I made a couple of mistakes in my verbal descriptions during the video. Sorry for all the banging around at about 10:00... At about minute 34:00 the hum balance pots for the filaments adjust the 60 Hz and not the 120 Hz from the full wave rectified power supply. I forgot to mention in the video about NFB in the 300B SET. I have a switch on the back of the amplifier to change NFB to either zero (0) NFB or seven (7) dB NFB. The switch was set to zero (0) so there was no global negative feedback being used in this amplifier in this video. I believe with the 7 dB NFB switch on, I get about one or two more watts with a bit lower THD.
So sorry about your cat. There’s no more suffering and his memories ARE sure to be with you . Thx for another great video! I’m wondering about the second harmonic down in the SE amp.... maybe due to nfb? Anyway, I’m Trying this crazy thing now... I’m going to use a bunch of relays to convert a 5881 Williamson pp into a “hybrid” amp that goes from a Williamson pp to a choke loaded set with the flick of a switch. The relays are going to rearrange connections so it adds the plate load choke and dc blocking cap (at the same time paralleling both output tubes and triode connecting them through a 100 ohm resistor between plates and screens). Just got a hold of some gorgeous scr made in France 33uF film capacitors for the dc blocking.
I just watch my video (I should watch it before I post...) and I mentioned that there was no NFB in the SET amplifier during this test. See my comment above. I am sure you can wire your amp to use a standard gapped OPT or the choke load with relays. I think I could build a PC out of relays if it didn't matter if it was the size of a city block... I love relays. It would really be nice if you could document the differences in performance with the flip of a switch. Interesting that I got some 3.3 uF, 2000V capacitors from France. Mine are flat and yellow and have, "iC MWR" on them. Stay safe.
David, Thanks for your videos. They have helped me build my own audio test bench. I would be interested in a detailed video about how you set up your test instruments and cabling. Such as input impedance settings of each instrument, any terminators or attenuators used, and general wiring diagram. Thank you.
I always enjoy all of your videos but the audio related ones are definitely my favorites. Thanks for your continued efforts in producing them. I'm sorry to hear about your cat. Pets have personalities and we become attached to them. I think that's as it should be. Fortunately we always have our memories and they stay with us. I like your idea of not using the past tense.
Something for you and Doug to think about. Look at distortion and harmonics musically. Start with C4 at 261.63Hz. The second harmonic will be C5 523.26Hz. Still a C. The 3rd harmonic will be 784.89 which isn't a note at all but close to a G5 which is 783.99. Close enough and tolerable to a degree. Take it up to a odd 5th harmonic at 1308.15Hz which lands somewhere between a D#6/Eb6 and E6. Yuk! The higher the odd harmonics go in frequency the worse it gets. Take a step back to the 4th harmonic at 1046.52Hz and you'll find that's C6. Yet another C. So if you were to press every C key on a piano, they're all even-order (octaves). You still have a C but you have a very complex C that sounds rich and complex but is still a C none the less. Our brains likes harmony and symmetry. It likes even orders and "happy chords". Also don't forget about intermodulation. Many harmonics beat against each other and create frequencies that are deadly to your enjoyment, cause listening fatigue, and distract the stereo focus. As if someone was mashing random keys on the piano. Push-pull (differential) stages cancel 2nd order harmonics. Single-ended stages are not capable of clipping symmetrically thus develop even-order harmonics. I have a simulation of a simple diode clipper that can symmetrically clip the top and/or bottom of a waveform, or both. If you'd like to see those FFT results, shoot me a message. I'd be happy to share it.
i like all of your vids most all you made keep up the good work and your shop clean i like tell me about lifying heaters elevated to safe level thanks GKL
Sir, your 300B spectrum profile looks like my 2A3 Loftin-White SET amp (2 mono blocks). I expected a dominate 2nd harmonic. Ok, what does it sound like. Wow! I was amazed at the articulation and bass extension using Hammond transformers and chokes. 3.5 Watts, 5% THD+N, as seen on the datasheet. Acid test - what does it sound like? Thanks for your video, all great stuff! Love analog!
