milen007 said:
I would go for the JJ 2A3-40. This is practically a 300B with 2.5V filament supply. It will not require necessarily a DC filament supply (with a normal 300B, IMO, it is necessary).
You could start with a simple 2-stage circuit, for example, a 6SN7 SRPP (or Mu-Follower) + the 2A3-40 with self bias at medium dissipation (for example, around 350V/60 mA).
You should get easily around 8W.
If this is your first amp, I think you will learn a lot of practical things from the above simple amplifier and then will be able to judge better for a more complex 12-13W amplifier (where you can continue to use the same output transformer and the 2A3-40).
Cheers,
45
There is no substitute for experience!
If the transformers are in the budget I think it is worth spending 200$ for the 2A3-40's that will last at least 3 times more than any pentode and can be used for many projects.... you don't to buy new tubes everytime while can still build a really new amp.
A simple 2-stage amp with self-bias, as starter, is nothing really difficult to understand. The practice, instead is best "book".
45
If the transformers are in the budget I think it is worth spending 200$ for the 2A3-40's that will last at least 3 times more than any pentode and can be used for many projects.... you don't to buy new tubes everytime while can still build a really new amp.
A simple 2-stage amp with self-bias, as starter, is nothing really difficult to understand. The practice, instead is best "book".
45
wakibaki said:
kevinkr said:
i think one of this two books already in my amazon shopping cart waiting to checkout since 2 months ago. thanks for the other book recommendation.
yep i plan to get some good read on tube amp. information on web seems scattered. maybe i should just get the book 1st
thanks for the encouragement. just confirmation that i got it right. JJ 2A3 - 40 is 2a3 tube right?45 said:
got any schematic that i can learn on it?
thx guys for all the inputs. really appreciate them. i do learn quite much in this treat from the pointer of you guys that i have the right "keywords" to google.
erwin
milen007 said:
No Milen it's just the name... in practice it is a 300B.....
The difference is in the filament which, like the 2A3, requires 2.5V supply.
If you want to spend less and have a good 300B, then the Valve Art is ok.
There are various models of Valve Art 300B: buy the normal one (which is a copy of WE) and don't buy that with mesh plate....
milen007 said:
You can start from this, for example:
http://www.megahertzaudio.it/schema_triodino_iii.htm
The only difference if you use the 2A3-40 (or a 300B) is the anode voltage and the cathote resistor for the power stage.
The cathode resistor for the 300B would be 1.2K in place of the 850 ohm in that schematic (it is designed together with the filament supply) and the anode voltage supply needs to 450V.
With 450V supply, you will get, in theory, 72V drop on the 1.2K resistor (i.e. 60 mA).
I wrote in theory because you must verify it in practice, because your tubes could be quite different from the average.... initially you can use a variable resistor (for example 2K) to adjust current. Then, once you bias the tube as you like, you replace the variable resistor with a fixed resistor.
If you use approx. 450V also for 6SN7 (because there is only 270 ohm in the second RC supply filter for 6SN7) then go for 6SN7GTB (GTA) types.
Other modifications are possible, of course, but I think this is a good starter.
The only problem of this circuit is the input sensitivity: you need approx. 3V rms to get 8-9W. So you need a very good preamplifier.
Cheers,
45
hi guys
i have decided to build this:
http://www.single-ended.com/como-armar.htm
this is integrated amp right? can i use preamp and leave out the potentiometer on the schematic? as i have just build pointz's 6t4 preamp that i like very much
as i have 12ax7 tele and sletvana in the drawer.
i need help specifying the power transformer requirement.
lets see:
ecc83 needs 0.15A for 12.6v heater supply. how much current for B+?
6550 needs 1.5A for 6.3v heather supply. how much current for B+?
5U4G need 3A for 5v heater supply
so i need power transformer of:
330v CT 330v how many amp? 200mA(guessing from the choke)? and 6.3v CT 4A and 12.6v CT 1A and 5v CT 4A.
please correct me if iam wrong
TIA
erwin
i have decided to build this:
http://www.single-ended.com/como-armar.htm
this is integrated amp right? can i use preamp and leave out the potentiometer on the schematic? as i have just build pointz's 6t4 preamp that i like very much
as i have 12ax7 tele and sletvana in the drawer.
i need help specifying the power transformer requirement.
lets see:
ecc83 needs 0.15A for 12.6v heater supply. how much current for B+?
