Quote:
Originally Posted by old_coot88
I had a Majestic TRF that used four '26's, three for RFs and one 1st audio. Didn't know till now that the tube had only a one year run.
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Yeah I think the short run of the 26 was pretty amazing. Tube development was running pretty fast in the late twenties and early thirties. By 1934-35 most of the development which would last decades until the end of the vacuum tube had completed. There were minor updates like octal bases on 1935, the glass button base 7 pin tube and 1947 the 9 pin. But the miniature tubes simply replicated the larger ones in a smaller size.
The 26 I believe was introduced because of manufacturing problems with the early UY227 or 27. The earliest 27's used a twin bored ceramic core to allow the filament heater wires. The ceramic was fit into the cathode sleeve. The earliest UY227 was a notoriously slow warming tube which took a couple of minutes. I suppose in your Majestic where a 27 I believe was needed for the detector the slow warm up was less obvious. (The 26 could not be used for the detector because of the AC filament hum problem).
I have an RCA Radiola 62 from 1928 with a row of seven 27's a UX-171A output and UX280 rectifier. The 27's I believe are all original. I have tested the emission and transconductance of the Radiola 62 UY-227's on my AVO Mark III tester and when warm they are still fine after 97 years. But it is hilarious how long it takes after switching the Radiola 62 on before it makes any sound.
The early 24's (UY-224) have the same slow warm up. The UY224A came out I think around mid 1929 and the A denotes a new heater cathode assembly using a ceramic paint on the helix wound filament wire in the cathode sleeve. It warms in about 40 to 50 seconds which was a considerable improvement.
From 1929 through 1933, the improvements were phenomenal and by 1934 the standard warm up of about 30 to 40 seconds had been achieved.