I think it sounds stunning good. It does heavy metal justice and classical music is over-the-top but as mentioned, sometimes I just want to punch the gas pedal a little and see it zoom so I suppose that is why I like a little more power sometimes.
Nice video as always! 👍 Talking about EL34s, I have used over 30 years quite frequently one particular early 60's german Dynacord Eminent instrument amp which is of a bit flimsy physical design but equipped with EL34 output stage and a surprisingly good OT. Unfortunately quite recently one output tube of the matched EL34 pair gave up (frying steak sounds, cracle & pop sounds etc.) so I had to install a fresh pair of EL34s. I have a collection of NOS Mullard, Siemens, Telefunken etc. EL34s, but I did not want to sacrifice them after checking out the today prices of those gems. 😀 However my local component dealer was selling Russian made Electro-Harmonixs 6CA7 tubes ( a beam pentode (or tetrode, who cares)) at a very low bargain price a few monts ago and I decided to try them. And I was surprised because the two individual tubes I bought were almost a perfectly matched pair and in addition they sounded very good, almost identical to NOS Mullards. Of course those russian made tubes probably don't last as long as NOS Mullards or Telefunkens but the price was ridiculously cheap. Do you have experience of those 6CA7 tubes? What do you think, will they last or fail in months and if you have tried them, did you like the sound?
I have had many more EL34's than 6CA7's. I think I still have a few genuine 6CA7's in the attic but I have not thought about working with them. I have too many EL34's... They are both listed as power pentodes so I have always believed they were 100% the same. That may not be true to a musician and I respect that but, assuming equal quality in a set of tubes compared to each other, I doubt I would be able to see any measurable difference in performance on the bench. For some reason, I seem to think the EL34 (or 6CA7) is slightly brighter than the 6L6. May just be my imagination. I have always liked the look of the EL34. I wonder sometimes how that affects the perceived sound ?? They are a fairly high voltage rated tube and as such are going to, by design, require a higher impedance output transformer. An absolute value for the value of impedance in an output transformer is just not necessary and often times not realistic in homebuilt equipment, mostly because of availability and cost of output transformers. Certainly, by engineering standards, a particular value of impedance is going to deliver the most amount of power and maybe lower THD but not necessarily the latter. Sometimes using a slightly higher impedance output transformer will yield a lower power level but improved THD. And then, there is that THD stuff again. We swear by it and use it to compare all amplifiers but we should surely know it is not the last-word, so to speak, in how we like the sound of an amplifier. I think in virtually all of my comments of how I like an amplifier, I tend to listen most carefully to the high frequency end. And then sometimes we just want to hear a different amplifier just like we want a different brand of beer - but we likely have our favorite. I seem to be drawn to low mu triodes running class-A for audio amplifiers. The 300B SET I have is heavenly but sometimes I want a little more power. I rarely listen to music over 95 dB SPL any more but sometimes when I press on the gas peddle, I want the amplifier to GO... lol I have had practically zero experience with vintage Russian tubes and a little with the higher end new ones made in the Russian countries. I find them OK.
@@ElPasoTubeAmps Well, EL34 is surely the tube if you want to build a pure class B p-p output stage with crazy B+ voltage and crazy peak power per tube. I have seen some old EL34 PA amps and they were a bit frightening with their 700+ V plate voltages. Of course the sound is not as clean as it would be if run at class AB.
Thank you for the great videos! Of the 2 FFT spectrum analyzer softwares you use. Which would you recommend, the ARTA or the True RTA? Is one more accurate than the other thought out the audio range? Again, I appreciate what you're doing!. Dave, Longview Tx
The one that I use now is TrueRTA. The FFT is good and it has a very nice print page but I found the oscilloscope to be useless but I have plenty of scopes. www.trueaudio.com/rta_down.htm
Exceeding 120 decibels maybe hard with consumer audio gear but it's not difficult at all if you use professional level drivers and amplifiers. Now getting past 150 decibels it gets a little challenging. And doing it at frequencies below 20 Hertz is even more challenging.
