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Heathkit Senaca, 6 and 2 Meter.

05/23/2011 11:47 PM

I have a Heathkit Senaca that has not been on the air in probably 40 years. We checked as much as we could all parts. We replaced the tubes with new ones, and we redid the neutralization on 6 and 2 meters for the 6146 driver tubes. It works fine, and loads correctly, and the audio is perfect as only a tube radio can be. Once it warms up, things go to hell real quick. The drive becomes erratic, and the audio gets choppy, then squeals like a banshee in heat. We have set it up about 2 inches off the table, and put a fan underneath to cool the 2E26 driver tube, and we put a fan on top to suck out heat from the 6146 final tubes. This helped a great deal and I was back on the air for a few days, then it started over again. I`m checking the 6 meter forums for answers, and any where else someone might know the cause and the cure. Thats why I have come here asking you guys. There are some pretty smart critters on here, and I`m open to suggestions. I`m old, but never too old to learn. Have a good day guys, I will. Bob KC0VEA

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#1

Re: Heathkit Senaca, 6 and 2 Meter.

05/24/2011 9:20 AM

Bob, it would not be unheard of to have problems with capacitors on a rig of that age. What type of capacitors does the unit have? Caps by their nature are temperature dependant, but can really be troublesome when they age.

Tom D.

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#2
In reply to #1

Re: Heathkit Senaca, 6 and 2 Meter.

05/24/2011 3:44 PM

Well tdesmit, we replaced the huge 450 volt caps with new smaller 450V caps, and this left a large gap, enough to install a fan .There are several bypass capacitors, about 40 of different values. My radio man has checked a bunch with his capacitance checker, and so far they test good.I`m wondering since the 2 meter portion AM does not work, if that is messing up the 6 meter AM section that does work, but won`t stay working. When he replaced those HUGE 450V Caps with new one 1/5 there original size, I questioned him if they would work. He seemed to think they would. He will call me on 6 meters here shortly, and it will work and sound great for a few days, then just before he says its ready, she goes off the reservation big time. He has one identical to it, and its had problems similar over the years, but he has it going pretty good right now, the problem is he changed so much stuff, he forgot what fixed it.Thanks for your help tdesmit, much appreciated. Bob KC0VEA

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#4
In reply to #2

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 12:06 AM

If the transmitter breaks into oscillation, you have to determine if it's an audio or RF oscillation. What I would do is pull the 6AQ5 when it squeals and see if that stops it. Then you have just isolated the source. Then look at the audio section if you have a scope and see which stage is the culprit.

Roger
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#6
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Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 12:27 AM

We will have to try that . I keep telling my buddy that we need to get the 2 meter AM working, then we can concentrate fixing the 6 meter side of it. The 2 meter coil is located next to the 6 meter coil, and they are adjusted for a coupling effect. This determines the drive output on both bands,and if one band is not working, then how can you get your coupling effect if there is no drive on the one band. I think both bands influence the other, and adjustments are made accordingly. My buddy thinks I`m about half right most of the time, but what do I know.?? I just spend the money, but even a old dog like me learns a trick now and then. Even a blind hog can find a Acorn now and then. I have a broke clock, but its right at least once a day. Thanks for your help. That was a good answer, Bob KC0VEA

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#8
In reply to #1

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 10:01 AM

My first thought too. The ceramics are probably fine, but the rolled wax-paper caps should be replaced with mylar.

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#12
In reply to #8

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 12:24 PM

You are right Deefburger, and thats what we did right off the bat. They were leaky, and they helped breath a better quality of life into this great old rig. The audio cleaned right up. We also cleaned every ceramic tube plug in, and cleaned every tube pin before plugging it in. We also checked every tube for shorts, and if gassy. I suspect a bypass capacitor, and ther are about 40 of them. Thanks old friend for the advice. Bob KC0VEA

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#13
In reply to #1

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 2:09 PM

GA

I would bet, just as you posted, that one or more caps are simply gone to wherever the cap heaven is, especially the electrolytics.....

Modern caps may look out of place in 40 year old equipment and are often far smaller, but I have a friend (of 30 years standing) here in Germany, a US citizen, who is both an electronics expert and radio Ham, he likes buying Heathkit stuff (ebay) and making it look and work like new.....he manages to find cap equivalents that look like the originals, but are in a fully working condition....

If it was me, I would use the best quality modern caps.....even if of a difference size and appearance, but that's just me!!

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#14
In reply to #13

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 2:20 PM

In many cases, because of the size differences, modern electrolytics can actually be "transplanted" into the old cases, thus keeping the look of the original. I can't say I've done this myself, but I know it's been done. The wax/paper wrapped style would be a little more difficult, but if a mylar equivalent would fit inside, that may even be doable. All depends on how much you are trying to keep the "look". As for me, if you can't see it with the case on, I don't think I'd go to that much trouble.

