Hello All,
I just built my first tube amp based on the JE Labs 2A3 2001 edition.
It’s a 6sl7 grounded cathode - cathode follower capacitor coupled to the 2A3. I drive the amp from the pre-amp output of my Stereo receiver into 100db/w/m horn type speakers.
The amp sounds OK…. But just OK
I’m looking for ideas for a better front end.
The first choice is to stick with a tube that fist into the 8 – pin socket.
However I’m open to switching to a 9-pin tube as a last resort.
So, of the following configs, what do you like.
A. grounded cathode (just use ½ of the tube)
B. SRPP
C. U-Follower
D. grounded cathode - cathode follower (as built)
E. OTHER
Thanks in Advance
I just built my first tube amp based on the JE Labs 2A3 2001 edition.
It’s a 6sl7 grounded cathode - cathode follower capacitor coupled to the 2A3. I drive the amp from the pre-amp output of my Stereo receiver into 100db/w/m horn type speakers.
The amp sounds OK…. But just OK
I’m looking for ideas for a better front end.
The first choice is to stick with a tube that fist into the 8 – pin socket.
However I’m open to switching to a 9-pin tube as a last resort.
So, of the following configs, what do you like.
A. grounded cathode (just use ½ of the tube)
B. SRPP
C. U-Follower
D. grounded cathode - cathode follower (as built)
E. OTHER
Thanks in Advance
I am a bit confused why you used a cathode follower cap coupled . I think I'd try parallelling both halves of the 6SL7 in a grounded cathode, plate coupled via capacitor to 2A3 grid. That would be very easy to obtain with minimal rewiring. You have not complained about a lack of sensitivity so obviously you have enough external drive available. This won't change much. It will get slightly better actually but not enough to hear. You may need to reduce R plate of the 6SL7 to as much as 1/2 original value as well as the common cathode R if you want the same tube current and operating characteristic as originally had with the first stage.
I am curious about the speakers you are using with it. Are they full range front horns?
I am curious about the speakers you are using with it. Are they full range front horns?
Bob,
My speakers are dual horn type 3 - ways... Klipsch KLF-20
Yes, the input sensitivity and output power are fine for my setup.
If I rememder correctly, 1.25V input = the 54V I need to drive the 2A3
(as built)
It's the preformance of the "horn sounds" I'm looking to improve.
Here is the link of the amp:
http://www.angela.com/catalog/how-to/SE.2A3.html
Thanks for the info
-Scott
My speakers are dual horn type 3 - ways... Klipsch KLF-20
Yes, the input sensitivity and output power are fine for my setup.
If I rememder correctly, 1.25V input = the 54V I need to drive the 2A3
(as built)
It's the preformance of the "horn sounds" I'm looking to improve.
Here is the link of the amp:
http://www.angela.com/catalog/how-to/SE.2A3.html
Thanks for the info
-Scott
My pick-up:
B. Or you might consider a choke loaded 6C45pi (you'll need to change the socket).
Ciao
Gianluca
B. Or you might consider a choke loaded 6C45pi (you'll need to change the socket).
Ciao
Gianluca
Hi Scott,
for simplicity, and to stay with two octal driver sockets, I would have a try at two paralleled 6sl7 sections per channel. Have a look at the EL34SE amp also shown at the Angela site to get the picture.
A problem is, that available B+ for the drivers in that 2A3 amp is a bit on the low side for 6SL7 anyway. 6SL7 sounds best with about 200V at plate, which would leave only 150V or so across the plate resistor in your circuit.
But at least it is worth a try, and a simple one to do, too.
Tom
P.S: You could also try something along the DC-coupled 6SN7 driver shown at that site implemented in the 300B SE amp. Again, no socket type change required. On second though, that even might be the better option, since it gives better driving capabilities (less driver Zo). The PT must be able to deliver 300mA more heater current at 6,3VAC, if you want to try this.
Tom
for simplicity, and to stay with two octal driver sockets, I would have a try at two paralleled 6sl7 sections per channel. Have a look at the EL34SE amp also shown at the Angela site to get the picture.
A problem is, that available B+ for the drivers in that 2A3 amp is a bit on the low side for 6SL7 anyway. 6SL7 sounds best with about 200V at plate, which would leave only 150V or so across the plate resistor in your circuit.
But at least it is worth a try, and a simple one to do, too.
