I know I have read about this being discussed but can't find the exact thread.
Are these two transformers the same?
https://www.edcorusa.com/gxse10-16-5k
https://www.edcorusa.com/gxse10-8-2_5k
If the impedance ratio is just a a squared function of the turns ratio these two transformers are the same. BUT somewhere in my soggy brain there is a voice telling me that if I try and use the gxse10-16-5k with an 8 ohm load giving me a primary impedance of 2.5k the primary inductance will be less then what I expect?
Are these the same transformers with different stickers? Or are they different? The reason I just don't order the gxse10-8-2_5k? Because I can purchase the gxse10-16-5k and have them in a week as appose to two months.
Edit: I plan to use them with some Tubelab SE boards. I see he has on his site that he has tried the xse15-8-5k, the gxse line has better low end performance.
Thanks
-bird
Are these two transformers the same?
https://www.edcorusa.com/gxse10-16-5k
https://www.edcorusa.com/gxse10-8-2_5k
If the impedance ratio is just a a squared function of the turns ratio these two transformers are the same. BUT somewhere in my soggy brain there is a voice telling me that if I try and use the gxse10-16-5k with an 8 ohm load giving me a primary impedance of 2.5k the primary inductance will be less then what I expect?
Are these the same transformers with different stickers? Or are they different? The reason I just don't order the gxse10-8-2_5k? Because I can purchase the gxse10-16-5k and have them in a week as appose to two months.
Edit: I plan to use them with some Tubelab SE boards. I see he has on his site that he has tried the xse15-8-5k, the gxse line has better low end performance.
Thanks
-bird
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While the reflected impedance between those two OPT's will be the same, the 5K unit will present a higher inductance on the primary at the low end. Given that the K-33 woofer in the Cornwall is nominally a 4 Ohm driver, the amp will have a very low damping factor even in the context of an SET amp. If I were you, I'd probably be looking at the 15W Edcor units at the 3.5K or even 5K:8 impedance ratios. The slightly lower max power to be had with the higher impedance OPT's will more than be offset by the lower distortion and better damping.
https://www.edcorusa.com/gxse15-8-3_5k
https://www.edcorusa.com/gxse15-8-5k
The additional $20 per pair for these bigger OPT's pales in comparison to the cost of the 300B tubes that you will be buying for this amp. Just MHO.
https://www.edcorusa.com/gxse15-8-3_5k
https://www.edcorusa.com/gxse15-8-5k
The additional $20 per pair for these bigger OPT's pales in comparison to the cost of the 300B tubes that you will be buying for this amp. Just MHO.
Thank you for the quick response.
I see that now, for the gxse-8-2_5k they give the spec of 6H for primary inductance, 149 ohm DCR, and 120mA current for rated performance. The gxse-16-5k they only tell you 80mA for the rated performance. Good catch
Is this for a 5k transformer ? If so then there may be very limited output under 100Hz . 149 ohms for such a small transformer indicates not many turns . The rule of thumb I use is 20H per 1K of Ra of the driving valve in triode SE . If you want to use midbass and up , probably fine . Hope this helps
316a
Unfortunately I did not win the auction. The pair went for $15 more then what they go for brand new.
It's probably for the best, I have been looking at Transcendar, the prices seem more then fair to me and the specs look really good.
What can be expected from a current production 300b in class A2? I have zero experience with DHT.
It's probably for the best, I have been looking at Transcendar, the prices seem more then fair to me and the specs look really good.
What can be expected from a current production 300b in class A2? I have zero experience with DHT.
Electra-print and Lundahl would both be good choices.. I've also had pretty good results from modestly priced Transcendars which seem to offer great value for the performance offered.
Note that the 300B is not really intended for class A2 operation. (I have designed and built a significant number of both PP and SE 300B amps over the years..)
8 - 10Wrms is possible with good tube life.. If you really want to push them and bend the rules by running them into A2 you can get 16W or so out of a single tube.. I've not done this, and I hear tube life is quite short even with genuine WE 300B.. (There was a Japanese 300B SE amp rated at 17W per channel from a single 300B per channel!)
Note that the 300B is not really intended for class A2 operation. (I have designed and built a significant number of both PP and SE 300B amps over the years..)
8 - 10Wrms is possible with good tube life.. If you really want to push them and bend the rules by running them into A2 you can get 16W or so out of a single tube.. I've not done this, and I hear tube life is quite short even with genuine WE 300B.. (There was a Japanese 300B SE amp rated at 17W per channel from a single 300B per channel!)
I have checked out Electra-Print, I would love to go with them. Like anything you get what you pay for, and if I can swing it Electra-print is now probably my first choice.
