A few months ago I wrote of the difficulties I encountered when I tried to build Sinclair's Black Watch kit. The description of my doomed struggle with Sinclair's electric parts produced conciliatory letters from readers and a message from an M. Persky of Sinclair Radionics, Inc., in New York. M. Persky admitted that "in the initial run of kits of which unfortunately, yours was one, there were some wrinkles."

M. Persky said that anyone who complained would get a new kit and, if I cared to send the pieces, they'd send me an improved Black Watch that gave the date as well as time. I wrote back that I no longer had my Black Watch kit parts — the only pleasure I got from the entire investment and experience was throwing it away.

This prompted a second letter from M. Persky with the information that M.P.'s 12-year-old daughter had successfully built a Black Watch kit. There are any number of comments I could make here, but instead I will bite my tongue and continue with this month's column which is devoted to a number of new toys.

•First, a progress report on the newest toy of all—the tv record. Philips, MCA, and Zenith have agreed on standards for the Philips-MCA tv record. This doesn't mean the units are any closer to production, but it gives an idea of what they'll be like if they ever hit the market. There will be both flexible and rigid records in two sizes — one slightly larger in diameter than the present audio single will hold 13 minutes of tv, the other the same size as the present audio album will hold 30 minutes of tv. These records will rotate at 1800 revolutions per minute (as opposed to 33.3, and 45 rpm) and are designed with stereo sound capabilities. RCA is also at work on its tv records, which will be significantly different from the above designs.

•Solid State Sales (P.O. Box 74, Somerville, Mass. 02143) is the first supplier to offer a solid state tv camera. For $225 they provide most of the parts in kit form to build the guts of a tv camera that has no tube — an integrated circuit reads the picture. This is the first step in a technology that will eventually produce Dick Tracy wristwatch tv's. . ,

•Those who want their own disco should check out Uher's new Mix 500, model A124 stereo mixing console. For $186 you can get a five-channel mono mixer switchable to a two-channel stereo mixer with an additional mono channel.

•Tubes are making a comeback in audio, despite the fact that audio technology abandoned tubes for transistors and, more recently, transistors for integrated circuits. Some audio people still feel the sound produced by tube amplifiers is warpier and more "real" than sound produced by transistors or integrated circuits. Tubes use more electricity, start to degrade as soon as they're plugged in, and have other drawbacks, but they do have "character" which the Japanese have been unable to duplicate with solidstate devices. Among the new generation of tube amplifier manufacturers is Lux Audio of America (200 Aerial Way, Syosset, NY 11791).

•Audio cassettes are more compact than albums, but not as easy to store. Esselte AB of Sweden designed a plastic attache-style cassette carrying case for $19.95 that holds 32 cassettes conveniently and compactly.

•Several readers have written asking where they can obtain Sinclair's power amp, preamp, FM stereo tuner, and quad kits. They're available in this country from Technology Trends, P.O. Box 732, Manhasset, New York, 11030.

•If it isn't in your local drug store yet, you can get the new Casio Biolator (a pocket calculator that also figures your biorhythms) at $29.95 from JS&A National Sales Group, 4200 Dundee Road, Northbrook, Illinois, 60062.

•Sony has introduced the second version of their Betamax — a $1,300 video cassette recorder-player that connects to your tv. You won't find it in any but the major cities. It is the first home video cassette system; if Sony sticks behind it, it should become the video cassette standard ala Philips audio cassettes. From reports I've had from owners — there are still problems...the tape's time base stability is such that the picture may not be all that great on older tv sets with poor capture ratios. Sony says all tv's can be modified to give a stable Betamax picture. I've yet to hear from anybody who's using it with a video projector, it may not be stable enough for that. But with Betamax cassettes as low as $13.85 an hour, Betamax is far and away the smartest video system for anyone who wants to tape off tv.

•One last time: Electronic Projects For Musicians by Craig Anderton is an interesting introduction to all those boxes that boost, distort, and bend the sound from electric guitars. 132 pages of do-it-yourself for $6.95 including a demonstration record and an introduction by Joe Walsh. From Guitar Player Productions, P.O. Box615, Saratoga, California, 95070.