to clean the tuner (and replace grommets), replace a couple of out of tollerance resistors, cap the tone control & clean the controls. I'll get the tubes tested too. I have some deoxit coming.

Got the tube tester working. Thing is ancient, and hasnt been used for years, but it is what I have. I probably should have tested the tubes 1st, and will in the future. I did have a bad experiance when I removed tubes from a good working radio (my favorite Zenith console I bought when I was 8 years old) to clean a layer of dirt off, and when I put them back in, it didnt work right. So, I am a little reluctant to do that until I have an idea of what I have. These were loktals, since then, I have read the socket contacts probably need cleaned. I never had access to this kind of info back when I used to work on these, only books and a retired tv tech back in the time.

[morzh]

Loctal contacts are way worse then old style....had similar problems with my portable Zenith 6G001. Deoxit did not help much. The contacts simply get loose and just a little dirt coupled with that is enough to deliver trouble.

I also notice something yesterday that could be a microphonic, but not sure - it only appeared on one song and was not there before that or after, this was while listening to the local station.
So I decided to withhold e judgement for a while.

As for teh micrphonic..

1. Is it my impression or 70 chassis is really flexible and is thinner sheet metal than in 90? When I pick it up, it clearly twists where the power transformer is under its weight; don't remember this in the 90 (or 20).

2. Could be a tube.
3. Have you replace the tuning cap's grommets?
4. Have you installed any caps (except the line filter) other than film or mica?
5. Is everything tightened well?

[gregb]

The number 27 tubes tend to be microphonic, if you have a spare or two give it a try.

Gregb

[morzh]

Tim

This is where RF coil and Antenna come.

   

[TV MAN]

Thanks so much! We definatly have different controls. I dont know which is correct. Mine is a larger, metal looking control. Seems the more I work with it the better is sounds. I noticed also the chassis seems flexible on mine. I still need to pull the tuner and give things a good cleaning and replace the grommets. Pulled the rest of the tubes and tested (helps when I get my old tester - well, testing again), found several weak tubes. The worst is the 47. I got about 20% out of it, and the old globe 24 1st IF tube was at about 25%. Osc. tube tested barely into the green as did the 27. Other 24s tested well into the good zone. So, this may be the cause of my weak reception. Now, the odd thing, when I reinstalled the tubes, seems the microphonics ceased, or at least dimished! The new 24s and 47 arrived Sat, and I didnt know it until Sunday. Ill get them tested and put in and see what happens. I do have all the bakelite blocks rebuilt and the large metal cans under the chassis, and filter caps. I havent bothered any mica or turned any screws. Trying to be very careful not to disturb anything except the immediate project. Still have a couple resistors to replace that are out of tollerance near the 47.

[morzh]

Tim, a pot is a pot is a pot, so as long as you see where the whiper is, it all that matters.
If you need help with that let me know.

[TV MAN]

This morning I got the new 47 and 24 ist IF tube in. The volume is definatly louder, but the only way I can get decent reception is to clip a wire on the cap of the RF tube. I can get a little something if I clip on the antenna connector, but if I touch the wire, it increases the strength, but eithers squeals or chirps like a bird. Must have been an old "farm radio" I wonder if there is something wrong in the RF coil or something. Going to pull it and look things over. Oh, it is NOT sensitive. I can pull just a few stations.

[morzh]

It should be so sensitive you moving your hand anywhere near the RF coil should make the radio scream.
Look at your antenna coils.
Check the whole circuit. Maybe your tuning capacitor is not soldered or something.

Also your volume pot could do a number on it.
You did check all tubes, right?

[TV MAN]

I did some checks. I unsoldered the wire from the vol control to the coil to check more thoroughly. The coil checked out ok. I had 9.4 ohm on the ant side and 4.8 ohm on the tube side. The volume control is dirty on the ant side, but checks 5k on outside lugs. I think cleaning will fix. I did power up and clipped a wire on the unsoldered wire to the coil and had good volume, but it did not help the sensitivity. When I touch the wire back on the control, it drops the signal a lot, but still picks up. With no ant, tuning the radio to the higher freqs, it hits a spot where the microphonics come back with a lot of feedback - etc. I have pulled the tuning condenser to clean. The screws to the wires werent very tight. Any recomendations on cleaning this? I wonder of those wire contacts the rub the main shaft are the problem. What about washing the dial? Any condensers that could be damaged with water? Any advice appreciated.

