Chronicling my journey into low power and open baffle
- Thread starter MKG
- Start date
MKG
Elvish-mark’d abortive, rooting hog
Good and bad news.
Finished rebuilding the little tube amp (internals- recap and addition of fuse and direct wired power, replacement of a resistor).
Plugged it in after attaching dummy loads, no shorts, no sparks. Hooked up sine wave generator and o-scope to measure output, noticed funky waveform rather than clipping. Turned the sine wave output down until it looked clean, calculations ended with 1.23w- wtf? Not right. Took a closer look, realized that one el84 tube wasn’t glowing. It was warm, so heater was obviously working.
Swapped left and right output tubes to see if it was a wiring/channel issue- it’s not, it’s the tube.
Swapped it back again and turned on for a brief minute and the one that wasn’t glowing started arcing internally and turning purple.
Really pretty light show, kinda like a Tesla coil in a bottle.
I’ve never seen or experienced a tube red plating, please see photo below and tell me if that’s what it’s doing.
My assumption is that the tube is bad- they were of unknown origin, untested, and tossed in with one of my random purchases (probably with this amp).
Anyhow, looks like I need to order a new pair of el84’s.
Betsys arrived today, more on those later.
Finished rebuilding the little tube amp (internals- recap and addition of fuse and direct wired power, replacement of a resistor).
Plugged it in after attaching dummy loads, no shorts, no sparks. Hooked up sine wave generator and o-scope to measure output, noticed funky waveform rather than clipping. Turned the sine wave output down until it looked clean, calculations ended with 1.23w- wtf? Not right. Took a closer look, realized that one el84 tube wasn’t glowing. It was warm, so heater was obviously working.
Swapped left and right output tubes to see if it was a wiring/channel issue- it’s not, it’s the tube.
Swapped it back again and turned on for a brief minute and the one that wasn’t glowing started arcing internally and turning purple.
Really pretty light show, kinda like a Tesla coil in a bottle.
I’ve never seen or experienced a tube red plating, please see photo below and tell me if that’s what it’s doing.
My assumption is that the tube is bad- they were of unknown origin, untested, and tossed in with one of my random purchases (probably with this amp).
Anyhow, looks like I need to order a new pair of el84’s.
Betsys arrived today, more on those later.
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MKG
Elvish-mark’d abortive, rooting hog
As said previously, Betsy drivers arrived, yay!
Unfortunately I didn’t make it out to go buy wood before covid-19 hit our community.
Both myself and my significant other are *high* risk- not because of age, but because I have serious lung issues (asthma & multiple bouts with pneumonia- lungs are too scarred to make it through another round, and my significant other is immunocompromised) so we’re essentially on lock down except for necessities that we can’t buy online.
But I’d really like to hear these things. Won’t be through the little amp I’m rebuilding’cause I’ve got to wait on a pair of el84’s to arrive, but I’d like to hear it through my working tube amp in the meantime.
As far as wood goes, I’ve got an old used air tray that measures 32” x 87” (see pic, it’s the wooden thing behind the smoker and air compressor. If you need to ship a casketed decedent via airline, the casket goes on this base and then a cardboard box minus one side goes on top- decedent never touches the wood, unlike with a combo unit where the decedent is strapped to the wood with a layer of plastic underneath and then covered in cardboard).
I’ve also got two 2’ x 4’ pieces of mdf, and two 4’ x 3.5’ pieces of particle board.
I’m tempted to cut a circle on each mdf piece to try them out- I could then make wings with plywood from the air tray if needed.
I don’t know if mixing materials in an open baffle build will have any effect on sound- but given that you can make open baffles out of cardboard (wish I hadn’t recycled all of our cardboard last month), I’m guessing it won’t have much if any of an effect.
Unfortunately I didn’t make it out to go buy wood before covid-19 hit our community.
Both myself and my significant other are *high* risk- not because of age, but because I have serious lung issues (asthma & multiple bouts with pneumonia- lungs are too scarred to make it through another round, and my significant other is immunocompromised) so we’re essentially on lock down except for necessities that we can’t buy online.
But I’d really like to hear these things. Won’t be through the little amp I’m rebuilding’cause I’ve got to wait on a pair of el84’s to arrive, but I’d like to hear it through my working tube amp in the meantime.
As far as wood goes, I’ve got an old used air tray that measures 32” x 87” (see pic, it’s the wooden thing behind the smoker and air compressor. If you need to ship a casketed decedent via airline, the casket goes on this base and then a cardboard box minus one side goes on top- decedent never touches the wood, unlike with a combo unit where the decedent is strapped to the wood with a layer of plastic underneath and then covered in cardboard).
I’ve also got two 2’ x 4’ pieces of mdf, and two 4’ x 3.5’ pieces of particle board.
I’m tempted to cut a circle on each mdf piece to try them out- I could then make wings with plywood from the air tray if needed.
I don’t know if mixing materials in an open baffle build will have any effect on sound- but given that you can make open baffles out of cardboard (wish I hadn’t recycled all of our cardboard last month), I’m guessing it won’t have much if any of an effect.
MKG
Elvish-mark’d abortive, rooting hog
After playing with xlbaffle for a bit, I decided **** it- this is an experiment and the baffles I make tonight are not going to be permanent, so I’m just gonna use what I have and have some fun.
So, I drilled holes in the 2’ x 4’ mdf pieces and used screws that were too long- I’ve got hinges and properly sized screws on the way from amazon, so I can cut them down next week and use plywood for temporary wings.
Ignore my shitty uneven weatherstripping, this was a slap together kind of thing. And yes, those are speakers holding down my speakers.
