Not just an replacement, but an improvement!


EML 45B

Uploaded: 29.12.2016

Released


The 45B tube is designed to build amplifiers with fully original "45 tube sound", but the 45B is able to do so at more than twice the output power. However the amplifier needs to be modified, or new designed. For this reason we give some of the background here first, additional to the tube data.

Some words about the classical RCA 45 tube, and it's recommended use.

The standard 45 tube is designed for speaker systems which can produce sufficient loudness below 2 Watt. For this, two classical operating points have been in use ever since, and these can not be improved. The 1.6 Watt circuit was intended for USA radios, which typically run at 250V DC Supply Voltage. The 2 Watt circuit is running at 275 Volts, and was commonly used HiFi amplifiers. The tube output power is always specified before the transformer. Given a normal transformer loss of 6...11%, the 2 Watt circuit delivers 1.8Watt at the loudspeakers, at low distortion. Designed 85 years ago, this circuit is a perfect balance between a few difficult choices, such as output power, distortion, damping factor and lifetime of the tube. After a careful study of the old RCA datasheets, using computer simulation software, we have to praise respectfully the good work by the RCA company. Meaning those working points are chosen perfectly, and distortion data was published totally correct by RCA. (So no attempts to make the tube look better, like was done in the old Western Electric 300B data sheet)

From the RCA circuits, it can be seen, the peak signal is limited by grid clipping. Meaning, the grid voltage would become positive, leading to a sudden increase of distortion, when if the output power is raised above 2Watt. Yet, as long we stay below 2Watt, the swing through the tube curves stays nicely away from the cut-off area of the tube, keeping 2nd harmonic distortion below -27dB, even at high signal. This works all so natural and self explaining, it is evident, the tube was designed to work like this. Without going to much in detail, it must be said such tubes behave also well in a Push Pull circuit. On the positive side is also, the working voltage is relatively low, so the complete amplifier becomes cost efficient. All together, this had made the 45 such a versatile and popular tube. Moreover, it has to be said, the RCA datasheets presents output power and distortion numbers fully exact. Comparing this to some of the blatant errors in the WE300B data sheet, gives only great respect for this RCA 45 data sheet.

The 45B tube

The classic 45 was designed for speaker systems needing less than 2x 2Watt of RMS power. Such speakers exist, but many other still excellent speaker systems, require up to 2x 4 Watt output power. Here is where the 45B comes in. The 45B can be used such to keep the sound character of the 45 tube, but do so at higher power. For this, some carefully chosen operating points are recommended below. These will all come near to the original 45 sound, in terms of harmonics development and damping factor, using similar transformer impedance too. For this reason you will see comparable distortion figures as with the genuine working points, only with the 45B that will achieved at higher output power. Additionally, some 45B working points are recommended with relatively high transformer impedance of 9k2, which aim for lowest possible distortion, lower as the classical 45.

The 45B tube will NOT give higher output power when the amplifier is not modified. However the 45B can be used normally instead of a standard 45, and will behave identical. So the modification of the amplifier can be done at a later time if required.

Distortion in percent or Decibel (dB)

In electronics, distortion can be expressed as percentage of the signal, or in dB. Using dB, is more related to human hearing, meaning a similar difference in dB, is experienced the same. This is why many technicians prefer dB. (See also Note6). As as rule of thumb it can be said, a 3dB change can be heard by anyone, but below that needs a trained ear.

The 26dB rule of thumb: -26dB of 2nd harmonics is the level at which most human ears just do not hear this distortion. So at -25dB or more, you will experience this as minimal distortion. Wheras harmonics added with a levels of -20dB or more, sounds not pleasant any more.

Some examples of 2nd harmonic distortion level
Sterile Sound
-36dB or better
Triode Sound
-27dB or better
Some can hear this as distortion, some can not.
-26dB
Can heard best by direct compare
-24dB
Can be heard always
-22dB
Not HiFi any more
-20dB

With SE amplifiers, the harmonics will be mainly 2nd harmonics. The Ratio of 2nd. harmonic to 3rd. harmonic is an amazing factor 350 with the 45 tube, and the 4th harmonic or higher is virtually not present at all. So we need to look only at the 2nd harmonic.

