Magnavox 153B Hepplewhite.

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Wed Dec 30, 2015 4:27 pm

The speakers have conical baffles they are not coaxial. I couldn't find a used speaker any larger than 4" diameter, so I used black construction paper, skiving the edges thin like a tire patch and used contact cement to stick well and strengthen the patch. It don't look too bad if I do say so myself.

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Wed Dec 30, 2015 9:38 pm

Did a slow run up to test the unit before putting everything back into the cabinet. Everything worked well the RFI in the house obliterated most of the AM band, but a couple of stations came in well and allowed the tuning indicator to do it's stuff. I had found a volt/wattmeter and used it inline to check it's draw.
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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Thu Dec 31, 2015 8:40 pm

Here is the tuning indicator both off and on station.





I pulled the receiver and performed one last bit of surgery on it. I replaced the outmoded 4 pin connector foe the FM converter to an RCA jack. I did the same with the FM converter. I was then able to connect my laptop to the console and really run it through it's paces. The thing played great except it had a buzz at certain notes. I found that to be the sliding glass door to the deck. Picked up WWV at midday here also.
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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Fri Jan 01, 2016 1:17 am

Nice job, 75!  I see your eye tube works like both of mine, with the edges of the display sharper than the rest.  Either all of them are wrong, or they are right.  In either case, I feel better about mine.  I put a NOS eye tube in my Imperial maybe 18 months ago, and it is already getting dim.

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Fri Jan 01, 2016 1:37 pm

Thanks.  It looks like the FM converter will need some more work, So I went to the thrift store to get something I found yesterday.  A Sansui PLL synthesized AM/FM/stereo tuner.  I am happy to say that thing doesn't perform any better than the consoles' ability to deliver the audio.  I am listening to the Neujahrstag Konzerte from Vienna as I write this.
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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sun Jan 03, 2016 3:36 pm

What issue(s) are you having with the FM? Just for what it is worth, you may or may not have the old traditional Magnavox FM drift situation to deal with. I have heard of folks who do not have that problem, but all mine have it that are not equipped with AFC. An MPX adapter tends to help on stereo tuners, but that option is not available on mono tuners. On a more positive note, I have not had SMD or a bad IF can yet. I have tinkered with using different tubes in the front end, with varying results. Signal strength, antenna placement and broadcast station integrity have an effect as well. I borrowed an XM tuner/doodad from a guy in the car club. XM is the bomb, and may be a belated Christmas present from me to me. I may never listen to broadcast radio again. The XM doodad plugs into the tape input. My God, what a difference. No drift, no noise, no commercials. Cost is something like $110 a year currently. It won't be long until it is that much a month. Rolling Eyes

Good luck, 75.

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sun Jan 03, 2016 3:52 pm

At this point, It just isn't functioning. It accepts power in the normal range, the dial lamp lights. There is an open eye. I will have to get my signal tracing artillery set up to go through it. Right now, I am retracing the recap wiring to make sure everything is all right. In the interim, the Sansui tuner does great and at $8 it is more in line with what I can afford Very Happy
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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sun Jan 03, 2016 5:14 pm

No hiss, no sound, nothing? The dial light works, the eye tube works, so you can assume the tubes are all lighting. If there is an audio tube of some sort, you might tickle its grid to see if it growls. Magnavox band switches have been known to be crabby. Is yours clean? Connections from FM adapter to chassis good? Antenna? I have never worked with one of the FM converters. Do you have a schematic you could share?

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sun Jan 03, 2016 6:19 pm

Here is the one I am working from.

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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sun Jan 03, 2016 7:35 pm

You can pretty much eliminate a problem behind the FM converter, since with the more modern tuner you hear sound. Probably first thing to do is to make sure all the coils and IF transformers are good. Then run voltage checks, starting at the rectifier cathode. If you have the voltages you should have, then the signal is being interrupted somewhere. I realize you don't need my help, I'm just thinking out loud. The signal is pulled directly off the detector with no further amplification, according to what I see. Interesting. Thanks for sharing, 75.

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sun Jan 03, 2016 8:39 pm

Appreciate the good thoughts. I'll get it eventually.
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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sat Jan 09, 2016 5:22 pm

I gave careful study to the questionable portions of the FM converter and found a connection I had failed to replace on pin 1 of the converter tube. I set the unit and ran it up on it's own to see if the eye tube would show anything. It didn't. I had an early date for supper, so I had to leave it. I powered it up when I got back and turned on the receiver and it sounded just as good as the synthesized tuner I just got. Now for some eye surgery.
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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sat Jan 09, 2016 8:53 pm

That pesky resistor in the eye tube socket, maybe?

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sat Jan 09, 2016 10:42 pm

according to the schematic and the layout below, there aren't any resistors in the socket.  One nice thing about these drawings, they all show the parts and their location by reference number.  The unit drifted off to silence after a whiles' operation.  I'm going to get out the oscilliscope, freq. counter and generator and do an alignment on it tomorrow before getting back to the eye problem. Item 43 is the resistor shown at the tube.

