Okay, after making several line amps I feel that I should be up to the task of making a amplifier. Granted I'm not quite up to the design part but if a suitable design can be found I'm ready to make it.
I'm thinking along the lines of a single ended amplifier because I already have enough Quicksilvers. My speakers are in the neighborhood of 102db 1W 1M so efficiency won't be a factor. I have a supply of KT90 and EL34 tubes so I am thinking along that line.
I have found several designs by Antique Sound that use a KT88 and a 12AX7 and another that uses a 12AX7 and EL34. Needless to say I can't post them because of copywrite laws. The only thing I would need for this would be the selection of the output transformer.
Any ideas on this or a more suitable circuit?
Thanks
Joe
I'm thinking along the lines of a single ended amplifier because I already have enough Quicksilvers. My speakers are in the neighborhood of 102db 1W 1M so efficiency won't be a factor. I have a supply of KT90 and EL34 tubes so I am thinking along that line.
I have found several designs by Antique Sound that use a KT88 and a 12AX7 and another that uses a 12AX7 and EL34. Needless to say I can't post them because of copywrite laws. The only thing I would need for this would be the selection of the output transformer.
Any ideas on this or a more suitable circuit?
Thanks
Joe
SE
Hi Joe ,
If your speakers are that sensitive and you're new to power amps why not consider a small triode such as 12B4a ? They're cheap , plentiful and linear . A decent sounding 1.5watt amp can be made with one of these using a 5k output transformer and a single driver valve such as 6SL7 , 5755 or 5751 (1 section per channel) . The next step would be 2A3's but this would be far more expensive !
Hi Joe ,
If your speakers are that sensitive and you're new to power amps why not consider a small triode such as 12B4a ? They're cheap , plentiful and linear . A decent sounding 1.5watt amp can be made with one of these using a 5k output transformer and a single driver valve such as 6SL7 , 5755 or 5751 (1 section per channel) . The next step would be 2A3's but this would be far more expensive !
Personally I wouldn´t use 12AX7 in a serious amp.
Have a look at PC/EC86 instead, or maybe a triodewired pentode like EF86 or E81L. Be creative!
With 102dB speakers I guess you could aim for low distortion rather than maximum power from the power tube, like using 5k load instead of 2,5k for a triodewired EL34.
Have a look at PC/EC86 instead, or maybe a triodewired pentode like EF86 or E81L. Be creative!
With 102dB speakers I guess you could aim for low distortion rather than maximum power from the power tube, like using 5k load instead of 2,5k for a triodewired EL34.
12B4A
The things sound far too good to have lived inside TV's and oscilloscopes for all these years ! I'm using mine with battery grid bias driven by a CCS loaded battery biased 14F7 (loctal 6SL7) . Crappy old console outputs , but sounds excellent . How are you using yours ?
Fuling said:Oh, did someone mention 12B4???
One of my absolute favorites!!
Far better than EL34!!!
The things sound far too good to have lived inside TV's and oscilloscopes for all these years ! I'm using mine with battery grid bias driven by a CCS loaded battery biased 14F7 (loctal 6SL7) . Crappy old console outputs , but sounds excellent . How are you using yours ?
I use them in a "Free Lunch" amp (direct coupled choke loaded input stage with the B+ for the input stage taken from the cathode of the power tube).
Input stage is 6C4 loaded by Hammond 150H 8mA chokes, output stage 12B4A parafeed with Hammond 30H 40mA choke and 125C OPT coupled trough a 4uF paper in oil cap.
I have future plans of a linestage using choke loaded 12B4A.
It´s a good tube to use with inductive loads because of the low plate resistanse (about 1Kohm).
Input stage is 6C4 loaded by Hammond 150H 8mA chokes, output stage 12B4A parafeed with Hammond 30H 40mA choke and 125C OPT coupled trough a 4uF paper in oil cap.
I have future plans of a linestage using choke loaded 12B4A.
It´s a good tube to use with inductive loads because of the low plate resistanse (about 1Kohm).
No need for a schematic !
6SL7 or 7F7 grid to 0V , 680K grid leak no stopper
100k resistor or 1mA CCS anode load (TO92 DN2540 + 2k pot)
1.25V NimH battery from cathode to 0V
12B4a 470 ohm grid stopper , 680K grid leak connected to 3 x 9V batteries (- to grid leak , + to 0V)
0.1uF polyprop coupler
12B4a cathode connected to 0V
Driver HT decoupled by 10uF motor run-20H choke to B+
Power supply is 240VAC to EZ81/1n4007 hybrid 4uF , 15H choke to 40uF of motor runs
Crappy 5k outputs circa 1965
Hope this helps , sorry about the batteries but I hate electrolytic bypasses !
