I have a few lifted pads on my board since some components have been changed several times. Many of the component holes on this board are used to make a connection from the top to the bottom of the board. Often that connection gets broken when a pad is lifted. In this case it may be necessary to solder tha component on both sides of the board. Of course it is impossible to solder the leads on the top side of the board on some components like C27. In this case I scrape some resist off of the runner on the top side, solder a thin bare wire (one strand from line cord or speaker wire) to the bare copper, run the wire through the component hole, insert the component, then solder the component and the wire to the remaining trace on the bottom side. Verify continuity before powering up the board.
I killed C27 twice, once by explosion, and changed its value twice. The pads on the positive lead are gone on both sides of the board! I think the part that is in there now is staying.....forever. Now that I have figured out how to keep the big voltage off of the board it shouldn't blow up any more.
OH yeah, It was cranking out the tunes again for a few hours, but it is silent now and will remain silent for the rest of the day. Football is on. Four games left in the season and one doesn't count.
I don't think that I have tried them yet. I probably have some somewhere, but it is probably easier to get some from Stan (ESRC) next time I'm there. I will stop in at his warehouse on Feb 11 on my way to the Orlando hamfest. 4 million tubes is a sight to see. I have been using 6GU5's since thay gave me a bit more gain and lower distortion than the 6CB6's. I got them from Stan for $2 each but I bought a bunch.
An interesting variation on Pete's design would be to try taking the Schade feedbacks from the UL taps on the OT instead of the plates. E-Linear, I think it has been called.
On the cheap OTs that I have measured, the inner 40% primary windings have better coupling (lower leakage L) to the secondary than the outer 60 % windings. And the outermost 60% winding (one side) coupling is just dismal. Some OTs have half the bandwidth on one side because of it. If that side's tube plate is free'd up to act as a current source (Schade feedback moved to the UL tap), then the leakage L of the outer 60% doesn't matter, since it is current driven now (that plate's voltage will now swing to whatever it takes to get the UL feedback voltage correct). The UL tap still provides the Schade voltage feedback with good accuracy to the actual secondary output (low leakage L). Best to do both sides, of course, for maintaining balance.
This would require dropping the 220K Ohm feedback resistors to around 88K Ohm. And if the output tubes are being operated at a higher B+ than the board B+, the board supply would need dropping some to get the original plate voltages on the 6CB6's.
I plan to try this out soon.
On the cheap OTs that I have measured, the inner 40% primary windings have better coupling (lower leakage L) to the secondary than the outer 60 % windings. And the outermost 60% winding (one side) coupling is just dismal. Some OTs have half the bandwidth on one side because of it. If that side's tube plate is free'd up to act as a current source (Schade feedback moved to the UL tap), then the leakage L of the outer 60% doesn't matter, since it is current driven now (that plate's voltage will now swing to whatever it takes to get the UL feedback voltage correct). The UL tap still provides the Schade voltage feedback with good accuracy to the actual secondary output (low leakage L). Best to do both sides, of course, for maintaining balance.
This would require dropping the 220K Ohm feedback resistors to around 88K Ohm. And if the output tubes are being operated at a higher B+ than the board B+, the board supply would need dropping some to get the original plate voltages on the 6CB6's.
I plan to try this out soon.
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The OPT's that I have been using do not have UL taps. I do have another set of rather crummy OPT's that do have taps, so I may have to try it next time the amp is on the work bench.
I did experiment with this some with this circuit. The results do seem to depend somewhat on the OPT, but in general I found that it did not work as well as taking the FB directly from the plates. Better distortion and FFT, and more power, with FB from the plates using sweep tubes. I didn't spend any time to figure out why... it just seems like some tubes work better in the e-linear connection than others.
Pete
The ugly (and highly unsafe) breadboard has been sitting in the middle of the living room coffee table and has seen a lot of play time, some of which has been quite loud. There have been no issues, it just rocks.
I have decided to name the ugly breadboard the Flamethrower 250 since it makes about 250 watts when fully cranked. I think that I am going to leave this one exactly as is. I will build another Flamethrower 250 in a pretty box and this one will then be available for further experimentation. I think I have all the parts for the build except for a few resistors. Of course the build will be documented and posted here. I think the only change I will make is to parallel the heater windings from the two power trasnformers to even up the load. I see no issues but there is another thread here about another amp using these transformers and the user is having issues with hum and heat. Mine are slightly warm and completely cold after hours of use.
http://www.diyaudio.com/forums/tubes-valves/177595-compactron-amp-lives.html
Today was one of those "tourist days". The kind of day that tourists pay big bucks for. 65 degrees, clear skies, and a gentle breeze. We haven't had very many this year. I decided that the tubes would remain dark and cold today....it's finally time to work on my speakers. If tomorrow is like today they will be done. Photo of the Back Yard Speaker Lab.