Distortion and (modern) Amplifier Design

Historical bias settings give us a 1.6 Watt operating point, and a 2 Watt operating point. The 1.6 Watt circuit has the advantage of a somewhat lower distortion, but it needs really a loudspeaker system which requires no more than 1.6 Watt. The advantage of this circuit seems only the low heat development in the tube, and lower working voltage. It has to be said that the lifetime of historical (NOS) 45 tubes is probably much higher in the 1.6 Watt circuit, as these tubes are very small dimensions, and they get quite hot in the 2Watt circuit. Yet EML 45 has better cooling, and lifetime is not reduced at maximum dissipation.

Unlike in the 1930's, high voltage capacitors were expensive, and had short life time. So a higher working voltage was an issue in the early days of HiFi, but today capacitors are low cost and reliable. This makes the 2 Watt circuit the first choice today. When the output signal of the 2Watt circuit is only 1.6 Watt, distortion drops even 2dB below that of the 1.6 Watt circuit, so -30dB is achieved with the 2Watt circuit at 1.6 Watt only.

Still, with loudspeakers requiring more than 2 Watt, the standard 45 tube reaches it's limits, and we know it does become a problem for many owners of loudspeakers. Initially 2Watt may seem sufficient, but after some time this may appear not so.

The EML45B gives more options. This tube can be used anywhere between 6Watt and 22Watt plate dissipation. In case plate dissipation is below 6 Watt, like in driver circuit, the classical 45 or 45M would be the better choice.


EML 45B

Side - Top


Plate curves

 

Transformers

Several working points in the table below will have just 10% higher DC current compared to historical bias points. This allows in many cases to use Single Ended 45 transformers that may already be available. With some other working points, up to 55mA it will probably require another transformer.

Keep in mind, transformers, have copper loss, iron loss, and stray loss. All together this can be 6...12% depending on the construction.

Low cost transformers: These will atypically have a smaller core, and in order to get enough windings on such a core, the wire needs to be thinner. So there will be higher copper loss, additional to iron loss which by itself is few percent too. For this reason, only finest transformers will be better than 94% efficiency, whereas some others can be as low as 89% efficiency. However there should be awareness, that the SE transformer can loose 5...11% of the output power, depending on it's quality. Given what a tube amplifier costs, it is not a good idea to save on the transformer, and loose the energy which was so expensively generated. Moreover it is a question, if such transformers that convert the tube output power into internal heat, are good sounding. Interesting, this trade off can be observed best when comparing the Lundahl LL1623 and LL1663, in the below table. LL11663 a fine transformer, but it is smaller dimensions. So you can see the difference in efficiency when comparing to the larger size LL1623 or others at the left column.

Transformer Effiency, some examples.
This data is collected by computer simulation, using all parameters.
Tango XE-5SNF-S
92,1%
 
Electra Print MK5KB
91,4%
Black Art 417 (6k)
93,3%
Hammond T16S8SE
91,9%
Bartolucci 17 (6k)
94,3%
Lundahl LL1663-040
91,6%
Lundahl 1623-060
94,4%
Sowther SE01
89,4%

Ultimate transformers: To avoid copper loss, the wire needs to be thick. In order to get still enough windings on the core, it will become larger size. On top of that, the wire length will increase by the larger core, and more wire thickness is needed to compensate that too. So low loss transformers can become very large dimensions. For SE transformers, the first consideration is a good frequency range. When there is a trade off between anything and else and frequency behavior, the frequency will have to come first. So SE transformers are often surprisingly large, just to get a few Watts out of them. As an example, a transformer like the LL1623-060 as used in the below table, has a core that has the dimensions same as a 250 Watt mains transformer, and yet in LL1623 construction it produces only 3.4 Watt, Single Ended.

Output power. There is great confusion about how many output power a classical 45 amplifier delivers. In the historical datasheets is always given 1.6 Watt or 2.0 Watt, but this means at the tube, before the transformer. After the transformer only 1.4 or 1.6 Watt is left. In the following table with operating points this can be seen on lines 1...3.

Conclusion: At the same distortion level, the EML45B is capable of delivering more than twice the output power. The historical bias point delivers 2 Watt at the tube, or 1.8 Watt at the transformer output with -27dB harmonics. The EML45 B at -27dB harmonics can deliver 4.4 Watt at the transformer output. This is a factor 2.2.


