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 Post subject: Radio Suggestions for a NooB
PostPosted: Aug Thu 02, 2018 9:29 pm 
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Location: Piedmont-Triad, NC USA
Well, not really a newbie... I have a Voice of Music 1428 integrated amp (and the 1435 tuner). I recapped the amp myself and now have the "tube" bug.

For my next project I'd like to find a tabletop radio that has am/fm/sw, and a phono input. I may have a line on a Matsushita Vista 640, but it doesn't have much of the mid/mod look (and might be a bit large for our kitchen). Lack of a sw tuner isn't a deal breaker, but I really want the phono (or aux) input.

What radios would fit the bill?

Peace,
Norm


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Fri 03, 2018 2:57 am 
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There have been many discussions and instructions on this forum about adding an aux input to vintage radios. If that is something you think you could handle, it would make your choice of a radio almost unlimited. I'm sure someone could provide you with a link to instructions.

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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Fri 03, 2018 2:35 pm 
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I’ve read several of those threads, and I’m not quite ready to mod a radio like that. Besides, I like keeping things as original as possible.

I’ve considered the am transmitter route as well, and may build one just for kicks at a later point.


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Fri 03, 2018 5:11 pm 
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Location: Albion, CA, USA, 95410
I like the look of the Telefunken radios from the late 50's. Look around for Telefunken Gavotte, Jubilate and others.

Upside: Great radios, great looks, well built. Excellent audio quality.

Downside: Tubes expensive, information harder to find, if the set wasn't made for export the only information will be in German. I have to admit that I am a little stuck with one I am working on right now.


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Fri 03, 2018 5:32 pm 
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You're looking for a kind of rare thing. The popularity of shortwave on consumer radios in the US dwindled after WWII (1946), while FM didn't gain popularity until the late '50s. There was a solid decade there where the average table radio was AM-broadcast only.

You really have many more choices if you look at European radios of the 1950s and '60s. Many of those sets have broadcast AM, long wave, shortwave, and FM. Export models for the US even have FM that goes all the way up to 108 MHz. But they tend to be huge. "Table model" often means you can set it on the floor and use it as a table. :wink:

Nonetheless, manufacturers would try anything, and there are a few choices in American consumer radios from the late '40s and early '50s. Here are a couple that come to my mind, which may or may not have aux inputs, and I'm sure there are others.


There are a few amateur communications receivers that included FM, like the Hallicrafters SX-43 and SX-42. And there are lots of choices if you look at console radios. This era of console is not very collectible, and can be obtained dirt cheap or even free. They were larger and more expensive when new, so they needed more features... which included more bands. The GE Musaphonic consoles (models 41-45), the post war Zenith consoles like the 12H090, the Crosley 146-CS and 148-CP... The list of consoles can get long.

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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Fri 03, 2018 10:36 pm 
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I read back over this, and I see you said shortwave is less important than an aux input. There are a good number of AM-FM radios with aux inputs. Some of them are a lot easier to find than the AM-FM-SW models.


Just to name a few.

As you get a little bit newer, AM-FM tuners all have aux inputs on them. But have really boring styling.

-Rodney


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Sun 05, 2018 4:28 pm 
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The Zenith AM/FM table radios are very good performers. However, only some have the phono switch, and it is often located on the back, awkward. Zenith C845 is an example.

Some AM only table radios with phono switches on the back are the Crosleys like the E-15. The Northern Electric Panda is tiny, but has the phono jack and switch on the back.
The Westinghouse H-122 AM radio has the phono knob on the front, a small footprint, and a bigger speaker. However, it needs to be thoroughly refurbished because of the large Candohm resistor on the chassis.

None of these examples have a power transformer, so the chance of a hot chassis issue comes up, especially in the kitchen. Most have B- floating, with a capacitor connection to the chassis. The new capacitor should be one that will not fail as a direct short, a Y type. The input from your external device should be isolated with a small audio transformer. I know you didn't want to get into it this deeply, but that is the reality of vintage electronics.

How about the Curtis Mathes 2918A? The ultimate kitchen radio. This pic is from the CM website.


Attachments:
Curtis_Mathes_Radio_1950_s.jpg
Curtis_Mathes_Radio_1950_s.jpg [ 49.26 KiB | Viewed 1941 times ]

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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Mon 06, 2018 3:20 pm 
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Location: Piedmont-Triad, NC USA
Wow... I like the look of that RCA 9-INT-1 (The GE T150B Musaphonic as well).

