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Author Topic: Cabinet Stereo  (Read 16837 times)
KL2NW
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Posts: 17




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« on: April 16, 2015, 11:08:24 AM »

I'm trying to fix up an old Magnavox Cabinet stereo. The radio works fine, but the phonograph does not work at all. When I pulled the output wires from the phonograph and plugged them into my ipod (what I'm really interested in doing since I have no records) the sound worked for a few seconds then faded out. The tubes on the amplifier are lit when the radio is playing, but when I switch it over to phonograph (ipod) the glow dies as the sound fades. I have never dealt with tubes before. Any ideas where I should start?

Related question: I'm looking at getting older radio manuals to learn about these tube things, specifically "The Radio Manual" by Orr. What edition should I get? Did they stop covering tube radios at some point? Do the older ones cover topics the newer ones wouldn't? What other books should I be looking at?

Thanks for any help!
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N3QE
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« Reply #1 on: April 16, 2015, 11:54:57 AM »

I recall that when the main function switch is in "phono", the power to the electronics are shut off when the turntable is not actually playing. Assuming that this is a full-blown changer, turning the tall black changer one notch will turn the turntable on, and twisting it to momentary "start" position will drop a record and land the needle. Then when the last record has played, the arm goes back to the rest, the motor shuts down, and the tubes shut down.

If you want to feed your iPod into the stereo, you do not want to use the turntable cartridge leads. Levels and RIAA equalization are all wrong. If the console has a selector position for "AUX" or "TAPE", use that. Barring that, hot wire into the radio audio with maybe an A/B switch and attenuator on the back.
« Last Edit: April 16, 2015, 12:17:15 PM by N3QE » Logged
K7MEM
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« Reply #2 on: April 16, 2015, 02:25:25 PM »

Related question: I'm looking at getting older radio manuals to learn about these tube things, specifically "The Radio Manual" by Orr. What edition should I get? Did they stop covering tube radios at some point? Do the older ones cover topics the newer ones wouldn't? What other books should I be looking at?

A good source of older manuals would be a Ham Fest. I try to go to every Ham Fest within 200 miles and they always have old manuals for sale for $5 or $6. Almost any manual by Bill Orr is good, but I don't know how easy the are to find. I have a hard covers copy of "The Radio Handbook", by Bill Orr, that is dated 1963 and I refer to it regularly. I have had it for 50 years and not quite ready to let it go yet. However, any of the manuals, like the ARRL Handbook, from the 60s and 70s, should have good information. They will be transitioning between tubes and transistors, but so will the older ones. My 1963 copy of "The Radio Handbook" has a computer section and talks about transistors. According to the book, there is a great future in computers. Well, I'll believe it when I see it. Going further back, you might look for the "Sideband Handbook", from General Electric. I have a PDF of the first edition, but its 150 MB. If you want it, I can put it on line for you.

Maybe look for a good copy of the RCA Tube manual. For audio/HiFi you might look for the old Howard W. Sams PHOTOFACT books. They produced lots of service/repair documents for radios and TVs but they also published books on various subjects, like Audio Amplifier Design.

And, don't forget the magazines. 73 Magazine is all on-line now with every issue from 1960 to 2003. There is also Popular Electronics, Electronics Illustrated, GE Ham News.
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Martin - K7MEM
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KL2NW
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« Reply #3 on: April 16, 2015, 07:22:12 PM »

N3QE, You're right. I flipped the tall switch on and it started working. The main selector switch has positions for Tape, AM, FM AFC, FM, FM MPX, and Stereo. Stereo makes the record player work. There is no tape player, but the center of the cabinet is empty, so that's where it probably went. FM and FM AFC both play the FM radio. I can't figure out what FM MPX is supposed to do. I'll probably solder a headphone jack to the tape leads on the switch for the mp3 player.

K7MEM, thanks for the advice, I'll look for all of those. Amazon and Ebay both have several versions of the "The Radio Handbook", but I'll try to hit a hamfest and page through a few before buying.
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W9GB
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« Reply #4 on: April 16, 2015, 09:25:35 PM »

Radios and Electronics equipment through the 1970s, still have MECHANICAL components
as well as vacuum tubes and some early solid-state components.