Tom
P.S: You could also try something along the DC-coupled 6SN7 driver shown at that site implemented in the 300B SE amp. Again, no socket type change required. On second though, that even might be the better option, since it gives better driving capabilities (less driver Zo). The PT must be able to deliver 300mA more heater current at 6,3VAC, if you want to try this.
Tom
Tom,
This amp started out as the JE Labs 6sn7-300B…
That amp sounded great but I gave up due to hum Problems which I thought where heater related.
I have since fixed the hum, changing to a 6sl7-2A3 amp in the process.
(Had nothing to do with the 300B heater).
So yes, changing to a 6sn7 is an option.
Here is what I’m thinking based on the replies so far:
1. Test with 6sl7 as SRPP, that’s easy and I have the parts.
2. Test as a U-follower…… even thought nobody has recommended that to this point!
3. Convert to 6sn7 per your suggestion
( which would be a good exercise for my next project ....)
I would still like to keep the input sensitivity around 1V.
Can I do that if I convert to the 6sn7?
This amp started out as the JE Labs 6sn7-300B…
That amp sounded great but I gave up due to hum Problems which I thought where heater related.
I have since fixed the hum, changing to a 6sl7-2A3 amp in the process.
(Had nothing to do with the 300B heater).
So yes, changing to a 6sn7 is an option.
Here is what I’m thinking based on the replies so far:
1. Test with 6sl7 as SRPP, that’s easy and I have the parts.
2. Test as a U-follower…… even thought nobody has recommended that to this point!
3. Convert to 6sn7 per your suggestion
( which would be a good exercise for my next project ....)
I would still like to keep the input sensitivity around 1V.
Can I do that if I convert to the 6sn7?
I built the JE labs 2a3 srpp version which I enjoy very much (though I have some hum issues of my own I am chasing down...)
I agree with dsavitsk, your amp can't sound better than what your reciever is feeding it. A potentiometer on the input, I used a 100k on mine, feed it directly from your source and see how it sounds.
The JE labs deluxe 2a3 with a single 6sn7 for input and driver is another option. ( I plan to try this one myself...)
http://members.myactv.net/~je2a3/se300b.htm
I agree with dsavitsk, your amp can't sound better than what your reciever is feeding it. A potentiometer on the input, I used a 100k on mine, feed it directly from your source and see how it sounds.
The JE labs deluxe 2a3 with a single 6sn7 for input and driver is another option. ( I plan to try this one myself...)
http://members.myactv.net/~je2a3/se300b.htm
Hugh,
For what it's worth, here are some of the steps I went through to fix the HUM with my amp. This is a letter I sent to Derek Walton, who was very helpfull with the 300B amp.
Hello Derek,
Good timing, I was planning on sending you an update.
I got the hum under 2mV.... but this is no longer a 300B amp.
After testing the 300B amp with my receiver as a pre-amp and on the 98dB/w/m speakers, I came to the conclusion that:
1. I did not need all the power of a 300B
2. I did not need the low input sensitivity level of the 6sn7 input/driver.
3. Getting the HUM out became my top priority.
I returned the 300B tubes and changed the amp to a 6sl7 2a3
(JE Labs SIMPLE 45) with the PSU based in your deluxe amp.
I'm happy with the amp I ended up with... but I think the 300B sounded better!
Right now I'm planning my 2nd amp for next winter. Right now I'm thinking of a 6sl7 2A3 PSE.... or a 6sl7/300B.
Here are the steps I went through to get rid of the HUM
1. when I switched to the 2A3, I had to by a separate transformer for the 2A3 heater, I believe this helped a lot. My next project will go this way.
By the way, hum pots didn't help. I have the R/C on the heater transformer ct.
2. I re arranged the tube's to the the GZ34 away from the input tube.
The first amp had the GZ45-6sn7-300B in line.
The current amp has the 6sl7-2A3-GZ34 in line.
My next project will keep all the PSU components- all the AC and all the single-path far away from one another.
3. I re did the grounding... I will still send you photos in a couple of weeks.
4. Now I heat the 6sl7 from T1, grounding the 6.3vac dropped the sound level (hum?) a LOT, but didn't change the amount of mV I was seeing at the speaker
5. PSU changes: with the 6sl7 I only need 1.5 mV. So I figured out I was not drawing enough current through L2. My PSU is now choke input:
10H-50uF-10H-50uf(B+)-300R-30uF(B++)
THIS CHANGE LOWERED THE HUM A LOT. Before the psu changes, I was about 4.3mV. With the psu as described above, I'm under 2mV.
