Zenith 6 S 152

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Zenith 6 S 152

Post by Ed in W. PA on Sun Mar 20, 2016 12:22 pm

I am presently working on this 6 tube floor model from approx. 1936-37. Two things, one this set uses the old dogbone type resistors. Looking at the parts list I see listed values such as 99 M ohms, 990 M Ohms, 400 M Ohms ect. Some values are listed clearly such as 2 Megohms, 4900 Ohms and so on. Am I looking at these as 99 ohms, 990 ohms, 400 ohms, if so, the resistors in this receiver have changed value by tremendous amounts { no surprise }. Secondly. the Candohm resistor has a few aftermarket resistors jumped around it. I will probably have to do something such as replaceing this network with individual resistors. Any idea of a good wattage to use? Also, I disassembled the tuning assembly in order to replace the belt as well as the grommets under the varicap and had great difficulty removing both the brass pointer as well as the red second hand pointer. The brass pointer seems to be a friction fit as I was able to remove it by gently twisting it back an forth till it came off. To re-install it should I just try to press it back on this tiny shaft, or would it be advisable to use some locktite or super glue? Any comments greatly appreciated. Thanks, Ed.

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Re: Zenith 6 S 152

Post by Wildcat445 on Sun Mar 20, 2016 12:48 pm

In the olden days (?!) values with an "M" suffix meant "K" or thousands in more modern terminology. So 99M means 99k. Megohms is typically specified. I like to use terminal strips to reproduce a Candohm resistor, using discreet components. Wattages would depend on those specified in the schematic. I would not use any type of adhesive when you re-install the dial pointer. Closer inspection may reveal that the loop that fits over the shaft is split. You may need to carefully squeeze that loop a bit so it fits tightly on the shaft, won't slip or won't allow the pointer to fall off. If it was glued on, it might not be possible to remove it without damaging other components if you ever wanted to get it off again.

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Zenith 6 S 152

Post by Ed in W. PA on Sun Mar 20, 2016 1:04 pm

The pointer that I was talking about is the brass one with the lightning bolt Z in the middle. It fits on the very end of the varicap shaft which is perhaps 1/16" in dia. and approximately 1/8" or 5/32" long and appears to be slightly tapered (maybe). It was on there very tight making me think some type of adhesive was used??? Thanks,Ed.

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Re: Zenith 6 S 152

Post by Wildcat445 on Sun Mar 20, 2016 2:01 pm

I'd be willing to wager that the taper is what holds the "Z" pointer on. I would not use any adhesive. You could squeeze the taper a bit with needle nose pliers if it needs to be tighter. It does not take much to hold it on. Be gentle with whatever adjustments you make. It might be easy to make matters worse.

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Zenith 6 S 152

Post by Ed in W. PA on Sun Mar 20, 2016 3:11 pm

I will try first to just push it on, and if it does not go all the way on ( it was up tight against the sholder originally ) I might heat it up with the soldering iron and try that. Even though I picked this radio up on the side of the road on trash day, it is still in repairable condition. I would hate to destroy anything due to haste or stupidity, this is why all the questions. The speaker is a little dirty but otherwise in excellent condition, the chassis has cleaned up some but still has a few rust spots. The candohm is mostly open and I have found all the resistors necessary to rebuild it using terminal strips. Most of the resistors I have checked so far have approximately double the resistance of what is called for on the schematic. Is this to be expected? Seems odd t
hat they have all drifted this much. This being my oldest attempt ( 80 yrs old ) to date, I see I have much to learn. Comments, criticism, and help appreciated! Thanks, Ed. p.s. most of the resistors I am going to use for the camdohm are 7 watt.

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Re: Zenith 6 S 152

Post by Wildcat445 on Sun Mar 20, 2016 4:37 pm

I avoid Zenith like the plague for several reasons. That said, if I found one in the trash pile, like you, I would try to save it or give it to someone who would. I have a 5-S-56 that belonged to my dad. It spent its useful life in his milking parlor. When I got it, there was no veneer on it at all. The chassis was nearly solid rust. Every capacitor in it was bulged and every resistor was at least double what it should have been. The field coil in the speaker was partially shorted. It was, and still is, a miserable radio. I have played that radio literally thousands of hours in that milking parlor, though. It has had a horrible life as far as being cared for is concerned. There is always something wrong with it. Another widget has died and now I need to fix it again. It currently is suffering from a dead rectifier for whatever reason. I re-veneered the cabinet and it resides in our home. I was gonna guess 10 watt on the candohms, but you are in the ballpark, and that should work just fine. I believe it to be reasonable to expect all the resistors in your radio to have drifted considerably during the passing 80 years. Let's hope we can find out how well your new cell phone works in 80 years! Good for you trying to save an orphan. Best of luck.

