Do you guys really not see that the feedback in the schematic posted by stajo is actually substantial, depending on the wiper position of the input pot?
The link in post #1 is no longer to the circuit diagram.
Have you heard 6K6 Nick?
260V regulated, without cathode bypass
Have you heard 6K6 Nick?
260V regulated, without cathode bypass
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All links work at my end (w10 & firefox). 6K6 no, I don't have that bottle. Is it good on microphony?
"Comprehensive Schematic" directs to page 9. No schematic there..
No microphony. I'll post a picture of those sexy French round plates tomorrow 😉
Weird thing. I see it. But I added it as attachment too since you don't. Is it also attached there now at your end?
Page 9 holds the schema. 6AQ5/el90 is also a nice little tubbie, B7G socket. Cant even count my numbers.
My message number is set to 50/page.
Whatever the reason, post 81 it is.
Thank you and till tomorrow.
My supply voltage is low at the moment. I have not yet got the proper transformer. Will take a few days.
Currently:
V+ = 190V
Vp = 93.4 ( tube1 ) 92.6 ( tube 2 ) ( Rp = 11K , Rk = 680 E )
Ip = 8.76 mA 8.81 mA
Av= 16.59 dB with 1000uF and 13.26 dB without 1000uF
I've used the 6L6 many years ago. Maybe I'll try it again. It was very good though I don't remember details. It drove a unity gain Latfet output stage.
Currently:
V+ = 190V
Vp = 93.4 ( tube1 ) 92.6 ( tube 2 ) ( Rp = 11K , Rk = 680 E )
Ip = 8.76 mA 8.81 mA
Av= 16.59 dB with 1000uF and 13.26 dB without 1000uF
I've used the 6L6 many years ago. Maybe I'll try it again. It was very good though I don't remember details. It drove a unity gain Latfet output stage.
Zo is 4K without the 1mF when it is 1.1K with it for those Rp, Rk, B+ values and operating point. It has some more 3rd harmonic and less output current drive now than at the original op. point of course but its passable till you go higher rail. All your numbers simulate nearly spot on. I don't see difference in gain dB for popping in the 6L6GC though.
I just plugged in the 6L6 ( Electro Harmonix )to see what happens.
Supply voltage +192 V
V plate 91.2 V ( tube 1 ) 90.8 V ( tube 2 )
I p = 9.21 mA and 9.29 mA
Gain = x 6.5 with 1000 uF ( 16.26 dB ) and x 4.4 with no 1000uF ( 12.87 dB ) All levels measured with a 0.2 V input.
Don't hear any immediate differences . Bass might be more full ? But that could be an illusion. I can't do any controlled AB tests now. Need more time for that. But I will play this all day and then switch back to the 6V6 to see if I can make out any significant difference. This currently doesn't appear so.
But a couple of points. The 6L6 seems more microphonic ! In fact you can hear the ' internal wires vibrating and dying down' ! So it's worse !
But the 6V6 had another problem. It picked up hum if a hand was placed near the tube. But if I grounded my other hand , it would go away. So it's very sensitive to electric fields. An earthed metal chassis is necessary and maybe a perforated shield around it also !
The 6L6 however didn't seems sensitive to the field around it ! Quite interesting . I , for no reason at all , expected the 6L6 to be not microphonic at all ! I think all this is being aggravated by a thin pcb and without a solid mount.
With a good board with proper mounting this problem of microphony would be quite low I think.
I need to change the output caps to film caps next.
After that I'll turn on the 6922 preamp this evening and see how it compares ! 🙂
How about a 845 ? 🙂
Supply voltage +192 V
V plate 91.2 V ( tube 1 ) 90.8 V ( tube 2 )
I p = 9.21 mA and 9.29 mA
Gain = x 6.5 with 1000 uF ( 16.26 dB ) and x 4.4 with no 1000uF ( 12.87 dB ) All levels measured with a 0.2 V input.
Don't hear any immediate differences . Bass might be more full ? But that could be an illusion. I can't do any controlled AB tests now. Need more time for that. But I will play this all day and then switch back to the 6V6 to see if I can make out any significant difference. This currently doesn't appear so.
But a couple of points. The 6L6 seems more microphonic ! In fact you can hear the ' internal wires vibrating and dying down' ! So it's worse !
But the 6V6 had another problem. It picked up hum if a hand was placed near the tube. But if I grounded my other hand , it would go away. So it's very sensitive to electric fields. An earthed metal chassis is necessary and maybe a perforated shield around it also !
The 6L6 however didn't seems sensitive to the field around it ! Quite interesting . I , for no reason at all , expected the 6L6 to be not microphonic at all ! I think all this is being aggravated by a thin pcb and without a solid mount.
With a good board with proper mounting this problem of microphony would be quite low I think.
I need to change the output caps to film caps next.
After that I'll turn on the 6922 preamp this evening and see how it compares ! 🙂
How about a 845 ? 🙂
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I don't remember picking hand field ever in my builds. Maybe you got an oscillation or lift the heater to cathode by 50V
I think it's just the mess of wires close to it. I don't see any oscillation on the scope ( 100 MHz).
The pcb just sits (with spacers) on another bare pcb with copper facing up. There is no connection to the mains ground at the moment. However both tubes behave differently to the same situation.
Is it worthwhile getting the Mullard and Tungsol 6V6 ? I have to get it either from the US or Singapore.
The pcb just sits (with spacers) on another bare pcb with copper facing up. There is no connection to the mains ground at the moment. However both tubes behave differently to the same situation.
Is it worthwhile getting the Mullard and Tungsol 6V6 ? I have to get it either from the US or Singapore.
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