The volume control at the input of a tube amp is usually 10K to 100K ohms. It's value is determined by the input capacitance of the first stage which can be substantial in a triode. Much over 100K can cause loss of high frequencies. It can be made as low as you want, depending on what the source can drive.
Most modern tube amp designs accept line level inputs and can indeed be driven by a CD player or the line outputs on a PC for a dedicated music machine. Some builders actually drive their tube amps with a phone, tablet, or other portable music listening device. These tend to put out slightly less than line level signals to avoid ear damage, so they might not drive all tube amps to clipping level. It's one of the requests I'm accommodating for the TSE-II. When I designed it in 2004 such devices only played crappy MP3's, now some are actually decent, and people want to drive their 300B amp with an iPhone.
And because of this, fake Bumblebee's exist. Smash one open and you will find an ordinary polypropylene cap.
and absorbed moisture, become leaky, and ......
The output transformers are the PRIMARY determining factor in how the amp will sound, and is where a good chunk of the budget should go. Tubes come next. Caps, resistors, and wiring / PCB are WAY down the list. It is not clear where the OP lives....shipping costs are a major factor in transformer choice.
CCS's were in use before the transistor was invented. They were found primarily in instrumentation, early computers, and other circuits where cost was not a factor, or extreme accuracy was required. The most common place to find one was in the tail of a differential amp. Look at the input sections of old Tektronix scopes.
There are patents for instrumentation, and even audio amps dating back to the early 50's (or further, that's as far as I have looked) featuring unique designs employing a CCS made with tubes.
See this thread for some examples:
augmented cathode follower?
Allen Wright's Super Linear Cathode Follower (SLCF) circuit evolved from the patents of Ross MacDonald. So did the cathode follower output stage that I have used.
Many thanks guys. Btw I live in US California.
Few more questions. What output tubes? I’ve heard a good things about 300b and 845. Are they worth it? In guitar amps output tubes choice makes significant difference. Mostly because we overdrive them. What about HiFi.
I’ve been thinking about Lundahl transformers , but not sure at this point. First I need to figure out what to build and then will figure out if they fit into the budget. But output transformers should be more or less easy upgrade, considering all specs are similiar. Correct me if I am wrong.
One more thing, I’ve been studying various schematics and see that some use few amplification stages while others more complicated. As an example McIntosh uses 3 to 4 stages. While the ones suggested uses just one or two. I suppose this is to achieve better lineriary when driving output tubes for more power. Can somebody clarify this for me?
One more thing. I have oscilloscope and tone generators. So pretty good equipped.
Thanks
Alex.
Few more questions. What output tubes? I’ve heard a good things about 300b and 845. Are they worth it? In guitar amps output tubes choice makes significant difference. Mostly because we overdrive them. What about HiFi.
I’ve been thinking about Lundahl transformers , but not sure at this point. First I need to figure out what to build and then will figure out if they fit into the budget. But output transformers should be more or less easy upgrade, considering all specs are similiar. Correct me if I am wrong.
One more thing, I’ve been studying various schematics and see that some use few amplification stages while others more complicated. As an example McIntosh uses 3 to 4 stages. While the ones suggested uses just one or two. I suppose this is to achieve better lineriary when driving output tubes for more power. Can somebody clarify this for me?
One more thing. I have oscilloscope and tone generators. So pretty good equipped.
Thanks
Alex.
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Guitarist1977-
I know this is a bit 'off route' from the direction of the thread, but you could consider building something like a RH84 using cheap (salvaged from console or from your guitar parts shelf) transformers while you are evaluating design choices for something better/bigger/more expensive.
It would give you some ideas about volume control at the input, and how much power you need for your room and tastes. Use your test gear to measure output, distortion, etc..Breadboard it or grab a baking pan for a chassis and you could wire one up in a weekend.
BTW, you won't get much 'love' for the RH (Alex Kitic) amps here from the 'big guns', but lots of people have built them and were satisfied.