The EML 45B Datasheet

EML 45B  Filament Ratings 
Filament Voltage 
= 2.5Volt (AC or DC) 
Tolerance on filament voltage
5%
Filament Current 
~ 1.5Ampere 
EML 45B Maximum Conditions
Plate Voltage 
420Volt 
Plate Current 
53mA 
Minimum Plate Dissipation
8.5Watt 
Continuous Plate Dissipation
22Watt 
Power Output in Class A 
5.2Watt 
Grid resistor

500k Ohm

EML 45B Factory Test conditions
Plate Voltage 
275V 
Plate Current
36mA 
45B Recommended Single Ended operating points.
Bias Method: Auto Bias.

Vb

Ua

Rk

Ug

Ia

Ra

Transformer
examples

Pa

η

Output

Damping factor

2nd harm. (dB)

Tube
         
Ω
See also note 2, 3, 4, 5
 
302V
250V
1353Ω
-46V
34mA
5k6
 
8.5W
18%
1.5W
4.1
28.2

45, 45M, 45B

334V
275V
1444Ω
-56V
36mA
4k6
 
9.9W
20%
2W
3.5
27
45, 45M, 45B
466V
384
2000Ω
-82V
41mA
9k2
LL1679-055 8-16Ω
15.8W
20%
3.1W
4.6
29
45B only. Note7
466V
384
2000Ω
-82V
41mA
6k5
LL9202-050 4-8-16Ω
15.8W
25%
4W
3.2
26.2
45B only. Note8
495V
408V
1800Ω
-87V
48mA
9k2
LL1679-055 8-16Ω
19.7W
18%
3.6W
5.1
29.3
45B only. Note7
495V
408V
1800Ω
-87V
48mA
6k5
LL9202-050 4-8-16Ω
19.7W
23%
4.5W
3.6
27.2
45B only. Note8
495V
408V
1800Ω
-87V
48mA
5k
LL1663-050 8Ω.
19.7W
26%
5.2W
2.7
25
45B only. Note9
495V
408V
1800Ω
-87V
48mA
5k
LL1663-050 8Ω.
19.7W
26%
4.5W
2.7
30.4
45B only. Note10

Credit: We want to thank Roger Modjeski, from the company RAM-LABS / Music Reference USA, for doing many detailed measurements on the 45B tube. It was shown, the published maximum distortion and maximum output power in this datasheet was achieved easily. Even so, the 45B seemed capable of doing more as published here. Thank you very much Roger!


EML 45B Mechanical Data

Size including Socket
(but excluding pins)

145 x 58 mm 

Weight of one tube:
140 Gram

Pin 1: Heater1
Pin 4: Heater2
Pin3: Anode (Plate)
Pin2: Grid

Ceramic UX4 Base
.
  • Note 1) With tubes, miniaturization and linearity do not go together well. This is explained by electrical fields having specific behavior which does not follow the miniaturization exactly. With the EML45, the plate is larger than the historical 45, which large size contributes to lower distortion. This is documented by an external company, and they report 30% lower distortion compared to historical 45. Read here.
  • Note2) Specified in idle condition. Under full signal, plate dissipation will be somewhat higher.
  • Note 3) η = Percentage of power consumed by the output tube that is converted into power at the load. For example, if a tube dissipates 12 watts of heat at idle and delivers 4 watts into the transformer, the plate efficiency would be 25%.
  • Note 4) Distortion drops considerably at lower signal. A distortion compare between two operating points should be made at the same output power.
  • Note 5) Transformer DC loss NOT included in Supply voltage. So depending on the chosen transformer, the Supply voltage needs to be chosen slightly higher, to compensate for the DC loss across the transformer.
  • Note 6) Use a scientific calculator, the formula is 20*Log R. Where R is the ratio. For R =100 you would find +40. For R=0,01 (equals 1%) you would find -40. Or use Excel instead. Enter this, and Excel will write -40 in the cell: =20*LOG(0,01)
  • Note 7) These working points give superior results for all parameters, being: Output power, distortion and damping factor.
  • Note 8) These working points provide damping factor and distortion similar to the RCA circuits. Yet at higher output power.
  • Note 9) This working point is optimized for highest output power, at the compromise of damping factor. Distortion may seem high at 5.2 Watt, but this reduces drastically at lower output signal of 4.5 Watt. For this see Note 10.
  • Note 10) This is the same working point as above, and it demonstrates an amazing 30.4dB low distortion, yet at 4.5 Watt still. However damping factor is not very high. This would be a meaningful application for loudspeaker systems using an active bass, so damping factor plays no important role.

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