Admiral 20z1
 

I pulled the speaker from my console to get things cleaned up and have come up with a problem that I hope someone has and answer for me. The speaker has a pretty brittle cone that will probably have to be fixed or replaced in the future. Mounted on the speaker are an Inductor from the power supply and an output transformer for the speaker itself. I thought it a bit odd to mount the choke on the speaker with a cable leading back to the chassis but I guess that is the way things were done. I measured the inductor with my meter and I have continuity with the ohms listed on the schematic. The problem is with the audio output transformer. It measures open with infinite ohms. I need a replacement or a good substitute. The schematic lists it as a Stancor A-3849 or Merit A-2930. I can not find this particular transformer for sale. The primary is listed as 4000 ohms impedance with a 3.2 ohm secondary. Since the speaker will probably need to be re-coned or replaced , I was thinking about using a more modern 4 ohm unit. Does anybody have a suggestion for a replacement transformer ?

Playthings of the past has one listed that you need :
1326-508 OUTPUT MERIT A-2930 SP (5K Z) TO 3.2 VC, 40MA, 5 WATTS, FIG 3 NEW (NO BOX).... 1 2 3/8 1 3/8 1 1/4 $5.75

He has a 20.00 min order, so maybe you can grab some other spare parts.

Thanks for the heads up. I usually use Google Chrome for my browser and I did a search for Merit A-2930 and got very little back. The website that you pointed me to had a link, but when I clicked on it , it came up with a text document so I went looking elsewhere. Later, at your suggestion , I tried Internet Explorer and the webpage came up just fine. Evidently Google Chrome has some security setting that prevents this page from displaying properly. At any rate, I now have a source for this particular transformer -- Thanks.

It actually is a text document as are most of the parts lists on that website.
Internet Explorer displays it inside the browser. Firefox, Chrome and probably every other browser, prompts you to download it.

I use Chrome also. If the .txt extension is associated with Wordpad in Windows file association and not notepad, it opens properly formatted when clicked on and downloaded.

I believe I have a complete spare speaker for that set here if you need it. Not perfect, but it all works. Measures 10 1/4" across the frame. The choke reads 95 ohms.

Kevin

Yes, bandersen, that seems to be the way it is. If a link comes up in the future I will know how to handle it - and I have another link to add to my list for parts.
Not to beat a dead horse, but I was wondering how critical a replacement transformer will be. My schematic indicates a 4000 ohm impedance primary/ 3.2 ohm secondary and I have seen several transformers with a 5000 ohm primary with 4 ohm secondary. Do you think this will be OK - I am thinking it will be cheaper to replace the speaker with a 4 ohm voice coil . The cone is really brittle and fragile at this time , but probably repairable.

That transformer would be fine. But before you throw in the towl on the one you have, have you tried resoldering the connections to the transformer windings?
Also, sometimes they break right at the connection point, and you can possibly reconnect the wire.

Kevin

Yeah, Kevin, I looked into it. The connections are intact right up to the core- still no continuity so it's shot. Out of curiosity, I pulled the transformer apart to see how it is constructed. Man, that was some thin wire for the primary. I should be able to get a replacement at a reasonable cost and I'm probably stressing too much over the little things. The transformer is tied to the plate of a 6as5 that just does not look right. I figure either the tube went south and took the transformer with it or the transformer shorted and took the tube out. Either way, fun and games.

Those fine wires sometimes just fail from corrosion with age. You could change that output tube to something closer to a 5000 ohm impedance, but I doubt you'd hear much difference.

Kevin

Thanks for the offer of the speaker , Kevin. I will keep it in mind for the future. I'm still in the process of listing all the caps and resistors that I will have to order to get the chassis up and hopefully running. I should be able to handle most of the work, I'm just not sure about a few of the Big items - like the picture tube, deflection coils, flyback , etc. If any of these are out, I don't know what I will do.

Upon cleaning the chassis I have a question if anybody cares to chime in. On the deflection yoke towards the rear is a collar that looks like it is made of paper or cardboard. The paper is falling apart and looks like critters have been at work.I am gluing it together as best as I can but it is quite brittle. I am assuming that this is not critical to the operation of the deflection yoke and appears to be some form of dust collar. Is this correct?