Cleaning switches and volume controls (De-Oxit Fader Lube)
 is mandatory on equipment of this vintage.

I have found a bad power switch - on back of volume pot (replacements at Radio Daze)
often to be an issue with these sets.

Helps to understand how a commercial FM signal is actually broadcast.
http://en.m.wikipedia.org/wiki/FM_broadcasting

MPX FILTER -- Required for Tape Decks, recording stereo from FM radio source.
Filters out 19 kHz pilot tone.
http://en.m.wikipedia.org/wiki/MPX_filter

Automatic Frequency Control (AFC) or Automatic Frequency Tuning (AFT)
http://en.m.wikipedia.org/wiki/Automatic_frequency_control

This locks in an FM station so it won't drift after you tune it in (useful with vacuum tube receivers).
Normal procedure for tuning in an FM station on a radio with an AFC position on the band switch is to place the switch in the FM position, tune in your station, then place the switch on FM AFC and leave it there until you change stations again.

Very old FM radios did not have AFC circuitry, so they are very prone to drifting while the set warms up.  AFC was first introduced in FM sets around mid to late 1950s, as I remember.
The first FM Stereo broadcasts occurred in 1961.

« Last Edit: April 16, 2015, 09:46:07 PM by W9GB » Logged
G3RZP
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« Reply #5 on: April 16, 2015, 11:29:49 PM »

One very useful book for learning about tube circuit design is 'Radiotron Designer's Handbook' by Langford-Smith.
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KAPT4560
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« Reply #6 on: April 16, 2015, 11:38:27 PM »

 Magnavox of this era built some impressive home consoles. They were a premium brand name. I agree with the preliminary switch contact and control cleaning.
 The tubes may be OK, but you will probably want to replace any electrolytic, wax paper and encapsulated paper capacitors.
 Resistors may have drifted high. Test a few to see if they are still within tolerance.
 The grease in the turntable changer has probably hardened into candlewax and should be cleaned and lubed.
 There are many online books about tube equipment. If you can find a model# or chassis# on your beast, you may find service information from Sam's or Beitman's. Magnavox can be difficult to identify and look up. The changer may have a separate model#.
 http://w5rkl.com/wp-content/uploads/2014/04/Inside-the-Vacuum-Tube.pdf
 http://mikeyancey.com/RCA_Radio_TV_Course_1958.php
 http://www.km5z.us/NRI_Radio_Course.php
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KD0FAT
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« Reply #7 on: April 17, 2015, 02:46:08 AM »

We had a Magnavox console stereo in the late '60s, and I remember that the turntable was only adequate, not up to the quality of a good component turntable.  The pickup cartridge was so-so, and the tracking weight was not adjustable. Now that vinyl is popular (and expensive) again, using the old Magnavox turntable will wear your records out faster than a new stand-alone turntable. There are several now available that can be used with the ipods, etc.  I recall that in the old days, any turntable that needed more than 1 gram of tracking weight at the needle was suspect.
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KW4M
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Posts: 24




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« Reply #8 on: April 17, 2015, 05:29:35 AM »

I have one of the late 60's vintage tube Magnavox console stereos in my office.  It has a pair of push-pull 6L6's for each channel.

The amplifier has an auxiliary input intended for a tape player.  I have it connected to the computer's soundcard output.  It sounds great and is an outstanding set of "amplified computer speakers."

It has been used this way for the past dozen years.
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N3QE
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« Reply #9 on: April 17, 2015, 08:44:50 AM »

N3QE, You're right. I flipped the tall switch on and it started working. The main selector switch has positions for Tape, AM, FM AFC, FM, FM MPX, and Stereo. Stereo makes the record player work. There is no tape player, but the center of the cabinet is empty, so that's where it probably went. FM and FM AFC both play the FM radio. I can't figure out what FM MPX is supposed to do. I'll probably solder a headphone jack to the tape leads on the switch for the mp3 player.

Out of curiosity, does this pic match the phono compartment on yours? There were several cabinet woodworking variations but the one below is very close to the one my mom in the 1960's about the time she got married, and I spent much of the 70's as a kid playing her Beatles and other 60's pop records on it. The pictures below are not my mom's (which is far more beat-up) but a truly pristine (restored?) example.