6550 needs 1.5A for 6.3v heather supply. how much current for B+?
5U4G need 3A for 5v heater supply
so i need power transformer of:
330v CT 330v how many amp? 200mA(guessing from the choke)? and 6.3v CT 4A and 12.6v CT 1A and 5v CT 4A.
please correct me if iam wrong
TIA
erwin
A power transformer of 150mA to 200mA should be fine to run both channels.
Just wondering though, not to muddy up the waters, but why not use ½ of a 12AT7 or a 6DJ8 and do away with the cathode follower all together? Do a search around here or the internet in general for Tubelab and check out the Simple SE. Uses ½ of a 12AT7 with a CCS load and it will drive anything from a 6V6 to a KT88. Bottlehead uses a similar driver (being a 12AT7 with a CCS load) to drive much more temperamental 2A3's and 300B's. The 12AX7 seems to have more gain than needed and with ½ as a follower burning what, 1mA or so? With a 12AT7 or 6DJ8 you get to utilize some of that gain from your preamp and you all together get to eliminate the cathode follower. If you decide later you don't want to use a preamp, the 12AT7 has more than enough gain/ability to drive a EL34 or KT88 straight from a CD.
Yes you can lose the input pot, just wire a 100k or so resister from grid to ground unless you want hear some wonderful sounds when the cables are pulled
Cheers
James
Just wondering though, not to muddy up the waters, but why not use ½ of a 12AT7 or a 6DJ8 and do away with the cathode follower all together? Do a search around here or the internet in general for Tubelab and check out the Simple SE. Uses ½ of a 12AT7 with a CCS load and it will drive anything from a 6V6 to a KT88. Bottlehead uses a similar driver (being a 12AT7 with a CCS load) to drive much more temperamental 2A3's and 300B's. The 12AX7 seems to have more gain than needed and with ½ as a follower burning what, 1mA or so? With a 12AT7 or 6DJ8 you get to utilize some of that gain from your preamp and you all together get to eliminate the cathode follower. If you decide later you don't want to use a preamp, the 12AT7 has more than enough gain/ability to drive a EL34 or KT88 straight from a CD.
Yes you can lose the input pot, just wire a 100k or so resister from grid to ground unless you want hear some wonderful sounds when the cables are pulled
Cheers
James
I used to design and build valve amps. I don't now, because I can get better long term results with Solid state. Trouble with valves is they need constant attention to maintain the original performance, and I simply could not be bothered.. Still, they are simple and fun. The various circuits all have their supporters, but the one thing that is absolutely critical is the output transformer. It is this that mainly makes the difference between an excellent and a so-so amplifier.
I agree that the output transformer, especially in a zero feedback SE amplifier, is critical to performance. However I don't know that I can agree with the constant attention and maintenance statement. True, every now and then valves (and bias/what not) will need to be checked and maybe replaced, that is just something one has to accept when they build or buy a tube amplifier. I have two amps here in my house that have been checked yet never have needed to be adjusted, and they are still running on the original tubes. One is about 25 to 30 years old and the other is older. Some have had amps running day in and day out for years without needing to adjust or replace valves.
My father was a service rep for the RCA theater division for years. He serviced many a drive in amplifier, some of the toughest yet most abused amps in the field. He did change out a lot of valves but it was for two reasons. One, the drive in amps where super abused; and two, if one tube was bad often all of them where changed, saved service calls, then tubes where cheap. Hardly ever though did he have to adjust anything bias wise. He remembers many a times walking into a drive in booth where some little rodent had chewed through the wires and the amps where pushing a dead short on the outputs. The amp wouldn't make any noise (obviously) and the plates on the 807's would glow white hot! After the amps where shut down, checked, and the wires fixed, they where fire back up and run just fine, good as new. This isn't something I would recommend with any tube amp, but I bet there would be a higher percentage of survival compared to solid state. He said too that often times when something failed just that section could be checked and the tube replaced. The input or output dies, replace the tubes, check everything, and it was back up and running. Now I know that not all tube amps do this, some fail catastrophically. However it seems that in a higher percentage of the time SS will always fails catastrophically.
