I would like to first thank everyone here for all their help! I would absolutely have not been able to complete this project without the help of this community.
Below you will see some images of my build hope you guys enjoy them!
This little guy made drilling the aluminum a breeze! 20$ at harbor freight for 2 different sizes... highly recommend
Finished case. You can see how crappy the tube holes came out. I drilled these before purchasing the bit I showed above and regret it! Remember the right tool for the job makes all the difference. I used black rubber gromets on all the case holes to prevent wire chafing.
Worked right out of the gate! Next to it is my restored 1970s Thorens TD-115 with a Shure V15 type V cartridge...Sweet sounding table.
Different angle of the completed amp
Some sweet tube glow (electroharmonix KT-88s)
Wiring... Amp is wired (I hope correctly) for ultralinear mode with CFB.
So just some additional questions...
1.) My amp is dead quiet no hum or buzz to speak of from the speakers, however there is an audible buzz/hum coming from the actually amp its self any ideas?
2.) The sound of this amp is amazing. I have really never heard human voice, drums, highs and midrange sound quite like this truly incredible! However the lower end seems to be lacking. Its not as if the amp is weak on the bass it is almost like there is no bass there like someone is filtering the signal at say 100hz (guess). Could this be due to component choice? I have very cheep generic mouser coupling caps installed. Could I have the amp wired up incorrectly? Everything else sounds too good to be wired incorrectly I would assume. If I turn up the bass on my preamp it helps but still not much.
3.) Motor run cap; as you can see I do not have a motor run cap installed. What does the motor run cap actually do for this amp? What kinds of sonic improvements would I expect if I instal one?
4) Coupling cap suggestions; now that I have a working amp I would like to upgrade. Any consensus on best bang for the buck?
5.) Tube rolling; would like to start tube rolling. I currently have an electro harmonix 12AT7 and Sovtek 5AR4 installed. Any suggestions on what I should try next?
Once again I would like to thank everyone for all their help!!!
Below you will see some images of my build hope you guys enjoy them!
An externally hosted image should be here but it was not working when we last tested it.
This little guy made drilling the aluminum a breeze! 20$ at harbor freight for 2 different sizes... highly recommend
An externally hosted image should be here but it was not working when we last tested it.
Finished case. You can see how crappy the tube holes came out. I drilled these before purchasing the bit I showed above and regret it! Remember the right tool for the job makes all the difference. I used black rubber gromets on all the case holes to prevent wire chafing.
An externally hosted image should be here but it was not working when we last tested it.
Worked right out of the gate! Next to it is my restored 1970s Thorens TD-115 with a Shure V15 type V cartridge...Sweet sounding table.
An externally hosted image should be here but it was not working when we last tested it.
Different angle of the completed amp
An externally hosted image should be here but it was not working when we last tested it.
Some sweet tube glow (electroharmonix KT-88s)
An externally hosted image should be here but it was not working when we last tested it.
Wiring... Amp is wired (I hope correctly) for ultralinear mode with CFB.
So just some additional questions...
1.) My amp is dead quiet no hum or buzz to speak of from the speakers, however there is an audible buzz/hum coming from the actually amp its self any ideas?
2.) The sound of this amp is amazing. I have really never heard human voice, drums, highs and midrange sound quite like this truly incredible! However the lower end seems to be lacking. Its not as if the amp is weak on the bass it is almost like there is no bass there like someone is filtering the signal at say 100hz (guess). Could this be due to component choice? I have very cheep generic mouser coupling caps installed. Could I have the amp wired up incorrectly? Everything else sounds too good to be wired incorrectly I would assume. If I turn up the bass on my preamp it helps but still not much.
3.) Motor run cap; as you can see I do not have a motor run cap installed. What does the motor run cap actually do for this amp? What kinds of sonic improvements would I expect if I instal one?
4) Coupling cap suggestions; now that I have a working amp I would like to upgrade. Any consensus on best bang for the buck?