I have decided to name the ugly breadboard the Flamethrower 250 since it makes about 250 watts when fully cranked. I think that I am going to leave this one exactly as is. I will build another Flamethrower 250 in a pretty box and this one will then be available for further experimentation. I think I have all the parts for the build except for a few resistors. Of course the build will be documented and posted here. I think the only change I will make is to parallel the heater windings from the two power trasnformers to even up the load. I see no issues but there is another thread here about another amp using these transformers and the user is having issues with hum and heat. Mine are slightly warm and completely cold after hours of use.
http://www.diyaudio.com/forums/tubes-valves/177595-compactron-amp-lives.html
Today was one of those "tourist days". The kind of day that tourists pay big bucks for. 65 degrees, clear skies, and a gentle breeze. We haven't had very many this year. I decided that the tubes would remain dark and cold today....it's finally time to work on my speakers. If tomorrow is like today they will be done. Photo of the Back Yard Speaker Lab.
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I'll be interested to hear about your horns. I suspect the TSE will be finding it's way out of the closet.
The ones in the picture are these:
http://www.diyaudio.com/forums/full-range/118236-s-p-q-r-ez10-cast-10-a.html?highlight=ez10
After they are done I will be making a set of these:
http://www.diyaudio.com/forums/full-range/172605-frugel-horn-mk3.html
http://www.diyaudio.com/forums/full-range/172937-frugel-horn-mk3-beta-builds.html
I haven't built any HiFi speakers other than my re-purposed Zenith radios in about 35 years. I decided that I wanted some horns after hearing some that cost more than my car, so I have to make them. I had been procrastinating for a couple of years and then two deals occurred almots simultaneously. I traded a Fisher tube receiver for the Audio Nirvana cast 10's and I traded some Tubelab boards and parts to Planet 10 for a pair of FE126EN with the full eNable treatment. The AN-10's showed up first so that pair got started first. Up until today they have only been worked on in Thursday night wood shop class.
The Flamethrower 250 must be kept away from this stuff. It could set the little Fostex on fire! The nicest sounding amp I have ever built (especially on those Lowther horns) is the 2WPC Tubelab SE with 45's or NX483's. The most dynamic was the 300Beast P-P amp which no longer works. It might be time for a rebuild.
The TV weather guy says 75 degrees with 0% chance of rain for tomorrow, so if they are right the speakers should be making sound tomorrow night. Everyone says that they will need up to 100 hours of break in. I have noticed some considerable loosening up of the 2 year old Silver Iris since I have been puonding them with power. They keep getting louder!
flamethrower_250
hey tubelab, can you name once more the opt's and power traffos and output tubes? thanks...
http://www.diyaudio.com/forums/atta...p-p-power-amp-design-flamethrower250_bb_a.jpg
hey tubelab, can you name once more the opt's and power traffos and output tubes? thanks...
http://www.diyaudio.com/forums/atta...p-p-power-amp-design-flamethrower250_bb_a.jpg
Power transformers were the 10lb surplus transformers sold a few months back on ebay. Tubes are 6hj5s and the output transformers were listed a few pages back but I do not believe they are still in production. If you read through the last 6-8 pages or so I bet every answer you need can be found with in those pages 🙂
The OPT's that I used were surplus open frame guitar amp OPT's that I purchased about 10 years ago. They were made by Schumaker in 1990 for ADA and surplussed shortly after that when ADA went out of business. They are 6600 ohms to 0-4-8-16 ohms. I get a 3300 ohm load by putting an 8 ohm load on the 16 ohm tap. I haven't seen them for sale recently but they do appear on Ebay from time to time.
Other builders have used the 100 watt Edcor CXPP types with good results. With 600 volts of B+ I get 125 WPC with 3300 ohms and 75 WPC with 6600 ohms. Any load between these values is OK with appropriate scaling in power output. 2500 ohms will deliver about 175 WPC but bigger output tubes are needed.
The power transformers were also surplus units recently sold on Ebay. They were also made by Schumaker but appear to be from the late 60's. The seller doesn't have any more listed but they may reappear. They were discussed here:
http://www.diyaudio.com/forums/tube...nds-power-15-a.html?highlight=10+pounds+power
The output tubes in my current version are 6HJ5's. I chose them because they are the biggest sweep tube I could find that doesn't have a plate cap and costs $5 or less. Any pin compatible sweep tube with 24 watts of plate dissipation could be used. I have used 6LR6, 6JS6C, 6KD6, 35LR6's and others.
Other builders have used the 100 watt Edcor CXPP types with good results. With 600 volts of B+ I get 125 WPC with 3300 ohms and 75 WPC with 6600 ohms. Any load between these values is OK with appropriate scaling in power output. 2500 ohms will deliver about 175 WPC but bigger output tubes are needed.
The power transformers were also surplus units recently sold on Ebay. They were also made by Schumaker but appear to be from the late 60's. The seller doesn't have any more listed but they may reappear. They were discussed here:
http://www.diyaudio.com/forums/tube...nds-power-15-a.html?highlight=10+pounds+power
The output tubes in my current version are 6HJ5's. I chose them because they are the biggest sweep tube I could find that doesn't have a plate cap and costs $5 or less. Any pin compatible sweep tube with 24 watts of plate dissipation could be used. I have used 6LR6, 6JS6C, 6KD6, 35LR6's and others.
