Tuner issues on RCA and Magnavox, others

[Motorola minion]

Having trouble with a console's tuner, when I really need to make sure amplifiers and record players work consistently well, is a time-waster.

Not knowing what was so very wrong with the tuner in these classic early 60s consoles, inspired me to action. There is no way I could call something fixed if it could not even get period-appropriate music on FM. Records are fine but there is AM and FM too.

I don't recommend RF work but a long time ago, part of my job was to set up (align) Loran-C navigation used in private aircraft and communications receivers used by the NSA. That alone got me used to the fact that IF and RF can be very strange, even at lower frequencies. It takes unconventional methods to make some designs work right.

Here is the RCA from 1961 (pre multiplex) that had the worst issue and, with several un restored 1961-1963 RCA's still in my collection, I knew I could not give up.

RCA_Victor_1961.jpg (11.48 KiB) Viewed 2071 times

[Motorola minion]

Here is a Magnavox 1ST228 of mine with the same issues the RCA PVCR185 has. This is a bit larger than a pair of petite Magnavox consoles I serviced in another post. It has a similar amplifier AMP-196, with bit more voltage than AMP-86 to make SE 6BQ5 perform better and a 12AX7 in place of 6EU7. The tuner is even more interesting. Even though it is a 59-series, it has a second preamp tube 6EU7 that the other sets' tuners did not have! This is the hotter version of those lower priced models.

[William]

That is the same amp and speakers as my little Columbia In the sun room. To tuner though, just volume, bass, and treble controls on the front of the unit. If I remember correctly the amp was a 196.

Bill

[electra225]

My experience with the six Magnavox instruments I have is that the smaller tuners, the five-knobbers with AFC, are actually better performers than the larger tuners with no AFC. On all of them, the antenna is critical. I'm sure, particularly on the larger tuners, that some tinkering with alignment would improve performance.

[TC Chris]

On all of them, the antenna is critical.

This is the big secret of FM performance. A crummy tuner with a good antenna will out-perform a good tuner with a crummy antenna.

In about 1968 I built my first stereo tuner, a Heath AJ-15. I was in college, in OH, and it was the age of album-oriented rock, and the nearest station was in Columbus, quite a few hills away. I bought a turnstile omni antenna, tossed a rope over the highest branch I could manage outside the ground-level dorm window, hauled the antenna up, and pulled in Columbus.

Chris Campbell

[Motorola minion]

Even the lead-in, usually twin lead 300 ohm, is critical. That short piece that runs from chassis to the cabinet back or terminal strip must be less than a 1/2 wavelength (64 inches).

So, when you test a tuner to align it, make sure it's connected before you start tweaking and peaking RF at both ends of the dial. This matters on all Zenith FM tuners I have seen, as well as all others.

[electra225]

I have often found on my own instruments, that one side of the twin lead has been broken by taking the back off then put back on. The twin lead is tugged on, breaking one side. I appreciate your sharing tips on how to improve performance in radio tuners.

[19&41]

I've found that a good accurate signal generator fed according to the mfr's specs helps greatly in alignment of receivers. The strength of stations can vary depending on even a person's movement within a room.