Help Needed - perhaps in wrong forum?
 

Hello VK,

New guy here! Been an AK member for a while, but have absolutely ZERO radio experience or knowledge.

Here's my dilemma: I purchased an old antique radio this past weekend as a 'late' Holiday gift for my Brother and Sister-in-Law. Craigslist purchase, paid $60, so not a huge problem if this ends up being a lost cause. Anyway, this unit 'looks' very similar to some of the old Grundig radios I've seen in the past, only it's made by a different company: EMUD, or Ernst Mastling ULM.D. It appears as if it's a model T-7.

Anyway.....got it home and have been bringing it up on the variac over the past day. It's at about 100 vac now.....and I've determined that the audio circuit is working. I can hear some 'scratching' when I wiggle some tubes, but more to the point, I can push the 'phono' button input selector and touch a screw in the back that is presumably the phono input hot connector and I get a good ac hum! There is also a 'tape' button, and the adjacent screw produces hum in that position albeit a bit lower in intensity....again presumably due to this being a lessor sensitive input.

So....this background being stated, I am getting ZERO RF through this thing! I have 3 bands: AM, FM, and SW and NONE of them produce so much as a glint of signal. There is a stick antenna and an FM Loop antenna...both hooked up and appearing to in good shape. But, I don't get the typical am buzz, no hiss in SW, and basically NOTHING in any position.

At this point, I'm 3 days away from traveling to Michigan where I plan to meet my brother and SIL and, hopefully, give them this functional radio. I might mention that it IS German....as is my Sister-in-Law....so the point of this gift was to bring a bit of acknowledgement of her past culture and roots into my consideration when adding to the bulk of Holiday gifts!

If I should be in the "Tech" forum, then I trust the moderator of this forum will move me. But, I'm hoping that perhaps a 'vintage' radio guy will have a clue where my problem might lie and be able to steer me there in a simplistic manner. Keeping my fingers crossed.

Thanks VK!!

Tom D.

Old radios should really be gone through electrically and old capacitors replaced at least as parts that are 40 or 50 years old can fail at any time. However, with the radio on, try cycling the bandswitch buttons on and off a dozen times. The contacts are probably dirty. If you can get to the switch, spray cleaner into it while working the buttons. The other thing to do is check the IF and RF tubes in the set, at least to see if they all light. Spray cleaner on the tube pins and plug in and out of socket several times while the pins are wet to clean the contacts.

Emud was a popular name last century. So the radio is probably a decent one. I wish I could offer a suggestion but with the short time you have available it would take too long to get you going.

Hey Bob and Reece,

Thanks for responding so quickly. I know 'time' is an issue here......and I may just pack up the radio and take it with me in it's present state, and then work on it some while in Michigan. We'll see.......I may just trade it for a fountain pen and give that to my Brother ....ho ho ho!

From what I can see.....all the tubes do light up. I have cycled through the switches several times.....and I don't get so much as a pop or thud on the audible side when the switches are being pushed. But....like I said.....I can push the 'phono' button and then touch the screw head in the back of the unit marked 'phono' and I'll get a good hum from the speaker. Same when hitting the 'tape' button.....only a reduction in gain, presumably at the input itself.....or a matter of sensitivity differential between the Tape and Phono inputs. However, in both cases, it's evident that the audio amplification section is functioning.....so at least I know that much. But, again, when selecting ANY radio band......no noise whatsoever. I did jiggle tubes a bit, and still not static or change in condition. All tubes appear 'lit' EXCEPT the 'tuning eye' tube that is part of the front panel....and something that I seem to recall would illuminate with a blue or orange glow....either more or less brightly according to signal strength. I can't see the number on this bulb.....it appears to be a Telefunkin of some kind......but it's doing nothing from a functional standpoint that I can see. One other comment...the two dial lamps were a bit oxidized and inop when I first started, but now they both illuminate fine. The rubber grommets that held them into the panel both disintegrated when I move the bulbs.....but the lights themselves seem fine. So....that's an indicator of continuity, corrosion, and available voltage.

I guess maybe I've made some progress in diagnosing this thing....but I fear that the next real step may be actually removing the chassis from the box....and that does NOT look easy. I may just have to wait until I get to Michigan to attempt that. But, for now....any further suggestions are welcome....and again, thanks for the comments thus far.

Tom

It's time to take a closer look. You need to measure the plate voltages on the tubes involved with receiving radio signals. There is a local oscillator that needs to be oscillating. There is one, maybe two, stages of IF amplification, and a detector of some sort.

The tuning eye tube is of no consequence. Deal with it once you get the radio working. The fact that it's not glowing implies loss of B+ voltage to part of the set. So you may have an open dropping resistor.

