hello:
I am making a SEU6lu8 amp. I do not have an ultra linear tap on the transformer I intend to use. The transformer has two primary taps. One 5k one 7k. Can I use the the 5k tap as the output tap and the 7k tap as the ultra linear connection to the screen. I was going to use a 1.2k resistor on the 7k tap to lower the DC screen voltage.
I am thinking this arrangement will give me ~ 2/7 ( 28%) Ul connection.
Comments and guidance appreciated.
Thank you
I am making a SEU6lu8 amp. I do not have an ultra linear tap on the transformer I intend to use. The transformer has two primary taps. One 5k one 7k. Can I use the the 5k tap as the output tap and the 7k tap as the ultra linear connection to the screen. I was going to use a 1.2k resistor on the 7k tap to lower the DC screen voltage.
I am thinking this arrangement will give me ~ 2/7 ( 28%) Ul connection.
Comments and guidance appreciated.
Thank you
That should work OK. Be sure the red lead on the OPT goes to the B+.
The far end of the winding to the plate & the other lead to the screen.
The 7K tap is the far end of the winding, so should go to the plate.
If the winding taps get mixed up, still not a problem. Just weird results.😱
I did build an experimental SE 6LU8 amp about 20 yrs ago. In triode & UL the performance was good.
But in straight pentode it didn't do well at all.🙂
The far end of the winding to the plate & the other lead to the screen.
The 7K tap is the far end of the winding, so should go to the plate.
If the winding taps get mixed up, still not a problem. Just weird results.😱
I did build an experimental SE 6LU8 amp about 20 yrs ago. In triode & UL the performance was good.
But in straight pentode it didn't do well at all.🙂
Thanks John:
My first go at it I hooked the 7k to the screen and only got a watt or so of out put. I will try switching them and see how that works.
I have not drawn a 7k impedance curve so I am unsure how it is going to work out. Everything I have read says 5k or less.
My first go at it I hooked the 7k to the screen and only got a watt or so of out put. I will try switching them and see how that works.
I have not drawn a 7k impedance curve so I am unsure how it is going to work out. Everything I have read says 5k or less.
Hello Rikaro:
Yes, I think that John captured that point in his note. I have hooked it up as he suggested, with a 7k primary and the 5k as screen with a 1.2k resistor. I still need to make a few other changes then I will test it again. My concern is surrounding the 7k primary and the 6lu8 pentode section. I am not getting very much output right now. It goes into wild high frequency oscillation without feed back and I need to figure out how much Plate to plate feedback is required. My other options are to try triode strapping or global feedback. I am hoping to get 3-4 clean watts from the amp when I get things sorted out. Maybe triode is the cleanest most pleasant hook up with these transformers.
Thanks
Yes, I think that John captured that point in his note. I have hooked it up as he suggested, with a 7k primary and the 5k as screen with a 1.2k resistor. I still need to make a few other changes then I will test it again. My concern is surrounding the 7k primary and the 6lu8 pentode section. I am not getting very much output right now. It goes into wild high frequency oscillation without feed back and I need to figure out how much Plate to plate feedback is required. My other options are to try triode strapping or global feedback. I am hoping to get 3-4 clean watts from the amp when I get things sorted out. Maybe triode is the cleanest most pleasant hook up with these transformers.
Thanks
Looking in my notebook of 20 yrs ago I was using a B+ of 350V. The Rk was 750R, so a drop of ~43V.
For UL operation the Rl was 6.8K. For Triode I used 4,2K, And the result in each case was a few watts. 👍
For UL operation the Rl was 6.8K. For Triode I used 4,2K, And the result in each case was a few watts. 👍
Hello John:
My B+ is 304v, I am using a 750R cathode resistor and landing on 33V on the cathode.
I do not have triode curves for the 6lu8. but I can tell that a 7K load and 71% UL does not yield more that maybe one watt. My transformer has a 16ohm tap. If I use the 16ohm tap will that give me a 3.5k reflection with an 8ohm load?
My B+ is 304v, I am using a 750R cathode resistor and landing on 33V on the cathode.
I do not have triode curves for the 6lu8. but I can tell that a 7K load and 71% UL does not yield more that maybe one watt. My transformer has a 16ohm tap. If I use the 16ohm tap will that give me a 3.5k reflection with an 8ohm load?
With a given Rplate into originally Zpri 7k and 8 ohm load on 16ohm output translates into Zpri 3,5k, the tube is loaded heavier, ac voltage will drop and B decrease. This would be a good thing on the low frequency side. On the other hand, a.o.t., copper losses will increase. First off, i would measure the 7k primary, the sec 0-8 and 8-16 resistances to get at least a rough idea of what to expect in relation to copper losses. If the transformer has allready highish copper losses with rated load, i would not use the 16 output with 8ohm load, otherwise sure, a full sec winding instead of a tapped off is a plus.
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