I just scored two slieves of 5 Raytheon sub mini pentodes , all JAN mill spec, astonishingly good quality .
A few euro's each ,and probably a lot cheaper by the 100 .
Its barely 10mm in diameter with 7 wire ended leads, and only about 25mm in lenght .
Various different current ratings are available to cover any need , I chose a 6.3 volt heater version ,that does about 7ma anode current with a gain of 70 in triode mode . These tiny tubes have great rigidity so microphonics is low compared to larger older styles. I have read that heat dissapation needs to be accounted for preferably direct contact to the valve glass especially in the higher powered ones . Heater cathode voltage as well as maximum anode voltage varies quite a lot from type to type as well .
Looks like they will make a very nice low level input stage either as cathode follower or anode loaded . I was thinking of a built in tube recovery module for a regular spring reverb tank , cathode follower input with MOhms of input resistance , I might try driving the springs from both ends in antiphase ,then in the join between the two pairs of springs on the longer tanks attaching a tiny rare earth magnets which will excite a two pole cut down guitar pickup positioned underneath , maybe seperate recovery coils for each spring could allow more flexibillity . I can wind my pickup coils with very much higher turns cause the spring itself doesnt have to support it , the lams and coil on the end previously used for recovery could be rewound easily to function from the usual 4 or 8 ohm speaker output transformer on a fender champ type output stage , a small multicore and cheap n cheerfull mini aviation plug will connect the pan to the driver amp , I have a pair of C core output single ended transformers off ebay en route , 3500:8:4 ohms , the driver amp can double as either a headphone or monitor speaker amp when required .
It might also be possible to combine both drive and output stage at the same time ,of course that kind of reverb is potentially unstable but Ive found when the tank drive is trimmed with with a wirewound pot, or maybe lightbulb limiter it works nicely and a 4 or 8 ohm tap gives tons of line level signal to your mixer or recorder .Simple switched coupling cap could allow the bass weight to be dialed or out of the sound and passive top cut could be added to the signal somewhere .
I know the pros will scoff at a reverb machine thats on the verge of oscillation ,feed forward or feedback or a combination of both I cant fully understand exactly , trying to borrow some of the ideas in the Akg springs . Seeing as Im doing it might as well do a stereo set , maybe even with some kind of matrixed/patched drive to multiple tanks .A mid/side drive/recovery arrangement of the tanks seems plausible in my head but but Im not smart enough to be able to visualise it .
Nice and simple also,just two tubes .Ill scribble out a schematic/ layout drawing later just to make things more clear .
A few euro's each ,and probably a lot cheaper by the 100 .
Its barely 10mm in diameter with 7 wire ended leads, and only about 25mm in lenght .
Various different current ratings are available to cover any need , I chose a 6.3 volt heater version ,that does about 7ma anode current with a gain of 70 in triode mode . These tiny tubes have great rigidity so microphonics is low compared to larger older styles. I have read that heat dissapation needs to be accounted for preferably direct contact to the valve glass especially in the higher powered ones . Heater cathode voltage as well as maximum anode voltage varies quite a lot from type to type as well .
Looks like they will make a very nice low level input stage either as cathode follower or anode loaded . I was thinking of a built in tube recovery module for a regular spring reverb tank , cathode follower input with MOhms of input resistance , I might try driving the springs from both ends in antiphase ,then in the join between the two pairs of springs on the longer tanks attaching a tiny rare earth magnets which will excite a two pole cut down guitar pickup positioned underneath , maybe seperate recovery coils for each spring could allow more flexibillity . I can wind my pickup coils with very much higher turns cause the spring itself doesnt have to support it , the lams and coil on the end previously used for recovery could be rewound easily to function from the usual 4 or 8 ohm speaker output transformer on a fender champ type output stage , a small multicore and cheap n cheerfull mini aviation plug will connect the pan to the driver amp , I have a pair of C core output single ended transformers off ebay en route , 3500:8:4 ohms , the driver amp can double as either a headphone or monitor speaker amp when required .
It might also be possible to combine both drive and output stage at the same time ,of course that kind of reverb is potentially unstable but Ive found when the tank drive is trimmed with with a wirewound pot, or maybe lightbulb limiter it works nicely and a 4 or 8 ohm tap gives tons of line level signal to your mixer or recorder .Simple switched coupling cap could allow the bass weight to be dialed or out of the sound and passive top cut could be added to the signal somewhere .
I know the pros will scoff at a reverb machine thats on the verge of oscillation ,feed forward or feedback or a combination of both I cant fully understand exactly , trying to borrow some of the ideas in the Akg springs . Seeing as Im doing it might as well do a stereo set , maybe even with some kind of matrixed/patched drive to multiple tanks .A mid/side drive/recovery arrangement of the tanks seems plausible in my head but but Im not smart enough to be able to visualise it .
Nice and simple also,just two tubes .Ill scribble out a schematic/ layout drawing later just to make things more clear .
