Hello ,
i have problems with my LL1660/20ma interstage transformers to drive directly the 6c33 triode.
I get a freq. cutoff 1-2 db continously from 10Khz. The -3dB point is 23Khz. I use a 6c45 with 40mA in ALT S 1:1,25 connection (gain ~50). I also tried the 5842 with 20 mA in that connection. On the scop you see a cutoff 1-2 dB continously from 10Khz. Probably it happen because the input capacitance of the 6c33 is ~11pF. But what could i do? I also need a gain in this circuit near 50 or more!
Thanx a lot
Barossi
i have problems with my LL1660/20ma interstage transformers to drive directly the 6c33 triode.
I get a freq. cutoff 1-2 db continously from 10Khz. The -3dB point is 23Khz. I use a 6c45 with 40mA in ALT S 1:1,25 connection (gain ~50). I also tried the 5842 with 20 mA in that connection. On the scop you see a cutoff 1-2 dB continously from 10Khz. Probably it happen because the input capacitance of the 6c33 is ~11pF. But what could i do? I also need a gain in this circuit near 50 or more!
Thanx a lot
Barossi
Hello,
the schematic looks like this:
http://www.republika.pl/diytriode/EC8010_GM70.gif
but i use 6c33 triode instead of GM70. The 6c33 runs with Ra=600Ohm experience electronics high quality transformer:
http://www.experience-electronics.de/deutsch/bauteile/eintakt-a-uebertrager.htm#a6c33 (A6c33)
Ub~200V, I~175mA
At the grid of the 6c33 i get a cutoff beginns from 10Khz with 1-2dB! I need help.
The 6c45 runs with 17ma, 175 at anode, interstage is LL1660/18mA in 1:1,25.
Thanks Barossi
the schematic looks like this:
http://www.republika.pl/diytriode/EC8010_GM70.gif
but i use 6c33 triode instead of GM70. The 6c33 runs with Ra=600Ohm experience electronics high quality transformer:
http://www.experience-electronics.de/deutsch/bauteile/eintakt-a-uebertrager.htm#a6c33 (A6c33)
Ub~200V, I~175mA
At the grid of the 6c33 i get a cutoff beginns from 10Khz with 1-2dB! I need help.
The 6c45 runs with 17ma, 175 at anode, interstage is LL1660/18mA in 1:1,25.
Thanks Barossi
Hi
A 6C33 has an input, (grid-cathode) capacitance of 33pF not 11pF. The total input capactance that will load the driver stage is the Miller capacitance, that will be 33 +(1+Av)*30.5, where Av is the voltage gain of the output stage and 30.5 is the grid to anode capacitance. With Av=2 the Miller capacitance is ~124.5 pF.
A 6C45 has an output impedance of ~1.2kohm, this will be transformed by the transformer to ~1.5kohm, the -3dB point will therefore be ~850kHz and therefore the input capacitance is not the real problem in your case.
I would assume that the problem is the transformer itself, you can try checking the frequency response of the driver circuit including transformer by disconnecting the 6C33 and put for instance a 10kohm resistor across the transformer output and measure the frequency response that way.
Regards Hans
A 6C33 has an input, (grid-cathode) capacitance of 33pF not 11pF. The total input capactance that will load the driver stage is the Miller capacitance, that will be 33 +(1+Av)*30.5, where Av is the voltage gain of the output stage and 30.5 is the grid to anode capacitance. With Av=2 the Miller capacitance is ~124.5 pF.
A 6C45 has an output impedance of ~1.2kohm, this will be transformed by the transformer to ~1.5kohm, the -3dB point will therefore be ~850kHz and therefore the input capacitance is not the real problem in your case.
I would assume that the problem is the transformer itself, you can try checking the frequency response of the driver circuit including transformer by disconnecting the 6C33 and put for instance a 10kohm resistor across the transformer output and measure the frequency response that way.
Regards Hans
The 6C45 has a quite high input capacitance that may be the cause of your problem.
Check the data sheet and do the same calculations as Hans but for the driver stage.
Carl
Check the data sheet and do the same calculations as Hans but for the driver stage.
