HH Scott Solid State

[jlovda]

I have a copy of the LT-112B instructions. Awhile back I tried to figure out where things around the IF and detector changed in the align position since the last version of the kit is virtually identical to version 1 of the 312-D. Time to go back.

I just looked in side the box. If you shine a bright flashlight on an angle into the RF Osc hole you can see the RF trimmer screw quite clearly. That is a very thin tiny slot! I may have to order a proper alignment screwdriver if I don't have anything that narrow.

Well, I attempted to try adjusting the RF trimmer cap. I found a station in the middle of the dial that was weak but got the stereo lamp to flicker. Until I got to each extreme end nothing changed. The meter sat at zero the entire time but the signal got weaker. I must have made 5 or more rotations in each direction of the threaded shaft. It made no difference whether the cover was off or on. The bottom cover of the front end is soldered so I cannot see what the trimmer actually looks like. The extremely strong station about one mile from my house gets the meter to about 7. The unit is cosmetically beautiful and it picks up quite a few local stations with only a tabletop rabbit ears but I guess it will live out the rest of its days in a kneecapped situation. It was already professionally aligned about a year ago. I didn't hear that much of a difference before or after that work.

 

[backmd]

Well, I attempted to try adjusting the RF trimmer cap. I found a station in the middle of the dial that was weak but got the stereo lamp to flicker. Until I got to each extreme end nothing changed. The meter sat at zero the entire time but the signal got weaker. I must have made 5 or more rotations in each direction of the threaded shaft. It made no difference whether the cover was off or on. The bottom cover of the front end is soldered so I cannot see what the trimmer actually looks like. The extremely strong station about one mile from my house gets the meter to about 7. The unit is cosmetically beautiful and it picks up quite a few local stations with only a tabletop rabbit ears but I guess it will live out the rest of its days in a kneecapped situation. It was already professionally aligned about a year ago. I didn't hear that much of a difference before or after that work.

which zip code are you in, I could lookup the expected signal strength of stations based upon you zip code on signallocator.com

 

[jlovda]

which zip code are you in, I could lookup the expected signal strength of stations based upon you zip code on signallocator.com

I already have a list from FM Fool. One thing I wish I had done was ask the person who did the alignment to make a list of the antenna input power (dBF) of his RF signal generator vs the rough number on the signal strength meter (1,2,3,...10). Awhile back I put my Fluke meter on the vertical scope output and could see a dramatic difference on the voltage between stations that moved the meter and those that didn't. Volts vs a few millivolts.

 

[backmd]

I already have a list from FM Fool. One thing I wish I had done was ask the person who did the alignment to make a list of the antenna input power (dBF) of his RF signal generator vs the rough number on the signal strength meter (1,2,3,...10). Awhile back I put my Fluke meter on the vertical scope output and could see a dramatic difference on the voltage between stations that moved the meter and those that didn't. Volts vs a few millivolts.

How many stations can you get vs how many are expected on FM fool?

 

[jlovda]

How many stations can you get vs how many are expected on FM fool?

I never counted. I'm just perplexed that I get quite a few stations, including stereo, that do not move the meter. No station registers between 1 and about 6/7. They are either zero or 8/9. I can visually get a sense of signal strength by looking at the deviation or swing of the center tuning meter around zero. The stereo lamp is also not operated by a switching circuit. It fades in and out as I tune across the frequency. It might just be my location. I live in what seems to be a half mile diameter shallow valley or depression. I always seem to be going slightly uphill when I head in any direction from my house.

 

[jlovda]

Here is an FMFool chart of my area.



WONE at 97.5 just makes the needle quiver. It would appear the needle only starts to move above -40dBm.

 

[backmd]

I never counted. I'm just perplexed that I get quite a few stations, including stereo, that do not move the meter. No station registers between 1 and about 6/7. They are either zero or 8/9. I can visually get a sense of signal strength by looking at the deviation or swing of the center tuning meter around zero. The stereo lamp is also not operated by a switching circuit. It fades in and out as I tune across the frequency. It might just be my location. I live in what seems to be a half mile diameter shallow valley or depression. I always seem to be going slightly uphill when I head in any direction from my house.

If I am hearing you correctly everything may be working properly except for the meter. The meter has bearings and I just fixed a meter with bad bearings. It measured well in terms of being around 490 ohms but would not budge, it would not move even with the voltage of the multimeter set to ohms. So I took a 1.5 volt AA cell and then it moved all the way to the R. So it was like your meter either zero or maximum. The surgery is very delicate, and it is well illustrated on youtube.

. Essentially the bearing is too tight and needs to be loosened. You have to delicately disconnect the meter and gently take the meter housing apart. Then under a magnifying illuminated loupe you have to gently turn the screwdriver that is inserted into the bearing assembly about 1/8 turn counterclockwise. You will see the meter then start to move freely and then you can reassemble it.

 

[jlovda]

The meter in the 312-D is actually a center tuning meter with the natural rest position in the middle. Center tuning works fine except there is not a very wide swing when passing a station. In the signal strength position there is an electronic "offset" voltage given to the meter to pull it to the left end. You can move this artificial zero by using the pot on the multipath board next to the front end box. It does not change the sensitivity of the meter, only the offset position.

 

[jlovda]

Just for fun, on FMFOOL I put in my address in the NW side of Chicago where I lived growing up in the 50's, 60's and 70's (roughly 15 miles from the Loop). Compare that to my current location in Canton, OH. Maybe where is nothing wrong with the meter or meter circuitry in my 312-D.

 

[rmp]

The LT-112B tuner, like the best of the early Scott solid state tuners, has a front end with 3 FETs and one NPN. Here is a photo of one on the bay that appears to have two of each. Could it work?