Tuning eye was glowing......I just couldn't see it in the afternoon light and with the voltage still at less than full level. But, once sun went down I could see both the glow in the tube from behind the set, as well as the green view of the tuning section. I guess I'll have to look up all the tubes to see what their function is, then get back w/ a report after voltages are taken. TSD

One of the common failures on these sets is loss of screen voltage in the IF's, the bypass cap shorts and takes out the screen dropping resistor (Usually a 1K resistor)
Also, I routinely replace the coupling cap to the last audio, It's one of the areas where a little leakage causes grief. Oh yes, the tuning eye being very weak is also common.

TV, Thanks for the info. I've clearly got WAY too much to learn about radios to be into this one at this time. Honestly......while I know a 'screen' as it applies to an audio tube.....I'm not sure how they relate to IFs in the radio world. So, I clearly need to go back to square one and do some study work. I'm pretty sure it takes YEARS to become proficient in radio repair......but maybe I can find a local 'mentor' who can school me a bit. I give AK a LOT of credit, as it's members have helped me greatly with my quest to learn about audio amplification. But, AF and RF are significantly different enough that I've stayed away from radio for all these years.

Anyway...........I do plan to pull the chassis and, I guess....just see what I see! I'll keep you all posted on my progress....if any! Again, many thanks!! Tom D.

It is not all that hard to learn to fix the simple stuff in most radios. As time goes by we get better and learn to trouble shoot the tough sets and grow as techs.

Hey Tom,

I appreciate the 'semi' pep-talk. The concept of 'time goes by' is one that is somewhat painful to me at the moment......3 days away from hitting 60! Not too sure how much 'time' I've got left......but, hopefully another decade or two. Just finished performing surgery on a wireless house phone......had a bad one w/ a good display, and a good one w/ a bad display. Trying to remove those hair-like LCD contact from micro-traces on the board while hands were somewhat shaky...well, just confirmed my suspicion that I'm not getting any younger! But, the successful operation helped retain my meager level of confidence. I really WOULD like to fix this radio......not just to present it to my brother and his wife as their 'late' holiday gift, but also to gain the learning experience. It does seem weird to me that the whole RF section would be dead.....all 3 bands. That seems to me like it should be something 'simple'.....like a switch or wire or contact.....or maybe that screen voltage previously mentioned. I am leaving Sunday for Michigan......and this radio is going with me. I'll be there for a week....and hopefully I'll get to the bottom of the problem before I leave....and can then 'gift' it to my brother and his wife. I'll have a pc there....and trust me.....I'll be back on this forum w/ up-dates and further question!! Thanks again Tom! REgards, Tom D.

You are almost 60?! Wow that's pretty old to be getting into electronics. I do repair work for fun and have a well equipped lab. But 60? No way! Actually, this summer I will be 80 years old. Been a ham since 1949.

Age is a state of mind. I'm also a weight lifter and jazz musician. Who cares about my age (except the young ladies)?

Bob, not anywhere close to Detroit, R ya?.....or anywhere close to the Pennsylvania or Ohio Turnpikes? I'd give my eye tooth to come meet ya, shake your paw, and have you look at this elderly radio............. TSD PS..... 80 eh? Well...... you give me strength!! Wish I'd started w/ HAM stuff when I was a kid. But, like I said....though new to the hobby....perhaps I can still learn....in time!! Tom D.

Tom, the day you stop learning is the day you might as well die. I am always learning, never so smug as to feel I know it all.

I am fairly close to you, but that also is a state of mind. I am actually in Los Angeles. "The land of orange juice, sunshine, and beautiful women."

Don't be intimidated by this stuff. What you need are some books on radio to start learning some of the lingo and get some background info. Buy or download and print out an RCA tube manual from the 50s or 60s, and read the front section. It's not very long, and you'll learn a lot about common circuits. Then, take a look at the back, and study the circuits section. I learned a lot from mine, the pages went from white to a dull grey in the first 5 years I owned it.

Hello Max,

Thanks for your comments. Good advice! I do believe that some years ago I did have that manual.....but seems to me that about 4 or 5 pages in I was so lost that I put the book aside.....again intimidated by the seemingly insurmountable of digesting what was contained within. In later years, and resulting from my love affair with guitars and amplifiers.......and accumulating a collection of old guitar amps in need of repair that shop prices prohibited me from doing anywhere other than at home myself....I ended up buying some of the more popular publications on guitar amp repair. After a couple of years of fumbling through all that, I got to where I could re-cap a power supply, 'tweak' a front end, replace a power or output transformer, and perform basic trouble shooting for simple repairs. About that time I made a decision to re-locate my home....sold off almost all the guitars and amps to help fund a new house....and basically got 'out' of that hobby. Then, about 3 years ago I took up tube amps in home audio thanks to the acquisition of a Dynaco ST-70. Again, my urge to take soldering iron in hand led to what is now a small collection of tube home audio amps of both separate and integrated types. Most have been acquired either broken or dysfunctional, so I give myself some credit for being at least modestly capable in that area. BUT......Radio?......to me, that's another whole area into and of itself! I'm sure there are some basic similarities.....but such can be said for many a comparison.....a canoe to a yacht, a glider to a Jet, a VW to Porsche, etc! And, I do believe that the whole concept of 'radio' involves technology that is completely unrelated to 'audio' in that the signal has to be 'detected' prior to amplification vs 'provided' in the form of a source like a record, tape, microphone, etc. So, this radio project really does have me intimidated! I'd give my eye tooth to have a local mentor.....although I can't express how grateful I am for this place!! AK has been a tremendous resource to me in working through issues on the audio amplification front....and I'm sure VK will provide the same. Anyway.....I prattle on! Sorry!! Again, thanks for the advice! Tom