This cover ? Yes, it's just there to protect the coil. Maybe you can fabricate a new one from some heavy paper stock ?

Yes, that's it. I will try to glue it together as best as I can, but I may take up your suggestion and make a new one. Is there a way to test the deflection coils. I can trace the wire leads and unsolder for a continuity test. I don't know if there is anything else I can do for test purposes. I have a few very small 'shiners' of wire on the front. Can I place something like lacquer on them for protection?

I'll bet the reason the choke is on the speaker is that at the time, they were transitioning from field coil speakers to PM. The chassis were set up for field coil speakers where the coil served the second purpose of power supply filter component. By doing it this way they didn't have to modify the chassis and could use either field coil or PM speaker whatever was available.

There are specific testers for flybacks and yokes like the Eico 944. If you don't have one, you can check the resistance like you said.

Shiners are spots where the wire lacquer has worn off ? I imagine lacquer would work, but I've never tried it.

Reece's comment about the speaker makes sense to me. I bet that is what is going on. Yes, Bob, there are a few exposed wires at the front of the coil but I can not see anything like a broken wire. Continuity check should tell me . I was thinking of using a product called Corona Dope- just to give those spots a bit of protection.

I got a partial order of capacitors in from Mouser and thought I would try my hand at stuffing on of the e-caps . The one I choose is mounted under the chassis and is not visible and very easy to get at. The cap is an aluminum can but is covered in a cardboard tube. Just two 40mf at 250v. I pulled the cap off of the chassis and the tube came off easily as it was just stuck on with a bit of black goop. The schematic and the cardboard tube both indicate that these caps are both 40mf but embossed on the aluminum can are 100mf and 30mf. I just thought that this is a bit odd. Anybody else run into this ? I will be replacing the caps with what is on the schematic. Just curious.

Give me a couple hours and I'll take a look at mine. I got my set over a year ago and have never pulled the chassis. You've got me curious to see what condition it's in.

My cap says 40 & 40 @ 250v on the cardboard. Measured actual 39 & 47uf in circuit. Can't easily get the cardboard off.

Kevin

Mine is 40 & 40 @ 250v too. Here are some pictures I took: http://www.flickr.com/photos/7003980...914784/detail/

Wow, that chassis is clean. I really like those wood floors in your house. :yes:

Kevin

That's good to know. I ordered caps from Mouser (Nichicon PZ's) but they are being sent in two separate orders . The ones I have coming are 47mf's at 450. I guess a little more voltage won't hurt.

Yeah, I was surprised too. I'm used to more rust and grime. Those floors are from the 1870s. I wish it was my house, but I'm just renting.

Those are good quality caps and more voltage is no problem.

Another question has come up. The image shows a pot that is used for the focus control. The pot is rated at 4 watts and 1350 ohms and is wire wound. The pot is apparently sealed and I was wondering if there is a way to clean it properly? The back of the pot looks like it is press fit or maybe welded on( hard to tell). I don't want to damage this part by taking it apart improperly. All of the other controls have a place that is open on the body of the pot to spray in deoxit and should not be a problem. Maybe I should leave well enough alone, but since I have the chassis torn down I thought this would be the time for cleaning. On the other side of the pot there is a brass shaft where I could spray a bit of deox but It does not seem like I would do very much good. Any opinions?

I'd leave it alone. I've yet to encounter a wire-wound focus pot that needed cleaning.

I sometimes wonder about everyone using Deoxit on carbon track pots. Is that really the correct thing to clean them with? My fear would be that it could mistake the carbon track for an oxide. Apparently it does work.

Kevin

Well, you know. I'm certainly no expert but Deoxit seems to be the defacto solution for contact cleaning. Its got my curiosity up, so I'm going to check around and see if I can find anything interesting on the subject. I'm going to leave the pot alone like bandersen suggests and move forward. I'm still waiting on a couple of parts orders so I have plenty of time to get into trouble.