Yep, 100 watts into 100 dB SPL speakers would be 120 dB. 150 dB being 30 dB more or 10^3 power gain, would be 100KW. I would say that would be difficult to get there. 🙂
@@ElPasoTubeAmps I built an array of Bassmaxx ZR-18 subs. With 2.83 vrms pink noise input bandwidth limited to under 100Hz into one pair in a LLT (tuning frequency 8Hz) Hemholtz resonator, the SPL at 4' is 112dB, unweighted. When the system is playing at a level where the "signal present" levels start to flicker, the SPL at 8' from the wall of speakers is 132dB below 40Hz. The ZR18s have a peak to peak excursion capability of 4", 3" of which is linear and a power handling of 3600W per driver. You can feel your heart stopping and your cloths flapping as if riding a motorcycle at highway speeds.
Nice to see you back again and talking about audio amplifiers. Is the 7591 amplifier is now your favorite, preferred to even the push pull 6B4G and 300B amps? Sorry about your fur buddy. I have cats myself. Great friends and companions.
Somehow I got swayed back to the 7591 because my friend picked up a McIntosh 225 which uses the 7591 and I really liked it. It is hard to say why we want to change sometimes. Maybe I am mellowing a little bit and don't need it so loud. These Tekton speakers sound great, to me, at a reasonable loud listening level which I rarely go to nowadays but they don't sound that good if I try to drive them over maybe 110 dB SPL. If I need to set my hair on fire, I have a Mac 2205 (210 watts per channel) that drive Klipschorns and I have truly measure them at over 120 dB. It is insane and can be downright scary to listen to music at that level.
Hey my friend, I am looking for a tube I am having a hard time finding. The tube is an 830. I have found many 830A, but can't find an 830. The difference is only that 830 is all terminated in the socket, but 830A is electrically the same but uses a plate cap. I have one 830 and want another for aesthetic. I want them for a SET stereo amp. I thought I might reach out to you because I know you have quite a collection of tubes..
Just wondering if you were to use the 12V Vacuum tubes that were created in 1957 because the transistors of the day were not ready for primetime and use a B+ of 12V and should give a few watts of power and should also work for RF.
I've got some of those little tubes but I have never used them. I have always wondered about the tubes in the warhead of some of the old proximity artillery shells in WWII. They sure had to take a tremendous G-force on being fired from a gun.
This 7591 amp is the one that rules my world in the house. It replaced all the McIntosh amplifiers. They are like collectors pieces now. I use a mono 6L6 amp in the backhouse driving my Tektons in parallel. Sounds like heaven.
I would love to make this amp. Any suggestions on output and power transformer brands that are readily available? Also, are there prints available? I have plenty of 816 and 866 tubes, so I may use one of these in the design...
Bill, I would suggest UTC transformers like the LS-57 or Acrosound like the TO-300 if you want to use vintage OPT. They can be pricey on Ebay. For a power transformer, if you want to use FWCT then a power transformer of somewhere around 720 volts CT or if you use a voltage doubler a transformer of 180 volts. Both should give you at least 450 volts DC for the plates. 6L6's require 0.9 A each for filament current so you will need 5A to include the 6SN7 drivers. If you chose to use EL34 then each tube wants 1.8A so you would need a filament supply of more in the order of 10A to be safe. These plate voltages I am suggesting above are using solid state rectifiers. Each channel should do a minimum of 20 watts which is sufficient for 110 dB SPL with most speakers. If you want to use vacuum tube rectifiers, you have to account for loss across the rectifier tube and the transformer voltages should be a bit higher like 800 VCT for FWCT or 200 volts for the doubler. Plate voltages above 450 VDC often require electrolytic capacitors in series to be in a safe-zone. I would use maybe two 220 uF @ 450 VDC in series, each shunted by 470K/2W resistors, etc... Hope this helps. On the other hand, Hammond Transformers makes some nice new transformers you might want to try. Hammond also has a good line of power supply chokes. I would use a 1.5H at 500mA choke, again, to be in the safe zone. I buy my chassis from www.mouser.com. They also sell Hammond transformers. Not sure what new OPT transformers cost but the UTC and Acrosound transformers are going to likely cost better than $500. Just some thoughts.
