Hi all
I've tested a few prospective driver tubes to see if i can improve my gm70 amp.
6e5p triode strap -what i'm using currently
D3a triode strap
6J9P (e810f) triode strap
EL84 triode strap
EF184 triode strap
all with g2 to anode via 300r resister and g3 to cathode
I made a test box yesterday so i could vary the bias voltage from -1 to -6 and the currant flowing thru the dn2540 from 5-28ma load was 100k//single dn2540 ht of 350v
I played with all the tubes to get the best thd figures within what the box could do. i need 64vrms for the -90v bias on the gm70, so i tried to get as close to this as i could but as i used a switched attenuator on my 4p1l preamp it was ~64vrms
tube ma g1 Va thd vrms out
6e5p 28 -3.5 180v 0.09 71:-0
D3a 17 -2.2 200 0.42 58
D3a 17 -2.2 200 0.47 80
6J9P 17 -2.0 166 0.18 66
6J9P 17 -2.5 166 0.67 95
6J9P 28 -2.2 208 0.066 67 just for fun 5.8w :-0
EF184 18 -2.16 207 0.38 68
EL84 was not much cop at these voltage swings but managed 0.004% at 2vrms, thats comparable to the 4P1L linestage i was using and my e-mu soundcard does 0.0009%
So on balance i think i'll stick with the 6E5p but i will bias it to 3.5v and a few more ma. wish the 6J9P anode diss was higher 0.06% at
~190v is impressive and 266v p-p swing from a 350v supply at 0.6%, what a tube.
hope all this is accurate and of help to gm70 builders etc
enzo
I've tested a few prospective driver tubes to see if i can improve my gm70 amp.
6e5p triode strap -what i'm using currently
D3a triode strap
6J9P (e810f) triode strap
EL84 triode strap
EF184 triode strap
all with g2 to anode via 300r resister and g3 to cathode
I made a test box yesterday so i could vary the bias voltage from -1 to -6 and the currant flowing thru the dn2540 from 5-28ma load was 100k//single dn2540 ht of 350v
I played with all the tubes to get the best thd figures within what the box could do. i need 64vrms for the -90v bias on the gm70, so i tried to get as close to this as i could but as i used a switched attenuator on my 4p1l preamp it was ~64vrms
tube ma g1 Va thd vrms out
6e5p 28 -3.5 180v 0.09 71:-0
D3a 17 -2.2 200 0.42 58
D3a 17 -2.2 200 0.47 80
6J9P 17 -2.0 166 0.18 66
6J9P 17 -2.5 166 0.67 95
6J9P 28 -2.2 208 0.066 67 just for fun 5.8w :-0
EF184 18 -2.16 207 0.38 68
EL84 was not much cop at these voltage swings but managed 0.004% at 2vrms, thats comparable to the 4P1L linestage i was using and my e-mu soundcard does 0.0009%
So on balance i think i'll stick with the 6E5p but i will bias it to 3.5v and a few more ma. wish the 6J9P anode diss was higher 0.06% at
~190v is impressive and 266v p-p swing from a 350v supply at 0.6%, what a tube.
hope all this is accurate and of help to gm70 builders etc
enzo
Yes 2 stage not inc preamp, but i need one of those as i listen mainly to LP, so i dont limit myself to <2vrms input. will try 4p1l sometime
I dont have any 12GN7A's but i'll look into them....
The most expensive tube was the el84, the rest were <£4 which i think is stunning considering how these tubes performed.
My gm70 measured 0.4% at 1w 5%at 15.5w (11k5 load 900v) so i'm looking to lower that, found a good operating point for the 6e5p just need to get one for the gm70's now.
p.s the 6e5p that went thru the wasing machine in my pocket measured ~15% higher thd!
enzo
I dont have any 12GN7A's but i'll look into them....The most expensive tube was the el84, the rest were <£4 which i think is stunning considering how these tubes performed.