Carl
Hello,
i checked again the hole circuit. The LL1660/18mA 1:1,25 was connected right. At pin 16 i connected the bias for the 6c33. I now lowered the gridstopper of the 6c45 to 150 ohm. I removed the 6c33 and grounded the LL1660 on pin 16. I paralled a 10KOhm resistor to the output of the LL1660. I measured 24KHz -3dB upper frequency limit, without (minimal) cutoff . Also i tried different Ia for the 6c45 15-22mA. Whitout Load on the 6c45-LL1660 circuit i measured upper frequency limit up to 28KHz without cutoff.While i measured a cutoff on the grid of the 6c33 begins from ~10KHz. The total circuit shows a cut off under max. Load 21,25Vpp into 8 Ohm Load (~ round about 7 Watt output power):
14Hz 70% (-3dB)
1KHz odB
15KHz 77,5%
20,5KHz 70% (-3dB)
What could i do? Seems that the driver circuit including LL1660 doesn't like the heavy capacitivy load from the 6c33. I think this is possibly the 80% problem the other 20% causes the output transformer of the 6c33.
I think i have to build a new circuit with a input tube (gain ~ 20) and a stable output driver stage with low Output-R, while the current consumption is limited by the LL1660/18mA 1:1,25 to ~20mA for this tube.
Any ideas? Or could i drive the 6c33 with one tube and the LL1660?
Many Questions?!?!
Thanks a lot!
Barossi😕
i checked again the hole circuit. The LL1660/18mA 1:1,25 was connected right. At pin 16 i connected the bias for the 6c33. I now lowered the gridstopper of the 6c45 to 150 ohm. I removed the 6c33 and grounded the LL1660 on pin 16. I paralled a 10KOhm resistor to the output of the LL1660. I measured 24KHz -3dB upper frequency limit, without (minimal) cutoff . Also i tried different Ia for the 6c45 15-22mA. Whitout Load on the 6c45-LL1660 circuit i measured upper frequency limit up to 28KHz without cutoff.While i measured a cutoff on the grid of the 6c33 begins from ~10KHz. The total circuit shows a cut off under max. Load 21,25Vpp into 8 Ohm Load (~ round about 7 Watt output power):
14Hz 70% (-3dB)
1KHz odB
15KHz 77,5%
20,5KHz 70% (-3dB)
What could i do? Seems that the driver circuit including LL1660 doesn't like the heavy capacitivy load from the 6c33. I think this is possibly the 80% problem the other 20% causes the output transformer of the 6c33.
I think i have to build a new circuit with a input tube (gain ~ 20) and a stable output driver stage with low Output-R, while the current consumption is limited by the LL1660/18mA 1:1,25 to ~20mA for this tube.
Any ideas? Or could i drive the 6c33 with one tube and the LL1660?
Many Questions?!?!
Thanks a lot!
Barossi😕
Hi Barossi,
It could be so that the problem is the LL1660, If the leakage inductance is high it can resonate with the input capacitance of the 6C33 and create a resonant circuit. Above the resonant frequency the response will fall rapidly.
In order to improve the situation I think you can do 3 things.
1 Connect a relatively low value resistor across the secondary of the LL1660, this will reduce the effect of the resonant circuit thereby giving a flatter response, but the gain will also be lower, try with 2.2kohm.
2 Buy a better transformer with less leakage inductance, maybe something from Tamura or Tango or maybe a better one from Lundahl.
3 Remove the transformer all together and build a different drive circuit, for instance the one that I showed earlier in the 6C33C SE tread, the circuit can be seen here: http://www2.gol.com/users/tube/se.html
Without interstage transformer coupling the high frequency response will be determined almost entiraly by the output transformer and with the Tango transformer I used the -3dB point is ~ 60 kHz
Regards Hans
It could be so that the problem is the LL1660, If the leakage inductance is high it can resonate with the input capacitance of the 6C33 and create a resonant circuit. Above the resonant frequency the response will fall rapidly.
In order to improve the situation I think you can do 3 things.
1 Connect a relatively low value resistor across the secondary of the LL1660, this will reduce the effect of the resonant circuit thereby giving a flatter response, but the gain will also be lower, try with 2.2kohm.
2 Buy a better transformer with less leakage inductance, maybe something from Tamura or Tango or maybe a better one from Lundahl.
3 Remove the transformer all together and build a different drive circuit, for instance the one that I showed earlier in the 6C33C SE tread, the circuit can be seen here: http://www2.gol.com/users/tube/se.html
Without interstage transformer coupling the high frequency response will be determined almost entiraly by the output transformer and with the Tango transformer I used the -3dB point is ~ 60 kHz
Regards Hans
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