LAZAROIU said:
"The EL300 tube is a very interesting and obtain good performance in audio amplifier applications.
A notice about your construction output OT is that transformers are small and I think you can get better performance if you use these sections for OT somewhat higher.
Low frequency response to be much better at 0dB, in my opinion!
In the picture I have another solution EL300 and amplifier with ECC83:"
I think that is an interesting topology.
I would like to know 'what is the damping factor at the secondary output'?
Thanks!
"The EL300 tube is a very interesting and obtain good performance in audio amplifier applications.
A notice about your construction output OT is that transformers are small and I think you can get better performance if you use these sections for OT somewhat higher.
Low frequency response to be much better at 0dB, in my opinion!
In the picture I have another solution EL300 and amplifier with ECC83:"
I think that is an interesting topology.
I would like to know 'what is the damping factor at the secondary output'?
Thanks!
Yaveaina and Josnio,
1. For where to put a volume control, Refer to artosalo’s schematic. Replace R6 with a 50k Ohm Audio Taper Potentiometer (call it R20). Connect the middle connector of R20 to R9 (the end of R9 that used to connect to R6). Connect Ground to the Counterclockwise end of R20 (Zero volume end). Connect the Clockwise end of R20 to the input connector (Max volume end).
2. Different tubes:
As to changing from EL34s to 6V6, 6L6, KT66, or KT88, this could cause trouble without paying attention to many details. The connections for the tube elements are different:
Pin EL34/6CA7 KT66/6L6/6V6/KT88
1 Suppressor NC / or Shield, i.e. old metal 6L6
2 Fil Fil
3 Plate Plate
4 Screen Screen
5 Control Grid Control Grid
6 NC NC
7 Fil Fil
8 Cathode Cathode
If there is a shield at pin 1, be sure to ground it.
Select R1 for appropriate cathode current, and appropriate Plate + Screen Watts dissipation. Select C1 Voltage rating so it is safe at any new higher Bias voltage. Select the grid resistor R31, not to exceed the Tube rating for Rg max when using cathode self bias.
Note: Filament current varies, 0.45A for a 6V6 to 1.6A for a KT88 Can your filament secondary handle 2x 1.6A (3.2A)?
Check that the B+ is rated for enough current to be able to run the higher plate current tubes, at the current you choose to run them. Higher plate currents may require different output transformers; and they may require different primary impedances for optimum results.
1. For where to put a volume control, Refer to artosalo’s schematic. Replace R6 with a 50k Ohm Audio Taper Potentiometer (call it R20). Connect the middle connector of R20 to R9 (the end of R9 that used to connect to R6). Connect Ground to the Counterclockwise end of R20 (Zero volume end). Connect the Clockwise end of R20 to the input connector (Max volume end).
2. Different tubes:
As to changing from EL34s to 6V6, 6L6, KT66, or KT88, this could cause trouble without paying attention to many details. The connections for the tube elements are different:
Pin EL34/6CA7 KT66/6L6/6V6/KT88
1 Suppressor NC / or Shield, i.e. old metal 6L6
2 Fil Fil
3 Plate Plate
4 Screen Screen
5 Control Grid Control Grid
6 NC NC
7 Fil Fil
8 Cathode Cathode
If there is a shield at pin 1, be sure to ground it.
Select R1 for appropriate cathode current, and appropriate Plate + Screen Watts dissipation. Select C1 Voltage rating so it is safe at any new higher Bias voltage. Select the grid resistor R31, not to exceed the Tube rating for Rg max when using cathode self bias.
Note: Filament current varies, 0.45A for a 6V6 to 1.6A for a KT88 Can your filament secondary handle 2x 1.6A (3.2A)?
Check that the B+ is rated for enough current to be able to run the higher plate current tubes, at the current you choose to run them. Higher plate currents may require different output transformers; and they may require different primary impedances for optimum results.
I am building the same amp. I am planning on buying a 2a 220v to 6.3v transformer >2a max. Should I try to find one which supplies currrent to both power inputs or use two transformers? I have been told by an expert that the 180v-250v source must go through a transformer before the pcb to provide electrical isolation and prevent users from being electrocuted even if the pcb says 220v just like mains where I reside. What is the best voltage to use between 180 and 250v?
What about OT? Must they be rated in ohms? No nV to xV rating?
how many kohms will be best?
*it was an expert on this site who was nice enough to save this tube noob's life btw
What about OT? Must they be rated in ohms? No nV to xV rating?
how many kohms will be best?
*it was an expert on this site who was nice enough to save this tube noob's life btw
Let's repeat the warning again - that's 220V DC not AC from the mains! Please read post 1 and 2 carefully, all your questions are already covered.
thanks
I have seen 4- 5k ohm and a link to a toroidial OT which says its made for el34 and is 3.2k ohms
What is the ideal resistance for OT? Surely we can get a more precise target.