Wow... here is the spec sheet on the HP 3561A analyzer. accusrc.com/uploads/datasheets/5350_3561a.pdf It goes from 125 micro Hertz to 100 KHz. I think you can measure Earth quakes and tsunamis with it but it sure seems like it would do the audio range very nicely. That is quite an instrument. The 3580A I have is rated 5 Hz to 50 KHz but as I mentioned, it is brutally slow on the low frequencies as I am sure yours would be also. HP sure made some nice stuff.
@@ElPasoTubeAmps Well thank you. Actually, the sweep/sample rate stays about the same because it is FFT. I need to work with it more, but Audio and speed is why I bought it. Got it off Ebay and upgraded the CRT to an LCD multi color display because the CRT had the static display burned in it. Everything else looks good and pretty clean inside. Just love the old HP stuff! Gold plated connectors and conformal coated boards. Going to have to come up with a handle though as mine is missing.
It is my experience from testing different amplifiers over the years that the Acrosound transformers do well at the lowest frequencies - even down to 10 Hz. As best I remember they were all Williamson designs the better ones using 807 tubes. Just my experience.
@@ElPasoTubeAmps You are welcome. We could still hear you so not a problem. You are always so good about your production and pay attention to your camera angles and micing!
So sorry to hear of your kitty cat! He is still with you every day. He made a difference in your life.
I made a couple of mistakes in my verbal descriptions during the video.
Sorry for all the banging around at about 10:00... At about minute 34:00 the hum balance pots for the filaments adjust the 60 Hz and not the 120 Hz from the full wave rectified power supply.
I forgot to mention in the video about NFB in the 300B SET. I have a switch on the back of the amplifier to change NFB to either zero (0) NFB or seven (7) dB NFB. The switch was set to zero (0) so there was no global negative feedback being used in this amplifier in this video. I believe with the 7 dB NFB switch on, I get about one or two more watts with a bit lower THD.
So sorry about your cat. There’s no more suffering and his memories ARE sure to be with you . Thx for another great video! I’m wondering about the second harmonic down in the SE amp.... maybe due to nfb? Anyway, I’m Trying this crazy thing now... I’m going to use a bunch of relays to convert a 5881 Williamson pp into a “hybrid” amp that goes from a Williamson pp to a choke loaded set with the flick of a switch. The relays are going to rearrange connections so it adds the plate load choke and dc blocking cap (at the same time paralleling both output tubes and triode connecting them through a 100 ohm resistor between plates and screens). Just got a hold of some gorgeous scr made in France 33uF film capacitors for the dc blocking.
I just watch my video (I should watch it before I post...) and I mentioned that there was no NFB in the SET amplifier during this test. See my comment above.
I am sure you can wire your amp to use a standard gapped OPT or the choke load with relays. I think I could build a PC out of relays if it didn't matter if it was the size of a city block... I love relays. It would really be nice if you could document the differences in performance with the flip of a switch. Interesting that I got some 3.3 uF, 2000V capacitors from France. Mine are flat and yellow and have, "iC MWR" on them. Stay safe.
I still think you do DAMN nice work! Your builds are beautiful!
David, Thanks for your videos. They have helped me build my own audio test bench. I would be interested in a detailed video about how you set up your test instruments and cabling. Such as input impedance settings of each instrument, any terminators or attenuators used, and general wiring diagram. Thank you.
50 ohms, BNC cables and connections will get you a long way. 😎
I always enjoy all of your videos but the audio related ones are definitely my favorites. Thanks for your continued efforts in producing them. I'm sorry to hear about your cat. Pets have personalities and we become attached to them. I think that's as it should be. Fortunately we always have our memories and they stay with us. I like your idea of not using the past tense.