The amps will not be pushed that hard during listening, I just would think a Mosfet follower as a driver would help drive the 300B's capacitance, and when listening to it the positive grid drive during hard transients will cut down on distortion. I guess the little extra head room A2 provides will be beneficial if and when I do listen to them a little louder then usual.
On a side note I did the speaker power test that Pano had setup with my Heresy II's and I found I mainly listen to 2-4 watts, 13.5w was at a level of uncomfortable SPL, I am willing to bet with Cornwall's I would need even less power. I am not trying to squeak as much power out of a 300B as possible, 10 watts should be more then plenty, but I do like what the "power drive" stage has to offer.
The amps will not be pushed that hard during listening, I just would think a Mosfet follower as a driver would help drive the 300B's capacitance, and when listening to it the positive grid drive during hard transients will cut down on distortion. I guess the little extra head room A2 provides will be beneficial if and when I do listen to them a little louder then usual.
On a side note I did the speaker power test that Pano had setup with my Heresy II's and I found I mainly listen to 2-4 watts, 13.5w was at a level of uncomfortable SPL, I am willing to bet with Cornwall's I would need even less power. I am not trying to squeak as much power out of a 300B as possible, 10 watts should be more then plenty, but I do like what the "power drive" stage has to offer.
IMHO the power drive should be thought of as "Class A2 capable" rather than "Class A2". Over the vastly vast majority of time with music, the tube will be running in Class A1, and only might peak into class A2 on rare occasion. So no reason to avoid* the power drive FET because of an imagined class change!
* though, if you're into the "simple circuit" philosophy, the MOSFET might seem like more stuff to maybe degrade the signal. I always the thought the "it's simple!" argument for SET amplifiers was kind of nuts -- if you look inside a power tube or its output transformer, you'll see there isn't a lot that is "simple" about it. The complication has just been moved from Rs and Cs over to mechanical and magnetic structures.
* though, if you're into the "simple circuit" philosophy, the MOSFET might seem like more stuff to maybe degrade the signal. I always the thought the "it's simple!" argument for SET amplifiers was kind of nuts -- if you look inside a power tube or its output transformer, you'll see there isn't a lot that is "simple" about it. The complication has just been moved from Rs and Cs over to mechanical and magnetic structures.
I agree, I really like the follower in there. I know the amp will rarely be pushed so I don't fear the follower being in there will shorten the life of the 300B. I think Kevin was nice in warning that the 300B isn't specifically designed for continual A2 operation and that doing so could shorten the life of the valve.
Generally if class A2 operation is not contemplated a more moderate operating point can be chosen.. The standard 60mA at 350V is not a bad starting point into a 3K primary if 7W or so will do the job.
I will admit I run them harder typically with 400V fixed bias at operating currents of up to 90mA (JJ only!!) into 3K which is good for about 10W @ 5% thd. (almost all second) still in class A1.. At normal listening levels the distortion will be an order of magnitude or more lower.
If you want to keep it pretty simple something like a choke loaded triode connected D3A running at 15mA or more will drive a 300B quite effectively, consider an IT like the Lundahl LL1635 if you can budget for them over time. (They're not terribly expensive)
I will admit I run them harder typically with 400V fixed bias at operating currents of up to 90mA (JJ only!!) into 3K which is good for about 10W @ 5% thd. (almost all second) still in class A1.. At normal listening levels the distortion will be an order of magnitude or more lower.
If you want to keep it pretty simple something like a choke loaded triode connected D3A running at 15mA or more will drive a 300B quite effectively, consider an IT like the Lundahl LL1635 if you can budget for them over time. (They're not terribly expensive)
Sorry for all the questions Kevin but it seems like you have a lot of experience with these tubes. I have not done any load lines for I do not know which tube's datasheet to use. Seems like you are a fan of the JJ 300B? I was looking at Electra-print's options and saw the 100mA, 3k, 15 watt transformer, they are expensive but go big or go home right
I have seen DRD schematics, I think Electra-print is using a 6AN4 instead of the D3A you suggest. It looks like a great design but unfortunately it's going to kill my wallet just going with their output transformers let alone having to get a couple of quality chokes too. Tom C's Damn good 300b looks like a good design as well, looks like he is using a cathode follower to drive the DHT.
So many options so little time.
I have seen DRD schematics, I think Electra-print is using a 6AN4 instead of the D3A you suggest. It looks like a great design but unfortunately it's going to kill my wallet just going with their output transformers let alone having to get a couple of quality chokes too. Tom C's Damn good 300b looks like a good design as well, looks like he is using a cathode follower to drive the DHT.
So many options so little time.
I've had very good luck with the JJ 300B and recommend it for replacement use in all of my old designs.
