Ok guys, THIS ONE had been conceived from few months ago. At first I wondered if anybody made a complete PP amp on a single bottle. .. I caught myself listening to jazz on very low levels at my job all the time, a bit of blues or blues-rock, that’s it. Not much of head-phones user so I decided why the H not?
After some research on candidates it came to compactrons (of course) and further looking narrowed it to the two options: 6U10 and 6K11/6Q11. I would not consider the exotic ECCL800 ones as they have the common cathode for all three-halves, and. .. are the top-tipped, which I dislike.
I opted on the 6U10 compactron. The original application of this project was the headphone amp, and most I wanted was to keep it “all tube on signal path” [ATOSP] concept except maybe some simple cathode CCS added.
BTW, the best sounding are RCA with side-getter, then equal Zeniths and Sylvanias -> International -> regular RCA -> and GEs did not shine at all. Ratheon sounded the crappiest. I had about 3-5 pieces of ea and my evaluation might be subjective, but I tend to think that the cheaper competitors figured a little more efficient technology. Anyways, out of what I have on-hands I’m opting for “RCA side-getter” for myself, rare ones actually.
. ..to be continued.
After some research on candidates it came to compactrons (of course) and further looking narrowed it to the two options: 6U10 and 6K11/6Q11. I would not consider the exotic ECCL800 ones as they have the common cathode for all three-halves, and. .. are the top-tipped, which I dislike.
I opted on the 6U10 compactron. The original application of this project was the headphone amp, and most I wanted was to keep it “all tube on signal path” [ATOSP] concept except maybe some simple cathode CCS added.
An externally hosted image should be here but it was not working when we last tested it.
BTW, the best sounding are RCA with side-getter, then equal Zeniths and Sylvanias -> International -> regular RCA -> and GEs did not shine at all. Ratheon sounded the crappiest. I had about 3-5 pieces of ea and my evaluation might be subjective, but I tend to think that the cheaper competitors figured a little more efficient technology. Anyways, out of what I have on-hands I’m opting for “RCA side-getter” for myself, rare ones actually.
. ..to be continued.
Here is where I am now at. Being shown, the project I estimate is 70% complete. What left is the PSU design/make on a pcb + putting 4 screws on the bottom cover corners, done. Here is the current pic:
I will post some experimenting and other info later on...
An externally hosted image should be here but it was not working when we last tested it.
I will post some experimenting and other info later on...
6AC10 /12AC10 is actually 3 x 12AT7 rather than 6DJ8
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Sure. I have it only on a scanned snippet (Ls - are 20 turns on a 0.25 wa 1K resistor). Red/green are measurements for ae channel. 1.25V on the input stage's cathode you get with 1K2 + 470uF6V instead of the red LED:
Then, I used 15 Wa Hammond trafo with switched secondaries to find out the best sound/outcome impedance, and it turned out be 20K per shoulder or 40K PtP for 6U10.
With figured 6U10 be it, I auditioned all I have in stash with several trafos, and I must tell ya that the comparable irons under $10 bill all. .. fit the bill. Unless you go for the oversized 15-20 watters.
I tried Hammond (the actual small-power OPTs), Poshan, Prem, TrafoBlock, Talema (not bad), some other brands – all sounded much very same, if I can call it “sound”. I finally opted for PREM as the best suitable on dimensions for the project. Ordered some custom ones – they came less quality and out of expectations comparing to standard ones. Unfortunately, they do not have any standard 1 x 115V -> 2 x 3V or so, I had to alter standards in order to make ‘em 40K PtP. The amp seems ok with down to 12K and even gives a bit more LFs with such, but the HFs are in decline, no wonder.
What at the end.
This might be all one lame project )) I‘m not arguing it. It is my first tube project from scratch and going not bad on my ****-scale. With the headphones the amp gives blowing deep bass, enough of highs, can’t claim it be the best balanced, BUT:
it is not bad with speakers. It “pumps out” some honest 0.25-0.3 Wa with 1-1.5% THD of the very tube-sound )) which is precisely of what I listen every day and several hours to, yeah. I also find it ok appropriate for evening listening on background at home.
An externally hosted image should be here but it was not working when we last tested it.
Then, I used 15 Wa Hammond trafo with switched secondaries to find out the best sound/outcome impedance, and it turned out be 20K per shoulder or 40K PtP for 6U10.
With figured 6U10 be it, I auditioned all I have in stash with several trafos, and I must tell ya that the comparable irons under $10 bill all. .. fit the bill. Unless you go for the oversized 15-20 watters.
