Hi Everyone,
I've built a lot of single ended gear using el84's, 2A3's, and 6B4G's. and I've owned/repaired/modded single ended gear using 6V6's, 6L6's, EL34's, KT88's, and 300B's. I've owned a few PP using 6L6's, EL34's, and EL84's.
Overall I've enjoyed the sound of the SE el84's and 2A3/6B4G's the most but I am starting to miss the bottom end and being able to use a variety of speakers. I have a bit of money at the moment I can use for audio and I'm debating what I should pursue.
The reason I've been thinking about a 6B4G PP is because I've heard a lot of people, that I respect their opinion, say they've really enjoyed them, even though it's PP they still seem to have a pretty high 2nd harmonic, it would give me some extra power to play with, better bottom end performance since it's PP. The down side would be the added expenses of 4 output tubes, and possibly making the circuit more complex by going with CCS and DC heater filaments. (with high efficiency speakers I really like having a very low noise floor, my el84 amp is 30 Db if I'm remembering correctly)
One other project I'm considering is modding my el84 monoblocks to run with either el84's or 6B4G's and then using my minidsp as a crossover with subs. I have James Audio outputs in it so I have multiple taps and could run both tubes at the their preferred output tap. I just know from past experience I would have to go DC for the 6B4G's filaments. Also I'm not sure if it's possible to have one driver stage that would work equally well for both tubes or if I would have to have to do separate driver stages.
Currently speaker wise my tube amps drive either my econowaved ElectroVoice Aristocrats or my Klipsch RP600's. I was gifted some custom speakers by a friend that have 21" woofers and enormous JBL mid horns but, one of the woofer's voice coils is rubbing 🙁 so they've just been sitting, also they're enormous and I don't really have the space to set them up properly. My only other speakers are my McIntosh XR 1051, after I recapped them I really enjoyed them (they mate very well with a Citation 16 I rebuilt from the ground up).
Also part of me thinks I'm a little insane for starting another audio project when I have about 6 other audio projects I have parts for but, the idea of building my first PP and getting 6B4G sound with more power and bottom end is an exciting thought.
The reason I was thinking about toroidy's outputs is because I like the idea of an extended frequency response and people that use them seem to be very happy with them. I do know that I would have to be careful of balancing the DC with a PP so I was thinking about using CCS to keep it balanced. In the end even if I don't go for the PP 6B4G I think I would still pick up a SE output from them just to play with. I am curious if I could squeeze more bottom end out of a SE el84 with one of their OT.
As a side note, that I might make another thread about is, my 6336a SET amp. I've noticed when comparing it to my other amps the mid-range seems muffled and I'm wondering if it's because of the driver stage (it's only using half of a 6SL7) or maybe that's just the sound of the 6336a? I'm wondering if I should mod it or just move onto something else.
Sorry for the long post there's just a bunch of factors effecting this decision for me.
As always any thoughts, ideas, input, is greatly appreciated
I've built a lot of single ended gear using el84's, 2A3's, and 6B4G's. and I've owned/repaired/modded single ended gear using 6V6's, 6L6's, EL34's, KT88's, and 300B's. I've owned a few PP using 6L6's, EL34's, and EL84's.
Overall I've enjoyed the sound of the SE el84's and 2A3/6B4G's the most but I am starting to miss the bottom end and being able to use a variety of speakers. I have a bit of money at the moment I can use for audio and I'm debating what I should pursue.
The reason I've been thinking about a 6B4G PP is because I've heard a lot of people, that I respect their opinion, say they've really enjoyed them, even though it's PP they still seem to have a pretty high 2nd harmonic, it would give me some extra power to play with, better bottom end performance since it's PP. The down side would be the added expenses of 4 output tubes, and possibly making the circuit more complex by going with CCS and DC heater filaments. (with high efficiency speakers I really like having a very low noise floor, my el84 amp is 30 Db if I'm remembering correctly)
One other project I'm considering is modding my el84 monoblocks to run with either el84's or 6B4G's and then using my minidsp as a crossover with subs. I have James Audio outputs in it so I have multiple taps and could run both tubes at the their preferred output tap. I just know from past experience I would have to go DC for the 6B4G's filaments. Also I'm not sure if it's possible to have one driver stage that would work equally well for both tubes or if I would have to have to do separate driver stages.
