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Topics - Bajaguy

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Tubes and Hybrids / Another cool but dangerous antique
« on: July 30, 2013, 05:27:05 PM »
Last night I went to a local swap meet and poked around for a couple of hours. I ran across a guy that had a couple of old guitars on his table, and after talking to him for a bit was given this old tube amp. Yea, it's one of the old line voltage man killers everyone talks about (series chained heaters, hot chassis, no transformers of any kind, etc.). I tried looking it up and found no reference to it at all on the web. It's in poor shape, more than likely not worth anything, and free (still my favorite part of any amp project :tu:)

 The two drivers are 50EH5 and for some reason somebody stuck an EL84 in where the preamp goes.... The good thing is all of the tubes tested good :dbtu:

 I'm still trying to decide what I want to do with it, mabey a hybrid with a couple of 12ax7's and a nice 15 to 20 watts of chipamp goodness......

 Just thought you'd enjoy the pictures!


I've been out on the road for the past couple of months, and this last weekend I ran into a guy that gave me a really nice looking Behringer bass amp that needed repair. I ended up in a hotel with WiFi for a few days, and thought I'd try to find some information on this amp. I have looked for the last couple of days for a schematic, but it's proving to be a tough on to find. I'm on the road, but I have the trusty old fluke multimeter and a bit of time so I thought I'd take a crack at this.

 I got her opened up and found that it's powered by a LM3886T. I pulled the input from the power Trans off and checked it. It shows as a 28-0-28, and measures at 31-0-31VAC. There's no discernible burn marks or broken components on any of the boards, but when you fire the amp up it sends a medium volume 60Hz tone through the speaker. There's a couple of sets of wires that run from the amplifier/power supply board to the preamp boards, but not having a schematic is a bit tough on figuring this out.

 Any chance someone has a schematic for this board or can give me a clue where to look next? I verified that the rectifier diodes are good, and none of the big caps are shorted, but I'm kind of lost from there.


Preamps and Effects / Switch pop blues
« on: May 24, 2013, 12:25:22 PM »
I've been screwing around with a few different preamp ideas over the last couple of months, and I decided to build a dedicated "test mule" tda2003 amplifier board to try out the different bread board circuits on. I bought a amp kit through one of the online places, and it works fantastic. I'm very pleased with the sound of the amp, but I've had other problems that are sending me into mental overdrive :duh

 One of the problems that I have been unsucessuful in fixing is a switch pop issue. I have a protoboard that has a modified MXR distortion plus and a mosfet clean boost on it. I've played it as a pedal, and it works great in front of everything I've plugged it into so far. I got this idea fron one of Juan's posts and tried to add it in as the preamp for this little amp, and the switch pop is driving me nuts. I originally designed the circuit to use 2 different 3PDT switched to turn each effect on and off separately, so when I decided to add it on to the front of my test mule (I call it Pepe), I used a couple of 9V relays I got from one of the online places to do the switching so I could use mini toggles or a foot switch to switch the effects on and off. The footswitch works great (and is quiet), and the switches work, but create a nice fat pop every stinking time. I added a 1uf cap across the relay coils and a diode to keep from blowing it up, but I'm still getting that pop from the front panel switches.

 I'm kind of lost here, but I figured I'd throw it out and see if the amplifier gods had another tidbit of info that might keep me from pulling my hair out :grr

 Thanks ahead for any help,


The Newcomer's Forum / A great find today
« on: May 09, 2013, 09:25:17 PM »
I was on my way home this evening and spied a head unit sitting on a table at a garage sale. I pulled in and looked at it, and when the gal told me it worked and the price was $35, it followed me home :tu:

 It's a Harmony 535 (tube), and is a loud 35 watts. The only thing I can say about it is it's way to clean, no crunch at all. Anyone know what forum might be the best to ask a few questions about hotrodding it a bit? I don't want to litter the SS forum up with a bunch of tube talk, but I trust the opinions on here and thought the question was worth asking.



The Newcomer's Forum / New Guy with an interesting design idea
« on: April 08, 2013, 04:22:42 PM »
Howdy! I'm new here, and found the forum while researching an idea for a bigger portable amp. I have been an electronics tech for a grass roots company for the last 14 years, and I've been fixing pedals and amplifiers for a few of my musicain friends for what seems like forever...

 There's a group of guys that I've hung out with for years that have been bitten by the cigar box guitar bug. They have built several 2, 3, and 4 string CBG's that sound awesome! They commonly play in the smoking area at work, which doesn't have access to power. Several have bought small 9V powered mini amps, but most of them have horrible tone and very small output. I built a couple of Noisy Crickets that were converted to cigar box amps, but the tone of those amps is horrible and not what anyone considers usefull. I built a MKII with the bridged LM386 chips and it was a flop with the group as well.

 My goal has been to design and build a small portable amp that's battery powered and has clean headroom with enough volume that they can play for at least an hour without recharge. I'd like to add in a SLA battery with a charging circuit that would allow the amp to be played off of the charging circuit without loss from the battery, yet keep the battery charged and ready for any excursion. The ability to charge the battery from a cigarette lighter in a car would also be very usefull.

The enclosure would be similar to a 10" x 10" x 5" cigar box built from 1/4" western red cedar, and I'd like to have the option of using 5", 6", or 8" speakers.

 I've been paging through the portable amplifiers that grace the pages here, and I'm sure there's a chip amp that will be perfect for this, but I'd like to get a few opinions on what would be the better route for this set up. I have a umble preamp that I built as a pedal that I'd like to use for the preamp section on this, but it's not a design requirement.

 Anyways, nice to meet everyone, and I'm interested in any ideas that may come up.



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