I tried Hammond (the actual small-power OPTs), Poshan, Prem, TrafoBlock, Talema (not bad), some other brands – all sounded much very same, if I can call it “sound”. I finally opted for PREM as the best suitable on dimensions for the project. Ordered some custom ones – they came less quality and out of expectations comparing to standard ones. Unfortunately, they do not have any standard 1 x 115V -> 2 x 3V or so, I had to alter standards in order to make ‘em 40K PtP. The amp seems ok with down to 12K and even gives a bit more LFs with such, but the HFs are in decline, no wonder.
What at the end.
This might be all one lame project )) I‘m not arguing it. It is my first tube project from scratch and going not bad on my ****-scale. With the headphones the amp gives blowing deep bass, enough of highs, can’t claim it be the best balanced, BUT:
it is not bad with speakers. It “pumps out” some honest 0.25-0.3 Wa with 1-1.5% THD of the very tube-sound )) which is precisely of what I listen every day and several hours to, yeah. I also find it ok appropriate for evening listening on background at home.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
This is the cutest tube amp I've ever seen. It beats the 1P24B 'Zwerg"
Zwerg - with two stubby glowing tubes on display!
An output transformer of such high impedance is indeed a problem, but because output power is so small, transformer may be also small, and custom winding a quality transformer shouldn't be a problem. With 6 mm stack of 25 mm Midcom permalloy laminations, 1000+1000 turns of 40 AWG wire will give 160 H (40K ct, -3 dB at 40 Hz). 20 turn secondary (4 Ohms) should go between primary halves.
An old time 6-8" Alnico speaker should sound really good with this kind of amp.
Zwerg - with two stubby glowing tubes on display!
An output transformer of such high impedance is indeed a problem, but because output power is so small, transformer may be also small, and custom winding a quality transformer shouldn't be a problem. With 6 mm stack of 25 mm Midcom permalloy laminations, 1000+1000 turns of 40 AWG wire will give 160 H (40K ct, -3 dB at 40 Hz). 20 turn secondary (4 Ohms) should go between primary halves.
An old time 6-8" Alnico speaker should sound really good with this kind of amp.
Yes that's what I recalled, but with a quick glance at the data sheet, I misread plate resistance for transconductance. 12AT10 it is.
Tnx, and it actually double-beats Zwerg as mine is socketed-tubes based.
Soo, slooowly but surely. .. the project is coming out. Here are some yesterday’s photos. Basically the amp is completed and working, but, due to a couple of times I had forgotten to power off the amp in the office on Fridays, and there is always a chance /me not coming on Monday, I decided to add the “to-standby” timer, for about 6.5 hours.
That required quite the additions, you see two triacs, one interrupts the B+ trafo, and another switches the filament's one so its out drops from 6.3 to 4V. The small circuitboard with two ICs will be made flat and placed on top of HV caps, have already been breadboarded.
It went just 1/10’’ short of space in height (it’s sticking out a little bit) as I decided to add the extra layer of insulation between Amp and PSU floors + a magnetic shield in between (made of computer PSU’s case). Gotta somehow fix this, I think of an aluminum frame made a little outstanding on a perimeter, which would also add some style to it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The last piece, 'to-standby timer' is in place, all tested and works as intended.
Gotta fix the case shortage and. .. it's good for the final screwdriver's action ))
Gotta fix the case shortage and. .. it's good for the final screwdriver's action ))
An externally hosted image should be here but it was not working when we last tested it.
Tnx, I designed the Soviet military equipment in the past (not a joke), hopefully I finish the amp this week. I got a small sheet of aluminum to make that extra spacer of about 2 mm or 1/12".
All trafos are PREM 6VA (OPTs) & 12VA. Unfortunately none fits "as is", so I had to rewind: a) the secondaries on OPTs completely, b) added a bit to a FL's secondary, c) and added a bit to HV's primary.
The HV was a custom-ordered MISTAKE, it came with twice higher exciting current than the standard would have, which would add 3 Wa to the total consumption which is unacceptable for such small unit, very disappointing. I will not go for their custom ones again: instead of admitting their fault, they sent me two different fabrication testing worksheets, the second one was "adjusted" towards higher "acceptable" current values.
Otherwise their stuff works well.
HAMMOND actually make similar line, next time I go for theirs
While operating the case goes up to approx 40 C which feels below hot or very warm; in standby it is barely warm. This flea amp sounds just a little louder than I need for the background listening, so evr worked out well, by ear it's about 0.3 Wa, maybe up to 0.5 per channel.