Currently speaker wise my tube amps drive either my econowaved ElectroVoice Aristocrats or my Klipsch RP600's. I was gifted some custom speakers by a friend that have 21" woofers and enormous JBL mid horns but, one of the woofer's voice coils is rubbing 🙁 so they've just been sitting, also they're enormous and I don't really have the space to set them up properly. My only other speakers are my McIntosh XR 1051, after I recapped them I really enjoyed them (they mate very well with a Citation 16 I rebuilt from the ground up).
Also part of me thinks I'm a little insane for starting another audio project when I have about 6 other audio projects I have parts for but, the idea of building my first PP and getting 6B4G sound with more power and bottom end is an exciting thought.
The reason I was thinking about toroidy's outputs is because I like the idea of an extended frequency response and people that use them seem to be very happy with them. I do know that I would have to be careful of balancing the DC with a PP so I was thinking about using CCS to keep it balanced. In the end even if I don't go for the PP 6B4G I think I would still pick up a SE output from them just to play with. I am curious if I could squeeze more bottom end out of a SE el84 with one of their OT.
As a side note, that I might make another thread about is, my 6336a SET amp. I've noticed when comparing it to my other amps the mid-range seems muffled and I'm wondering if it's because of the driver stage (it's only using half of a 6SL7) or maybe that's just the sound of the 6336a? I'm wondering if I should mod it or just move onto something else.
Sorry for the long post there's just a bunch of factors effecting this decision for me.
As always any thoughts, ideas, input, is greatly appreciated
Hi
When considering output transformers, do not worry so much about things like "extended frequency response". This sounds like marketing. Be more concerned about harmonic distortion.
For push-pull, you should find excellent iron locally. Toroidy has come a long way from when they started out, but they are still in Poland... The problem with transformers is that they are heavy, and shipping them can cost a LOT.
In the US I would definitely look at EDCOR and Electra-Print and Antek. I personally like to buy transformers when I travel for business (not these days due to covid). I got some very nice and affordable Antek power transformers in the US. You are lucky to have these companies to buy from!
Push-Pull amplifiers will generally have lower distortion than single ended ones if they are designed well. Also, push-pull output transformers will not need to be quite as large as single ended ones to get the same power.
Some people would wonder why anyone would ever consider building single ended amplifiers after taking a close look at push-pull. Ok, designing push-pull amplifiers is more challenging than single-ended ones.
Its probably wise to finish other projects first.
6336a midrange sounds poor? did you do some measurements? I would not blame 6SL7, but it is also not really a driver.
When considering output transformers, do not worry so much about things like "extended frequency response". This sounds like marketing. Be more concerned about harmonic distortion.
For push-pull, you should find excellent iron locally. Toroidy has come a long way from when they started out, but they are still in Poland... The problem with transformers is that they are heavy, and shipping them can cost a LOT.
In the US I would definitely look at EDCOR and Electra-Print and Antek. I personally like to buy transformers when I travel for business (not these days due to covid). I got some very nice and affordable Antek power transformers in the US. You are lucky to have these companies to buy from!
Push-Pull amplifiers will generally have lower distortion than single ended ones if they are designed well. Also, push-pull output transformers will not need to be quite as large as single ended ones to get the same power.
Some people would wonder why anyone would ever consider building single ended amplifiers after taking a close look at push-pull. Ok, designing push-pull amplifiers is more challenging than single-ended ones.
Its probably wise to finish other projects first.
6336a midrange sounds poor? did you do some measurements? I would not blame 6SL7, but it is also not really a driver.
Given the cancellation that occurs in the O/P transformer, AC heating of PP 6B4s can be perfectly satisfactory. Also keep in mind that other than filament voltage, 6B4s and 2A3s contain the "same" triode. AC heating of PP 2A3s is definitely satisfactory.