Something for you and Doug to think about. Look at distortion and harmonics musically. Start with C4 at 261.63Hz. The second harmonic will be C5 523.26Hz. Still a C. The 3rd harmonic will be 784.89 which isn't a note at all but close to a G5 which is 783.99. Close enough and tolerable to a degree. Take it up to a odd 5th harmonic at 1308.15Hz which lands somewhere between a D#6/Eb6 and E6. Yuk! The higher the odd harmonics go in frequency the worse it gets. Take a step back to the 4th harmonic at 1046.52Hz and you'll find that's C6. Yet another C. So if you were to press every C key on a piano, they're all even-order (octaves). You still have a C but you have a very complex C that sounds rich and complex but is still a C none the less. Our brains likes harmony and symmetry. It likes even orders and "happy chords". Also don't forget about intermodulation. Many harmonics beat against each other and create frequencies that are deadly to your enjoyment, cause listening fatigue, and distract the stereo focus. As if someone was mashing random keys on the piano.
Push-pull (differential) stages cancel 2nd order harmonics. Single-ended stages are not capable of clipping symmetrically thus develop even-order harmonics.
I have a simulation of a simple diode clipper that can symmetrically clip the top and/or bottom of a waveform, or both. If you'd like to see those FFT results, shoot me a message. I'd be happy to share it.
Thanks for that lesson in harmonics.
I love seeing those old UTC true Fidelity output transformers. They don't make them like that anymore!
i like all of your vids most all you made keep up the good work and your shop clean i like tell me about lifying heaters elevated to safe level thanks GKL
Sir, your 300B spectrum profile looks like my 2A3 Loftin-White SET amp (2 mono blocks). I expected a dominate 2nd harmonic. Ok, what does it sound like. Wow! I was amazed at the articulation and bass extension using Hammond transformers and chokes. 3.5 Watts, 5% THD+N, as seen on the datasheet. Acid test - what does it sound like? Thanks for your video, all great stuff! Love analog!
I think it sounds stunning good. It does heavy metal justice and classical music is over-the-top but as mentioned, sometimes I just want to punch the gas pedal a little and see it zoom so I suppose that is why I like a little more power sometimes.
8192 Bins is where it's at, or if you want a better but slower scan then 16384 Bins will work.
Nice video as always! 👍
Talking about EL34s, I have used over 30 years quite frequently one particular early 60's german Dynacord Eminent instrument amp which is of a bit flimsy physical design but equipped with EL34 output stage and a surprisingly good OT. Unfortunately quite recently one output tube of the matched EL34 pair gave up (frying steak sounds, cracle & pop sounds etc.) so I had to install a fresh pair of EL34s. I have a collection of NOS Mullard, Siemens, Telefunken etc. EL34s, but I did not want to sacrifice them after checking out the today prices of those gems. 😀
However my local component dealer was selling Russian made Electro-Harmonixs 6CA7 tubes ( a beam pentode (or tetrode, who cares)) at a very low bargain price a few monts ago and I decided to try them. And I was surprised because the two individual tubes I bought were almost a perfectly matched pair and in addition they sounded very good, almost identical to NOS Mullards. Of course those russian made tubes probably don't last as long as NOS Mullards or Telefunkens but the price was ridiculously cheap.
Do you have experience of those 6CA7 tubes? What do you think, will they last or fail in months and if you have tried them, did you like the sound?
I have had many more EL34's than 6CA7's. I think I still have a few genuine 6CA7's in the attic but I have not thought about working with them. I have too many EL34's...
They are both listed as power pentodes so I have always believed they were 100% the same. That may not be true to a musician and I respect that but, assuming equal quality in a set of tubes compared to each other, I doubt I would be able to see any measurable difference in performance on the bench. For some reason, I seem to think the EL34 (or 6CA7) is slightly brighter than the 6L6. May just be my imagination. I have always liked the look of the EL34. I wonder sometimes how that affects the perceived sound ??
