dinu said:Proud to display my work.
The chassis is a cigar box tarted up a bit with a couple coats of varnish. I went really cheapo on this project so the power transformer is a 270EX. I guess I should have known it's a bit underpowered.
Trying to drive my Joseph audio RM25si speakers is almost futile. they have an 88dB sensitivity and I suspect that may be overstated.
A link for the curious:
http://www.josephaudio.com/specs.rm25simk2.html
I'm buiding a pair of Buschhorns this weekend with a nice little 4.5" driver from MTM. They should sound alot better. I tried listening to the amp on my headphones and, if I could get that sound out of a pair of speakers, I would be very happy.
Finally and certainly not least, a heartfelt thank you to JSN. Yours was the most informative, newbie friendly, and encouraging article I have found on the topic. Being a big fan of Nelson Pass, I would suggest that your article is the vacuum tube equivalent of Nelson's Zen article.
http://i125.photobucket.com/albums/p70/dinui/IMG_2352.jpg
http://i125.photobucket.com/albums/p70/dinui/IMG_2339.jpg
dinu.... that is beautiful. great "thinking out side the box" with the cigar box chassis.
I'm seriously considering putting this amp together. I'm also seriously considering picking up a pair of Monitor Audio Silver RS6 speakers speakers. MA recommends 40-120 watts to power these speakers (they're rated 90dB). Would the boozehound put out enough power to make these sing?
Thanks man. About those speakers, I seriously doubt you'll get any output you'll be happy with. This is a seriously low power amp. My Joseph Audios are 88-89 dB and the sound is awful. This little amp is almost all the way up and the listening level is nowhere near where I'd like. I won't even mention the distortion. It's not the amp's fault though. That's why I'm building the Buschorns.
PS
I got a very nice pair of 6V6G's from Leeds Radio. They're old but Mint and they have that beautiful bottle shape.
In my construction, I got very different voltages on the back side of that dropper resistor. 5K was only dropping the supply to the 6SN7 to about 220V so I ended up increasing the resistor value until I got it right. 30KR did the trick and the front end supply is now at about 180V. The sound is very wooly though, even in a pair of Shure E2c headphones. I'm now wondering if the voltage on the front end is too low. Other designs I've seen using the 6SN7 use a higher plate voltage usually about 220v which is what I originally had. Anyone have any advice on this?
PS
I got a very nice pair of 6V6G's from Leeds Radio. They're old but Mint and they have that beautiful bottle shape.
In my construction, I got very different voltages on the back side of that dropper resistor. 5K was only dropping the supply to the 6SN7 to about 220V so I ended up increasing the resistor value until I got it right. 30KR did the trick and the front end supply is now at about 180V. The sound is very wooly though, even in a pair of Shure E2c headphones. I'm now wondering if the voltage on the front end is too low. Other designs I've seen using the 6SN7 use a higher plate voltage usually about 220v which is what I originally had. Anyone have any advice on this?
I could only guess
So here goes
6R is the nominal impedence. Using the 4R tap would load the transformer/tube more than the 8R tap but both would work. Some speakers exhibit a very wide impedence range depending on frequency. Again, A guess. This is my first amp with an output transformer.
BTW Can you tell me where I can check out the transformers you're considering? I may upgrade (eventually)
So here goes
6R is the nominal impedence. Using the 4R tap would load the transformer/tube more than the 8R tap but both would work. Some speakers exhibit a very wide impedence range depending on frequency. Again, A guess. This is my first amp with an output transformer.
BTW Can you tell me where I can check out the transformers you're considering? I may upgrade (eventually)
I wouldn't blow something up in the amp using the 8ohm tap with the 6ohm speakers? (this assumption is from my brother, who's knowledge base I question). Would it drive the 6v6's to distortion?
Magnequest Robin Hoods ... I think JSN recommended these at some point. That's how I heard about them.
Magnequest Robin Hoods ... I think JSN recommended these at some point. That's how I heard about them.
You're definately not blowing up anything. The worst that happens is you overdrive the output tubes and the tranny gets too hot. Using the 8R tap is the safer bet anyway. Check out the speaker and see if they published an impedence curve. You may find that these, like some other speakers, have a minimum impedence as low as 2R or even less at some frequencies. If the signal was such that that particular frequency was played continuously for a long period, your amp would be driving a 2R load. But when does that ever happen unless you're listening to those time stretched recordings of classical music elapsed over 24 hours?
Thanks for the link.
Thanks for the link.