As was pointed out, High RP/low gm triodes, like those in a 6SL7, are poor drivers of loads. Believe it or not, a small piece of "sand" solves the problem. DC couple a ZVN0545A source follower to the triodes plate and it no longer has to deal with a "difficult" load. The tweaked RCA phono setup illustrates the buffering technique.
As was pointed out, High RP/low gm triodes, like those in a 6SL7, are poor drivers of loads. Believe it or not, a small piece of "sand" solves the problem. DC couple a ZVN0545A source follower to the triodes plate and it no longer has to deal with a "difficult" load. The tweaked RCA phono setup illustrates the buffering technique.
Attachments
I thought that increased frequency response was an aspect of all toroidal output transformers?
Also the fact that they have a higher primary inductance I thought that was a desirable trait.
Reference:Choosing an Output Transformer
The toroidy 5k SE is rated at 27.5 H and it's priced close to Edcor's GXSE15-5K (about $14 difference) and the Edcor is only ~17.7 H
The shipping quote was about $54 which I didn't think was that bad for two transformers weighing a total of 9.7 lbs. For comparison I went on Edcor's website and threw a 9.75 lb transformer in the cart the shipping quote came up as $57.50 So the economy shipping from Poland is cheaper.
I've used Edcor transformers many times, they make good stuff, I think my only gripe would be that they don't have a middle of the road option, like I mentioned earlier they have the ~17.7 H $43 outputs (GXSE15-5K) and then they jump to the 50 H $94 outputs (CXSE25-5K)
Electra-Print is about $133, Antek I didn't see any of their transformers listed for audio output use?
I did some bench tests on it a while ago, it measured well (I want to say about 1.25% @ 1 watt) but, you can definitely notice that part of the mid-range is veiled / muddled when A/B listening with other amps, even my Father picked up on it which surprised me since he's not into audio. (I didn't build this amp I picked it up second hand to play with, I thought the 6336a seemed interesting)
Attachments
I was wondering if I should try implementing this circuit using 12AU7's from cascadetubes.com or do you think the method using the ZVN0545A would be more effective?
Attachments
I would suggest stepping up to a nicer output transformer to get more bottom end.
Even going to the biggest Edcor single ended transformers will give you significantly more low end compared to the GXSE stuff.
Pick the tube you want to use, then buy a nice pair of output transformers to go with it. Good transformers for 2A3s aren't likely to be good transformers for EL84s.
Even going to the biggest Edcor single ended transformers will give you significantly more low end compared to the GXSE stuff.
Pick the tube you want to use, then buy a nice pair of output transformers to go with it. Good transformers for 2A3s aren't likely to be good transformers for EL84s.
I wince anytime a 12AU7 section is used as a common cathode voltage amplifier. That triode is non-linear and (IMO) should serve only in the cathode follower or "concertina" phase splitter roles.
DC coupling the little FET to a tube's plate is a "no brainer". Among other things, heater power and heater to cathode potential worries are absent. The only "gotcha" is power on transients and that's dealt with by adding a protective 12 V. Zener diode between gate and source.
Even wimpy types, like the 6SL7, 12AX7, and EF86, have no problems driving the tiny capacitances of the ZVN0545A.
While it is simplistic, thinking of FETs as heaterless pentodes is (IMO) not a bad idea. OTOH, current controlled, low impedance, BJTs in the signal path give me the "hebe jeebies".
That muddied sound is likely poor transient response. The frequency response might be good. The THD might be good too. But without excellent transient response, your amp will sound muddy. It is not easy to measure transient response. You just have to design with it in mind.
I am looking at your schematic and I see a 20kOhm gridstopper. This seems to be far too big. I would try 1kOhm unless someone more experienced with 6336a says otherwise.
You might lose some lower frequencies by dropping the whopper value of that grid stopper, but your cathode by-pass cap on the 6SL7 looks too small as well. Make it at least 100uF. This should help you get decent bass response too.