They are a fairly high voltage rated tube and as such are going to, by design, require a higher impedance output transformer. An absolute value for the value of impedance in an output transformer is just not necessary and often times not realistic in homebuilt equipment, mostly because of availability and cost of output transformers. Certainly, by engineering standards, a particular value of impedance is going to deliver the most amount of power and maybe lower THD but not necessarily the latter. Sometimes using a slightly higher impedance output transformer will yield a lower power level but improved THD. And then, there is that THD stuff again. We swear by it and use it to compare all amplifiers but we should surely know it is not the last-word, so to speak, in how we like the sound of an amplifier. I think in virtually all of my comments of how I like an amplifier, I tend to listen most carefully to the high frequency end. And then sometimes we just want to hear a different amplifier just like we want a different brand of beer - but we likely have our favorite.
I seem to be drawn to low mu triodes running class-A for audio amplifiers. The 300B SET I have is heavenly but sometimes I want a little more power. I rarely listen to music over 95 dB SPL any more but sometimes when I press on the gas peddle, I want the amplifier to GO... lol
I have had practically zero experience with vintage Russian tubes and a little with the higher end new ones made in the Russian countries. I find them OK.
@@ElPasoTubeAmps Well, EL34 is surely the tube if you want to build a pure class B p-p output stage with crazy B+ voltage and crazy peak power per tube. I have seen some old EL34 PA amps and they were a bit frightening with their 700+ V plate voltages. Of course the sound is not as clean as it would be if run at class AB.
Yes first comment love your channel been having serious problems with my build
What is going on with your build?
Good tech session. Thanks for the look.
Thank you for the great videos! Of the 2 FFT spectrum analyzer softwares you use. Which would you recommend, the ARTA or the True RTA? Is one more accurate than the other thought out the audio range? Again, I appreciate what you're doing!. Dave, Longview Tx
The one that I use now is TrueRTA.
The FFT is good and it has a very nice print page but I found the oscilloscope to be useless but I have plenty of scopes.
www.trueaudio.com/rta_down.htm
Exceeding 120 decibels maybe hard with consumer audio gear but it's not difficult at all if you use professional level drivers and amplifiers. Now getting past 150 decibels it gets a little challenging. And doing it at frequencies below 20 Hertz is even more challenging.
Yep, 100 watts into 100 dB SPL speakers would be 120 dB.
150 dB being 30 dB more or 10^3 power gain, would be 100KW. I would say that would be difficult to get there. 🙂
@@ElPasoTubeAmps I built an array of Bassmaxx ZR-18 subs. With 2.83 vrms pink noise input bandwidth limited to under 100Hz into one pair in a LLT (tuning frequency 8Hz) Hemholtz resonator, the SPL at 4' is 112dB, unweighted.
When the system is playing at a level where the "signal present" levels start to flicker, the SPL at 8' from the wall of speakers is 132dB below 40Hz.
The ZR18s have a peak to peak excursion capability of 4", 3" of which is linear and a power handling of 3600W per driver.
You can feel your heart stopping and your cloths flapping as if riding a motorcycle at highway speeds.
Nice to see you back again and talking about audio amplifiers. Is the 7591 amplifier is now your favorite, preferred to even the push pull 6B4G and 300B amps? Sorry about your fur buddy. I have cats myself. Great friends and companions.
Somehow I got swayed back to the 7591 because my friend picked up a McIntosh 225 which uses the 7591 and I really liked it. It is hard to say why we want to change sometimes. Maybe I am mellowing a little bit and don't need it so loud. These Tekton speakers sound great, to me, at a reasonable loud listening level which I rarely go to nowadays but they don't sound that good if I try to drive them over maybe 110 dB SPL. If I need to set my hair on fire, I have a Mac 2205 (210 watts per channel) that drive Klipschorns and I have truly measure them at over 120 dB. It is insane and can be downright scary to listen to music at that level.
Hey my friend, I am looking for a tube I am having a hard time finding. The tube is an 830. I have found many 830A, but can't find an 830. The difference is only that 830 is all terminated in the socket, but 830A is electrically the same but uses a plate cap. I have one 830 and want another for aesthetic. I want them for a SET stereo amp. I thought I might reach out to you because I know you have quite a collection of tubes..