Tom D.

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#15
In reply to #14

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 2:57 PM

Thats what I have done tdesmit, I replaced those old caps with the new Mylar of the same voltage.I really don`t care what it looks like inside, I just want it to be the best sounding rig on 6 meters, and to be reliable. I have a Globe HyBander that talks on 2 and 6 meters. Not the prettiest radio I got, but definately the loudest, and bullet proof. You can use it and abuse it, and it keeps trucking on. Several people on 6 meters would like to have it, but its not for sale. Thanks tdesmit, and Andy from Germany for all your suggestions. Bob KC0VEA

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#3

Re: Heathkit Senaca, 6 and 2 Meter.

05/24/2011 10:39 PM

I can't help with your problem since i just got my license a few months ago and have never used tubes (or AM, I have a 2-meter FM rig), but I wanted to wish you good luck.

Please let us know when you find the problem.

KD8OSW

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#5
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Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 12:15 AM

Thank you Harry. I hope you are enjoying the 2 meter band. I scour the country, old barns, basements, ham fest, obituaries, you name it. I buy these old tube transmitters, and receivers, restore them, then put them back on the air. AM is the only place I talk. I have side band, FM, but I don`t get the thrill like I do putting a old AM rig back on the air. I also build all of my own antennas, and towers. I seldom buy anything, I just make what I need.I just had one big tower stolen, but I still have 7 towers standing, and 3 more to build. For my 2 meter rig I built 4 Yagi antennas, 4 elements each. I co-phased them together onto a 56 ft. tower with a rotor. The radio is a Icom V-8000, that does 75 watts, going into a box that does 800 watts, going through those 4 Yagis co-phased together.I can hit the repeater most times in Columbia, or Kansas City most times. Thats 200 miles as the crow flies. Not to shabby if I say so myself. Have a good day, 73`s Bob KC0VEA

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#7
In reply to #5

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 8:26 AM

I had a Heathkit stereo amp and noise would start once it got warm. After replacing suspect tubes and switches, the final solution was to resolder all the connections. They looked sound visibly but apparently rosin flux in the solder had deteriorated the integrity of the connections. Sounds like you have plenty of experience in with old equipment, but you might consider this if all else looks good.

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#9
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Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 11:55 AM

Your right Ridgeback, and that was the first thing we did. We visited all the solder connections, then we visited all the ground connections. We also cleaned all the function switches with Tarn-X, then neutralised with alcohol.One of the air variables had a bent fin, and that effected the drive. That the entertainment value of this old equipment. Some of this stuff I run like my Globe Champion 300-A, is built like a tank. Talk about bullet proof. Some of this stuff, if not loaded properly will fail in a hear beat. I have a few Globes built by WRL Radio, and I would never get rid of them. They are rock solid on frequency, great audio, and if you screw up, they will usually hang in there, and are very reliable. Not the best looking rig in the world, but very dependable.Also, very heavy. The transmitter weighs 125lbs, by itself. But it puts out on AM 265 rock solid watts, with great audio. Thanks for your suggestions ridgeback, 73`s to you. Bob KC0VEA

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#10
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Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 12:03 PM

As a after thought, I wanted to explain something else. I have been chastised in the past for long, hard to read post cause I never space my replys. I want everyone to know that I do break my replys up. When I preview my comments, they are spaced like I typed them, nice and neat, easy to read. BUT, when they are posted to this forumn, they are one continuos ramble, and this makes me look bad. I have properly spaced this reply, but when you read it, it will be one long ramble?? Thanks guys, 73`s, Bob KC0VEA

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#11
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Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 12:17 PM

Also ridgeback, today I will swing by the local Radio Shack in town and pick up some equipment coolant. The nearest town from me is 30 miles one way, but this coolant will work nicely on something like this. I have to take the wife to the airport, and put her on a plane for Arizona. She will visit the grand kids for 10 glorius days. When she goes on vacation, I`m on vacation. What I will do is put this rig into a heavy duty cycle and make it fail, then spray the bypass capacitors with this freezing compound. The offending capacitor should work fine immediately, letting the radio come back to life. There are about 40 bypass capacitors in this rig, and my capacitor tester says they are all good. That may well be under test, but something is getting hot and failing, then works again when the rig cools off. If this don`t find the culprit, then I will be forced to replace all the capacitors. 73`s for now guys, I`m fixing to have a lot of fun. Bob KC0VEA

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#16

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 4:37 PM

Being mindfull of the hi voltage on these boat anchors, take a plastic or wooden rod & tap/move each component while the rig is working properly & then when it has warmed up & has the squeal. What we are looking for is a bad solder connection or a part that has a bad internal bond. A heavy plastic clothing hanger can be cut up to make plastic rods.

