EH Scott Radio Enthusiasts

The Fine Things are Always Hand Made

While I wait for some re-chroming to get finished on my Scott 16, I decided to start on my 16A.

Question: There are a LOT of Tobe and Sangamo molded capacitors in this thing.  What are they, Mica or molded paper?  Do they hold up or should they all be replaced?

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The Scott 16A lives again!  All tubular, electrolytic, but not the  caps that look like mica's, were replaced (stuffed).  AM has been re-aligned. FM need s a little work yet.  "Music Control"  needs something as only the "N" works - not a big problem right now.  The speaker in the photo is not original but is vintage.  Sounds pretty good not being in a cabinet.  This radio will be a shelf queen in this configuration.  It gives me noise free FM  in my work space as I work on other projects.  I will build an appropriate enclosure for the speaker to give a reasonable frequency response.  If I find an appropriate empty cabinet, i may purchase it to make a more original combination.  I may even add a CD player/mp3 player for those times when nothing reasonable is on the radio.

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A lot of what look like mica capacitors in the scratch suppressor (music control) circuit are actually molded wax paper capacitors that will need to be replaced.

Norman 

Thanks Norman. when no one replied regarding my original question, I decided to power up without changing all the Mica lookalikes.  All is fine except for the Music Control.  I'll dig into that sometime in the future.  it's a pain to get at since the entire sub-assembly needs to be lifted out.  Thankfully, there are only a few wires that need to be un-soldered.    The radio works great without that, but it would be nice to get it working.  The FM section seems to be all ceramic capacitors so no problem.  Hopefully the rest of the Mica lookalikes are in fact Micas's.  Time will tell.

Am section is pretty much aliened.  I've never done an FM alignment so I need to do a little work yet.  I found that just the position of my fat body affected meter readings.  would like to try an alignment using the O-scope but not sure yet how to do that.  More research required! 

You may find it functions only on phono setting - I don't really know. 

FYI - some history.

That 4 tube 'Music Control" on the Scott Labs Metropolitan 16A is the H H  Scott (Herman Hosmer Scott) Dynaural noise reduction circuit. This circuit also became available as an optional outboard  addition for the post war Scott 800B. Consider it a further developed version of the dynamic record scratch suppressor of the  E. H. Scott Lab. late 1930's Philharmonic and Phantom models. Speculation - no law suit in return for access to the new circuit.)

The E H Scott 2 tube record scratch suppressor circuit cut the high frequencies only at low volume.  The H H Scott circuit does that and also cuts the low frequencies as a rumble filter. H H Scott's Dynaural circuit was originally developed early 1940's for radio stations to improve the quality of 78 records being broadcast.  Evidentially, after Scott Labs began to offer it, H H Scott about 1948 entered the retail audio business with his own Dynaural noise reduction preamps for record players -model 111-A (3 tube for high output cartridges) and 112-A  (4 tube for magnetic cartridges). It was power from an octal plug inserted in the radio output tube socket into which the output tube was then re-inserted. Soon HH Scott offered a preamp model 120-A with equalization selectors, bass, treble and loudness controls and that also powered an Dynaural outboard unit. Finally HH Scott offered his mono block 6L6 amp model 220-A. Thus, H H Scott ushered in 1950's quality component Hi-Fidelity audio. I have examples of  both Dynaural units, the preamp and mono block amp in my collection because of the connection to E H Scott radios.

Thanks for the history.  The manual suggests that it should do something even in the radio positions.  Instead, the audio goes dead and there is a hum.  I haven't traced the "chinese RR tracks" on the schematics to see exactly what is switched into the circuit in the various switch positions.  Is there an explanation of how the circuit works anywhere?  That entire circuit, including the tube sockets, are mounted on a separate assembly that is removable with relatively few wires removed.  I haven't found any explanation of how adjustments are made.  Since I don't intend to use a turntable, the circuit is of little use to me other than curiosity and originality.  Eventually, I want it to work.  The tubes are NOS, but I have not tested them to be sure they are good.  I may do that first before getting into the circuit itself. 