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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sun Jan 10, 2016 1:31 am

"Drifted off to silence" as in the tuner went totally dead?  Could you possibly have lost a tube, as in dead filament for some reason?  As in the rectifier taking a dump?  The thing was playing well, yes?  Hard to imagine that it went suddenly out of alignment, enough to quit working.  Is resistor item #43 the one that affects eye tube operation, or am I daft for some reason?  Thinking out loud again, and certainly mean no disrespect, but I'd check some voltages next, starting at the cathode of the rectifier.  This is an interesting project, 75.  Thanks for sharing.  Very Happy

Edit: Are you sure the tuner went dead?  Could your amp have gone south for some reason?  Good luck.


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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sun Jan 10, 2016 9:56 am

I've done a couple of period FM/AM units that have behaved just like this one in FM mode. If it is on the edge of alignment, it will go dead during burn in. Also, I have replaced resistors 43, 44, and 45. 44 and 45 because of possible rework damage and 43 for good measure. The tube illuminated open and shows edge formation when on a station, but does not close.
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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sun Jan 10, 2016 12:43 pm

Interesting. I don't remember ever doing a total FM alignment in my life. I have a little Howard 482 FM converter that acts kinda like yours is. I really have not found the usual suspects as being a problem. I wonder.......


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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sun Jan 10, 2016 1:53 pm

Well, if there are any variable components that may dirty or oxidized contacts, alignment time is a good time to clean them. It will also allow you a functional foundation to troubleshoot any devalued components. I used to have to do that to a substantial number of FM receivers every work day. Most were crystal controlled, but they needed alignment nonetheless.
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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sun Jan 10, 2016 4:11 pm

Discriminator alignment is apparently critical on the stereo tuners. More advanced equipment than what I own is required to work with discriminators. The typical RF and IF alignment may not be any more difficult than on AM. I appreciate you sharing your experience.

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sun Jan 10, 2016 5:55 pm

I went through the alignment on the unit up to the discriminator. The 6SH7 tube seems to be microphonic. If I even barely touch the envelope, the output signal will go dead. the rest, I was able to get about a 1/3 improvement in the read levels. The tube in the unit is a glass envelope 6SH7GT. I put the unit back on the console and there was a substantial improvement in the entire bandspread, but that tube is sensitive to any slight touch or jar. I am going to try a 6SH7 with the metal shell.

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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sun Jan 10, 2016 6:13 pm

Could the substitution of the specified 6SH7 metal tube with a GT version have caused a poor shielding condition? Perhaps a microphonic tube compounded by poor shielding is causing your problem? You are getting close, good luck. Very Happy

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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sun Jan 10, 2016 6:16 pm

Just in the way of discussion, have you run that FM converter enough yet to determine if drift is going to be an issue? I ask this question of anyone who works on any type of tube Magnavox tuner. This condition seems to be worse on the stereo tuners in all honesty.

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sun Jan 10, 2016 7:49 pm

Looking now at how it is affected, I have to say that the failure appears to be with the 6SH7 and with the unit on for about 3 hours, It dies not appear to drift, but will just abruptly cease function. I would guess that it is abruptly changing it's function. The alignment procedure calls for signal levels produced by the 3 IF stages, then a discriminator alignment with the measurement of a DC level at the final output. I can't get a stable reading at that point. There has to be both a 10.7 MHZ and then a 10.775 signal injected and they are supposed to be exact freqs. I dare say that was no mean feat in 1946 with the bench artillery commonly available at the time. But if I just gently tap the soft part of my finger atop the 6SH7, it ceases. I have to admit that crystal controlled FM receivers are much more stable.
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Re: Magnavox 153B Hepplewhite.

Post by Wildcat445 on Sun Jan 10, 2016 8:54 pm

I read an article one time on limiters vs. discriminators. I don't recall what the difference is exactly. IIRC, earlier FM tuners used discriminators, and limiters came along later. Zenith used limiter circuits. Magnavox used a discriminator circuit. You'd know more about what I am referring to than I do. The drifting I have experienced typically occurs when the tuner is first turned on, and goes away after components reach operating temperature. During the first 15 minutes or so.

Your thinking is that the 6SH7 being wonky is not allowing a stable alignment, right? Did you see anything when you tested that tube that would confirm that suspicion, or is this just a substitute and note any difference type of thing?

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Re: Magnavox 153B Hepplewhite.

Post by 75X11 on Sun Jan 10, 2016 10:38 pm

There were two types of discriminators, the limiter discriminator and the phase discriminator. Armstrong held the patent on the limiter. And you are correct about the 6SH7. I have had a couple of marginal tubes get by the tester. Sometimes their signal handling capabilities aren't revealed under test.
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Re: Magnavox 153B Hepplewhite.

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