The meter reads 4.4 mV, but I read 2.7 mV with the amp off, so I guess the hum would be 1.7mV
Update 2/2/2006
Add 80v dc to 6sl7 heater ct.. Hum is now arounf 1mV
For what it's worth, here are some of the steps I went through to fix the HUM with my amp. This is a letter I sent to Derek Walton, who was very helpfull with the 300B amp.
Hello Derek,
Good timing, I was planning on sending you an update.
I got the hum under 2mV.... but this is no longer a 300B amp.
After testing the 300B amp with my receiver as a pre-amp and on the 98dB/w/m speakers, I came to the conclusion that:
1. I did not need all the power of a 300B
2. I did not need the low input sensitivity level of the 6sn7 input/driver.
3. Getting the HUM out became my top priority.
I returned the 300B tubes and changed the amp to a 6sl7 2a3
(JE Labs SIMPLE 45) with the PSU based in your deluxe amp.
I'm happy with the amp I ended up with... but I think the 300B sounded better!
Right now I'm planning my 2nd amp for next winter. Right now I'm thinking of a 6sl7 2A3 PSE.... or a 6sl7/300B.
Here are the steps I went through to get rid of the HUM
1. when I switched to the 2A3, I had to by a separate transformer for the 2A3 heater, I believe this helped a lot. My next project will go this way.
By the way, hum pots didn't help. I have the R/C on the heater transformer ct.
2. I re arranged the tube's to the the GZ34 away from the input tube.
The first amp had the GZ45-6sn7-300B in line.
The current amp has the 6sl7-2A3-GZ34 in line.
My next project will keep all the PSU components- all the AC and all the single-path far away from one another.
3. I re did the grounding... I will still send you photos in a couple of weeks.
4. Now I heat the 6sl7 from T1, grounding the 6.3vac dropped the sound level (hum?) a LOT, but didn't change the amount of mV I was seeing at the speaker
5. PSU changes: with the 6sl7 I only need 1.5 mV. So I figured out I was not drawing enough current through L2. My PSU is now choke input:
10H-50uF-10H-50uf(B+)-300R-30uF(B++)
THIS CHANGE LOWERED THE HUM A LOT. Before the psu changes, I was about 4.3mV. With the psu as described above, I'm under 2mV.
The meter reads 4.4 mV, but I read 2.7 mV with the amp off, so I guess the hum would be 1.7mV
Update 2/2/2006
Add 80v dc to 6sl7 heater ct.. Hum is now arounf 1mV
I tried the 6SL7 SRPP, but it kills the bass, and runs out of puff. 2A3 needs a lot of drive voltage, which is why the cathode follower is a better driver. My version of this circuit sounded pretty good. I have also tried 6SN7 cascaded (like the 300B circuit) and that sounded pretty decent.
1/2 6SL7 sounds bad, it will not drive the 2A3 to full output.
In the end, the sound of a SET will depend on many things, the output transformers being most important. The driver stage is the next most important thing IMHO.
1/2 6SL7 sounds bad, it will not drive the 2A3 to full output.
In the end, the sound of a SET will depend on many things, the output transformers being most important. The driver stage is the next most important thing IMHO.
Shifty,
Is your circuit the same as the JE Labs 2A3 SE?
If it's different, can you post your version of the circuit?
Also, what brand of 6sl7 are you using?
Thanks, Scott
Is your circuit the same as the JE Labs 2A3 SE?
If it's different, can you post your version of the circuit?
Also, what brand of 6sl7 are you using?
Thanks, Scott
I drove a 2a3 with 1/2 6SL7 for a long time and was pretty happy with it. I would try that first, then parallel both halves just to see if you like it better.
The sound of 6SL7's vary a lot by construction and brand. I like the round plate versions better than the flat plates. RCA in particular. I would normally leave tube rolling as the a tweak, but there really are big differences between 6SL7's
Also, as suggested, try running your source straight without the preamp.
5687/7119 type tubes also work very well as drivers for 2a3's, but they are 9 pins.
-- Dave
The sound of 6SL7's vary a lot by construction and brand. I like the round plate versions better than the flat plates. RCA in particular. I would normally leave tube rolling as the a tweak, but there really are big differences between 6SL7's
Also, as suggested, try running your source straight without the preamp.
5687/7119 type tubes also work very well as drivers for 2a3's, but they are 9 pins.
