This page will describe a vacuum tube guitar amplifier which I call the 1930-10. 1930 stands for the year in which all of the parts including tubes could have been salvaged by junking almost any radio of the 1929/1930 era. The -10 stands for the expected power output.
The cabinet was built by a local contractor out of MDF and is very heavy. An Eminence 820H speaker has been installed. the chassis is still in work. The tube lineup will be: 24A preamp, 27 second preamp interstage transformer driver, PP 45s output, and a 80 rectifier.
You might find the following interesting: I made a suggestion to the editor of “The Tube Collector” magazine that an article on the cathode to heater leakage problems of early indirectly heated cathode tubes might be interesting. No article was published, but I received an Email from the editor Luddwell Sibley. His Email was almost an article in itself.
There were some ills in early versions of the 199 and 24.
The 199 suffered from performance problems to some degree, to the point that DeForest, ca. 1931, introduced a 499 with oxide-coated filament in place of thoriated tungsten. They loudly proclaimed better operation – their advertising said so. Of course, by then, the market was purely for replacement tubes.
On the 24, there was a small scandal when the 24A came out. It did not give secondary emission from the plate to the same degree. As a result, “dynatron’ receiver oscillators that depended on the secondary effect would not work.
Thee was some rumbling between Arctirus and RCA, and maybe others, about the warmup time of 24s and 27s. One of them had started out with a heater insulated by a ceramic rod that had two lengthwise holes. The heater was threaded up and back through the holes. Then the rod was inserted into the cathode tubing. The resulting assembly had high thermal inertia, i. e., took a long time to heat up. In a radio that also used 26s, 45s, and an 80 this was annoying. I think Arcturus went to a more successful scheme where they simply coated the heater wire with ceramic particles and folded it into the cathode tubing. I think they claimed 7-second warmup, vs. 15 or more seconds otherwise. There may have been boasts of lower leakage as well. I’ll have to dig out the Arcturus promo handouts.
I don’t think your guitar amp is exposed to problems. Quick warmup is pleasing but not critical. The secondary-emission problem in the 24 won’ t bother you. I think the preamp stage is likely to be reasonably quiet. (The Gates Radio Company, in the early ‘30s, made broadcast audio gear with 24As in preamps, and thereby kicked the filament supply batteries out of radio stations.)
Circuit details and a schematic will be posted here when the amp is complete and tested.
Long Rope Ranch 