5.) Tube rolling; would like to start tube rolling. I currently have an electro harmonix 12AT7 and Sovtek 5AR4 installed. Any suggestions on what I should try next?
Once again I would like to thank everyone for all their help!!!
embedded images not working please see attachments on this post.
Is my B+ of 412 with a 560ohm resistance and 25w calculated dissipation too small? Would I benefit from higher B+ or lower cathode resistance ?
Is my B+ of 412 with a 560ohm resistance and 25w calculated dissipation too small? Would I benefit from higher B+ or lower cathode resistance ?
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I'm sorry I can't really contribute to your thread but I do have a question to ask if you don't mind.
Is that blue glow always visible to the naked eye on the KT88's or is that something caused by a light or the camera?
Nice and neat build. Those big KT88s always look awesome. Let me try to answer some of your questions.
1. PTs can hum. Some rubber grommets between the PT and top plate might help, but you have to ground it separately then.
2. With the big honkin Edcor OPTs you chose, you should get good bass. Give it a few weeks to break in and there's a good chance you'll notice an improvement in range.
3. The motor run cap gets wired in parallel with C2, so that increases the capacitance in the power supply. This is an extra reservoir to draw from during peak demands. Not sure what it will do for sound, but it sure looks cool!
4. Lots of people use AuriCaps.
5. Different output tubes will probably be the most fun. Some people on here have done selector switches to change the cathode resistance for the most flexibility in tubes. Also be sure to try the combinations of Triode/UL and CFB.
Have fun with it. It's such a great little amp and I never get tired of mine.
1. PTs can hum. Some rubber grommets between the PT and top plate might help, but you have to ground it separately then.
2. With the big honkin Edcor OPTs you chose, you should get good bass. Give it a few weeks to break in and there's a good chance you'll notice an improvement in range.
3. The motor run cap gets wired in parallel with C2, so that increases the capacitance in the power supply. This is an extra reservoir to draw from during peak demands. Not sure what it will do for sound, but it sure looks cool!
4. Lots of people use AuriCaps.
5. Different output tubes will probably be the most fun. Some people on here have done selector switches to change the cathode resistance for the most flexibility in tubes. Also be sure to try the combinations of Triode/UL and CFB.
Have fun with it. It's such a great little amp and I never get tired of mine.
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My 2 cents:
#1: I've got a bit of PT buzz audible from 1-2 feet from the amp, nothing to worry about if it doesn't reach the speakers. I actually found that part of it was the choke (cured with grommets).
#2: I think DMB is right on the mark. The OPTs aren't holding anything back. We can't really know from here how severe the lack of bass is, but you could check to be sure you haven't unintentionally wired it for CFB on one or both of the speakers. Speaking of, what kind of speakers are you using?
#3: If you don't have any hum now, you may not have to worry about another cap. Class A amps draw constant current, so having extra cap 'headroom' isn't strictly necessary (provided you don't have any hum as is).
#4: I've got Auricaps in my SSE and they seem good. Can't make a direct comparison, though. The amp I'm working on now (RH84) has Orange Drops. If I go more 'upscale' once I'm satisfied that this RH84 runs fine, I'll probably choose Auricaps.
#5: I very much like my KT88s, but usually I use a pair of SED EL34s ("Winged C"). Less bass, but better midrange & detail in my amp. I still swap every now and then though. I have run KT88s, EL34s and 6L6GCs with a 560ohm Rk without a problem.
I get a nice blue glow in most of the output tubes I've tried.
Great looking build!
#1: I've got a bit of PT buzz audible from 1-2 feet from the amp, nothing to worry about if it doesn't reach the speakers. I actually found that part of it was the choke (cured with grommets).
#2: I think DMB is right on the mark. The OPTs aren't holding anything back. We can't really know from here how severe the lack of bass is, but you could check to be sure you haven't unintentionally wired it for CFB on one or both of the speakers. Speaking of, what kind of speakers are you using?
