Midland 13-885

 

 

Classic Status: Early 70's 23 channel SSB Base.

Appeal: My original first SSB Base.

Condition: Cosmetic: Good. Electrical: Good

Acquired: Original, 1976 trade.

This is my Midland 13-885, a 23 channel, AM/SSB base station.  This radio was manufactured in December of 1971, and was the "upgraded" model to the older 13-880b, which recently reflected the FCC's new higher 15 watt PEP SSB input power rating (It had been 10 watts PEP input prior to 1971).  Among the radio's most noticeable features was a large S/RF/SWR meter, a clock, and a clarifier which varied both transmit/receive frequency about +/- 800hz.  The rig has a straight-forward dual conversion (on AM, single conversion on SSB) receiver, and included a pulse gate noise blanker.  The transmitter was designed to produce a basic 3 watt nominal AM carrier power output and derived the extra power for SSB by utilizing the unregulated 23V raw power supply voltage to power the driver and final transistors in the SSB mode.  The drawback to this scheme, was that if you ran the rig off of an external 12V source (Such as in a mobile), the SSB power output would be the same as the AM carrier power.  The roughly double supply voltage increased the SSB power output to close to 9-10 watts in its stock form.  The crystal synthesizer utilized 11 Mhz and 7 Mhz crystals to generate the 23 (24) channels for both AM and SSB modes. 

For a little background history on this particular radio, the Midland has been in my possession since 1976, and has had a pretty eventful life.  I don't know who the original owner was.  But the rig first came into our local group by way of Steve.  In fact, it was this exact rig, installed (sitting on the front seat) in his mobile, which was the first SSB rig that I ever talked on back in 1973, when I was still restricted to a 100 mW walkie-talkie.  In early 1974, the Midland was sold to Blue Bandit, who then ran it for a year or so as he got his feet wet in the CB hobby.  Bandit often complained about the rig's poor adjacent channel rejection (he called it a "bleed box"), and that likely hastened his desire for a new radio, and the Midland's eventual sale to my friend and neighbor Channel Master, who was itching to get his first SSB radio.  He ran it for a less than a year, before mother nature intervened and sent a bolt of lightning down his antenna and feedline.  Unable to get the rig running again, he traded it to me for a SSB mobile radio that I had recently picked up.  Once in my hands, I managed to get the rig running again by replacing defective audio output transistors and a power supply regulator.  But the lightning strike had also damaged the R.F. Gain control to the point where if you backed it down, signals would decrease until the control reached about 3/4 down at which point signals would start increasing again.  But otherwise the radio seemed to be operational again.  For the next 4 years, I used this rig as my primary base.  Interestingly, the bad adjacent channel rejection did not seem all that bad to me.  It wasn't nearly as good as my Comstat 25, but it wasn't so bad that I couldn't enjoy using it.  I discovered that much of the bleedover problem was exacerbated by running the noise blanker on.  Keeping it off helped a lot, and I also joked that the lightning had made the radio tighter.  Sometime in the late 70's, I added an additional ceramic 455 Khz filter which narrowed the receiver bandwidth considerably and helped to reduce splash from adjacent channels.  On the the other side, the transmit modulation was very strong, and the radio was known to splatter a few channels.  It was also a bit on the tinny side, which was most noticeable when running a D-104 microphone.  From the time I got the radio though, I was not satisfied with its measly 3 watt AM power (My Comstat put out 6 watts by comparison), so I set out to juice that level up.  Eventually I changed the final and driver transistors to higher gain devices and managed to get AM power up to 5 watts while SSB power jumped to almost 15 watts.  In 1977, when the 40 channel band plan became law, I added crystals to the Midland to give me the 15 new channels above 23 (I already had access to 24 and 25, which are between 22 and 23) plus an additional crystal to give me up to 27.455.  The original clarifier circuit was replaced by a variable capacitor in series with an inductor to give me a -10Khz drop to fill in the gaps that occur every 4th channel on the 23 channel dial.  The newly improved Midland continued to be my primary radio from my Channel 10 days, throughout the Channel 13 days, and was the rig which recorded most of my audio clips made in the later 70's.  In 1981, I finally retired the 13-885 in favor of a newer 40 channel PLL SSB rig, and it pretty much sat inactive from then on, its usefulness limited to primarily my station clock.  Then in the mid 80's, I lent the rig to my father-in-law.  While in his care, a water main broke and flooded his basement with muddy water, which submerged all of his equipment, including the Midland.  I was able to flush out the mud (It felt weird blasting a radio with a garden hose), dry the rig out with a hair dryer, and bring it back to life again.  But not long afterward, the clock stopped running and the meter movement developed problems.  I eventually got the rig back and it again sat on a shelf.  Sometime in the late 90's my classic radio nostalgia had started up and I began to play with the Midland again to see if I could improve its performance.  I transplanted the meter movement from a similar meter and restored meter functions.  I also changed some capacitor values in the modulation circuit to reduce the tinny modulation and make the audio response more flat.  But other than occasional use, the rig has pretty much sat on a closet shelf for the last 7 years and it's been only recently that I've brought the rig out to do a classic radio review, and I gave it a complete tune up alignment.  My initial receiver sensitivity findings were shockingly disappointing, and required some changes to get the final numbers.