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#17
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Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 6:32 PM

That is a good idea Doug. I`m still leaning towards a bad bypass capacitor , that only fails when this rig is worked hard.Also, I feel we need to get the 2 meter up and running on this rig as it effects the settings on 2 and 6 meters. The 2 and 6 meter coils have a coupling effect, as well as the neutralization rods. A friend of mine who built one of these years ago from a kit emailed me and told me I was RIGHT!! The 2 meter settings do effect the 6 meter setting, no doubt about it. Once we figure out why it has no or very little drive on 2 meters, I bet the rest just falls into place. What was that I said earlier that this broke clock of mine is right at least once a day!! I`m just a radio operator, but now I`m starting to feel like a Technician. Maybe I should get more involved in the repair aspect more often. Lets see, 700+ volts on the B+ side, NAHHHHH. I`ll let my buddies do the repair, I`ll just stick to trouble shooting, and talking. Works for me. 73`s guys, Bob KC0VEA.

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#18
In reply to #17

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 8:14 PM

Bob

If you can troubleshoot it and figger out which part is bad, then you should be able to fix it. Then you will be a radio repairman !

Do you have one of those fancy-dan IR Thermometers ? If so, with the rig cold, turn it on and watch the temperature of several of your bypass caps. The bad one (assuming it's shorting as it gets hot) will rise faster than the others. That one should be replaced first and maybe your problem will be solved.

However, if the bad cap opens, then it will not change temperature. In that case, you can simply add a bypass cap in parallel to various caps and your problem should eventually disappear when you find the open cap.

Have you taken voltage readings of the various stages of the transmitter ? If you have a shorted cap, the voltage on that pin will be ZERO.

(I got my first job that way, by finding a shorted cap. I was in tech school and wanted/needed a job just for some experience so I stopped at a small radio shop and asked if I could work for him, even if he could not pay me. He pointed to his bench and told me of a new radio right out of the box, that didn't work. Said if I could fix it, he'd let me work. Took about 10 minutes, taking voltage readings and I found a shorted cap on a screen grid, mixer stage. Replaced it and the receiver came to life. I had my job and that got plenty of experience I wanted working for him)

I still say that you shouldn't need a fan on your boat anchor. They were designed with heat in mind and they play well when it's SUMMER ! About the only thing needing fan cooling will be power amplifiers, like the Johnson THUNDERBOLT or the Heath SB200, Drake L4-B.

Your problem is taking me back to my days as a service tech and I'm truly interested in your problem. I still have an old DRAKE 4-Line that has been in storage for 40 years but when I get my tower in the air I plan to fire up the Drakes and see how far they will talk. Maybe I'll have to do some troubleshooting on them, too.

RoGrrr
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#19
In reply to #18

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 9:51 PM

Well RoGrr we don`t have any of that fancy dan IR Thermometers, thats why i`m picking up a can of fast freeze. I`m hoping that will help eliminate some problems.My buddy Jim thinks its a waste of money, but since we are stalled until we find the problem, I figure I got nothing to lose. I`m also of the belief that we have to get the 2 meter side working, as there is coupling that is SUPPOSED to be going on. With no drive on the 2 meter section, its hard to adjust anything if it can`t couple. The 6 meter and the 2 meter coils are close together, and they are SUPPOSED to have a coupling effect, which they are not. Also, we adjusted the Neutralization rods for 6 meters, but they cannot be right, as we never adjusted the 2 meter for lack of any drive. According to the book, one plays off the other, if adjusted right. Also, I`m a radio operator only, and my buddy Jim is a tech of sorts. He has never been to school, he is self taught. Someone else with proper schooling could probably have it fixed inside of a hour. I`m a wannabee tech, and Jim is sorta tech, if that makes any sense. But, we are having fun, and we must be doing something right, as we have fixed a lot of these old tube transmitters, and put them on the air. They all work well, except this Heathkit. No telling what has been done to it before we got it. Thanks for your help. Bob KC0VEA

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#21
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Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 10:05 PM

As a side note, I want everyone to know how much I appreciate all these good helpful answers. BUT, I think some people are not reading all the post. This radio works like a champ for a few days, then it goes off the reservation. When Jim checks everything he can, it checks out 100%. We load it back up like the book calls for, and we may talk on it for 3 minutes, or 3 days before it acts up again. All the capacitors check ok, with a capacitance checker. Even the two we found that were cracked open tested ok. We replaced them cause they needed it. One of these caps is getting hot, but test good. Soooo, we are going to run it through a tough duty cycle, and make it fail, and we will have a can of quick freeze ready. Its that, or replace all 40 caps . When we hit it with the quick freeze, it should come back to life, ??? Thanks guys, Bob KC0VEA

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#22
In reply to #21

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 10:13 PM

I 've read the other responses and have a futher comment. Not to insult the guy who changed the capacitors, but I want to remind him that using a voltage rating higher than the original will add more tolerance to heat. I am sure he adhered to the equal microfarad rating, already.