I don't know, these could be bits of generalizations, but my 2 cents.
Cheers
James
My father was a service rep for the RCA theater division for years. He serviced many a drive in amplifier, some of the toughest yet most abused amps in the field. He did change out a lot of valves but it was for two reasons. One, the drive in amps where super abused; and two, if one tube was bad often all of them where changed, saved service calls, then tubes where cheap. Hardly ever though did he have to adjust anything bias wise. He remembers many a times walking into a drive in booth where some little rodent had chewed through the wires and the amps where pushing a dead short on the outputs. The amp wouldn't make any noise (obviously) and the plates on the 807's would glow white hot! After the amps where shut down, checked, and the wires fixed, they where fire back up and run just fine, good as new. This isn't something I would recommend with any tube amp, but I bet there would be a higher percentage of survival compared to solid state. He said too that often times when something failed just that section could be checked and the tube replaced. The input or output dies, replace the tubes, check everything, and it was back up and running. Now I know that not all tube amps do this, some fail catastrophically. However it seems that in a higher percentage of the time SS will always fails catastrophically.
I don't know, these could be bits of generalizations, but my 2 cents.
Cheers
James
Hi James
thanks for the suggestion, i have looked at the board before, and has forgotten till you suggest it. thats very wide option to be tried. seems quite good option. but i got abit doubt working with pcb as we cant try out few type of resistors or capacitors without damaging the pcb.
happen to me with my ss amp. till now i have no idea where i ruin the pcb. but its a good choice once build and leave it there. easier and less messy.
not sure if this board last long with my itchy hands. but with less part count, i think will consider it as i might be able to find other soldering alternative if i ruin the board.
thx for the suggestion.
erwin
thanks for the suggestion, i have looked at the board before, and has forgotten till you suggest it. thats very wide option to be tried. seems quite good option. but i got abit doubt working with pcb as we cant try out few type of resistors or capacitors without damaging the pcb.
happen to me with my ss amp. till now i have no idea where i ruin the pcb. but its a good choice once build and leave it there. easier and less messy.
not sure if this board last long with my itchy hands. but with less part count, i think will consider it as i might be able to find other soldering alternative if i ruin the board.
thx for the suggestion.
erwin
rjb said:
I don't think so. A well made valve amp will work flawlessly for years. I do check my amps approx. every five years and the first one I built, an EL34 PP, is now 11 years old with all the (chinese!) tubes in perfect shape.
The output transformer has to be good as any other critical component. The only real problem can be its cost.
However it can make a difference (an improvement) in small SS amps, too...
45
The smell of burning fibreglass in the morning
It's a combination of much larger currents and PCB based construction. About 20 years ago I worked as a board stuffer/service tech for a broadcast electronics company.
One of my strongest memories is of when a 150W mosfet amp was powered up with the supply rails reversed. Or rather, when said amp was re-power with the rails corrected and the fuses replaced.
The output devices were now short circuit. On application of power umpteen amps ran from +48 to -48. The PCB traces got HOT and the ensuring fire and copious amounts of black smoke rapidly emptied the building.
When the fire was brought under control, only the chassis was salvagable.
HOT
rjb said:
It's a combination of much larger currents and PCB based construction. About 20 years ago I worked as a board stuffer/service tech for a broadcast electronics company.
One of my strongest memories is of when a 150W mosfet amp was powered up with the supply rails reversed. Or rather, when said amp was re-power with the rails corrected and the fuses replaced.
The output devices were now short circuit. On application of power umpteen amps ran from +48 to -48. The PCB traces got HOT and the ensuring fire and copious amounts of black smoke rapidly emptied the building.
When the fire was brought under control, only the chassis was salvagable.
HOT
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.