Servicing info on RCA U70 UHF to VHF converter

[Jonathan]

Hello,

I recently received an RCA U70 UHF to VHF converter. Was there any servicing documentation released on these things? I was suprized to finmd that all the caps were ceramic, but I'm not really sure why I was expecting paper caps to be found in a device that tunes UHF frequencies.

BTW, was there any TV station or translator that anyone knows of that broadcasted on channel 83?

Thanks.

Jonathan

I have one of those converters, too, though I was lucky to have one in working condition. It's a strange beast (mine's a Sylvania). It broadcasts the converted VHF signal across several channels, so I turn the VHF dial till I find one without a legitimate VHF signal to compete (usually channel 4 works best for my area). I then turn the UFH tuner on the set to the station I want. It's very touchy, so it takes a bit of trial and error to set everything up (you have to fine tune both the converter and the VHF tuner on the TV). It sure makes me appreciate the patience people must have had to buy and use one of these things instead of springing for a UHF set. I'll use it once in a while with my Predicta, but I'd rather just grab a modern portable TV with UHF than fiddle with the thing.



Joe

[Jonathan]

Well, most of them I assume use ceramic capacitors, and other than the resistors going bad or the tuner actually breaking, or the tubes go bad, I don't really see much failures, but I never worked with them before. I'm going to clean this one up, test resistors, put a good AC cord in it as well as a 1A fuse and hope for the best.

Jonathan

[Bill Cahill]

Pleae replace electrolytic capacitors, first. Also, the ceramic capacitors do have some tendency to short. I've even had shorted disc capacitors. Let me know how it works. I have bad experience of poor reception with U 170. Thanks.

[Bill Cahill]

Please replace electrolytic capacitors, first. Also, the ceramic capacitors do have some tendency to short. I've even had shorted disc capacitors. Let me know how it works. I have bad experience of poor reception with U 70. Thanks.

[Jonathan]

Bill,

I'm definately going to replace the electrolytics. I'll test resistors for drift and ceramics for shorts. Do the germanium diodes go bad too? I'll lubricate the tuning shaft and clean the contacts in the selector switch and replace the lamp if burned out. From what I hear, the U70 is a nice converter and works well, but from the looks of the tuner, misalignment looks easy to do. The bad reception could be because of misalignment, but I'm not the one to ask.

Thanks.

Jonathan

[Bill Cahill]

Sorry for long wait. Yes, they do often go bad, but, usually from leakage. What doesn't help is they started off leaky when new. Your'r on the right track. If you find another complete one, please let me know. Want one. Bill

[Steve McVoy]

These converters have no RF amplifier, and feed the UHF directly into the mixer diode. As a result, they have horrible noise figures, and perform much worse than a modern TV set (or VCR) in weak signal areas. If you live close to the transmitter, they work fine.

[wa2ise]

Originally Posted by joe_tbird

(mine's a Sylvania). It broadcasts the converted VHF signal across several channels, so I turn the VHF dial till I find one without a legitimate VHF signal to compete (usually channel 4 works best for my area). I then turn the UHF tuner on the set to the station I want. It's very touchy, so it takes a bit of trial and error to set everything up (you have to fine tune both the converter and the VHF tuner on the TV). It sure makes me appreciate the patience people must have had to buy and use one of these things instead of springing for a UHF set.

Joe

THis can explain why many early UHF TV stations failed. Many viewers probably would just go with an easily tuned in VHF station rather than bother with the UHF converter hassles. Around 1964 or so the FCC mandated that all new TV sets were to have UHF tuners. Helped a lot, but unless you were the only UHF in town, getting viewers to tune your UHF station in was still a two step process. Turn the VHF dial to "U", and then mess with the UHF dial. If you were the only UHF in town, most people probably have you set on the UHF dial and when the twist the VHF dial across "U" your station is there.

An exception would be if both UHFs were Spanish language, then that community would never leave the UHF band and only twist the UHF knob. Or
small towns with all 3 networks on UHF channels. Binghamton NY had 2 of the 3 networks on UHF, and one of the networks on channel 12 if I recall correctly. That would make for a lot of dual knob twisting....

[peverett]

I live near Austin, Texas which only has one VHF station.

Can anyone guess why? Hint-his initials are LBJ. He owned it in the 1960s.

Austin was large enough to support all three networks on VHF. Also, for some reason even PBS in on UHF.

[David Roper]

Although seen in some areas on VHF stations, PBS on UHF affiliates is quite certainly the norm.

[peverett]

The PBS station where I am originally from, Oklahoma, is on channel 13. It just made VHF. I guess that this is why I was supprised that the local PBS station was on UHF.

In fact, all of the stations in Oklahoma City were on the VHF band when I lived near there. I believe that they have UHF stations now, but the orignal VHF ones are also still active.

[maxm]

Here in Chicago we have two PBS stations, the "main" station on 11 (WTTW) and a smaller lower budget station on UHF 20 (WYCC).

[Chad Hauris]

It seems like more often than not, the PBS station is on ch. 13 if it's a VHF...and on a lot of cable systems, even when the PBS station is a UHF it's often cable ch. 13.

[Jonathan]

If I amplify the signal with a UHF amplifier I'm thinking I should get better performance. I have the capacitors I need to restore it, just got to actually install them as well as a fuse holder and power cord.

Jonathan