These are quick fixes. My next suggestion would be to follow Eli Duttman's advise. What he proposes will take almost no space and is very inexpensive.
If you still have poor transient response, I am afraid to say it is probably your power supply.
Your power supply is CLCRC. I never build this anymore. ever. I like to do LCLC or LC<regulator> for pre-amps and smaller stuff.
You need that first choke to work as an energy reservoir but putting a cap in front of it defeats that functionality. Of course you will lose a lot of B+ by taking it out, so you're kind of stuck with that now. Sorry for this... maybe your amp will run well at a lower B+ though. You should simulate it first perhaps.
I am looking at your schematic and I see a 20kOhm gridstopper. This seems to be far too big. I would try 1kOhm unless someone more experienced with 6336a says otherwise.
You might lose some lower frequencies by dropping the whopper value of that grid stopper, but your cathode by-pass cap on the 6SL7 looks too small as well. Make it at least 100uF. This should help you get decent bass response too.
These are quick fixes. My next suggestion would be to follow Eli Duttman's advise. What he proposes will take almost no space and is very inexpensive.
If you still have poor transient response, I am afraid to say it is probably your power supply.
Your power supply is CLCRC. I never build this anymore. ever. I like to do LCLC or LC<regulator> for pre-amps and smaller stuff.
You need that first choke to work as an energy reservoir but putting a cap in front of it defeats that functionality. Of course you will lose a lot of B+ by taking it out, so you're kind of stuck with that now. Sorry for this... maybe your amp will run well at a lower B+ though. You should simulate it first perhaps.
Last edited:
As an aside, the article from Eric Lowdon is from 1951. It is of course 100% correct.
I am usually not too worried about bass response, but it is indeed important. All you need to do is as what the primary inductance is. Pretty much any reputable manufacturer will immediately supply this information.
I would still go for Edocor or Elektra-Print since they are closer to you. There are probably others closer to you too that are very good.
Economy parcels take a LONG time to get there from overseas, and I have had a few dropped along the way.
Ian
I am usually not too worried about bass response, but it is indeed important. All you need to do is as what the primary inductance is. Pretty much any reputable manufacturer will immediately supply this information.
I would still go for Edocor or Elektra-Print since they are closer to you. There are probably others closer to you too that are very good.
Economy parcels take a LONG time to get there from overseas, and I have had a few dropped along the way.
Ian
I was also shocked by how affordable the shipping to the US on the Toroidy transformers was on the quote I received. I want to try some of them in my next build.
I agree, it would be great if Edcor added an intermediate transformer between the little guys and the huge ones. On my last build, a PP 6V6, I used electraprint and they were here in about a week and, to my ear, sound great. The only negative is they smelled strongly of varnish for months. I'd leave them outside in the sun hoping it would go away but it took a long time. So instead of waiting a couple months for the edcor iron to be built I waited a couple months for the iron to stop smelling so I could bring the amp inside the house.
I agree, it would be great if Edcor added an intermediate transformer between the little guys and the huge ones. On my last build, a PP 6V6, I used electraprint and they were here in about a week and, to my ear, sound great. The only negative is they smelled strongly of varnish for months. I'd leave them outside in the sun hoping it would go away but it took a long time. So instead of waiting a couple months for the edcor iron to be built I waited a couple months for the iron to stop smelling so I could bring the amp inside the house.
When troubleshooting this amp a few years ago those 20k ohm gridstoppers were actually swapped out for a 1.8k ohm ones, which corrected some other issues it was having. I forgot to update the diagram.
You have won me over, I would like to try the ZVN0545A's but I don't have any experience with them, if it's not too much to ask could you make a circuit diagram of them in my amp so I do it correctly?
Sorry for the delay in my response, I'm taking physics over the summer and it's extremely concentrated. That's part of the reason I don't mind waiting for transformers to ship since I wont have the time to build an amp till this class is over. (but I will have enough time for some mods on the weekends 😀 even if I have to make the time)