Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ponchojack on September 15, 2013, 06:14:04 pm
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Thought some of you designing low powered amps on old tubes might find this interesting. RCA publishing in 1959 some interesting circuit designs based on their then current tube offerings. Many devices at that time did not use PTs and used the line voltage to directly drive the tubes, and then serialized the filaments. You say how? Well how about a 50v filament? The 50EH5 was popular in "record players" and radios. Here is a link to my dropbox file (pdf) of the manual: https://dl.dropboxusercontent.com/u/85352883/Rca_hifiTubeAmpCircuits.pdf
You might say that no PT is too dangerous. What got me thinking back on these circuits was some serendipity; My wife's hair dryer crapped out. IT uses a 120V wall wart pigtail that has a built in ground fault for bathroom use. Seems like this may just cover the safety issue (sort of). Take a look at the "low cost HiFi Amplifier". Looking at the 12AX7 input stages this could get tonally interesting especially with some diodes and cap changes in the power section.
I'll have to do some savaging to try this thing out.
Poncho