Hi
I am playing with some tests on double C core , 0,1 mm laminated for a p-p of KT88-120.
The first one, about 50 w at 30hz, seems to be fine.
This second test is for a double p-p of KT120, about 120 w at 30Hz (checked).
1- http://www.multitask.it/kt120/Trafo-Litz1.jpg
one photo with a 120
The difference with the previous one is the secondary with a Litz cable (150 wires, 0.08 mm)
2-http://www.multitask.it/kt120/Trafo-Litz2.jpg
you can see the wires
The first test is a open loop BW at 1w - 8 ohm:
3-http://www.multitask.it/kt120/1-Litz-1w-8ohm-NoFB.jpg
the -3 dB a 120 kHz, is very good
4- http://www.multitask.it/kt120/2-Litz-10w-8ohm-NoFB.jpg
open loop at 10 w 8 ohm
same BW
5-http://www.multitask.it/kt120/litz/comp100pF.jpg
this is a THD vs Freq at 50w with a FB of 16 dB and 100pF comp.; the result is very interesting.
I have to increase Z at low frequency; I am waiting the new prototype.
6-http://www.multitask.it/kt120/8-Litz-50w-FREQ-comp100pF.jpg
BW at 50 w with 16 dB of feedback; -1 dB at 150 kHz.
There are little indecision at high freq.; I am testing a solution.
The next future is to have a new proto with also the primary with Litz also for s.e.
These protos are made with a F.I.A.T. in Rome; I hope in future they wiil have a commercial destination.
Ciao
Walter
I am playing with some tests on double C core , 0,1 mm laminated for a p-p of KT88-120.
The first one, about 50 w at 30hz, seems to be fine.
This second test is for a double p-p of KT120, about 120 w at 30Hz (checked).
1- http://www.multitask.it/kt120/Trafo-Litz1.jpg
one photo with a 120
The difference with the previous one is the secondary with a Litz cable (150 wires, 0.08 mm)
2-http://www.multitask.it/kt120/Trafo-Litz2.jpg
you can see the wires
The first test is a open loop BW at 1w - 8 ohm:
3-http://www.multitask.it/kt120/1-Litz-1w-8ohm-NoFB.jpg
the -3 dB a 120 kHz, is very good
4- http://www.multitask.it/kt120/2-Litz-10w-8ohm-NoFB.jpg
open loop at 10 w 8 ohm
same BW
5-http://www.multitask.it/kt120/litz/comp100pF.jpg
this is a THD vs Freq at 50w with a FB of 16 dB and 100pF comp.; the result is very interesting.
I have to increase Z at low frequency; I am waiting the new prototype.
6-http://www.multitask.it/kt120/8-Litz-50w-FREQ-comp100pF.jpg
BW at 50 w with 16 dB of feedback; -1 dB at 150 kHz.
There are little indecision at high freq.; I am testing a solution.
The next future is to have a new proto with also the primary with Litz also for s.e.
These protos are made with a F.I.A.T. in Rome; I hope in future they wiil have a commercial destination.
Ciao
Walter
I alway use the complete amp.
I check every stage, from input to grid of output tubes, the linearity and thd.
In this trafo the ratio is 20:1 this means that at 50w - 8ohms on primary I have 400 Vrms anode-to-anode,.
The input stage and phase splitter have a BW of 200 kHz ( -0.2 dB) with a good thd.
At 20 Vrms on input of grid of KT120 I have 0,19 % ( no feedback)
The power stage is pentode connection not UL ( much easier 🙂 )
Ciao
Walter
I check every stage, from input to grid of output tubes, the linearity and thd.
In this trafo the ratio is 20:1 this means that at 50w - 8ohms on primary I have 400 Vrms anode-to-anode,.
The input stage and phase splitter have a BW of 200 kHz ( -0.2 dB) with a good thd.
At 20 Vrms on input of grid of KT120 I have 0,19 % ( no feedback)
The power stage is pentode connection not UL ( much easier 🙂 )
Ciao
Walter
Your transformer seems, even now, very good to me comparing with many commercial ones.
The little differences may come from the amplifier circuit itself. I will follow this thread anyway.
I promised my son to make a "tube ampli" for him but, good transformers are too expensive to buy. And they will not sell the core/bobbine material here where i am in small quantities. So i have no chance to make one by myself either.
Ever think to sell transformers you make ?
(Using Litz wire is indeed a good idea to overcome the skin effect at higher frequencies.)
The little differences may come from the amplifier circuit itself. I will follow this thread anyway.
I promised my son to make a "tube ampli" for him but, good transformers are too expensive to buy. And they will not sell the core/bobbine material here where i am in small quantities. So i have no chance to make one by myself either.
Ever think to sell transformers you make ?
(Using Litz wire is indeed a good idea to overcome the skin effect at higher frequencies.)
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Now I am testing some prototypes.
Mainly pp but I am waiting one s.e. for 300B.
The company that follow me, F.I.A.T., is little and I hope to define some good stuff so will be possible to sell.
I suppose will be two lines, one normal and one "super".
The prices will be not high for the normal production, the "super" will have a alluminium box.
Regarding the test I prefer to check with the real circuit if (of course) it has good THD vs level.
At AUDIOreview magazine, in Italy, my friend Fabrizio is developping a circuit to test the O.T.
It is an amplifier that can develop ( the first test on simulation) about 200 Vrms with a verly low THD and Zout.
It will be not complicate to build ( with a pcb) but we need some time again.
Ciao
Walter
Mainly pp but I am waiting one s.e. for 300B.
The company that follow me, F.I.A.T., is little and I hope to define some good stuff so will be possible to sell.
I suppose will be two lines, one normal and one "super".
The prices will be not high for the normal production, the "super" will have a alluminium box.
Regarding the test I prefer to check with the real circuit if (of course) it has good THD vs level.
At AUDIOreview magazine, in Italy, my friend Fabrizio is developping a circuit to test the O.T.
It is an amplifier that can develop ( the first test on simulation) about 200 Vrms with a verly low THD and Zout.
It will be not complicate to build ( with a pcb) but we need some time again.
Ciao
Walter
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Joined 2009
Paid Member
To get a fast transient response, the system must have a high BW as much as a minimum 100KC/s.
No need for litz wire, it may help with distributed capacitance due to its twisted nature in an audio transformer but no need at audio frequencies.
Anyway, good job on the transformers. They look good, what is the core area on the cores you are using? Or just the dimensions?
Cheers
Matt.
Anyway, good job on the transformers. They look good, what is the core area on the cores you are using? Or just the dimensions?
Cheers
Matt.
Better frequency and power response. For big transformers can be important to tame skin effect and proximity effect becoming unacceptable with large size wire. I can't see any usefulness for the primary though. Not that one needs bags of power above 10KHz but often many OT's at such frequency already have substantially increased distortion at 1-2W! The winding scheme can help to extend the power response for a given wire size but at some point there is a limit and becomes impractical or impossible.
Extended FR e PR, with resonance as high as possible and well behaved, is a plus for amplifiers using fb.
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