The Back Yard Speaker Lab closed at 6 PM last night. I made it to 8 PM before the EZ10's were connected to the Flamethrower 250. Several EZ10 builders stated that the Audio Nirvana drivers would need at least 100 hours of break in time before they sounded good. There is no damping material in the cabinets yet either. Of course I had to see how they worked, and the Flamethrower was already connected, so they met.
The first test was to crank up Dave Brubeck's Take Five to see how the snare drum hits sound. So good that I listened to the whole CD. The alto sax sounds like it is in the room. The bass sounds OK, but other CD's revealed the need for some fiberfill. Loreena McKennit has a rather shrill voice that can sound nasty, almost painful on a bad system, but came through clear here no matter how loud I played it. Flamenco guitar sounds very realistic too. The acid test was some Apocalyptica cranked up rather loud. There is some bass boominess, which is to be expected at this point.
These drivers claim a 96db efficiency. The Silver Iris claims 96 db also. AB testing reveals that the EZ10's are louder for a given volume setting. of course the Silver Iris can be played much louder since they can eat all this amp can make.
I am not touching the speakers until they have seen 100 hours. So, I connected them up to a 15 year old Panasonic boom box, tuned it to the local rap music station, cranked it up and left for work.....
The first test was to crank up Dave Brubeck's Take Five to see how the snare drum hits sound. So good that I listened to the whole CD. The alto sax sounds like it is in the room. The bass sounds OK, but other CD's revealed the need for some fiberfill. Loreena McKennit has a rather shrill voice that can sound nasty, almost painful on a bad system, but came through clear here no matter how loud I played it. Flamenco guitar sounds very realistic too. The acid test was some Apocalyptica cranked up rather loud. There is some bass boominess, which is to be expected at this point.
These drivers claim a 96db efficiency. The Silver Iris claims 96 db also. AB testing reveals that the EZ10's are louder for a given volume setting. of course the Silver Iris can be played much louder since they can eat all this amp can make.
I am not touching the speakers until they have seen 100 hours. So, I connected them up to a 15 year old Panasonic boom box, tuned it to the local rap music station, cranked it up and left for work.....
I set the volume so that it is just audible at the property line. It's quite loud inside the room. The full throttle testing with the Silver Iris was a different story. It was F'in LOUD everywhere!
Why not just hook them to a variac and a transformer - that would also give the suspensions a workout....
Getting way off topic here, but I can't resist. The cats were away yesterday, so I decided to see if I could get my Boston Acoustic A60s to break in a bit. I refoamed them a year or two ago and it really killed the bass. The new foam is pretty stiff. I use them in my shop and I miss the punch they used to have. Anyway, I slapped them in parallel with the speakers that were already hooked to the ST70 and dimed it for a couple of hours with some Armin van Buuren. That was loud.
After a while, I noticed that the speakers normally hooked up to the ST70 were sounding a bit flabby. They are a pair of old Realistic Nova-18s that I bought back when I worked at the Shack (circa '94, I suppose). I bought them to replace my older MC-2001s, which I also still have out in the garage. The Novas are not the best speakers, but after a few mods they sound pretty good for what they are. I use them as a sort of "rear" channel for our long, narrow basement.
Anyway, when I popped the grill off, some bits fell on the floor. 🙂
After a while, I noticed that the speakers normally hooked up to the ST70 were sounding a bit flabby. They are a pair of old Realistic Nova-18s that I bought back when I worked at the Shack (circa '94, I suppose). I bought them to replace my older MC-2001s, which I also still have out in the garage. The Novas are not the best speakers, but after a few mods they sound pretty good for what they are. I use them as a sort of "rear" channel for our long, narrow basement.
Anyway, when I popped the grill off, some bits fell on the floor. 🙂
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Having read this thread a couple of times already I think this amp would be a good first diy tube project for me. I think it would be a lot of fun. I just ordered the PCB.
Is there a reason not to select tubes with a plate cap? Are any of the current dollar list tubes from ESRC compatible? I'm not sure if these sweep tubes are very common my side of the pond, but at these prices I'll happily order some from ESRC.
Is there a reason not to select tubes with a plate cap? Are any of the current dollar list tubes from ESRC compatible? I'm not sure if these sweep tubes are very common my side of the pond, but at these prices I'll happily order some from ESRC.
It's just simpler and safer. If high voltage is your goal, then the plate cap is actually a good thing. You don't have to worry about arcing in the base. Since these tubes don't have plastic bases and the sockets are ceramic, I don't know at what point that may be an issue. The plastic octal bases are more prone to this.
Ok thanks Russ. I'll guess I'll make do with what I can get, be it plate cap or not. I'll make some kind of tube cage anyway to prevent my kids from touching.
I think the higher voltage is too good to resist seeing how George has fared with this red board. I would like to get at least 2x50W out of this amp to drive my 89dB/W/m speakers. I'll put some ideas for a chassis on paper and start collecting parts.
I think the higher voltage is too good to resist seeing how George has fared with this red board. I would like to get at least 2x50W out of this amp to drive my 89dB/W/m speakers. I'll put some ideas for a chassis on paper and start collecting parts.