My gm70 measured 0.4% at 1w 5%at 15.5w (11k5 load 900v) so i'm looking to lower that, found a good operating point for the 6e5p just need to get one for the gm70's now.
p.s the 6e5p that went thru the wasing machine in my pocket measured ~15% higher thd!
enzo
yes 11k5 lundahl 1620. as i remember the 1620 can be configured at a few different impeadences so i could try a lower load but 15 watts is fine for me and i get the damping factor. 8k seems like a good comprimise.
Im using rc coupling at the moment .1uf 1500v and 1uf 1200v pp caps and 100k grid leak, i wouldnt mind trying transformer coupling but the weight and expense put me off!
I'm using a mu follower with 6e5p's as the ccs, but i'll try other topoligys and see what i like. my wife doesnt understand when an amplifier is working why its not finished!
very kind offer of a 12gn7a, could i swap with 3Da and or EF184? i have a few of those
enzo
Im using rc coupling at the moment .1uf 1500v and 1uf 1200v pp caps and 100k grid leak, i wouldnt mind trying transformer coupling but the weight and expense put me off!
I'm using a mu follower with 6e5p's as the ccs, but i'll try other topoligys and see what i like. my wife doesnt understand when an amplifier is working why its not finished!
very kind offer of a 12gn7a, could i swap with 3Da and or EF184? i have a few of those
enzo
I have done almost similar tests a couple of years ago.
The main difference is that I had adjustable cathode resistor instead of adjustable bias. I also tried both bypassed and unbypassed cathode resistor.
My results with 6J9P and 6E5P are quite equal.
But I found some even more linear types: 6S45P, 6J11P and 6J52P.
For example 6S45P gave 100 Vrms with 0,34 % THD when Ub = 350 V, Ua = 200 V, Ik = 20 mA and RL = 100 k.
My conclusion of the tests I have done is that high gm-type tubes are most linear.
Typical 6SN7 was one of the worst.
The main difference is that I had adjustable cathode resistor instead of adjustable bias. I also tried both bypassed and unbypassed cathode resistor.
My results with 6J9P and 6E5P are quite equal.
But I found some even more linear types: 6S45P, 6J11P and 6J52P.
For example 6S45P gave 100 Vrms with 0,34 % THD when Ub = 350 V, Ua = 200 V, Ik = 20 mA and RL = 100 k.
My conclusion of the tests I have done is that high gm-type tubes are most linear.
Typical 6SN7 was one of the worst.
I feel a little sad, because I didn't manage to get it to sound with 6E5P as a driver, althought it seems a very linear tube on paper. The mids were somewhat harsh. But this tube has great potential, Ia and Pa. I remember I used 1k as a grid resistor, otherwise the tube easily oscillated. My amp is 6P45S output tube based SE.
Compared with other tubes, I have tested E180F, D3A, E280F and E810F.
E180F and E810F for now give me the best sound for my taste. D3A has the best gain, but it sound a little harsher for my ears than E180F. E280F is between E180F and D3A and has great stage and dynamics. I use CCS 10m45s cascoded as load, mu out. I love swapping these tubes sometimes.
All these tubes sound similar and ok compared to what 6E5P sounded to me - detailed, but harsh and intolerable. I use a 220R resistor from g2 to anode.
Any advice?
Compared with other tubes, I have tested E180F, D3A, E280F and E810F.
E180F and E810F for now give me the best sound for my taste. D3A has the best gain, but it sound a little harsher for my ears than E180F. E280F is between E180F and D3A and has great stage and dynamics. I use CCS 10m45s cascoded as load, mu out. I love swapping these tubes sometimes.
All these tubes sound similar and ok compared to what 6E5P sounded to me - detailed, but harsh and intolerable. I use a 220R resistor from g2 to anode.
Any advice?
The grid stopper and g2 resistors have practically no effect to THD.
But the used anode load, cathode resistor and supply voltage have a lot.
And you do not mention about these essential things at all ??
How did you ensure that you used optimum conditions with 6E5P.
What were your THD values with 6E5P ?
But the used anode load, cathode resistor and supply voltage have a lot.
And you do not mention about these essential things at all ??
How did you ensure that you used optimum conditions with 6E5P.
