Re: LL1674 as a parafeed 4:1 output - Dave Davenport - K&K Audio / Lundahl Transformers

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Re: LL1674 as a parafeed 4:1 output

Posted by Dave Davenport (M) on May 27, 2004 at 09:55:04

In Reply to: LL1674 as a parafeed 4:1 output posted by MaciekP on May 27, 2004 at 01:36:21:

Let me take a shot at this since I have experience using the LL1674 in a parafeed configuration.

1. Can you estimate what is the max Rp of the tube to get the good LF with LL1674 in parafeed 4:1 configuration?

I use a pair of 6N1P in bridged parafeed, each tube has 4400 Ohms nominal plate resistance. Double this for the two in series. The bass is fine. I haven't noticed much if any change in the bass with different tubes.

2. What is the recommended min. capacitance of parafeed capacitor

There are several formulas available but I have not found one that gives consistent results. The only way I have found to find the right value is build the circuit and measure the very low frequency - less than 20 Hz, response.

3. What resistor value is the best for secondary termination, if any?

This is a controversial topic. I prefer the sonics with no secondary termination.

4. What is the max output voltage for this transformer ratio?

It depends on frequency. I did measure it but I don't recall off hand my measurement. I do know that it is totally adequate for preamplifier output use. However it is not enough for use as an interstage.

5. Do I really need a plate choke?

Well, if you are going to parafeed you need some kind of high impedance load in the plate circuit. That is the definition of parafeed. You can use a large resistor, a choke, or a constant current source. I prefer a CCS.

Dave

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Follow Ups Full Thread

Topic - LL1674 as a parafeed 4:1 output - MaciekP 01:36:21 05/27/04 (10)

I did it! - MaciekP 11:58:14 06/04/04 (5)

Have you tried listening with the transformer connected - Bas Horneman 08:51:56 06/07/04 (3)

mod picture - MaciekP 09:22:20 06/07/04 (0)

Re: Have you tried listening with the transformer connected - MaciekP 09:10:36 06/07/04 (1)

Actually a typical mu-stage is tapped from - Bas Horneman 09:48:35 06/07/04 (0)

Cool! Really love it when people report back on their - Bas Horneman 08:46:35 06/07/04 (0)

Re: LL1674 as a parafeed 4:1 output - Dave Davenport 09:55:04 05/27/04 (3)

Re: LL1674 as a parafeed 4:1 output - MaciekP 10:15:21 05/27/04 (2)

Re: LL1674 as a parafeed 4:1 output - Dave Davenport 17:56:10 05/27/04 (0)

Re: LL1674 as a parafeed 4:1 output - KevinC 10:19:57 05/27/04 (0)

Follow Ups

Re: LL1674 as a parafeed 4:1 output - Dave Davenport 09:55:04 05/27/04 (3)

Re: LL1674 as a parafeed 4:1 output - MaciekP 10:15:21 05/27/04 (2)

Re: LL1674 as a parafeed 4:1 output - Dave Davenport 17:56:10 05/27/04 (0)

Re: LL1674 as a parafeed 4:1 output - KevinC 10:19:57 05/27/04 (0)

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