Well, it's become clear to me at this point that the severe distortion that I'm experiencing is most likely due to dc saturation. I've found that taking the hard way sometimes can be a valuable learning experience and this time is no exception.
I have found a very interesting article about various methods for connecting a OPT, many of which divert the dc plate bias outside the OPT.
http://members.aol.com/sbench/outstru.html
The one I'm most interested in is the Mosfet CCS example but am unsure how to implement this design for the boozehound amp. Can this circuit be plugged in directly? Do I really need a much higher B+ supply?
I have found a very interesting article about various methods for connecting a OPT, many of which divert the dc plate bias outside the OPT.
http://members.aol.com/sbench/outstru.html
The one I'm most interested in is the Mosfet CCS example but am unsure how to implement this design for the boozehound amp. Can this circuit be plugged in directly? Do I really need a much higher B+ supply?
I don’t think your problem is DC saturation per say. If your transformers came from a SA amp to start with, they are gaped and designed to withstand a DC current. Although it very possible that you are drawing more current then they can handle. Try raising the cathode resistor to 1K to test this. Also the first schematic shows the coupling cap as .022, should be .22.
The output schemes you link are more of a redesign, than a repair of your amp and if you want to play with them I would start fresh. The CCS will require almost doubling your B+. If you have a couple of chokes on hand you could implement the parafeed.
On the other hand you might just need more power. You say you’re building a pair of Buschorns? If you have the drivers, mount them to a pair 2’x2’, or larger bits of cardboard, or the bottoms of a pair of boxes, open at the back and see how that sounds…John
The output schemes you link are more of a redesign, than a repair of your amp and if you want to play with them I would start fresh. The CCS will require almost doubling your B+. If you have a couple of chokes on hand you could implement the parafeed.
On the other hand you might just need more power. You say you’re building a pair of Buschorns? If you have the drivers, mount them to a pair 2’x2’, or larger bits of cardboard, or the bottoms of a pair of boxes, open at the back and see how that sounds…John
john,
here's the transformer i used. It's from Antique Electronic Supply Under Miscellaneous.
P-T31
TRANSFORMER, OUTPUT, 8 WATT, SINGLE ENDED
Specifications
Power: 8 watts
Primary: 5K ohm single-ended
Secondary: 8 ohm
Mounting centers: 2.375", U-bracket
Weight: 0.7 lbs.
very small. I built the buschorns and they sound pretty much the same as my josephs, bad, just a bit louder. This is not a commentary on the speakers though. When plugged into my regular solid state amp, they sound wonderful I'm very happy with them.
You may be right on about just having too little power. My power transformer is a bit under rated tooI'll have to just bring the amp back to the shop this weekend and give it a good once over.
My observation that good SE output transformers are very expensive led me to believe that maybe the cost was mostly due to the fact that they have to carry the dc on the primary. It occurred to me that eliminating the dc from the transformer primary may lead to good performance with much smaller/less expensive transformers.
here's the transformer i used. It's from Antique Electronic Supply Under Miscellaneous.
P-T31
TRANSFORMER, OUTPUT, 8 WATT, SINGLE ENDED
Specifications
Power: 8 watts
Primary: 5K ohm single-ended
Secondary: 8 ohm
Mounting centers: 2.375", U-bracket
Weight: 0.7 lbs.
very small. I built the buschorns and they sound pretty much the same as my josephs, bad, just a bit louder. This is not a commentary on the speakers though. When plugged into my regular solid state amp, they sound wonderful I'm very happy with them.
You may be right on about just having too little power. My power transformer is a bit under rated tooI'll have to just bring the amp back to the shop this weekend and give it a good once over.
My observation that good SE output transformers are very expensive led me to believe that maybe the cost was mostly due to the fact that they have to carry the dc on the primary. It occurred to me that eliminating the dc from the transformer primary may lead to good performance with much smaller/less expensive transformers.
Well, so much for that theory. I don’t have any experience with the P-T31 but I hate to condemn it out of hand.
I have an old 6v6 TV console amp with some pretty dinky output iron . It doesn’t blow me away with it’s thunderous bass, or scintillating highs but all in all, its very nice and will drive my Horn Shoppe horns to a good level. They were inspires by the Buschorns so should be close enough for comparison.
My gut says something else is up. See what you find when you get them on the bench. Recheck the voltages at the plates and cathode (6sn7 too) and maybe consider raising the voltage to the 6sn7. I don’t think 180V shouldn’t work but sometimes making a change like that can fix the problem or help point you to the true source.