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W9GB
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Posts: 3380




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« Reply #10 on: April 17, 2015, 10:40:11 AM »

I worked on a Curtis Mathes of this same vintage (almost identical cabinet) in 1982,
unfortunately an earlier repair attempt by an EE student didn't work and the
phonograph changer was removed (and lost by the EE student).

LIFE LESSON -- IF You are Over your Head -- Bow out gracefully.
Apprentice and Novice disease.


The repair ??
The Potentiometer switch ... which in early 1980s cost about $1.00 and $3.00 shipping from Canadian warehouse.
---
Part is actually easier to find today (thanks to Internet)

SPST Potentiometer switch (S-POT1)' $1.25
http://www.radiodaze.com/spst-potentiometer-switch-item-s-pot1/
« Last Edit: April 17, 2015, 10:44:44 AM by W9GB » Logged
G3RZP
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Posts: 1320




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« Reply #11 on: April 17, 2015, 12:55:07 PM »

the phonograph deck looks suspiciously similar to a UK made Garrard SP25......
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W9GB
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Posts: 3380




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« Reply #12 on: April 18, 2015, 04:05:32 PM »

Regarding your iPod attempt with Phonograph,
Needles/Cartridges of this era were usually HIGH-Z out (high impedance, 20-50 kHz)
and required phono pre-amplifiers.  I just sent 3 old Gates broadcast (1960s) versions to W9NUP


1965 - Garrard
http://www.garrard501.com/history.html
The Garrard 401 was launched to replace the 301.
It was produced until 1977 when over 50,000 units had been sold,
and it is still treasured by enthusiasts around the world.
--
The Model SP25 was launched with the Mark I version.
It was so popular it continued for many years up to the Mark IV version.
A disco version, the Disco 80 was also produced.
----
NEEDLE DOCTOR -- St. Louis Park, MN
http://www.needledoctor.com
« Last Edit: April 18, 2015, 04:16:39 PM by W9GB » Logged
KL2NW
Member

Posts: 17




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« Reply #13 on: May 03, 2015, 12:39:51 PM »

Out of curiosity, does this pic match the phono compartment on yours? There were several cabinet woodworking variations but the one below is very close to the one my mom in the 1960's about the time she got married, and I spent much of the 70's as a kid playing her Beatles and other 60's pop records on it. The pictures below are not my mom's (which is far more beat-up) but a truly pristine (restored?) example.

The turntable looks exactly the same. Mine even has the diamond shaped label in the back. My controls are on the other side, though, and in between is an empty space. My cabinet is pretty beat up. I put some furniture polish on it and it looks ok for the shop, which is where it will live. I'm hoping to have a mp3 player input as well as wiring the shop computer into it.
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KC4MOP
Member

Posts: 960




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« Reply #14 on: June 03, 2015, 05:18:03 PM »

Regarding your iPod attempt with Phonograph,
Needles/Cartridges of this era were usually HIGH-Z out (high impedance, 20-50 kHz)
and required phono pre-amplifiers.  I just sent 3 old Gates broadcast (1960s) versions to W9NUP


1965 - Garrard
http://www.garrard501.com/history.html
The Garrard 401 was launched to replace the 301.
It was produced until 1977 when over 50,000 units had been sold,
and it is still treasured by enthusiasts around the world.
--
The Model SP25 was launched with the Mark I version.
It was so popular it continued for many years up to the Mark IV version.
A disco version, the Disco 80 was also produced.
----
NEEDLE DOCTOR -- St. Louis Park, MN
http://www.needledoctor.com


A magnetic phono cartridge requires a pre amp. The cartridge in that console is probably a ceramic or crystal type, with your HI-Z output of a couple of volts. And freq response would surprise me if it got down to 20 hertz. Maybe 60 to 10K hertz, would be stretching it.
Those consoles were commonly referred to as electronic coffins. Not much you can do with them but to accept what the manufacturer built. There is, to this day, quite a rage for Magnavox consoles. Probably for the very nice furniture design.
My favorite console was a middle 60's unit from Zenith. Solid state and a lot of audio power for its day. My cousin wanted to show off the bass response, because he played the pipe organ in church. He played "Maybe" by the Chantels with the foot pedal bass from an organ used in the recording.

Fred
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