Any suggestions on where to find C-Core or R?
I am in thailand.
Anyone know of a thai c-core or r-core OT manufacturer here?
180-250v is
How is that done?
Any threads or links which give instructions?
Why the airgap?
assuming my fullranges use 8 ohms
I came across this formula
((Primary turns / sec turns)^2) * 8 = desired resistance
220/20 = 11
So an 11v or a 12v PT (from 220v) would be ideal ratio for rewinding?
Using 3.2 kohms as desired resistance
From suggested toroidy.pl OT link
(20^2)*8=3,200 ohms
is that going down the right track?
Thanks
I have seen 4- 5k ohm and a link to a toroidial OT which says its made for el34 and is 3.2k ohms
What is the ideal resistance for OT? Surely we can get a more precise target.
Any suggestions on where to find C-Core or R?
I am in thailand.
Anyone know of a thai c-core or r-core OT manufacturer here?
180-250v is
How is that done?
Any threads or links which give instructions?
Why the airgap?
assuming my fullranges use 8 ohms
I came across this formula
((Primary turns / sec turns)^2) * 8 = desired resistance
220/20 = 11
So an 11v or a 12v PT (from 220v) would be ideal ratio for rewinding?
Using 3.2 kohms as desired resistance
From suggested toroidy.pl OT link
(20^2)*8=3,200 ohms
is that going down the right track?
Thanks
Okay so dedication, logic, and staring at lots of freq response curves all to the extent of trusting yo' heart seems to be looking likely to pay. Found a guy who makes O.T.s local and C-core is the shape which has suddenly fallen within my price range. I am using the PCB but slightly modifying the end result by rounding the corners at every junction. cutting all the points which are created. I went to the maker's house and we tested several O.T.s with a similar SE amp his C-cores outperformed E and L s they were tall rectangular prisms which had been cast or bent into a flat sided oval stadium like shape
@phi112358 - Please keep the discussion on topic, your OT post above has been removed.
im going to use this as an output stage afaik. This 12ax7 el34 SE 10w*2 amp will live between my the SE DAC which outputs via both headphone and 2*rca jacks at an estimate at 1v or equivalent to your average home CD player, and my pair of full range speakers which are 8" 35w. The source (DAC) will be fed from a DC lab psu. On the psu there is an option of 1.5A or 3A. Looking at its design, the 3A mode uses two transistors where the 1.5A mode does not use them. Both are running through a rectifier and filters(of course) . If there are any theoretical advantages to one mode or the other, I would like to hear any thoughts about them. (The power source for the DACs is using a multi tap transformer (~12 taps).
The el34 12ax7 se amp will be using a sovtek 12ax7 and 2 jj el34s and fed from a massive 220v>240v and 6v transformer, and I will post info on OTs asap. I'm looking for the best schematic available for that use Will post OT info ASAP
Thanks
The el34 12ax7 se amp will be using a sovtek 12ax7 and 2 jj el34s and fed from a massive 220v>240v and 6v transformer, and I will post info on OTs asap. I'm looking for the best schematic available for that use Will post OT info ASAP
Thanks
Hi, Guys ...
I´m little confused about negative feedback connected to secondary on output transformer ... I have SE EL84, schematics comes from old Stereo Czechoslovakia amplifier from year about 1966, in original version, there´s OT for "Hi-Fi" use, NFB with 2K7, I use OT from old televisions ... i like to build new amp with the same tubes and I like to use toroidal trans from Toroidy.pl, TTG-EL84 ... I still need NFB for this OT ?
Thank´s for your opinions ...
I´m little confused about negative feedback connected to secondary on output transformer ... I have SE EL84, schematics comes from old Stereo Czechoslovakia amplifier from year about 1966, in original version, there´s OT for "Hi-Fi" use, NFB with 2K7, I use OT from old televisions ... i like to build new amp with the same tubes and I like to use toroidal trans from Toroidy.pl, TTG-EL84 ... I still need NFB for this OT ?
Thank´s for your opinions ...
Good morning, after a few months of using this amplifier with 8ohms speakers I intend to use it with a new ones with 4 ohms impedance. Is it enough to connect to the correct transformer output?
I have these: TTG-EL34SE - Tube output UL transformer [3,2kOhm] EL34 / 6L6 SE - Shop Toroidy.pl
Will I have to change the value of R7? Will I expect greater output power? Any change in the supply voltage? Grateful for the attention
I have these: TTG-EL34SE - Tube output UL transformer [3,2kOhm] EL34 / 6L6 SE - Shop Toroidy.pl
Will I have to change the value of R7? Will I expect greater output power? Any change in the supply voltage? Grateful for the attention
It depends, if you use EL34 or 6L6 then the transformer you are talking about will do good. no need to re-bias, if the primary impedance is the same on the new transformer, but it is not bed to check it after you change the transformer. Not all the transformers are born identical.