Funny Zenith should come up... I stumbled across one over the weekend, a c725c. I bought it for a song. I know I'm dealing with a "hot" chassis, but it does have the phono input on the back. Owner said it worked as recently as this past Christmas. When I got home I powered it up with my dbt, and the bulb glowed dimly then faded out. Radio did nothing.

I pulled the cover off and the bumblebee cap rolled out (in several pieces). Bits of tin foil were blown around like New Year's Eve party confetti. From what I've read, this is common.

As far as isolating an input source I'm going to build one of these: https://antiqueradio.org/iPodAdaptor.htm

Are there any good methods for making a hot chassis safer?


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Tue 07, 2018 4:52 am 
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The Zenith Super Sapphire is a good choice. That 7 tube circuit can be found in dozens of AM/FM radios of that era and starting in the post war years when FM was a novelty. The circuit was perfected by the time your radio was born.

It needs the Electrolytic capacitors in the power supply replaced with individuals under the chassis. Always clip the leads to the old cap can.

One modification you can look into is to ensure that the neutral side of your power cord is marked with a bit of White tape so you always plug that prong into the Wide slot in your properly wired wall outlet. I say this because your power cord serves also as the FM antenna, so you want to keep it.
Taking this one step further, change the wiring to the switch so that it cuts power to the radio when shut off. It was typical at that time for one wire, could be the hot, to go to the diode and the other, could be the neutral, to go to the switch. Switch off, the diode was still hot electrically.
It could be plugged in the other way, but best would be hot to the switch first, then the diode.

Read up on Selenium rectifier, better to have a silicon diode in there for a daily driver.

Always have the knobs installed when the radio is plugged in. The chassis screws can give you a shock, so unplug when moving the radio.
Don't let an energized radio fall into a bathtub or sink full of water, that would be suicide. But with common sense, millions of people survived the tube radio era.

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Burl Ives, RIP, oldtimer.
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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Wed 08, 2018 11:08 pm 
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I found the schematic for this radio and, yup, the power switch completes the connection to ground:

Image


So... is making this radio "safer" as easy as rewiring it like below... (and using a polarized power cord where N would go to ground and Hot to the switch)?

Image


Hmmm... looking at the second schematic it seems like the switch should be before C44A instead of after it.

Where's the best place to insert a fuse (and what type)?


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Thu 09, 2018 5:05 am 
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Yes I would put the switch ahead of the cap.

A fuse could go on the neutral where the switch was and it will still blow. Best on the hot side, I believe.
I don't normally worry about a fuse in a series string radio as a tube filament will blow in the case of a dead short.
But we can't keep sacrificing tubes in that way forever.

A 1 amp slo-blo is ok for there, or a 800 milliamp would be better, but I haven't done the math for your 7 tube radio.

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Watch the doughnut, not the hole.
Burl Ives, RIP, oldtimer.
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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Aug Thu 09, 2018 7:25 pm 
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One way to make the set safer if you plan on running audio in through the phono input is to put two, .01uF caps, one for positive, the other for negative leads of the jack. In this way the level of current will be driven way down, as in I believe somewhere in the neighborhood of 2 millamps. A GFCI outlet trips at 5 milliamps for comparison. As also mentioned adding a polarized plug will definitely help too.


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Sep Sun 16, 2018 8:21 pm 
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So I did the recap this weekend. All was well and good until...

Before I begin, I did plug the radio into my DBT before powering it on. I got nothing. Dead. But the bulb did not indicate a dead short and stayed on dim like the radio was working. I unplugged it all and put the radio straight to the power strip. Turned it on. Slight crackle, then the magic smoke. Turned off the power strip... unplugged it. It was on for less than 10 seconds.

I burnt up R40. Turns out that I wired the replacement for the selenium rectifier exactly backwards. So R40 took it all on the chin. Nice smell... only my 15 year old's Axe body products smell slightly less appealing.

The big question: is the damage limited to R40, or did I hurt C1 a & b? (they didn't get hot or melt anywhere so I'm hopeful)

What say ye?


Last edited by nmwhitneyjr on Sep Mon 17, 2018 2:44 am, edited 1 time in total.