What were your THD values with 6E5P ?
No THD measured, but.
-1.2V fixed battery bias
28mA Ia
~110 Ua
8k resistor load
330V supply
It seems to me in pretty linear zone judging from the triode strapped graphic.
According to my knowledge your operation conditions are very far from optimum.
The first and absolute requirement is to use CCS loading. Otherwise optimum linearity and high output voltage can not be achieved.
When high output level is required the grid voltage must be relatively high.
With -1,2 V the grid current begins to flow almost at once.
In whole, this is very typical situation among such hobbyists who only evaluate circuits by listening.
You had bad operating condition but the reason for bad sound is entitled to the used tube only.
The first and absolute requirement is to use CCS loading. Otherwise optimum linearity and high output voltage can not be achieved.
When high output level is required the grid voltage must be relatively high.
With -1,2 V the grid current begins to flow almost at once.
In whole, this is very typical situation among such hobbyists who only evaluate circuits by listening.
You had bad operating condition but the reason for bad sound is entitled to the used tube only.
if the gain is ~ 30 then for 180v drive you'll need 180/30 =6v p-p into the tube and that means driving it 1.8v positive. I dont think the 6e5p is great A2, i think the 6J9p is good A2 which accounts for its voltage swing. most designs limit themselves to -1 so 1.2 bias gives about 12v before grid currant is likly to flow.
I do need to actually listen to these tubes and alot of them have similar pinouts other than pin8/9, the 6e5p is compleatly different though.
i have 6J52 6P15p-ev and 6P1P on there way for tests.
I did measure the 6s45 but my signal generator at the time was too limp to give good results. tested at bias points between 1.25 to 3v in .25 volts and found 0.031 at 22ma -1.75/160 this is before i added variable currant, will give it another go for big voltage swings.
p.s i'm ignoring alot of max specs here as lifetime on a 1-2£$ tube will not keep me up at night!
6c45pi
g1 Va rmsout %
1.25 139.6 0.48 0.082
1.5 150 0.46 0.07
1.75 160 0.455 0.031
2 1.71 0.445 0.042
2.25 181 0.447 0.07
2.5 192 0.447 0.087
2.75 202 0.448 0.09
3 212 0.449 0.0
enzo86
I do need to actually listen to these tubes and alot of them have similar pinouts other than pin8/9, the 6e5p is compleatly different though.
i have 6J52 6P15p-ev and 6P1P on there way for tests.
I did measure the 6s45 but my signal generator at the time was too limp to give good results. tested at bias points between 1.25 to 3v in .25 volts and found 0.031 at 22ma -1.75/160 this is before i added variable currant, will give it another go for big voltage swings.
p.s i'm ignoring alot of max specs here as lifetime on a 1-2£$ tube will not keep me up at night!
6c45pi
g1 Va rmsout %
1.25 139.6 0.48 0.082
1.5 150 0.46 0.07
1.75 160 0.455 0.031
2 1.71 0.445 0.042
2.25 181 0.447 0.07
2.5 192 0.447 0.087
2.75 202 0.448 0.09
3 212 0.449 0.0
enzo86
just had a go with a 6c45pi
speaking of A2....
these tests had a 600r resistor in the grid tag to subdue the oscilation that kicked in as i raised the currant
Best results were all at 28ma
-1.08 155v 28ma 0.15% 61vrms/170p-p
and tried for max swing before clipping, i'm sure you could get more but i'm using a switched attenuator so adjustment is coarse.
-1.42 171v 28ma 0.29% 85vrms/238 p-p
So the 6c45 is up with the best but needs running heavily in A2 to do it 1.5vrms/4.2p-p in at 1.1v bias so 1v+ on the grid. This was driven by my 4P1L preamp Z out~1-2K and thru the 600r resistor so doesnt need to source much currant it seems.
enzo
speaking of A2....
these tests had a 600r resistor in the grid tag to subdue the oscilation that kicked in as i raised the currant
Best results were all at 28ma
-1.08 155v 28ma 0.15% 61vrms/170p-p
and tried for max swing before clipping, i'm sure you could get more but i'm using a switched attenuator so adjustment is coarse.
