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Re: Problems with LL1660 driving 6c33! Need help!

217.236.53.116

Posted by Haukito on October 29, 2003 at 08:14:34

In Reply to: Re: Problems with LL1660 driving 6c33! Need help! posted by vry on October 29, 2003 at 02:49:33:

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!

Haukito

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