This will be the thorough and final cleaning of the chassis before I reassemble for keeps. Yes, all tubes tested. I got no response moving my hand near the RF coil, only when I clip a lead where I mentioned.

[morzh]

I washed my cap in dish soap and then dried it just shaking the water off and leaving it on a paper towel for as long as I did not need it, but it will be dry the next day for sure.
I am not sure what the film inside those trimmer caps made of, looked like it got soggy after the wash, but it dried up and seems t be OK.

Those two spring contacts rubbing against the shaft are grounds, and there are two of them, so should provide good connection.
The screws for the stator - keep them screwed tightly when washing the cap, then after wiping/shaking water off, unscrew and let dry, so whatever got inside will evaporate.

I simply wiped the dial with alcohol.

Microphonics: get into where it is pronounced and using a insulating rod with something soft at the end, keep touching and lightly pressing at any suspected elements. Tubes, tuning cap's vanes (very lightly though they are fairly thick to be bent easily), even coils.

Also, apply some twisting effort to the coils' shielding cans to re-establish the Ground connection - often times they are floating due to oxide build-up. Twisting even if the can does not move breaks the oxide and reestablish connection.
You can easily check that with moving your finger closer to the 1st RF can - the volume of the current playing station goes way up (did do that in both 70 and 90 in my case) and touching it simply tries to rip the cone of the speaker. After twisting that should disappear. (well you did that already..still).

What else.....


PS. Have you check all voltages? Especially those coming off of that big multi-tap resistor?
Check all voltages at the 2nd detector.
PPS. The last thing is - the radio could be BADLY out of alignment. This will screw the sensitivity.
Once done with assembly, try to align. See if it comes back.

[TV MAN]

Last night I washed the tuning condenser. One observation - the main shaft has some wear on one side in the front groove where it sits in the tuner slot. The shaft is out of round in that spot and wobbles when turned. It is not loose. I checked for shorts, and didnt find anything anywhere the shaft is turned. This am I tightened all the screws, replaced the grommets (not real happy with it tho)and reconnected. Powered up and same problem.

I replaced the 27 with a better one (havent gotten the new one yet), and this helped a little. I was running this through an isolation transformer, but when I connected to the a/c line, it did pick up better. It seems stable, but I still cant anything above about 900khz except noises, squealing, etc. I do now have some effect when I put my hand near the RF coil. I am able to use the ant clip on the chassis now. I have plenty of volume now, but it still isnt very sensative or selective. I am thinking it's time to try the alignment. Riders manual mentions a procedure, but I havent found it yet. Anyone know where I can find this?

[morzh]

Tim,

Stop trying to find the reason in a tuning cap's shaft and do the alignment. You are chasing a ghost right now.

The procedure, well, it is in the Rider manual, and it is very simple.

http://www.nostalgiaair.org/PagesByModel...013833.pdf

Look at the very last page at the top left corner.

[TV MAN]

Alright, time for alignment. Got it. Thank you for the link. Has anyone managed to get a volume control like mine open to clean?I tried to shoot cleaner inside, but havent been successful yet. It still works at this point. If anyone has repaired one of these successfully, advise me. At this point, I am prepared to drill a small hole and shoot the deoxit in that way.

[morzh]

I am not even sure how mine opens, as there is that cap and it has no tabs. I guess it is either glued or snapped and I decided not to try to find out - spraying Deoxit inside through the large rivets worked for me.

Does yours have any hole that looks like it could lead to the element?

[jerryhawthorne]

Some of the early volume controls have a cap over the back. My Fada 46 did. I was ready to drill but discovered that dang cap popped right off after removal of the pot (space problem) and a little help from a large jewelers screwdriver. Spraying didn't help in my situation as the carbon track was just plain mostly gone.

[Image: http://i303.photobucket.com/albums/nn129...e/pot1.jpg]
Best Jerry