Not that my advise has worked so well, so far
but hey it’s free …John
I have an old 6v6 TV console amp with some pretty dinky output iron . It doesn’t blow me away with it’s thunderous bass, or scintillating highs but all in all, its very nice and will drive my Horn Shoppe horns to a good level. They were inspires by the Buschorns so should be close enough for comparison.
My gut says something else is up. See what you find when you get them on the bench. Recheck the voltages at the plates and cathode (6sn7 too) and maybe consider raising the voltage to the 6sn7. I don’t think 180V shouldn’t work but sometimes making a change like that can fix the problem or help point you to the true source.
Not that my advise has worked so well, so far
but hey it’s free …JohnJohn,
Thank you for the input. I always appreciate the help. I'll try and get some answers this weekend and post. At this point, I'm just stabbing in the dark. I had no idea about the coupling cap. That'll have to change. I thought about just forking out cash for a nice pair of OPT's but how disappointed would I be if that turned out not to be the problem?
Dinu
Thank you for the input. I always appreciate the help. I'll try and get some answers this weekend and post. At this point, I'm just stabbing in the dark. I had no idea about the coupling cap. That'll have to change. I thought about just forking out cash for a nice pair of OPT's but how disappointed would I be if that turned out not to be the problem?
Dinu
I'm totally new to electronics in general, and I am thinking about following this guide. I've read it a couple of times now, and I think by following the pictures and matching them up with the schematics, I should be able to get things figured out.
I guess I have three questions for the forum today. One, I figure I should already know the answer to, but I haven't been able to figure it out yet: What's the power this amp outputs? I'm looking online at amps that put out around 500W, and that seems like it might be overkill for my purposes, but I can't seem to figure out just how powerful this amp is.
Two, I'm thinking that I will hate life if I don't put a remote control on this amp, and I'm surprised that nobody seems to do this. What's the deal? Does anybody have any advice to offer for doing this? Also, I think I am going to put two inputs, unless that's considered a terrible idea.
Three, I'm finding that the boozehound instructions are excellent, but I am having trouble figuring out in my mind what all the various pieces are in the actual finished product. Is there any kind soul out there that's willing to mark up the picture with labels? If JSN would be willing to update the site, I think it would make the whole thing much easier to understand.
Thanks in advance for any help that people are willing to give, and sorry for the long post. This looking like a fun project...provided I don't electrocute myself!
I guess I have three questions for the forum today. One, I figure I should already know the answer to, but I haven't been able to figure it out yet: What's the power this amp outputs? I'm looking online at amps that put out around 500W, and that seems like it might be overkill for my purposes, but I can't seem to figure out just how powerful this amp is.
Two, I'm thinking that I will hate life if I don't put a remote control on this amp, and I'm surprised that nobody seems to do this. What's the deal? Does anybody have any advice to offer for doing this? Also, I think I am going to put two inputs, unless that's considered a terrible idea.
Three, I'm finding that the boozehound instructions are excellent, but I am having trouble figuring out in my mind what all the various pieces are in the actual finished product. Is there any kind soul out there that's willing to mark up the picture with labels? If JSN would be willing to update the site, I think it would make the whole thing much easier to understand.
Thanks in advance for any help that people are willing to give, and sorry for the long post. This looking like a fun project...provided I don't electrocute myself!
Hi mlissner,
FWIW some advice from newbie to newbie : read a book, find a friend with electronics knowledge or buy a kit.
I'm serious.
From your post it seems your knowledge is just not good enough about electronics to make this a certain succes (please note the word certain). There are quit a few traps and real life risks (as you state as a joke).
Anyway, if you will persue (and you should) I am willing to point out what goes where. (and there my knowledge ends).
A good technical book to read is "Inside the vacuum tube" by Rider.
Jeroen
BTW :
- the amp will give not even 5W, so what speakers do you have?
- there are remote volume control kits available on the web
- you can add as many inputs as you want as long as you add a selection switch
FWIW some advice from newbie to newbie : read a book, find a friend with electronics knowledge or buy a kit.
I'm serious.
From your post it seems your knowledge is just not good enough about electronics to make this a certain succes (please note the word certain). There are quit a few traps and real life risks (as you state as a joke).
Anyway, if you will persue (and you should) I am willing to point out what goes where. (and there my knowledge ends).
A good technical book to read is "Inside the vacuum tube" by Rider.