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Zenith 6S 152

Post by Ed in W. PA on Sun Mar 20, 2016 7:29 pm

Although this is the first "big" and "old" Zenith I have played with I have restored quite a few Transoceanics and a number of sets from the Royal series of radio and have found them to be well made and of high quality. As far as television sets go Zenith was one of the finest sets made and one of the easiest to service, that is until they went to Mexico around 1980 then after that their sets were cheaply built and poor quality. I think the main problem I have with this repair-restoration is that the service literature is so scant. Thanks for the insight, Ed.

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Re: Zenith 6 S 152

Post by Wildcat445 on Sun Mar 20, 2016 7:57 pm

You are right. My avoidance of Zenith would be for radios made mainly pre-war. We are on the same page about Zenith after the war. I just find the pre-war stuff is a pain to work on and to get working right. Some guys feel like that about Philco. It's what you are used to and have the best success with.

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Zenith 6 S 152

Post by Ed in W. PA on Mon Mar 21, 2016 10:51 am

Here is the next dilemma, the on-off switch is reading in the megohms. I will try to repair this however necessary. I am beginning to see what you mean WC about why you steer clear of Zenith! I started this project and plan to see it through, hopefully to a successful conclusion. Regards, Ed.

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Re: Zenith 6 S 152

Post by Wildcat445 on Mon Mar 21, 2016 12:10 pm

The power switch should show infinite ohms (open) when "off" and should show nearly zero ohms when closed "on".  If it reads megohms in either position, it is possible that the switch is just stuck, which I have certainly seen before.  My suggestion would be to squirt some contact cleaner into the switch and work it real good.  That should free up the contacts so it will work again.  The ultimate test is to see if the tubes light with the switch turned on.  This would not be a Zenith problem, per se, but an old radio problem.  The thing is 80 years old and it was resting.  Perhaps it is being crabby about you waking it up!  Good luck.  Very Happy

Take things a step at a time and you'll do fine. Old radios are like old cars in that you have to replace a part in order to find the next bad part!

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Zenith 6 S 152

Post by Ed in W. PA on Mon Mar 21, 2016 1:00 pm

The switch was measuring megohms in both positions. Removed the control, disassembled control, 1 little shot of Deoxit in sw, 1 shot electrical cleaner, switch now OK. The volume control is different from contemporary types as it has an inner band that contacts the resistive material when pressed upon by a rotating non-conductive wiper. I cleaned this inner band and applied a thin coat of silicone grease. Control and switch now seem to be functioning. On to the next nightmare! Thanks for listening, Ed.

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Re: Zenith 6 S 152

Post by Wildcat445 on Mon Mar 21, 2016 1:26 pm

You did well! Very Happy

Congratulations!

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Zenith 6 S 152

Post by Ed in W. PA on Mon Mar 21, 2016 4:06 pm

Thanks WC. Looks like every cap and every resistor from here. The vari-cap took half a day to clean up but it tracks between the two gangs to within 1 or 2pf across the whole range. The IF cans cleaned up nice as well. Just hope everything works as good as it looks. Regards, Ed.

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Zenith 6S 152

Post by Ed in W. PA on Tue Mar 22, 2016 10:20 am

Well as I feared I had to replace every cap and every resistor. In all 13 caps, 13 resistors in addition to rebuilding the candohm and replacing the electrolytics. I also noticed that one of the paper caps was of special construction. Don't know exactly what makes this special except that instead of having wire leads it has ( had ) braided leads similar to thin ground straps. The value is .05 mfd @ 600v and bypasses to ground one of the grids on the converter tube. I would have saved it but the ground side of this cap was soldered to ground along with the rather large ground straps coming from the varicap and some other components and I had cut the leads off flush to get it out. The replacement is just a regular .05mfd. Hope I didn't cause myself a problem. Next thing is to install the varicap and see if this thing will fire up. Ed

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Re: Zenith 6 S 152

Post by Wildcat445 on Tue Mar 22, 2016 12:49 pm

I wonder if that cap was one of Zenith's (in)famous "RF chokes". I don't see a problem with what you did. The "fire up" will tell the tale. Good luck.

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Zenith 6 S 152

Post by Ed in W. PA on Tue Mar 22, 2016 1:18 pm

Thanks WC. There is going to be a delay in firing this up. The grommets I ordered for mounting the varicap were the wrong ones. Ordered the right ones today and hope to get them by the end of the week. If that cap in question was one of Zeniths RF choke caps I may never know, unless someone on this forum knows something about this. Thanks again, Ed.

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Re: Zenith 6 S 152

Post by Wildcat445 on Tue Mar 22, 2016 1:36 pm

Perhaps if you would identify the cap in question, someone would chime in here with more definite information.

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Zenith 6 S 152

Post by Ed in W. PA on Tue Mar 22, 2016 2:47 pm

The schematic is Riders vol 7 page 17 chassis 5634. The cap in question is C-20 and is located by the band sw and connected to the cold side of the Antenna coil. The cap itself is marked 22-487F, 05mfd @ 400vdc and has a band around one end marked "ground side". Unfortunately with what is left of the leads I was able to check it and except for a little leakage it is fine and does not measure any inductive value. As I stated before the leads that were on it originally were not wire, but braided like ground strap. Thanks, Ed.