316a
burnedfingers said:Well, I guess I hadn't thought of the 12b4a. Do you have a schematic that you would care to share? I have several 5751's and 6sl7's. I will be building a set of 2A3's soon
There is nothing that says that I can't have all three designs. I will start out and make my progressions.
Joe
6SL7 or 7F7 grid to 0V , 680K grid leak no stopper
100k resistor or 1mA CCS anode load (TO92 DN2540 + 2k pot)
1.25V NimH battery from cathode to 0V
12B4a 470 ohm grid stopper , 680K grid leak connected to 3 x 9V batteries (- to grid leak , + to 0V)
0.1uF polyprop coupler
12B4a cathode connected to 0V
Driver HT decoupled by 10uF motor run-20H choke to B+
Power supply is 240VAC to EZ81/1n4007 hybrid 4uF , 15H choke to 40uF of motor runs
Crappy 5k outputs circa 1965
Hope this helps , sorry about the batteries but I hate electrolytic bypasses !
316a
burnedfingers said:
An externally hosted image should be here but it was not working when we last tested it.
Tim
Hey Tim, never thought you'd try using a transistor!
How is it? Or did you steal some design parameters from someone
else and add it to your own tube output?
I have a few suggestions... Here goes.
First off, I would imagine you'd get a way nicer amp by
using a tube for the input stages and transistors for the output.
I can blame you for choosing any specific arrangement though, since you are the designer and it's your choice.
I must ask, how does it sound? I think the thermal stablility
will be a bit absurd with the transistors, perhaps we need
a CCS if possible to keep things a little more concentric, I'm not sure.
Also, I imagine you'd get more "t00bey" sound if you use
a tube input, since the tube will be imposing it's qualities on
the most important part of the amplification, the voltage gain.
The transistor should be relatively transparent in the output stage if used properly in class A with a CCS arrangement. Maybe I could give you some design ideas for stable transitors?
These are just my suggestions so please don't take them personally. I know you're into tube sound, so maybe we can make it more authentic in traites?
Anyway, I'm amazed that you tried a transistor design, good work!
How is it? Or did you steal some design parameters from someone
else and add it to your own tube output?
I have a few suggestions... Here goes.
First off, I would imagine you'd get a way nicer amp by
using a tube for the input stages and transistors for the output.
I can blame you for choosing any specific arrangement though, since you are the designer and it's your choice.
I must ask, how does it sound? I think the thermal stablility
will be a bit absurd with the transistors, perhaps we need
a CCS if possible to keep things a little more concentric, I'm not sure.
Also, I imagine you'd get more "t00bey" sound if you use
a tube input, since the tube will be imposing it's qualities on
the most important part of the amplification, the voltage gain.
The transistor should be relatively transparent in the output stage if used properly in class A with a CCS arrangement. Maybe I could give you some design ideas for stable transitors?
These are just my suggestions so please don't take them personally. I know you're into tube sound, so maybe we can make it more authentic in traites?
Anyway, I'm amazed that you tried a transistor design, good work!
It was a cheezy breadboarded design to see how much power I could squeeze out of the relatively high-current-capable 12B4. Something like 200mA in that circuit?
I used transistors because, little as I know about them, I figured I could hack something together that'd drive the tube adequately. Obviously the 330k base resistor for instance, was selected and probably will not work again in practice.
And hmm... welcome to the tubes forum! It's about damn time
Tim
I used transistors because, little as I know about them, I figured I could hack something together that'd drive the tube adequately. Obviously the 330k base resistor for instance, was selected and probably will not work again in practice.
And hmm... welcome to the tubes forum! It's about damn time
Tim
Re: SE
Yep, very nice in PP with a CCS 6N1P driving them. I threw a pair together as a breadboard experiment and was really surprised at how good they were. Not quite enough power for the Khorns when I wanted to rock out, but should do fine driving my mid/high horns if I biamp.
Joe,
the 12ax7 doesn't drive a KT88 (trioded) very well in grounded cathode. Might do better as an SRPP, but I suspect it'll still be a tone control.
316a said:
Yep, very nice in PP with a CCS 6N1P driving them. I threw a pair together as a breadboard experiment and was really surprised at how good they were. Not quite enough power for the Khorns when I wanted to rock out, but should do fine driving my mid/high horns if I biamp.
Joe,
the 12ax7 doesn't drive a KT88 (trioded) very well in grounded cathode. Might do better as an SRPP, but I suspect it'll still be a tone control.