Jeroen
BTW :
- the amp will give not even 5W, so what speakers do you have?
- there are remote volume control kits available on the web
- you can add as many inputs as you want as long as you add a selection switch
As a newbie... I'll second that.
A kit is a great way to start. Everything is there for you, there is minimal troubleshooting, and it gives you a point of reference to ask questions from.
I would recommend doing some reading before you go too far. I've found that the learning is a bit difficult (to decipher) at first, but as you acquire more and more knowledge things become a bit easier to understand and you'll have informed questions to ask.
A third note... be careful. There are lethal amounts of electricity in tube amps. I.E.- it can kill you.
keep asking questions.
john.
A kit is a great way to start. Everything is there for you, there is minimal troubleshooting, and it gives you a point of reference to ask questions from.
I would recommend doing some reading before you go too far. I've found that the learning is a bit difficult (to decipher) at first, but as you acquire more and more knowledge things become a bit easier to understand and you'll have informed questions to ask.
A third note... be careful. There are lethal amounts of electricity in tube amps. I.E.- it can kill you.
keep asking questions.
john.
Thanks for the excellent responses. Yeah, I recognize the inherent dangers involved in this project, and I am sure I'll be able to avoid them (the motivation is ample). My figuring is to:
- Keep one hand in pocket when working
- Plug in ONLY when done
- Discharge capacitors after plugging in
- Pay attention!
I've been reading up in several books already about basic electronics, and I think I'm beginning to get it, but I have a bit of a road ahead. I'll look into that book.
I'm asking questions early and often, so I don't think I am ready either, but I think I'll be ready before I begin.
The speakers this is going into are Klipsch, SF-2 floor-standing models. They say they take a max of 100W, so it sounds like they might be a rather poor match but it seems odd to me that such a powerful amp would be so weak relative to the speakers.
- Keep one hand in pocket when working
- Plug in ONLY when done
- Discharge capacitors after plugging in
- Pay attention!
I've been reading up in several books already about basic electronics, and I think I'm beginning to get it, but I have a bit of a road ahead. I'll look into that book.
I'm asking questions early and often, so I don't think I am ready either, but I think I'll be ready before I begin.
The speakers this is going into are Klipsch, SF-2 floor-standing models. They say they take a max of 100W, so it sounds like they might be a rather poor match but it seems odd to me that such a powerful amp would be so weak relative to the speakers.
Yea, build a kit. It’s a great way to get your feet wet. Plus kits are fun, you get all the parts you need, all the holes are in the right place and if you run into trouble, there are people who have ‘been there’ who can help.
For you I would recommend the Bottlehead SEX amp kit. The manual is great, big pictures, and there is an education in every box.
It goes like; Next we build the power supply, it does, this that and the other thing and uses….and so on.
By the time your are done you will have a good and painless grounding in electronic bits and what they are used for. You’ll know a resistor from a capacitor and a film cap from a…. well you get the idea. Plus you end up with a great sounding amp. Do it.
Then build your from scratch amp. We’re not going anywhere…John
For you I would recommend the Bottlehead SEX amp kit. The manual is great, big pictures, and there is an education in every box.
It goes like; Next we build the power supply, it does, this that and the other thing and uses….and so on.
By the time your are done you will have a good and painless grounding in electronic bits and what they are used for. You’ll know a resistor from a capacitor and a film cap from a…. well you get the idea. Plus you end up with a great sounding amp. Do it.
Then build your from scratch amp. We’re not going anywhere…John
Thanks again for all the responses. I've done some following up on the ideas mentioned above.
That vacuum tube book looks a little more specific than I think I need. I'm looking for something that will get me off the ground with audio electronics in general if anybody has any recommendations for that.
My other question is what kits people would recommend. I looked at the S.E.X. kit, but it's pretty pricey. I'd like to build an amp that would work with the above-mentioned Klipsch speakers, but I'm not sure what that would mean.
If I need to do more research before posting more, let me know. I don't want to be a time drain on people here, but I'm a little uncertain where to begin.
That vacuum tube book looks a little more specific than I think I need. I'm looking for something that will get me off the ground with audio electronics in general if anybody has any recommendations for that.
My other question is what kits people would recommend. I looked at the S.E.X. kit, but it's pretty pricey. I'd like to build an amp that would work with the above-mentioned Klipsch speakers, but I'm not sure what that would mean.
If I need to do more research before posting more, let me know. I don't want to be a time drain on people here, but I'm a little uncertain where to begin.
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