older tubes question

[mtx11]

i got 2 old rca victor radios. one has one of each of these tubes 3v4 , 1u5 , 1u4 , 1r5 .

the other has 6f6 , 6h6, 6k7 , 6a8 , 5z4 , 6f5 .

i saw that the 6f6 is like a lower power 6v6, and the 5z4 is like a 5u4 recitfer tube.

can i make and amp using any of these tubes. there black metal tubes. if i can use them are there some link you can point me to for ideas.

[Rob Mercure]

If you're limiting yourself to these tubes crafting the amp will be tricky but it can be done. You've already identified an output pentode and the rectifier - the 6F5 is like one side of a 12AX7 and the 6K7 is a signal pentode that would work. The 6H6 dual diode detector is generallly useless (but "cute" as it's about the smallest octal tube commonly produced) while the 6A8 pentagrid converter could be wired as a pentode I guess.

The other set of tubes is for a battery radio - all of these have directly heated cathodes. For "kicks" I made a "Herzog" style distortion box (think Randy Bachman of the Guess Who) using a 3V4 output tube. If you've got the radios you've already got output transformers that match. But if the radios are in good shape they may be worth more sold as is and using the money to buy a kit from Bruce or other vendors. While there isn't much market for the low voltage battery tubes I suspect that someday these will become more valuable for restoration work.

As far as ideas for these tubes search the web for a RCA Receiving Tube Manual from around 1946-50 and copy the audio circuits from the radio examples in the back (biasing the battery tubes can be a bit tricky). Right off the top of my head I'm not sure what number manual you need - perhaps #10 or so.

Rob