First, here are the updated bench numbers....

Receiver (Updated): 

Sensitivity AM: .5 uV for 10db S+N/N  

Sensitivity SSB: .3 uV for 10db S+N/N 

Adjacent channel selectivity: 72db @ 10Khz.

I.F. Frequency: 1st 7.8 Mhz, 2nd 455 Khz. (AM Only)

 

Transmitter:

AM Power: 4 watts with forward swing.

SSB Power: 14 watts

AM Modulation: 100+%, 15 watts peak.

2nd harmonic suppression: -60dbc.

Other spurious emissions: -40dbc worst case.

 

Now for my subjective "seat-of-the-pants" review of the radio.....

 

I was in a state of shock when I saw how poor the initial receiver sensitivity numbers were.  I had to put in 2uV (Not .2) to get a 10db S/N ratio. The funny thing is that I had used the rig for all those years and I really never noticed the less than ideal receiver sensitivity.  Then again, most of my talking was done within a 5 mile radius, so I wouldn't have noticed anyway.  After alignment didn't correct the problem, I suspected that the lightning damaged R.F. gain pot was the culprit and when I bypassed it, sure enough the receiver numbers jumped considerably, and I was now able to record about average sensitivity for the vintage of the rig.  The unusually good adjacent channel selectivity number is directly the result of the extra I.F. filter that was installed.  But that number tells only part of the story.  The phenomenon of Bleed over is really a combination of a few different phenomena.  The first is adjacent channel rejection, which is a measure of how sharp the I.F. filter bandwidth response is, and its ability to reduce signals 10 Khz (or more) away.  There is also the case of splatter where a dirty transmitter is emitting a very wide signal, which goes beyond the boundaries of the desired channel, and will spread onto the adjacent channel where no amount of receiver filtering can eliminate it.  Then there is R.F. overload, where a strong signal several channels away will overload and "desense" the receiver, resulting in desired signals dropping, sometimes completely.  It was this latter overload issue which was the biggest problem for the 13-885 in the old days.  Since there is no one really close to me now, the overload problem will not be as prevalent as it once was.

 

In actual on-air operation, I was a little bit disappointed.  Operating this radio was not as pleasant or rewarding as some of my other classic radios were (When your stable includes a Tram D201, it's hard to objectively compare).  The receive audio was somewhat tinny and subject to speaker vibrations.  This can probably be corrected with a better speaker and improved shock mounting.  The speaker is not original, and it has been replaced twice before, so this defect is probably not a design flaw.  Indeed, I don't recall having this problem back in the 70's, and the audio quality was much better. Then again, I was much younger then, and more willing to deal with practically anything just to have a radio like this.  I've become much more discriminating in my old age.  The S meter readings are not as linear as on the Hy-Gain 623 (Not many are), with the readings looking closer to being about 5 db per "S" unit.  I was also disturbed to find a fair amount of transmitter spurs.  Since I had done extensive tinkering in this area 30 years ago while trying to increase power output, I can't be certain that I am not the cause of at least some of the spurs.  Most are better than -40db down, but there are far more of them than I would expect there to be.  I was also turned off by the lack of receiver sensitivity as it did seem that the radio was not all that hot with the weaker signals.  It also seemed to be slightly more prone to my network interference than some of my other radios.  On the plus side, the squelch action is smooth and pleasant, and the reworked transmitter audio quality is very good.  The radio seems to sound better with a Turner +3 desk mike, as its flatter audio response makes a better match for this rig.  Talking on SSB brought about good reports on audio quality as well, with again the Turner being the favored microphone.  All told, the radio probably needs a bit more work to bring back to its original glory.  On the other hand, considering that this radio has survived multiple owners, a lightning strike, years of serving as an experimental platform for an up-and-coming-still-had-much-to-learn engineer, a flood, as well as the passage of time, I'd say it's faired pretty well.  Overall, I think the issues with receive speaker audio can be worked out and, at that point, this rig will compare more favorably with my other rigs.

 

Update: I came into possession of a 13-885 "parts radio". I transplanted the clock, the speaker and the RF Gain pot into my Midland. The receive audio is now much better, the clock again functions, and the meter movement is back to what it was originally designed for.  Subsequent "test drives" of the radio, during our weekly classic radio roundups, have left me with a far more favorable impression than during my last review. I am now contemplating removal of the extra crystals and the modified clarifier and returning the radio completely to stock condition.

 

 

 

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