Hi,
A 12AX7A in SRPP does NOT have the same frequency response as a simple anode follower using the same tube.
For OPT coupled amps with a falling response from 30KHz and up, having a Mhz input is not going to help much bar, perhaps, phase response.
Other than that, there are Miller compensation tricks and topologies that can cancel it out.
Certainly, if it's a very wideband amp you're after it probaly won't cut it...
To me, wideband isn't the target, it's welcome though, but phase response at any given output power is; the proof is in the humble 2A3 PP amps I drive a two-way speaker with.
The endresult is musical and those speakers just disappear given a half decent source.
Now, tell me if that's not a good thing to have??
Oh...to add insult to injury: that PP pair of 2A3s is driven by the humble 12AX7A with aplomb and bandwidth is only limited by the OPTs.
It'll be better off with a 6SL7? Probably. Unfortunately I only have one life.
It's a grey world outside...it really is.
A 12AX7A in SRPP does NOT have the same frequency response as a simple anode follower using the same tube.
For OPT coupled amps with a falling response from 30KHz and up, having a Mhz input is not going to help much bar, perhaps, phase response.
Other than that, there are Miller compensation tricks and topologies that can cancel it out.
Certainly, if it's a very wideband amp you're after it probaly won't cut it...
To me, wideband isn't the target, it's welcome though, but phase response at any given output power is; the proof is in the humble 2A3 PP amps I drive a two-way speaker with.
The endresult is musical and those speakers just disappear given a half decent source.
Now, tell me if that's not a good thing to have??
Oh...to add insult to injury: that PP pair of 2A3s is driven by the humble 12AX7A with aplomb and bandwidth is only limited by the OPTs.
It'll be better off with a 6SL7? Probably. Unfortunately I only have one life.
It's a grey world outside...it really is.
Ok I will narrow it down to either a PP 12B4a or a PP 2A3. What the heck I need both don't I? You can never have enough amps right?
Tim
I appreciate the fine schematic you posted, I would like to rock a little harder than what that baby can offer.
Frank
Your teasing me again talking about the 2A3's. This has got to be one of my weaknesses. Nothing against the 300B but the 2A3 has a distinct sound. Point me to a good PP 2A3 design will you?
Well everyone has convinced me to trash the 12AX7 design I was thinking of.
Joe
Tim
I appreciate the fine schematic you posted, I would like to rock a little harder than what that baby can offer.
Frank
Your teasing me again talking about the 2A3's. This has got to be one of my weaknesses. Nothing against the 300B but the 2A3 has a distinct sound. Point me to a good PP 2A3 design will you?
Well everyone has convinced me to trash the 12AX7 design I was thinking of.
Joe
Hi,
Every single tube has a distinct sound.
I'd say nothing against a 2A3 but the 300B has a distinct sound...same same but different...except the price?
Now I don't want to discuss design magic but you actually can make one sound like the other...something I'd like to keep for post 8.000....
And what if it uses a 12AX7A? Now I'm really teasing...just imagine: 1 12AX7 as input + splitter and than a PP 2A3.
No global feedback, no bypass caps...doesn't that sound like a wet dream?
Oh, and it does kick serious but too....
Clevor Trevor,
Every single tube has a distinct sound.
I'd say nothing against a 2A3 but the 300B has a distinct sound...same same but different...except the price?
Now I don't want to discuss design magic but you actually can make one sound like the other...something I'd like to keep for post 8.000....
And what if it uses a 12AX7A? Now I'm really teasing...just imagine: 1 12AX7 as input + splitter and than a PP 2A3.
No global feedback, no bypass caps...doesn't that sound like a wet dream?
Oh, and it does kick serious but too....
Clevor Trevor,
12AX7
If you knew the prices I get for Mullard 12AX7 you wouldn't use them either ! Personally I think 12AX7's belong in non-DIY equipment such as vintage and guitar amps . I've used the things a few times and put it like this : the projects were never keepers with the things in . It's pretty simple with 6SN7 , it's a decent sounding valve ! You can't go far wrong
316a
Sch3mat1c said:
Ditto! I thought you absolutely had to use a 6SN7 for every damned thing, from driving the hallowed 300B to even.. another 6SN7!
Tim
If you knew the prices I get for Mullard 12AX7 you wouldn't use them either ! Personally I think 12AX7's belong in non-DIY equipment such as vintage and guitar amps . I've used the things a few times and put it like this : the projects were never keepers with the things in . It's pretty simple with 6SN7 , it's a decent sounding valve ! You can't go far wrong
316a
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