My first shot at a guitar amp build was something like a Dumble or Trainwreck - what a mess. I had more success when I went back to simpler amps and 'worked up the ladder'.
I know this is a bit 'off route' from the direction of the thread, but you could consider building something like a RH84 using cheap (salvaged from console or from your guitar parts shelf) transformers while you are evaluating design choices for something better/bigger/more expensive.
It would give you some ideas about volume control at the input, and how much power you need for your room and tastes. Use your test gear to measure output, distortion, etc..Breadboard it or grab a baking pan for a chassis and you could wire one up in a weekend.
BTW, you won't get much 'love' for the RH (Alex Kitic) amps here from the 'big guns', but lots of people have built them and were satisfied.
My first shot at a guitar amp build was something like a Dumble or Trainwreck - what a mess. I had more success when I went back to simpler amps and 'worked up the ladder'.
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Tube choice does make a difference.
The 845 is an old transmitting tube. I designed and built a single ended amp using the 845 tube and it sounds nice. The 845 does it's best on high voltages, over 1000 volts kind of high. I get 30 watts per channel on 1050 volts. It's over KILL for your speakers and maybe for your health....1000 volts plays for keeps.
The 300B is another good tube. It has such a broad "sweet spot"in its plate curves that it's hard NOT to make a good amp with 300B's. It will give you 8 to 10 watts in a single ended amp, and 20 watts class A push pull, or 30 watts class AB push pull. I have done both SE and P-P amps with the 300B. It's also the most popular tube choice for the TSE board. They are not cheap tubes though. I got some Chinese and Russian 300B's nearly 20 years ago and they were $30 to $50 each. I haven't checked prices lately. There are premium brands that go well into the hundreds of dollars EACH, and NOS Western Electrics are in the thousands! I was present whey we ran a bunch of different 300B's through a TSE with $10,000 Lowther based speakers. Some people could reliably pick out the WE tubes, but I could not.
Better quality OPT's are BIGGER than an "equally specced" OPT of lesser price. It's usually easy to put in a bigger OPT, thus covering up the holes in the chassis, but you need to plan for that when you lay out the chassis.
Some amp designers use lots of negative feedback to make the specs look better, and improve the damping factor of the amp. This reduces the overall amp gain, thus requiring more stages to get the same overall gain. Others prefer to use minimal or no feedback and thus need only 2 or 3 overall stages. There are valid arguments for both sides, and plenty of room in the middle.
Your speakers and the type of music you play will make a big difference here.
Want to crank some Pink Floyd or Depeche Mode through some 15 inch speakers and rattle the windows? A multi stage push pull amp with a good bit of feedback might be the best choice, UNLESS the speakers were designed for a lowish damping factor. I could rattle the windows in the house across the street with a KT88 based SSE in UL mode (15 WPC) with cathode feedback turned on using a pair of 15 inch Hawthorne Silver Iris drivers (96dB) mounted in old console radios.
Like simple music through high efficiency speakers? a 45 tube or even a triode connected 6V6 making 2 watts per channel was very LOUD on those $$$$ Lowther horns at 106dB efficiency. Need more power (5 WPC) use an EL 34 in triode mode. It sounds good too.
Plus one vote for the RH84. I have two- one that uses only the 6BQ5 tubes, and the other can use most of the 6L6 family of OPTs. They are both wired point to point, not that I don't like the PCB. All my solid state amps have PCBs and I've almost worn out several traces on the Marantz 1200 boards with all my mucking about. Not a problem with point to point wiring. Thing is, I can't hear any difference between PCB vs point to point, so I just listen to the music.
I never talked to or met Alex Kitic, suggest that anybody has a problem with the guy or his designs design their own amps and put them out there on DIY Audio so people can build their designs and critique them.
Super Bowl and some beer drinking is going to start soon. Lots of music to listen to that will last the rest of my life. As John Cougar sang- forget all about that macho **** and learn how to build some amps. Or, something like that...