-1.42 171v 28ma 0.29% 85vrms/238 p-p
So the 6c45 is up with the best but needs running heavily in A2 to do it 1.5vrms/4.2p-p in at 1.1v bias so 1v+ on the grid. This was driven by my 4P1L preamp Z out~1-2K and thru the 600r resistor so doesnt need to source much currant it seems.
enzo
Completely agree. For a driver why not implementing a gyrator in mu-follower output instead of an CCS? The gyrator in mu follower will provide the lowest output impedance and sufficient current in particular if you are planning to drive the valve in A2.
I'm currently refining my driver for the 4-65a SE amp which demands 200Vpp at the grid in A2. I'm testing a 46 (triode-strapped) in filament bias with the gyrator. Yes, a waste of heat, but the 46 sounds brilliant in my experience. The driving results are very good at maximum drive: 0.18% THD @ 200Vpp
46 DHT driver final tests | Bartola Valves
Testing THD on a driver only makes sense if it's done a full swing (e.g. 200Vpp) and loading it properly. I use 100K load albeit cannot reproduce yet the A2 load until output stage is breadboarded.
4P1L in triode is a fantastic choice in terms of drive, anode resistance, linearity and sound. I'm sure if biased at 250V/20-30mA will provide the needs here?
Cheers,
Ale
4P1L is definatly on the cards for me but will involve more work to test and finally impliment in the amplifier, two more tx and reg boards to fit into a two chassis heavy, hot amplifier.
p.s re: 6c45pi.. the minimum thd was with 2nd and 3rd harmonics equal, if the currant was dropped the 2nd and hence thd went up, but the spectrum improved with a lower 3rd and the harmonics over 4th went into the noise floor. so perhaps 22-3ma would be a better comprimise at ~.2%
enzo
p.s re: 6c45pi.. the minimum thd was with 2nd and 3rd harmonics equal, if the currant was dropped the 2nd and hence thd went up, but the spectrum improved with a lower 3rd and the harmonics over 4th went into the noise floor. so perhaps 22-3ma would be a better comprimise at ~.2%
enzo
I'm near farnham surrey, I'm actually using a mu follower with a triode connected 6e5p, 900v ht so i'm not short of volts and i dont plan any excursions into A2, at least not in the GM70's! sounds nice to me.
My opt are rated at 14w at 11k5 so the 15.5 its making at 5% is probably my lot for now, but i'd like 15w at <5%
Im not planning on using the 6c45, but sticking with the 6e5p's, 0.09% at 200v made my jaw drop open! and keeps things single stage. Though these tests have made me realise how precise the bias needs to be at these outputs. might go with some regulated fixed bias supplies on drivers as well as output valves.
I'm using a 337 negative regulator for the -90v bias on the outputs for now, just one supply to both gm70's derived from an 18v secondary with voltage multiplier, so plan to build individual regulators, probably a better raw power supply too. maybe a shunt reg with a series zenner chain like i believe the MJ statistical reg and a rotary switch to adjust the bias point....
I've not had a chance to hear any of these valves, other than the 6e5p, on the gm70 yet so these are just figures, but listening tests will be fun
My opt are rated at 14w at 11k5 so the 15.5 its making at 5% is probably my lot for now, but i'd like 15w at <5%
Im not planning on using the 6c45, but sticking with the 6e5p's, 0.09% at 200v made my jaw drop open! and keeps things single stage. Though these tests have made me realise how precise the bias needs to be at these outputs. might go with some regulated fixed bias supplies on drivers as well as output valves.
I'm using a 337 negative regulator for the -90v bias on the outputs for now, just one supply to both gm70's derived from an 18v secondary with voltage multiplier, so plan to build individual regulators, probably a better raw power supply too. maybe a shunt reg with a series zenner chain like i believe the MJ statistical reg and a rotary switch to adjust the bias point....
I've not had a chance to hear any of these valves, other than the 6e5p, on the gm70 yet so these are just figures, but listening tests will be fun
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