I went looking on the Caig website. They seem to recommend their D100S (without solvent). But I doubt the solvent would hurt any of the old metal and carbon pots. I just seemed to remember some discussion over on ARF a few years back about it harming the carbon track. I guess I was mistaken. Sorry for the false alarm.

http://store.caig.com/s.nl/ctype.KB/.../.f?category=9

Kevin

While waiting for an order of caps to come in I thought I would get things ready and pull one of the cans from the chassis to restuff. I unsoldered the leads OK but the caps lugs were twisted over and soldered to the chassis. Not going to happen. My little 60w soldering station won't make a dent in the joint. So - looks like I will be mounting terminal strips instead. I remember when I was younger and getting interested in electronics I had a Weller soldering 'gun'. Long gone , but I think it was about 100 watts or so. Now,that would of come in handy today.

For chassis connections, the physical size of the iron becomes more important than watts. You want something that can hold the heat when you put it up against a large surface area.

Kevin

Here's a whole thread on the topic: http://www.videokarma.org/showthread.php?t=249677

After much thought I decided that the one thing I needed to know was the condition of the CRT for my set. After all, without a working tube , not much of anything is going to happen. I was able to get continuity with a meter but after that nothing can be determined. I went on ebay and found a tester that I was able to afford and won the bid, a Sencore CR161. The meter arrived DOA. Actually, it was just like the seller said, the red light comes on so it MUST be working. Well, no guarantees , that's the way it goes. I didn't have a schematic or actually any paper work for the tester but thru a very generous fellow member (marty59) I got the necessary schematic. I found that a pot and a diode were burned out so I was able to order a replacement from Mouser and Radio Shack. I replaced the parts this evening but it looks like the tube is not in good shape. This is truly depressing. I was hoping for at least a weak tube, but the meter shows very little emission at all. Since the meter was DOA and I had to repair it to get it working , I even wonder if the meter is working properly to give me a good test. I do have a nice orange glow from the filament and I can adjust the filament voltage so I think that part is working. I tried the rejuv functions but nothing changes. At this point I don"t know what I can do. The tube is a 12LP4A and I don't know if any are available for replacement. Bummer.

How long have you had the CRT running ? I let them run for a few hours or even overnight when I first get a set. It seems after siting around for decades they take a little while to wake up.

Really. I had no idea. I just let it run for maybe 5 minutes or so. So I guess I need to give it a try, nothing to lose at this point. I'll hook it back up to the tester and leave it on emissions test and check it in the morning.

Well, it looks like my luck has run out on this tube . I left it connected to the tester in the emissions test mode for a good 12 hours and I am still not getting any meter movement on the emissions. I tried the rejuv again and no change. Looks like my excursion into tv restoration has come to an abrupt end . With my limited budget my options are few. I would like to thank the members that have helped me out thus far - your advice has been priceless .

I hope a 12LP4 finds it's way to you somehow. You never know what may turned up at a garage or estate sale.

If you do find one or decide to work on another set, I'd avoid using the rejuv. function. It can easily blow off all the cathode coating and leave you with 0 emissions.

I'll keep my eyes open for another tube down the road. I really did not want to use the rejuv. function but I felt I had nothing to lose at that point. I'll keep reading the posts from this forum also. Really a bunch of nice folks and brimming with good advice. For now , I will pack this project up and look for something else to come my way.

Sorry to hear your CRT is weak, I know it's a big let down. Did you by chance try testing with a slightly higher filament voltage- say 7-8 volts? If the emission comes up at all, that would give you some indication if the tester is working correctly.

Something will show up eventually, but it can take a lot of waiting. Keep your eye on the local Craigslist, even for what looks like a junker set. You never know when a good CRT is lurking in a ugly old cabinet.

In the mean time try to find another restorer in your area and verify the condition of your CRT tester. Best of luck.

Kevin

I haven't tried a higher filament voltage. I may try it later on. Wouldn't you know it. There's a 12LP4A up for bid right now on ebay. Of course my finances are shot , so I am going to have to pass for now. I wouldn't even know what a fair price would be for something like that. I would actually prefer to deal with a fellow VK'er .