The DRD is an interesting design, but subject to a lot of interactions which frankly I find annoying...lol
Results are commensurate with the quality of the iron and from experience I can say that Electra-Print SE output transformers deliver consistently good results and are worth scrimping and saving up for.
I would actually recommend a non-drd design with D3A and choke or IT coupling. These days I am tending towards the IT for coupling duties. I like Lundahl for IT transformers as they are well engineered and consistent performers - and not too expensive. I would extend this to their output transformers too, but I find all of those winding interconnections to be annoying.. LOL
There are many good choices, I would just avoid a couple of the more done to death variants. I now think low rp and relatively high current/high transconductance types yield a better overall result, and I started from somewhere else. Single driver stages are my preference but close to the limit for tubes like the 300B and GM70 which are my current preferences.
The DRD is an interesting design, but subject to a lot of interactions which frankly I find annoying...lol
Results are commensurate with the quality of the iron and from experience I can say that Electra-Print SE output transformers deliver consistently good results and are worth scrimping and saving up for.
I would actually recommend a non-drd design with D3A and choke or IT coupling. These days I am tending towards the IT for coupling duties. I like Lundahl for IT transformers as they are well engineered and consistent performers - and not too expensive. I would extend this to their output transformers too, but I find all of those winding interconnections to be annoying.. LOL
There are many good choices, I would just avoid a couple of the more done to death variants. I now think low rp and relatively high current/high transconductance types yield a better overall result, and I started from somewhere else. Single driver stages are my preference but close to the limit for tubes like the 300B and GM70 which are my current preferences.
The Western Electric data sheet still provides relevant information for choosing operating points with good quality 300B tubes.
Here: www.tubebooks.org/tubedata/we300a_b.pdf
I have noticed that some of the cheaper Chinese 300B tubes in the past did not survive for extended periods at plate voltages much in excess of 300V and I believe this was because in those particular tubes a large area of filament was exposed to the plate with no intervening grid structure. The tubes could never be biased to full cut off and at higher voltages enough current would flow in the uncontrolled regions of the plate to destroy the tube.. I am not sure this is the case today, but wise to check.
I have found TJ 300B of various versions as well as Sophia (oem'd by TJ) to be reliable and good sounding as well.
I will say the JJ 300B has been pretty hard to beat for reliability and is one of the best sounding I have used on a consistent basis, and is reasonably priced for its quality point.
http://www.tubebooks.org/tubedata/we300a_b.pdf
Here: www.tubebooks.org/tubedata/we300a_b.pdf
I have noticed that some of the cheaper Chinese 300B tubes in the past did not survive for extended periods at plate voltages much in excess of 300V and I believe this was because in those particular tubes a large area of filament was exposed to the plate with no intervening grid structure. The tubes could never be biased to full cut off and at higher voltages enough current would flow in the uncontrolled regions of the plate to destroy the tube.. I am not sure this is the case today, but wise to check.
I have found TJ 300B of various versions as well as Sophia (oem'd by TJ) to be reliable and good sounding as well.
I will say the JJ 300B has been pretty hard to beat for reliability and is one of the best sounding I have used on a consistent basis, and is reasonably priced for its quality point.
http://www.tubebooks.org/tubedata/we300a_b.pdf
My daily use 300B amplifier: triode mode D3a -LED bias-, DN2540 cascode CCS as anode load, V-Cap capacitor to the FET source follower -powerdrive-, 300B, 5K:8 custom wind OPT, 400V a-c voltage. It's a 10W amp (above 6W in A2 mode).
I tried some high gm -trioded- pentode (E810F, E180F, E280F, D3a, C3g). For me the best ones is E280F (refinement) and D3a (the most powerful).
I built (actually rebuilt an amplifier) to my friend a similar amp with C3g and 5k:8 Transcendar OPT. It has very pleasant sounding.
I tried some high gm -trioded- pentode (E810F, E180F, E280F, D3a, C3g). For me the best ones is E280F (refinement) and D3a (the most powerful).
I built (actually rebuilt an amplifier) to my friend a similar amp with C3g and 5k:8 Transcendar OPT. It has very pleasant sounding.
Attachments
Can you please elaborate? Are you saying to use with IT or without? I see that the D3A's transconductance (as triode) is 41,000
plate and plate resistance is 1.9k giving a mu of .041*1900=77. Seems like a great tube Looking at Telefunken's triode plate curves it doesn't look that linear though, is this why everyone loads it with a CCS?I need a lot of coffee to get me through my stash of tubes, I will pick through to see what I got for high gm tubes. This will also give me time to figure out how I am going to skin this cat called driving a 300B.
Hi Euro71, thanks for the info.......I will have a look at the C3G.
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