I didn’t want to disassemble my main shop system so I just hooked it up to my test system (a modified Diy Chinese tube preamp and an akitika gt-102 kit amp)
First impressions- it’s not lacking in bass. Bass is clear and present- and while I can’t feel it like I can in my other systems, I was expecting to have to supplement these with a sub.
Mids are excellent. Clear and natural.
Highs are clear but too bright for me- but most are.
All in all, a good start. I’m looking forward to building and tuning proper baffles, trying it with the little tube amp I’ve been working on, and rolling off the highs to match my ears.
I also need to clear out some more room in my shop so that I can separate them more.
So, I drilled holes in the 2’ x 4’ mdf pieces and used screws that were too long- I’ve got hinges and properly sized screws on the way from amazon, so I can cut them down next week and use plywood for temporary wings.
Ignore my shitty uneven weatherstripping, this was a slap together kind of thing. And yes, those are speakers holding down my speakers.
I didn’t want to disassemble my main shop system so I just hooked it up to my test system (a modified Diy Chinese tube preamp and an akitika gt-102 kit amp)
First impressions- it’s not lacking in bass. Bass is clear and present- and while I can’t feel it like I can in my other systems, I was expecting to have to supplement these with a sub.
Mids are excellent. Clear and natural.
Highs are clear but too bright for me- but most are.
All in all, a good start. I’m looking forward to building and tuning proper baffles, trying it with the little tube amp I’ve been working on, and rolling off the highs to match my ears.
I also need to clear out some more room in my shop so that I can separate them more.
Poultrygeist
Lunatic Member
great start!
Poultrygeist
Lunatic Member
Not much activity on the diy forum. Most of the diy stuff I do most folks could do so it gets lost there. Folks who don't think they can diy don't go there so that's why I like to share projects on regular forums.
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I went down this path a couple of years ago. I bought Betsy drivers and installed them in 'tombstone' style plywood OBs. I liked them but really missed some lower end and ended up aping the Caintuck Tombstone speakers. The Betsy sits up top with Eminence Alpha 15" woofers below. Great, but I ended up with a complicated (for me) amping and wiring arrangement. They sound fantastic, especially when pulled away from the walls. They were inexpensive to make, fun as heck to play around with, and I haven't felt compelled to change them out since I built them. It might be worth checking out the Caintuck site for ideas. He also sells baffles, plate amps and complete speaker units as well. FWIW.
Lavane
Lunatic Member
I saw a set of these drivers in bartertown.Definitely worth following along. Thanks for the tip on the Betsy drivers!
Lavane
Lunatic Member
I haven't messed with OB's much yet, but I do find myself building and liking lower powered single ended or PP amplifiers. The simpler the the design, the better. 6 months or so ago I built a simple single ended pentode amp that uses very few parts and a single 6LR8 TV sweep tube per channel. They have a single triode and a pentode in one bottle. So far it's one of my favorites. Nice clear highs without being harsh, great midrange and surprisingly great bass. All from a tube never meant to be used as an audio tube. Freq. response is only 40hz-18khz, but man it sounds good! If it wasn't for the fancy chassis the cost would have been just shy of $200.
5.5wpc of tube goodness.
5.5wpc of tube goodness.
Lavane
Lunatic Member
They aren't cheap due to shipping unfortunately. But they are nice. They come in a flat pack, a bag of screws and rubber o-ring feet. Nice thick aluminum and easy to drill and punch. With shipping from China it came close to $100. Even with the chassis being 1/2 off. I just wish I had bought one more of the remaining blank PCB's to build another using one of the 3 other different tube types that can be used. I bought a total of 4 tubes I found at $5 each. It's cheap to retube too!
Poultrygeist
Lunatic Member
Are you guys familiar with the Spud amp? I've wanted one for years but can't justify another amp.
https://spudkit.com
https://spudkit.com
I'm moving away from tubes and into well-priced and objectively-tested audio of late. My goal is to reduce the hobby to a simple value and functionality exercise. However, I own a couple of ChiFi amps, a Gemtune X-1 and a Miniwatt, that have served me very well. The Miniwatt was a purchase from MassDrop (now just Drop) a year or two ago for only $99. I have no doubt they wouldn't test particularly well, but they sure look great and I'm happy to have them on hand, and happy they didn't cost much.
The Spud kit looks great and would help with building skills development. I'd struggle with the almost $400 it costs though.
The Spud kit looks great and would help with building skills development. I'd struggle with the almost $400 it costs though.
Lavane
Lunatic Member
The term Spud came about from the squat, fat Compactron tubes. 9 to 13 pins. Many like the one I built, use the 9 to 10 pin Novar and Mag Novar tubes.
Spud Amps are fun to build and usually cheaper due to fewer parts and cheaper TV tubes. Compactrons have 4 or more sections. So you can have the driver and output in one tube. Pete Millett sells a blank PCB for a 20wpc PP spud amp.
MKG
Elvish-mark’d abortive, rooting hog
If you don’t mind me asking:
Was this circuit your own design or that of another?
If it’s your own design, are you willing to share the schematics & bom?
If it’s someone else’s design, do you have a link to any other info about it, such as schematics and bom?
how much did the iron cost you?
Thanks!
Poultrygeist
Lunatic Member
This kit uses the single ended pentode 6CL6/6197 and good for 2 or 3 watts.
Lavane
Lunatic Member
Depending on the tube used the amp I built can put out 1.4wpc to 5.5wpc.
Also can be wired to run triode strapped, pentode or UL. I went UL with the 6LR8's for the huge output of 5.5wpc.
I really wish I had bought a other board before they were all gone. One tube is just like the 6LR8, but with an anode cap.