Just wondering if you were to use the 12V Vacuum tubes that were created in 1957 because the transistors of the day were not ready for primetime and use a B+ of 12V and should give a few watts of power and should also work for RF.
I've got some of those little tubes but I have never used them. I have always wondered about the tubes in the warhead of some of the old proximity artillery shells in WWII. They sure had to take a tremendous G-force on being fired from a gun.
This 7591 amp is the one that rules my world in the house. It replaced all the McIntosh amplifiers. They are like collectors pieces now. I use a mono 6L6 amp in the backhouse driving my Tektons in parallel. Sounds like heaven.
I would love to make this amp. Any suggestions on output and power transformer brands that are readily available? Also, are there prints available? I have plenty of 816 and 866 tubes, so I may use one of these in the design...
Bill,
I would suggest UTC transformers like the LS-57 or Acrosound like the TO-300 if you want to use vintage OPT. They can be pricey on Ebay. For a power transformer, if you want to use FWCT then a power transformer of somewhere around 720 volts CT or if you use a voltage doubler a transformer of 180 volts. Both should give you at least 450 volts DC for the plates. 6L6's require 0.9 A each for filament current so you will need 5A to include the 6SN7 drivers. If you chose to use EL34 then each tube wants 1.8A so you would need a filament supply of more in the order of 10A to be safe.
These plate voltages I am suggesting above are using solid state rectifiers. Each channel should do a minimum of 20 watts which is sufficient for 110 dB SPL with most speakers. If you want to use vacuum tube rectifiers, you have to account for loss across the rectifier tube and the transformer voltages should be a bit higher like 800 VCT for FWCT or 200 volts for the doubler. Plate voltages above 450 VDC often require electrolytic capacitors in series to be in a safe-zone. I would use maybe two 220 uF @ 450 VDC in series, each shunted by 470K/2W resistors, etc... Hope this helps. On the other hand, Hammond Transformers makes some nice new transformers you might want to try. Hammond also has a good line of power supply chokes. I would use a 1.5H at 500mA choke, again, to be in the safe zone. I buy my chassis from www.mouser.com. They also sell Hammond transformers.
Not sure what new OPT transformers cost but the UTC and Acrosound transformers are going to likely cost better than $500. Just some thoughts.
I have an HP 3561A analyzer. Is that useful for audio spectrum analysis? It is an FFT analyzer.
Wow... here is the spec sheet on the HP 3561A analyzer. accusrc.com/uploads/datasheets/5350_3561a.pdf
It goes from 125 micro Hertz to 100 KHz. I think you can measure Earth quakes and tsunamis with it but it sure seems like it would do the audio range very nicely. That is quite an instrument. The 3580A I have is rated 5 Hz to 50 KHz but as I mentioned, it is brutally slow on the low frequencies as I am sure yours would be also. HP sure made some nice stuff.
@@ElPasoTubeAmps Well thank you. Actually, the sweep/sample rate stays about the same because it is FFT.
I need to work with it more, but Audio and speed is why I bought it.
Got it off Ebay and upgraded the CRT to an LCD multi color display because the CRT had the static display burned in it.
Everything else looks good and pretty clean inside.
Just love the old HP stuff! Gold plated connectors and conformal coated boards.
Going to have to come up with a handle though as mine is missing.
What brand/type transformers will routinely include ≤ 20Hz in the minimum THD range (29:40 min in video)?
It is my experience from testing different amplifiers over the years that the Acrosound transformers do well at the lowest frequencies - even down to 10 Hz. As best I remember they were all Williamson designs the better ones using 807 tubes. Just my experience.
@@ElPasoTubeAmps Thanks for you reply. Interesting video.
Your mic isn't working....
After watching my video tonight, I see that my lapel mike is actually not working... Thanks...
@@ElPasoTubeAmps You are welcome. We could still hear you so not a problem. You are always so good about your production and pay attention to your camera angles and micing!