I did not measure the frequency range of OPTs, as it's silly to expect the Hi-Fi quality from such the build, but while breadboarding I tried/auditioned every piece (including the case - do not laugh, the OPTs lay right on top of FL & HV ones, and with thin steel sheet in between the interference seems below marginal), this process took like 4 months to figure everything to possible best, and I must tell the sound is pleasing as much as you could get.
All trafos are PREM 6VA (OPTs) & 12VA. Unfortunately none fits "as is", so I had to rewind: a) the secondaries on OPTs completely, b) added a bit to a FL's secondary, c) and added a bit to HV's primary.
The HV was a custom-ordered MISTAKE, it came with twice higher exciting current than the standard would have, which would add 3 Wa to the total consumption which is unacceptable for such small unit, very disappointing. I will not go for their custom ones again: instead of admitting their fault, they sent me two different fabrication testing worksheets, the second one was "adjusted" towards higher "acceptable" current values.
Otherwise their stuff works well.
HAMMOND actually make similar line, next time I go for theirs
While operating the case goes up to approx 40 C which feels below hot or very warm; in standby it is barely warm. This flea amp sounds just a little louder than I need for the background listening, so evr worked out well, by ear it's about 0.3 Wa, maybe up to 0.5 per channel.
I did not measure the frequency range of OPTs, as it's silly to expect the Hi-Fi quality from such the build, but while breadboarding I tried/auditioned every piece (including the case - do not laugh, the OPTs lay right on top of FL & HV ones, and with thin steel sheet in between the interference seems below marginal), this process took like 4 months to figure everything to possible best, and I must tell the sound is pleasing as much as you could get.
Com-ple-ted! 
btw, the case is Hammond 1590CBK.
In the very hands that made it to exist:
Now it took its place in my office, mated with Minimus-7:
Happy building!
btw, the case is Hammond 1590CBK.In the very hands that made it to exist:
An externally hosted image should be here but it was not working when we last tested it.
Now it took its place in my office, mated with Minimus-7:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Happy building!
Shef visited me several days ago and I had a chance to see and to listen to this flea-power amp. Here is my impression. Please keep in mind that it was compared to a 6B4G P/P amp that is 20x larger and sounds at least at a level of RM10.
I was very impressed with how small this amp is. It's definitely the smallest tube amp that I have seen. Nice looking too! Even though the amp is so small, it was able to produce enough power for Tekton Pendragons (95dB, 8 Ohm) to sound loud enough for casual non-overwhelmingly loud listening in a 15x10ft room. I usually listen to the music just a touch louder. I think I measured sound pressure at 1m at about 85dB. There was a tiny hint of hum if you put your ear into the speaker. My 6B4G makes more hum than that! Super impressive!
We listened to various music - classical, jazz, country, vocal, rock. Overall amp sounds very musical with good midrange and base. It was definitely fun and pleasure to listen to. Classical music and vocal was nice. I was surprised how well it was able to reproduce complex symphony music. Rock was missing energy and dynamics, which was expected considering the output impedance. The only other area for improvement was some lack of details. We thought that it was probably due to lack of high frequency. But, it's also possible that the details were lost in a cheap interconnect that I had to use to connect to its 3.5mm input. But, then again, it was compared to an amp with OPT larger than this amp.
Kudos to Mr. Shef for this neat design!
I was very impressed with how small this amp is. It's definitely the smallest tube amp that I have seen. Nice looking too! Even though the amp is so small, it was able to produce enough power for Tekton Pendragons (95dB, 8 Ohm) to sound loud enough for casual non-overwhelmingly loud listening in a 15x10ft room. I usually listen to the music just a touch louder. I think I measured sound pressure at 1m at about 85dB. There was a tiny hint of hum if you put your ear into the speaker. My 6B4G makes more hum than that! Super impressive!
We listened to various music - classical, jazz, country, vocal, rock. Overall amp sounds very musical with good midrange and base. It was definitely fun and pleasure to listen to. Classical music and vocal was nice. I was surprised how well it was able to reproduce complex symphony music. Rock was missing energy and dynamics, which was expected considering the output impedance. The only other area for improvement was some lack of details. We thought that it was probably due to lack of high frequency. But, it's also possible that the details were lost in a cheap interconnect that I had to use to connect to its 3.5mm input. But, then again, it was compared to an amp with OPT larger than this amp.
Kudos to Mr. Shef for this neat design!
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