This is a great book for the beginner:

http://www.richardmcwhorter.com/AllA...FiveRadio.html

My learning process began with tube testing. Once I got good at working my tester I began testing tubes on a favorite nonfunctional AA5 set and found some bad ones.
I took the set to a local shop that had restored tube radios for sale and procured some new tubes. The owner and talked about the set some, and I was told that given that the set hummed it needed new electrolytics. I was sold some, and instructed on the installation procedure. That night I replaced the lytics and it came to life! That was a thrill far better than just collecting radios, that I was instantly hooked on. Soon I was doing lots of recappings which brought most all of my sets back to life(except for a few dogs). I got more interested in how stuff worked and began reading plenty of books on radio and TV (which I eventually started working on for more of a challenge).

A Superhetrodyne AM radio is basically a string of amplifiers (with a couple of other simple supporting circuits). The signal starts at the antenna and goes to an RF amp (some sets don't use an RF amp stage) from there it goes to one of two circuits that both do the same thing. The signal is now at the mixer or converter stage the mixer is an amp that combines two signals...The station and the oscilator signal. The station is tuned with a band pass filter consisting of a fixed coil and the larger half of the variable capacitor before it enters the mixer. The oscilator signal either originates in a seperate tube in sets that use a mixer-osc stage or is generated within a converter tube (which is clever way of making a single tube act as both a mixer and an osc.). An oscilator is a circuit that generates an AC wave form (which in an AM radio is an RF frequency sine wave). The oscilator frequency is tuned in step with the channel tuning such that when the osc frequency is subtracted form the station frequency a fixed lower frequency is obtained. When the station and osc are signals mixed the osc frequency DOES subtract from the station to form a fixed frequency that contains the modulation of the station. This fixed frequency output is called the IF signal and is usually at 455KHz for AM radios. This signal is then sent to 1, 2, or more stages of IF amplification, and then to the detector. The detector in an AM radio is very simple...all it consists of is a diode which rectifies the IF signal to recover the audio signal. From then on it is an audio signal who's processing you are already familiar with.

The Superhetrodyne has two major benefits over other older designs. The mixer/converter hetrodyning process makes the set more selective (meaning that closely spaced stations that might otherwise run together making it impossible to tune only one can be seperated and tuned individually).

The same process also makes the set more sensitive to weak stations. This occurs because if we design a tube RF amp to function over the entire AM band and put a variable band pass filter at it's input it's gain would be far less than an amp designed to function over the bandwith of a single station. Basically the converter/mixer system grabs and converts any selected station and converts it to a new single RF frequency which we call IF (standing for Intermediate Frequency) this frequency can than be amplified by that single station width maximum gain amp I mentioned a few sentances back.

AM stands for amplitude modulation. One can simulate the action of an AM station in the audio frequency spectrum with a audio sine wave generator and an audio amp. If you play the generator (at the higher end of frequencies than you can hear) through the audio amp and you vary the volume control you modulate the amplitude of the output. This modulation waveform when viewed on an oscilloscope appears as a sine wave that expands out from center and contracts back towards center. If your hands could move fast enough you could generate a deep bass note by varying the volume control, but it would likely be unnoticed as this modulation cancels/averages it's self out when heard on the speaker and the generator is predominantly noticed. Now if we halfwave rectify the output and filter the generator signal from it we will only hear the deep bass volume control fluctuations. And then if we turn off the generator the deep bass sound also disapears despite none of the generator signal reaching the speaker. This occurs because the high frequency generator is acting as a carrier for the deep bass generated by rotating the volume control back and forth at the rate of a low audio freqency. This is exactly how an AM radio transmitter and reciever work only in a radio transmitter the audio generator from the above illustration is replaced by an RF source and the hand working the volume control is replaced by a circuit that varies the "volume" of the RF in step with the audio program content that the station sends. The diode in the above example represents the most basic radio that can be made to work.

I need to go to bed now, but can describe the operation principals of radio better or answer questions/clarify later on.