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Author Topic: Raytheon JAN6418 sub-miniature pentodes  (Read 12163 times)

dogbox

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Raytheon JAN6418 sub-miniature pentodes
« on: February 09, 2010, 06:45:22 AM »
Hey there,
I'm new to the forum and Electronics/DIY, but fast becoming addicted. This forum looks like an excellent resource - so much info. Thus far (since Xmas) I have successfully put together a couple of electronics store beginner kits - .5 watt "champ" amplifier (based on Lm386 chip), FM radio tuner, a couple of general guitar gadgets stomp pedals. My latest "conquest" ;) was this little beauty from Oatley electronics here in Australia - http://secure.oatleyelectronics.com/files/K270notes.pdf which is based around a pair of Raytheon JAN6418 sub-miniaturepentodes - hmm forgot I even ordered it  - a pleasant "Beerloom" from ebay.

Last night I finished it and attached a couple of phonojacks and tried it out with the little .5 watt amp then into an 8" speaker that lives in an epiphone valve junior that has a phono jack attached (EVJ was not turned on) - sound was just distorted mush. Then I tried it through the EVJ powered up and the thing really roared!! There was massive gain boost, and some nice distortion at low levels. A bit noisy as it isn't cased yet and has aligator clips hanging everywhere and the EVJ isn't super quiet itself. But I really like the sounds I was getting:)

I would like to make myself an amp using this tube preamp and matched to a simple IC based amplifier. The documentation for the preamp states...
 "The gain of this preamplifier is adjustable from 0 to 100 times, the output voltage can be up to 5V P-P (1.8V RMS) with a fresh 9V battery, and the widest frequency response extends from 20Hz to 30kHz."

Can anyone suggest an IC amp project that would be suitable-please refer to the specs in the link above for more details-theres a schematic. I'm keen to start making my own circuit boards. Gen Guitar gadgets has some info and a pcb for a Craig Anderton LM383 amp-would this be a good starting point http://www.generalguitargadgets.com/pdf/ggg_ca_practice_amp.pdf ?? Any suggestions or assistance with this greatly appreciated.

Given that I can't really design or barely read a schematic at this stage (but not for lack of trying), I'm especially keen to find out how to power this amp. At the very least I'm thinking I could figure out how to install the tube pre in a stompbox case but I would love to have it all in the one case. I have an old small behringer bass amp case to house it all.
Any suggestions or assistance with this greatly appreciated.
cheers

mnturner

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Re: Raytheon JAN6418 sub-miniature pentodes
« Reply #1 on: April 18, 2010, 09:32:01 AM »
hey dogbox,
 I just found out about those little valves, I'm pretty interested in getting some to put into a preamp.
How much power do you plan on getting out of the IC amp? LM386's can only really dissipate about 1 watt, which isn't much. And the THD quoted on the datasheet is 0.2% at 125mW, which is fairly high compared to other IC amps. I think you should check out the LM3886, it can produce much more power and has better distortion figures and is pretty much as simple to use as the LM386. That way if you decide you want more power you don't need to build a whole new amp. The only problem you might have is the power supply, the 3886 needs a much higher voltage than the 386; the best way to do it is to run it off AC which is a bit more complicated than using batteries. The 386 isn't a bad option if you only want a tiny practice amp though.

dogbox

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Re: Raytheon JAN6418 sub-miniature pentodes
« Reply #2 on: May 06, 2010, 12:19:22 PM »
hey dogbox,
 I just found out about those little valves, I'm pretty interested in getting some to put into a preamp.
How much power do you plan on getting out of the IC amp? LM386's can only really dissipate about 1 watt, which isn't much. And the THD quoted on the datasheet is 0.2% at 125mW, which is fairly high compared to other IC amps. I think you should check out the LM3886, it can produce much more power and has better distortion figures and is pretty much as simple to use as the LM386. That way if you decide you want more power you don't need to build a whole new amp. The only problem you might have is the power supply, the 3886 needs a much higher voltage than the 386; the best way to do it is to run it off AC which is a bit more complicated than using batteries. The 386 isn't a bad option if you only want a tiny practice amp though.
Hi mnturner,
Yeah that jan6418 tube preamp works well-but a bit delicate. Theres a trimpot and 2 sets of dip switches on kit that I built so can equalise and adjust the output to suit whichever amp I use. The only down-side is that the tubes are really microphonic and tend to ring if bumped in any way while being played. can end up with a high pitched squealling feedback real easy - have tried damping with rubber grommets - not made much difference. Its fine for home recording use (if your real carefull) but definitely not good for stage use as any vibrations seem to set off the ringing!! I need to use some kind of padding inside the case and really lock the mini tubes down somehow - thinking about dipping them in liquid silicone rubber?? Unlike normal tubes - these give off no heat or light that I can discern - so maybe thats feasible.

Yes i now have a lm3886 kit from chipamp.com and looking forward to building that one real soon. Have been distracted with playing around with jfet preamps, piezo disk contact mics, ruby and noisy cricket amps, effects and more effects. The penny is dropping and I now can understand schematics and breadboard up small projects. Awsome fun.

Good luck with the mini tubes.
cheers