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#24
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Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 10:29 PM

Yes he did.

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#26
In reply to #22

Re: Heathkit Senaca, 6 and 2 Meter.

05/26/2011 3:57 AM

Good post.

Also nowadays there are different electrolytic caps with different temperature ranges, the OP should buy the ones good for the highest temperature range.....

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#28
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Re: Heathkit Senaca, 6 and 2 Meter.

05/26/2011 7:31 PM

Andy,

Thanks for the GA- also you make some very good points. You may have noticed newer capacitors are mostly non-polarized. I've read it's because of new polymerized electrolytic barriers, but something smells of ease of production?!

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#29
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Re: Heathkit Senaca, 6 and 2 Meter.

05/27/2011 10:16 AM

Why do you call yourself DRFREON?

I thought Freon was as good as completely banned!!

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#25
In reply to #21

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 11:06 PM

OK, you're right about missing something in an earlier post. You say that there is a cap getting hot. Even tho it tests good, REPLACE IT, anyway ! It saves more time than $$$$ and caps are not supposed to heat up, anyway.

Chart your voltages before, and when it oscillates, do some more DC voltage checks and compare them.

Without a manual, I can't offer more advice than I've already given. Yes, I've scored several points for good answers, but that's not my goal, nor is it the point of this QSO. You want to get back on the air and I'd like to hear that you succeeded in going live again and how you succeeded. If you think that you're not a technician, you're wrong. Becoming a technician is a lot of experience, both book-learned and practical (hands-on, like you're doing). I learned the basics from books and word of mouth (teachers). I can now service some things and get them working. After over 40 years of measuring and soldering, I still don't consider myself to be a technician who knows everything but I do have some idea how/where to start when my (something) quits and I need it fixed, be it a radio, a car, water heater or whatever else. You are on your trek in the same direction.

Best of luck to you and keep posting about anything you are working on. How is it they say - INQUIRING MINDS WANT TO KNOW !

RoGrrr
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#20

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 10:00 PM

I have two suggestions. Clean all components with a self drying, dielectric electronic solvent wash and carefully blow off any dust and remaining solvent with dry, compressed air. Look for heat sink(s)- sometimes the components come loose or the thermal-conductive compound drys out. Both steps seem logical, as the problem is likely heat related.

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#23
In reply to #20

Re: Heathkit Senaca, 6 and 2 Meter.

05/25/2011 10:25 PM

Well DRFREON, we have used Tarn-x to clean all connections, then neutralised with 91% alcohol. This has always worked for us in the past. BUT, I will pick some of this up on my way back from the VA hospital. It cannot hurt, and may do some good. I`m like you, I think its a heat related problem. My buddy emailed me and told me we needed to get the 2 meter side working, as it effects the 6 meter settings. Without the 2 meter side, adjustments will not be accurate, and it will run hot. It will adversely effect the new tubes I installed also. He should know, he built a Heathkit just like it from a kit. Thanks for your imput, Bob KC0VEA

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#27
In reply to #23

Re: Heathkit Senaca, 6 and 2 Meter.

05/26/2011 9:48 AM

Just another thought...Have you checked your grounds? Intermittant squeal under load can be related to a bad or broken ground connection. Not just the unit, but the bench! Weather can alter it, temp can alter it, and mice can ruin it!

Second, Hows your house wiring? Is there anything else turned on in the house that might be the source? If there is a multi-point ground on the house, and or faulty wiring/equipment, then a signal or current loop may be forming and SQUEEEEEEEEEL! Transmission trouble.

Third, and this might be a stretch, but how far are you from the line trasformers? Those are your final long line signal filters too. If you have neighbors on the same segment as you, you might consider an isolation transformer to feed your bench, with a single point solid ground.

I worked in broadcast radio and numero uno for any equipment hook up was grounding and clean power, THEN equipment check, other wise you can chase your tail for days.

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#30
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Re: Heathkit Senaca, 6 and 2 Meter.

05/28/2011 7:48 PM

I know everything you have said here is true, and we have checked all those. We are reevaluating our previous checks, and found the socket for the 2E26 driver tube not up to snuff. Jim resoldered two suspected joints. and changed out a capacitor that checked good, but we suspect is heating up. He put the radio back on the air, and she sounded great for about 3 hours, then the drive went south to zero, but came back on its own. It hung in there for about a hour more, then got flaky, so we quit for now. Jim is going to pull the socket, and what ever else he thinks needs looking at, and we will try again in a few days. Thanks everyone for your help. Bob KC0VEA

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