You can search for a transformer that has 0 - 4 - 8 ohm output.
You can search for a transformer that has 0 - 4 - 8 ohm output.
I junt want to use the amp with other speakers (4ohms) mantain everything the same. My tubes are EL34.
I was doing some measurements and got: I over R1 (artosalo drawing) 72mA with R1 390 ohms, Vplate (EL34) 358V. can someone tell me what power are the el34 to dissipate? Are they working in a safe zone?
I was doing some measurements and got: I over R1 (artosalo drawing) 72mA with R1 390 ohms, Vplate (EL34) 358V. can someone tell me what power are the el34 to dissipate? Are they working in a safe zone?
josino,
If R1 is the EL34 self bias cathode resistor, then:
390 Ohms cathode resistor, and 72mA (0.072A)
390 x 0.072 Amps = 28 Volts
358 Volts - 28 Volts = 330 Volts Plate to Cathode
330 Volts x 0.072 Amps = 23.76 Watts plate plus screen dissipation; the EL34 plate is rated for 25 Watts.
Recommendation: Use Good EL34 tubes.
The Toroidal transformer you referred too has both 4 ohm and 8 Ohm taps. Use the 4 Ohm tap for the 4 Ohm speakers.
If R1 is the EL34 self bias cathode resistor, then:
390 Ohms cathode resistor, and 72mA (0.072A)
390 x 0.072 Amps = 28 Volts
358 Volts - 28 Volts = 330 Volts Plate to Cathode
330 Volts x 0.072 Amps = 23.76 Watts plate plus screen dissipation; the EL34 plate is rated for 25 Watts.
Recommendation: Use Good EL34 tubes.
The Toroidal transformer you referred too has both 4 ohm and 8 Ohm taps. Use the 4 Ohm tap for the 4 Ohm speakers.
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Thank you very much for the quick reply. I had an idea what these calculations would be .... I'm using JJ EL34, Do you have any (make / model) that suggests?
Well, i was wrong, i use EL34EH from electro Harmonix. I did some measurements today with the oscilloscope and got about 5W rms (charge of 8ohms, input 450mv and 355V in EL34) in UL mode. Is it typical value? Will I get less in triode mode, right? If switching output transformers can increase the value too? Thanks for help
Well, i was wrong, i use EL34EH from electro Harmonix. I did some measurements today with the oscilloscope and got about 5W rms (charge of 8ohms, input 450mv and 355V in EL34) in UL mode. Is it typical value? Will I get less in triode mode, right? If switching output transformers can increase the value too? Thanks for help
josino,
A current schematic of your amp would be helpful, including voltages, resistances, transformer impedance and screen tap %.
You list an input of 450mV. Did you increase the input level until you got too much distortion, and then back it down to 450mV where the distortion was reasonable? That is a measurement for 'undistorted power'.
When you get 5 Watts out for 450mV input (with the volume control turned to maximum) are you asking "is that normal"? If you convert the 5Watts into 8 Ohms into a voltage, then Vout/Vin is a 'measurement of Gain'.
Undistorted power, and Gain are two different things.
You can have lots of gain but no power, you can have lots of power but no gain, or you can have both.
5 Watts at OK distortion levels may be perfectly normal for a single ended ultra linear mode EL34 that has about 24 Watts plate plus screen dissipation. That is 5/24 = 0.208, or 20.8% efficiency.
What is you amplifier's distortion percent at 5 Watts, either THD, or 2nd and 3rd harmonics?
A current schematic of your amp would be helpful, including voltages, resistances, transformer impedance and screen tap %.
You list an input of 450mV. Did you increase the input level until you got too much distortion, and then back it down to 450mV where the distortion was reasonable? That is a measurement for 'undistorted power'.
When you get 5 Watts out for 450mV input (with the volume control turned to maximum) are you asking "is that normal"? If you convert the 5Watts into 8 Ohms into a voltage, then Vout/Vin is a 'measurement of Gain'.
Undistorted power, and Gain are two different things.
You can have lots of gain but no power, you can have lots of power but no gain, or you can have both.
5 Watts at OK distortion levels may be perfectly normal for a single ended ultra linear mode EL34 that has about 24 Watts plate plus screen dissipation. That is 5/24 = 0.208, or 20.8% efficiency.
What is you amplifier's distortion percent at 5 Watts, either THD, or 2nd and 3rd harmonics?
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