#3: If you don't have any hum now, you may not have to worry about another cap. Class A amps draw constant current, so having extra cap 'headroom' isn't strictly necessary (provided you don't have any hum as is).
#4: I've got Auricaps in my SSE and they seem good. Can't make a direct comparison, though. The amp I'm working on now (RH84) has Orange Drops. If I go more 'upscale' once I'm satisfied that this RH84 runs fine, I'll probably choose Auricaps.
#5: I very much like my KT88s, but usually I use a pair of SED EL34s ("Winged C"). Less bass, but better midrange & detail in my amp. I still swap every now and then though. I have run KT88s, EL34s and 6L6GCs with a 560ohm Rk without a problem.
I get a nice blue glow in most of the output tubes I've tried.
Great looking build!
Aw, nuts, that's right. I hate giving out bad info on boards when people are trying to learn. Sorry and thanks for the correction, Soda.
I'd actually expect weaker bass with triode (although triode w/o CFB is what I prefer personally). Play it for awhile and you may find it opens up nicely. The big OPTs and KT88s should get you decent bass.
It didn't jump out at first, but you can run the KT88s much harder (up to 42W) with a smaller cathode resistor. Could this be hurting his bass, Soda?
I was kind of wondering about that, too. DJ, didn't you say in another thread that you're used the XPWR035? I'd expect a higher B+ with that and a 5AR4. What choke are you using?
More power/dissipation = better bass sounds right to me (within spec, of course). UL provides more power but less damping than triode mode and has higher output Z. Bass should be more, but not as 'tight'.
I'd try triode mode w/o CFB just to see what kind of difference it makes in balance. Both the Klipschs and Paradigms should still be able to play pretty loud (I regularly use my SSE with Klipsch Heresys in triode). Depending on the speaker impedance curves, you might find a better match.
If that fails, then start tearing into that board!
More power/dissipation = better bass sounds right to me (within spec, of course). UL provides more power but less damping than triode mode and has higher output Z. Bass should be more, but not as 'tight'.
I'd try triode mode w/o CFB just to see what kind of difference it makes in balance. Both the Klipschs and Paradigms should still be able to play pretty loud (I regularly use my SSE with Klipsch Heresys in triode). Depending on the speaker impedance curves, you might find a better match.
If that fails, then start tearing into that board!
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I am using the XPWR155 (700V (350-0-350) at 200mA center tapped, 6.3V at 5A and 5V at 3A) with a Sovtek 5AR4 that i got off ebay. The choke is the XC75 (2H at 200mA DC) I also installed the CL-140 ICL and 2 UF4007 diodes the George recommends to help prolong rectifier life. Do you think they may be the cause of the low B+? Should I reduce the the resistance of my cathode resisters down from 560 to something lower to generate more dissipation?
I used the same PT in my build, sound is perfect. If you're concerned about your sound WITH cathode feedback I'd re-visit how you have your cathode feedback connected, not all OPTs are the same, it could be you're experiencing POSITIVE feedback instead of negative feedback which is what you want, not positive feedback. I run mine UL with CFB bass is fine. Here's what George wrote up in the assembly manual:
"Cathode feedback is used in this diagram. The secondary of the OPT’s are connected to ground on the PC board so a separate connection is not needed. Note the reverse connection of the output transformer secondaries. This is needed on many OPT’s to get NEGATIVE feedback to the cathode of the output tube. If unsure of your particular OPT’s try wiring the secondaries each way (swap the two secondary wires, leave the primary alone). Chose the connection that produces the lowest volume."
Cheers,
Bob
Could he try a different brand 12at7. I am new to tubes but this was an inexpensive swap I read I could make to my amp to change the sound. I have a tung sol 12at7 and I tried a nos ge 6201 5 star and the difference was unbelievable in the bass. Mids and highs increased with the ge tube but I lost a good amount of bass. I am running EH 6550s in triode mode and get pretty good bass with the tung sol. Just wondering your thoughts on this.
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