K&K Audio / Lundahl Transformers

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K&K Audio / Lundahl Transformers

Suitable lundahl line output transformer for 6C45PI

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Hi Kevin,

I am thinking of building a preamp, using the 6C45PI with Lundal line output transformer, my choice the ll1671 ,ll1660 or ll1692a?
What plate voltage to use and how many ma to bias? Was thinking to drive about 200V ,40ma, can advise?

Follow Ups:

RE: Suitable lundahl line output transformer for 6C45PI - akltam 04:46:30 12/23/14 (0)
I have built pre-amp for 6C45 using LL1660 gapped at 25mA and 30mA.

I think 40mA at 200V is way too high. You should consider the rating of 6C45 which is I think is about 4w. (You should check it).

If you decided to go for 6C45, I think 160V at 25mA is about it. Cathode resistor at 51 Ohm.

I have also tried Da3 in triode mode which I think sound more musical and better than 6C45. If you go for Da3, you should set it at 18-20mA (try LL1660 gaped at 18mA).

Just my 2 cent.
Alan
RE: Suitable lundahl line output transformer for 6C45PI - KevinC 09:04:34 12/02/14 (1)
The LL1671/XX will work but you will get a bit of bass roll-off ( <2dB) at 30Hz. The LL1692A/XX will not have that problem and is the best choice.

I have no design experience with the 6C45P, so I can't help you with the current and voltage. I would do a search on AudioAsylum Tube DIY forum and www.diyaudio.com and see if there is a consensus about this.

Kevin Carter
K&K Audio
www.kandkaudio.com
- RE: Suitable lundahl line output transformer for 6C45PI - drsx 23:11:57 12/02/14 (0)
  The higher the current, the more prone to oscillation. At 40mA it will be very hard to control, and unless you need the drive it is probably too high. ~18mA and 150V is a very good spot in my experience, but even then, 2 grid stoppers, 4 cathode stoppers, and a plate stopper are required. Your best bet is SMD resistor touching the pins. With through hole and ptp construction, you'll never get close enough. Also, teflon sockets seem to help. If you feel like there is any edge or etchyness or hardness to the sound, it is oscillating.

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