I had an open filament in the 6B8 - bad solder on the pin.  It tested ok on Bob Dobush's tester but went dead when put in the radio.  Now at least I get something happen in all switch positions.  It's drastic and quite worthless on radio programming.  Not sure what the noise reduction would do on noisy records.  I didn't change any of the molded mica lookalikes so perhaps there is still a problem in there.  I probably won't pursue it any farther since I don't think it to be useful on radio.  Maybe if I were to ever try to sell it I'll go farther.

I had a lot of problem getting the FM to track properly.  I have it close now but it's still off a bit in the middle. Plus, the dial hits the stop at about 88.4 mhz and on the other end, at about 107.4.  there is a station at 107.9 that I do listen to on occasion.  I did get it to tune but it messed up the rest of the dial dramatically.  Plus, if I went just slightly past it, the radio would go dead.  I suspect the oscillator didn't like the coil/cap settings and just quit. Oh well, it's a country station and I have a zillion others!  As I said before, this is the first FM receiver I've worked on so I have a lot to learn.

I've got this radio working pretty good.  I changed all of the Sangamo and Tobe caps as I suspect they were molded paper. Now the noise reduction works somewhat.  I can't find any info on how to adjust it.

I have a question on FM alignment for this unit.  I aligned it by peaking the IF and Limiter transformers as per the instructions given in Sam's.  it works fine except that the high's are a muted when compared to a 1960's Scott 350D tuner and a 1970's Sherwood S8900A.  For example, in listening to Jazz, the cymbals "shimmer" on the Scott 350D and the Sherwood, but are muted on the 16A.  if I take the output of the Sherwood and run it through the amp and speaker of the 16A, it sounds quite good.  I suspect that the peaked band pass of the IF transformers and limiter transformers is too narrow on the 16A, reducing the high frequency response.  I've attempted to "stagger tune" the IF, but to not much success.  I will play with it again.  Does anyone have any experience with this?  Can you point me in the right direction to find specific info on widening the response characteristics of the IF transformers?  I'd like to play with it to improve the frequency response of the 16A.

Perhaps I'm expecting too much out of a 1940's radio!

thanks!



Robert Feenstra said:

I've got this radio working pretty good.  I changed all of the Sangamo and Tobe caps as I suspect they were molded paper. Now the noise reduction works somewhat.  I can't find any info on how to adjust it.

I have a question on FM alignment for this unit.  I aligned it by peaking the IF and Limiter transformers as per the instructions given in Sam's.  it works fine except that the high's are a muted when compared to a 1960's Scott 350D tuner and a 1970's Sherwood S8900A.  For example, in listening to Jazz, the cymbals "shimmer" on the Scott 350D and the Sherwood, but are muted on the 16A.  if I take the output of the Sherwood and run it through the amp and speaker of the 16A, it sounds quite good.  I suspect that the peaked band pass of the IF transformers and limiter transformers is too narrow on the 16A, reducing the high frequency response.  I've attempted to "stagger tune" the IF, but to not much success.  I will play with it again.  Does anyone have any experience with this?  Can you point me in the right direction to find specific info on widening the response characteristics of the IF transformers?  I'd like to play with it to improve the frequency response of the 16A.

Perhaps I'm expecting too much out of a 1940's radio!

thanks!

Robert;

One thing to do as you align the FM circuitry is to keep reducing the input signal level as you progress from 1st. IF to 2nd IF etc. The idea is to avoid having the Limiter stages from going into limiting. If the Limiters go into limiting, it is virtually impossible to determine the best peak setting for the alignment. The interstage IF transformers in these older receivers are sharper/more selective than those of FM tuners and receivers made after the advent of FM stereo multiplex broadcast and reception. One thing I have noticed with my 800B model is that the FM Discriminator tuning is significantly more critical for best reception and bass response than more modern receivers. The tuning really needs to be spot-on.