I never talked to or met Alex Kitic, suggest that anybody has a problem with the guy or his designs design their own amps and put them out there on DIY Audio so people can build their designs and critique them.
Super Bowl and some beer drinking is going to start soon. Lots of music to listen to that will last the rest of my life. As John Cougar sang- forget all about that macho **** and learn how to build some amps. Or, something like that...
Thanks a lot for your advice.
I did some reasearch today. I looked through various designs,
Then I measured how loud I usually listen to the music. It turned out that I usually don’t turn it up to more than 85db.
Considering this I think something like 10 watts would be more then enough. Taking into account that 85db from my speakers is about .01 watt.
Now I am torn between SE vs PP design. Though lean more towards SE. I have quite broad interests in music from rock to metal to jazz and classical.
Is there SE design that will give tighter bass response? Lots of the designs I saw use either cathode bias with resistor or ccs for power tube. Would fixed bias help with bass response? What SE design has widest bandwidth, provided that transformer is of highest quality?
I did some reasearch today. I looked through various designs,
Then I measured how loud I usually listen to the music. It turned out that I usually don’t turn it up to more than 85db.
Considering this I think something like 10 watts would be more then enough. Taking into account that 85db from my speakers is about .01 watt.
Now I am torn between SE vs PP design. Though lean more towards SE. I have quite broad interests in music from rock to metal to jazz and classical.
Is there SE design that will give tighter bass response? Lots of the designs I saw use either cathode bias with resistor or ccs for power tube. Would fixed bias help with bass response? What SE design has widest bandwidth, provided that transformer is of highest quality?
Hi guitarist1977, I just want to share my experience, on the last years I built 3 amp, a 30+30 W PP on RCA schematic, very powerful and I thought that’s it I got a fantastic amp in my system, then came across a schematic of a low power amp just 1.3 watt SE based on TV Vertical tubes 6CY7 and I was blowed away by the sound stage, really awesome capable also to drive my Fostex FE206En Full Range 96dB, then I recently build again a SE based on a forgotten tube also very inexpensive 6W6, total power 3.9 watt x channel, THD 0.80%, again awesome sound stage and power for a little 3.9watt, here schematic, so I really realise for my taste SE are much better than PP, also simplicity is also in my opinion a key point, regarding power transformer and OPT I am very happy with Edcor and Hammond….best regards
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Good work!
Individual bias for each of the parallel tubes.
The Parallel SE OPT has 1/2 the primary impedance of the single tube SE OPT (also, it must not saturate at the new 2X current).
Individual grid stopper resistors.
Always be careful to design the driver stage to drive 2x the capacitance when you double the output tubes.
Individual bias for each of the parallel tubes.
The Parallel SE OPT has 1/2 the primary impedance of the single tube SE OPT (also, it must not saturate at the new 2X current).
Individual grid stopper resistors.
Always be careful to design the driver stage to drive 2x the capacitance when you double the output tubes.
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Yes thanks. The output impedance of the paralleled driver stage is about 2200 ohms. I don't know what the Miller capacitance of the 12W6GT is, and to be honest I didn't give it much thought with the low impedance driver, but say it is 200pF x 2 = 400pF. If my calculations are correct, the -3dB point would be 74KHz.
The output transformers are rated at 15W so they are OK for 70mA. I read on a Edcor blog that the GXSE are rated at 100mA.
This is one of the best sounding amps I have. Highly recommended to build.
The output transformers are rated at 15W so they are OK for 70mA. I read on a Edcor blog that the GXSE are rated at 100mA.
This is one of the best sounding amps I have. Highly recommended to build.
+1
I upgraded my ST-70 to the tubesforhifi board (used in the Bob Latino kit) and I think the Bob Latino kit would be the best one-stop, bang-for-buck kit for the OP’s budget and watts requirement.
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