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Re: Zenith 6 S 152

Post by Wildcat445 on Tue Mar 22, 2016 5:05 pm

Cap C20 has a notation (spec L '03) whatever that means. The braiding would indicate some type of shielding to me, but it does not show that on the schematic that I see. Your guess is good as mine, but I'd say just using a typical 630 volt film cap should work fine. For what that is worth........

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Re: Zenith 6 S 152

Post by Bill Cahill on Wed Mar 23, 2016 8:00 am

Using a 630 volt capacitor will be fine.

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Zenith 6 S 152

Post by Ed in W. PA on Sat Mar 26, 2016 12:17 am

Well, after all this work I am pleased to say it works. Only one bump in the road though, the terminal marked Z located between the antenna terminal and ground seems to be wired incorrectly. The schematic shows terminal Z wired to a contact on the band switch, and a dotted line on the schematic seems to indicate that terminal Z and G need to be jumpered together. I found terminal Z wired to the cold side of C1 ( a padder on the secondary of the antenna coil ) thus effectively grounding the stator of the varicap and the antenna coil. I could shoot a 456Kz signal into the grid of the IF tube as well as the converter and get a strong tone, that's how I found the ground. for now I just lifted the jumper I had between Z and G and the set came to life. This wire looks like its been there a real long time but could serve no purpose other than to disable the front end of this receiver. I need to find the proper place to land this wire because it looks like its purpose is to change the impedance of the primary of the antenna coil on band B. Other than that everything seems good- no static, no whisteling or howling and decent reception on my outside antenna. Alignment next then I need to start on the cabinet which is not that bad but will be a challenge due to my lack of woodworking skills. Regards, Ed.

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Re: Zenith 6 S 152

Post by Wildcat445 on Sat Mar 26, 2016 1:56 am

I believe I remember a story that the shortwave on radios was disabled during World War 2 for differing reasons. It is possible that is what happened to your radio. Good luck.

My 5-S-56 is a master of howling. Oscillating is its forte. Mine has a weird power supply that basically connects the positives of the filter caps to the center tap of the power transformer. The output filter cap serves as cathode bypass for the output stage. It has howled all the time I've been around it, nearly 60 years. I have threatened to rewire the power supply in a more conventional manner. You are fortunate that yours does not have such tendencies.

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Zenith 6 S 152

Post by Ed in W. PA on Sat Mar 26, 2016 12:28 pm

If this was some ones attempt at disabling shortwave, they were successful at disabling SW as well as MB as well. I found the correct pin on the band switch and connected it there. Got lots of stations on SW on my longwire antenna. The sensitivity switch had to be in "Foreign" position though for both SW and MB as there was very poor reception when it was in "Local". Perhaps an alignment will help this. I saw examples of similar sets on various websites and it looks like antennas were fabricated by running wire around the inside of the bottom portion of the cabinet. Also I saw a version of a Zenith Wave Magnet in the bottom of one set, a type of loop antenna. I plan to experiment until I find something that works as this set absolutely needs some kind of external antenna. WC, I really appreciate all the help you have given on this project, and thanks to you too Bill C. Regards, Ed.

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Re: Zenith 6 S 152

Post by Wildcat445 on Sat Mar 26, 2016 2:46 pm

When you set the switch to "Local" it may lower the sensitivity of the radio. I always run my radios in setting for maximum sensitivity. Back during WW2, there was a law/rule/custom that families of "enemy combatants" were required to have all but the broadcast band disabled on their radios. I bought a Philco 40-180 that was painted John Deere green. It has its shortwave bands disabled, presumably since the set was new. A longwire antenna goes a long way (no pun intended) to make any old radio perform better.

Helping is what we are here for. Don't be a stranger. It is always interesting to get involved in someone else's project in some small way. Very Happy

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Zenith 6 S 152

Post by Ed in W. PA on Sat Mar 26, 2016 11:32 pm

I guess I spoke too soon. I aligned the set today and things seemed to go normally. stretched out about 10 feet of wire and let it cook on KDKA 1020 the local 50 kw blowtorch about 15 miles away. After playing only about 15 min much crackling then greatly reduced volume, oddly similar to SMD ( which I know can't be the issue here due to actual trimmers in the IF cans ). Cooling down makes this scenario repeatable. As of right now I have traced the problem to something before the G1 pin of the 1st ( and only ) IF section. While doing the IF alignment each trimmer needed to be tightened down quite a bit, a bit more than I would have liked. I backed the adjustments off and started again several times but results were the same. I guess I am taking the long way around the barn saying I suspect the first IF transformer ( hope not ) because the set played for three hours without incident the night before the alignment. You really gotta love this hobby. Regards, Ed.

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