On the issue of installing your Metropolitan 16A in a cabinet, you will find installation in a cabinet made for an 800B will have vertical space to spare for the 16A tuner chassis. You would have to check about space for the H H Scott scratch & noise circuitry. I bought a 16A cabinet to house my 800B unit and ran into the issue of not enough vertical space due to the extra height of the Tuning Rotor Disc assembly at the back of the tuner chassis. I had to take the top of the cabinet off (it unscrews on the one I bought) and add 1/2 inch thick mahogany spacer boards to lift the entire top up enough for the 800B chassis to have enough space. Dave installed one Scott receiver in a TV cabinet that had doors on the front and made a few modifications to fit his radio into that. It looks quite nice. A custom cabinet can be made of course, but expect to pay accordingly, unless you can do the work yourself and be satisfied with the result.

Joe

Thanks Joseph.  Yes, I did keep the signal level as low as possible to avoid activating the limiters.  The 16A has 2 limiter stages so I had to be very careful.  In looking at the response curve of the IF and Limiter transformers with my spectrum analyzer, it is quite sharp and limits the frequency response.  75KHz markers on either side of 10.7MHz center frequency are well down the response curve.  Far more than 3db.  I realize that the full frequency response is not necessary since we are not needing the multiplex portion of the FM signal, but it is definitely muted on the top end.  I was hoping there was an accepted way to widen the curve to get a flatter top with the 75KHz frequencies a little less attenuated.  I've played with detuning the primary one way and the secondary the other, but all I can get is a distorted response curve. So, for now, I'll leave them peaked.  But I have to say that listening to my Sherwood or HH Scott in Mono is a far cleaner sound than the 16A.  Eventually, I'll play with it again.

Robert;

One acceptable way to broaden the IF and detector response is to add a resistor across the primary and secondary of IF and detector windings. It might change the tuning just slightly, but depending on what resistance you apply across a winding the amount of response broadening will change. One way you could optimize for the result you desire would be to use a variable resistor that you can adjust while watching the markers on the screen and adjust for the desired response, then remove the variable resistor, measure the value and use a standard fixed value closest to the value the variable resistor was set to, then recheck response.

One advantage of broadening the IF and detector response using a resistor is that if you ever change your mind it is easy to reverse and put it back like it was originally.

I worked on a Sears Silvertone model 8127D which featured an AM/SW/FM radio plus record changer and wire recorder with programmable clock for unattended off-the-air recording. That unit was designed in a similar manner to the E H Scott 800B and 16A in that the IF and detector circuitry was rather high-Q and very selective. That can be useful if you happen to want to receive a weak station close in frequency to a local strong station. That particular Silvertone was made for Sears by Colonial Radio Corp. of New York. It featured a 4-gang FM tuning capacitor with tuned antenna input, RF plate tuning, Mixer grid tuning and Local Oscillator tuning. I don't think anyone else did that until Harman-Kardon produced their Citation III FM tuner and Fisher introduced their FM-1000 tube type tuners in the 1960s. The Silvertone 8127D has the same sharp IF and detector tuning and the same response to tuning in a station. The sharp response seems to be fairly common among better FM radio designs of that era. Colonial Radio only made about 500 of that model I am told and later primarily produced communications equipment for the U.S. Military.

I also worked on a Fisher 202-R AM/FM tuner which has 6 IF stages on FM similar to the Fisher FM-1000 and it also has a sharper IF response than later Fisher tuners, although not as sharp as these older examples we are discussing here.

Joe

Great!  Thanks. That's a new thing to try.  I do remember now that being mentioned is some literature that I had read.  I had forgotten about that.  I just finished playing with the de-emphasis caps and was able to boost the treble response quite a bit.  Enough that I may be satisfied for now with this radio as my shop radio, which is the role it plays.

Thanks again.

Rob

Rob;

I started to mention the de-emphasis aspect but failed to. That is an easy fix for the treble response of these older receivers. Many of the older receivers had speakers that even when they had tweeters lacked the high end response we have become accustomed to with more modern receivers. You might also want to look at the tone control modifications that Norman has posted for the 800B. I am not sure if those ideas had been incorporated in the 16A or not without examining the 16A schematic. The 800B had a fault in the line amplifier stages in which the cathode resistance was way too high and made the circuit prone to hum. The changes to the circuit include reducing the cathode resistance and elimination of the choke which was used in the bass control circuit.

Joe

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