-- Dave
sgerus, I removed the volume control on mine. after dabbling with octals, I shifted to 9-pin drivers. two tubes I really liked are-
- 6072 in SRPP
- 417A/5842 single section driver
i like the 417A best, and currently drives mh 45 (plate choke loaded) and my 10Y/50/300B amp (resistor loaded) both with grid choke on power tube.
here's what my JE Labs 2A3 looks like without the volume pot-
Right now, my two amps use 417A/5842 drivers and I like them, however, I'm also planning to use a Pentode driver. Can somebody comment on what I came up with-
- 6072 in SRPP
- 417A/5842 single section driver
i like the 417A best, and currently drives mh 45 (plate choke loaded) and my 10Y/50/300B amp (resistor loaded) both with grid choke on power tube.
here's what my JE Labs 2A3 looks like without the volume pot-
An externally hosted image should be here but it was not working when we last tested it.
Shifty, mine is configured like that and I can't complain about bass. It's fast, and deep enough for my dance and techno vinyls. could it be that i'm still missing something? I don't have a subwoofer. My speaker is a pair of Altec 406-8Y in an Altec 604 cabinet which was custom made and unfinished, still. The mid-horns are Oxford and the super-tweeter is Fostex FT17H
An externally hosted image should be here but it was not working when we last tested it.
Right now, my two amps use 417A/5842 drivers and I like them, however, I'm also planning to use a Pentode driver. Can somebody comment on what I came up with-
An externally hosted image should be here but it was not working when we last tested it.
Scott,
Thank you for your notes on hum reduction. I too have seperate 2.5vac heater supplies for each 2a3. My layout is well spaced between driver/ outputs and PS. I think I was too obsessive about running everything to the star ground. I'll try grounding stages locally, and running the local grounds to the star ground on the next go round.
I did try floating my HV supply and and using a regulated bench supply (HP-712b) for B+. I don't think I'll try this again until I have an isolation transformer, but it did prove my B+ supply is just fine and isn't adding any hum.
Next up is DC heaters, though I've read the sacrifice in sound quality isn't worth the gain of getting rid of the hum. Can't tell till I hear it myself.
I think I may try Tom's suggestion of parrallel 6sl7 sections myself. One reason I chose the JE labs 2a3 srpp as my first SE amp is all the options of drivers and circuits with minimal parts changes and costs. A new amp in an evening for a couple of bucks...
Thank you for your notes on hum reduction. I too have seperate 2.5vac heater supplies for each 2a3. My layout is well spaced between driver/ outputs and PS. I think I was too obsessive about running everything to the star ground. I'll try grounding stages locally, and running the local grounds to the star ground on the next go round.
I did try floating my HV supply and and using a regulated bench supply (HP-712b) for B+. I don't think I'll try this again until I have an isolation transformer, but it did prove my B+ supply is just fine and isn't adding any hum.
Next up is DC heaters, though I've read the sacrifice in sound quality isn't worth the gain of getting rid of the hum. Can't tell till I hear it myself.
I think I may try Tom's suggestion of parrallel 6sl7 sections myself. One reason I chose the JE labs 2a3 srpp as my first SE amp is all the options of drivers and circuits with minimal parts changes and costs. A new amp in an evening for a couple of bucks...
Gluca said:
This and ArnoldC's suggestions will take your amp out of the 6SL7 mediocrity and to a completely new level. Would your speakers be able to take the dynamics?
The screen grid 'works' with reference to the cathode not to ground, so if you return the sg voltage chain to the cathode and decouple the lower resistor you can dispense with the cathode bypass capacitor... and it sounds better.
I use a high Gm pentode with a VR tube between sg and cathode as I've found this sounds best. I've used 12GN7, D3a, EL84, PL802, C3m, C3g succesfully and they all sound better than any of the triode drivers I've tried.
Several others have built this circuit and all have found it better than previous attempts with triodes. The secret is to use a high Gm pentode.
If you want to use a low Gm pentode then use it as the first stage of a pentode Aikido and it will drive a DHT extremely well.
My favorite triode for driving a 2A3 is the 6N6P but the pentode is more open and transparent.
ciao
James
I use a high Gm pentode with a VR tube between sg and cathode as I've found this sounds best. I've used 12GN7, D3a, EL84, PL802, C3m, C3g succesfully and they all sound better than any of the triode drivers I've tried.
Several others have built this circuit and all have found it better than previous attempts with triodes. The secret is to use a high Gm pentode.
If you want to use a low Gm pentode then use it as the first stage of a pentode Aikido and it will drive a DHT extremely well.
My favorite triode for driving a 2A3 is the 6N6P but the pentode is more open and transparent.
ciao
James
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