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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Sep Sun 16, 2018 8:32 pm 
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A selenium rectifier drops a few volts itself... Maybe 30V?... Not sure. So you probably have to make R40 bigger, more resistance to drop some more voltage and get the output voltage down where it's supposed to be. And if dropping more voltage, it will probably have to be rated to handle more than 1 Watt.

If you put the diode in backward, you just wouldn't get B+... Not clear how that would burn up R40. What's the voltage rating on your first cap (C1A)? If you've got a 160V cap in there, you might have stressed it. Probably better to put something higher-rated in that spot. I'd probably use a 450V cap there. You could replace it again for peace of mind.

Radio should play with DBT in the circuit. If it doesn't, it won't without it either.

Know what you mean about the Axe... My son went through that stage. Don't know if he outgrew it (think he did), but at least he moved out. :)

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Measure it with a micrometer, mark it with chalk, cut it with a chainsaw.


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Sep Sun 16, 2018 9:23 pm 
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I did add a 5 watt 25ohm resistor after the diode and before R40... but since I had the whole shebang in backwards, the resistor took the 120VAC hit (that's my assumption, anyway). The caps I used (C1 a & b) are 350v rated so I think they might be ok.


Last edited by nmwhitneyjr on Sep Mon 17, 2018 2:45 am, edited 1 time in total.

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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Sep Sun 16, 2018 11:58 pm 
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Norm, it's not clear to me how R40 would've gotten between the switch and the heater string, but if you say it did, I'll take your word for it.

Also, it's not clear why C41A & B, which are down in the heater string, would get involved here... they have power applied anytime the switch is on anyway. They aren't affected by the rectifier. The caps you should be concerned about are C1A and C1B.

You're not by chance using a different schematic than the ones posted above? I'm looking at the two schematic excerpts you posted on Aug. 8th.

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Measure it with a micrometer, mark it with chalk, cut it with a chainsaw.


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Sep Mon 17, 2018 2:43 am 
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You are correct... I mis-typed above (meant to say C1 a&b). I went back and corrected the typos.

Honestly, I'm just wild-guessing on why R40 blew. It could have been our planetary alignment with Mars... or maybe it was just it's time.

However, after replacing R40 and correcting the diode direction, I did another power up. No smoke or other excitement. AM section works... but it doesn't pick up more than a handful of stations (I was checking at night, with tropical depression level rains, so there's that).

Nothing on FM but faint static. There is a 6BJ6 acting as an FM RF Amplifier. I think it's defunct. I can't see any filament glow (not necessarily conclusive) but the tube does not get warm.


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Sep Mon 17, 2018 5:36 am 
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This is a series string radio circuit. The schematic shows all the filaments in series. So the filament of one tube
can not possibly be bad if the radio plays at all. A 6 volt tube will be cooler than those with higher filament voltages.
So that's not it.

Make sure the band switch is making good contact when on FM. Then try some voltage measurements.

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Burl Ives, RIP, oldtimer.
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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Sep Tue 18, 2018 11:46 am 
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So it's like an old set of Christmas tree lights... one goes out then the whole string goes out... that makes sense.

I cleaned all of the pots and fired it up again... no real change on the AM/FM reception.

I checked voltages. I was getting 140V after the diode and 138V and 81V (at the Source locations on the above schematics). Not perfect, but seemingly close enough for everyone to work.

I had an old Zenith console pull that had known good tubes in it. Only two of those were compatible (V3 and V4 both 12BA6). I put those in and bingo, we had FM reception (and much improved AM).

Then the SAC came along and made me clean up my workspace (aka, the kitchen table).

Many thanks for the help!


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 Post subject: Re: Radio Suggestions for a NooB
PostPosted: Sep Tue 18, 2018 12:34 pm 
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I would focus on AM & SW as your VM already provides FM. For listening you cannot beat a 1936-1940 console with more modern octal base tubes. 9 or more tubes for the most part guarantees an RF amp for shortwave sensitivity. 10 tubes may include push-pull audio for 8-15 watts or more audio output vs 3 watts for a single-ended audio amp. Look up proposed console schematic on nostalgia air site to see if a RF tube & perhaps push-pull audio is included or ask here.

Note- I would not refuse a 3 watt amp if cabinet is in great shape with local pickup option saving $150+ shipping charges.


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