 

[jlovda]

The LT-112B tuner, like the best of the early Scott solid state tuners, has a front end with 3 FETs and one NPN. Here is a photo of one on the bay that appears to have two of each. Could it work?

Are you looking at the case style of the transistors? To me it looks like every other LT-112B and 312-D front end. Two transistor FET cascode RF, FET mixer and bipolar oscillator. I have never seen a unit or a schematic where the mixer was a bipolar. The cheaper units had a three transistor design with a FET RF, bipolar mixer and bipolar oscillator.

 

[rmp]

Yes, I am looking at the case style. There are actually two interior photos of this tuner on the bay. Check both. I think there's been a substitution.

 

[backmd]

If you took a multimeter, preferably a fluke and hooked it up in parallel with the meter and measured the voltage at various positions on the dial scale. That way you could see if there is enough voltage to make the meter move or not.

 

[backmd]

Also based upon the data from FM fool and given that you are in a valley, which would decrease your signal even more, you probably are not going to get good reception. But again we have not ruled out bad bearings which would be predicated upon the voltages at the meter itself. The only way to rule that in or out is #73 above, with any sort of precision and accuracy. If the multimeter has a smooth progression without the extreme swings that you are seeing, then the bearings are more likely, and you already have a youtube video of how to fix that. Any other questions?

 

[jlovda]

Also based upon the data from FM fool and given that you are in a valley, which would decrease your signal even more, you probably are not going to get good reception. But again we have not ruled out bad bearings which would be predicated upon the voltages at the meter itself. The only way to rule that in or out is #73 above, with any sort of precision and accuracy. If the multimeter has a smooth progression without the extreme swings that you are seeing, then the bearings are more likely, and you already have a youtube video of how to fix that. Any other questions?

The potentiometer on the multipath board appears to set the meter offset for the signal strength position. The meter moved smoothly when rotating the pot. Second, on the 312-D the meter is glued with double sided tape to the back of the dark smoked plastic front panel. During my restoration work I retaped the panel and the meter with new (very strong) tape. I don't feel like trying to pull it out. The bottom line is that there are only two stations in my area worth listening to and they are between -40 and -55 dBm signal strength. The meter seems to start moving above -45 dBm. The tuner was purchased for nostalgic reasons. I'm finished.

John

 

[backmd]

The meter bearings are good when you rotated the pot so the meter is good, also the tuner guru restored your tuner. The only issue is the two stations at -40db and -55db. So the tuner works. I am using the Scott LT112B tuner because the trumpets are much more real on the one good jazz station WDCB 90.9 in the chicago area. That is the one good thing about a major city. But I could swear I heard continuous machine gun blasts many miles away at 444am. That is the one bad thing about a major city.

 

[jlovda]

Where in the Chicago area are you located? I grew up and into my college years around Fullerton and Central. When I was in college at the U. of I in Champaign I was fortunate to live on the eighth floor of a high rise dorm. It was amazing how many central Illinois stations I could get on my KLH 18 tuner with just a dipole.

 

[backmd]

Where in the Chicago area are you located? I grew up and into my college years around Fullerton and Central. When I was in college at the U. of I in Champaign I was fortunate to live on the eighth floor of a high rise dorm. It was amazing how many central Illinois stations I could get on my KLH 18 tuner with just a dipole.

southwest suburb Willowbrook. I went to Champaign also. I remember getting the best possible FM yagi and mounting it to the top of the chimney above the 3rd floor of the fraternity house to try to get the chicago classical station WFMT 98.7. However 150 miles was not possible back in the day since I did not have an antenna amplifier. I even got one of the frat brothers to help me mount that sky high antenna. No way I would do that now, I lose my balance walking to the bathroom in the middle of the night now. 8th floor dorm could have been Bromley Hall. I was on the 8th floor also and enjoyed the swimming pool at 8am in the morning. Bromley had a pool and after getting wait listed for housing I could have been at the ceiling level of Clark Hall for overflow housing or in a single on the 8th floor at Bromley with the swimming pool!
I also have a KLH18 tuner and that was rated stereophile class B in 1966 or so. It has a similar design with LC IF stages and a diode matrix for MPX decoding. I think the horns are much more realistic with the LC IF and MPX diode matrix. That is the same design as you well know as the Scott LT112B tuner.

 

[backmd]

The meter in the 312-D is actually a center tuning meter with the natural rest position in the middle. Center tuning works fine except there is not a very wide swing when passing a station. In the signal strength position there is an electronic "offset" voltage given to the meter to pull it to the left end. You can move this artificial zero by using the pot on the multipath board next to the front end box. It does not change the sensitivity of the meter, only the offset position.

Well that is a terrific way to rule out bad bearings, the center tune meter evidently works in your 312D, when switched to center tune. My LT112B is likely similar, switching that meter to 4 different applications.

 

[jlovda]

The 112-B meter has the alignment position which, to the best of my deciphering, taps into the IF at a spot where there is no AGC.

I lived on the eighth floor of Olgesby Hall at the Florida Ave. residence halls at the south end of the campus. I was on the south side facing the farms. Beautiful views of the round barns and the farmland. At the time the WPGU antenna was on the roof of the building but, amazingly, I never had an overload problem with my 312-D. During my senior year in 68-69 my system consisted of a JBL SA-600 amp, 312-D tuner, Dual 1019 turntable and KLH Six speakers. I would have to say this was probably better than 99% of stereos in the dorm. I was lucky it didn't get stolen. Quite honestly if it wasn't for the fact I was an EE always upgrading I probably would have been VERY happy with this system even today. I still have the Dual. I also still have the Who Sell Out album I bought at Rose Records across from the EE building on Wright St.