- Posted by Dave Davenport (A) 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 capacitorThere 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
Follow Ups:
- Re: LL1674 as a parafeed 4:1 output - MaciekP 10:15:21 05/27/04
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- In Reply to: Re: LL1674 as a parafeed 4:1 output posted by Dave Davenport on May 27, 2004 at 09:55:04:
thanks,
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.
Is 0.47uF a good starting point?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.
If it is about 22V at 20Hz in 1:8 ratio, so the primary should handle 2.5V...and it is probably something I should expect from the output from 4:1 config I think.Maciek
- Re: LL1674 as a parafeed 4:1 output - Dave Davenport 17:56:10 05/27/04
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- In Reply to: Re: LL1674 as a parafeed 4:1 output posted by MaciekP on May 27, 2004 at 10:15:21:
Hi Maciek
Sorry that I left that out. Kevin's response was correct.
Dave
- Re: LL1674 as a parafeed 4:1 output - KevinC 10:19:57 05/27/04
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- In Reply to: Re: LL1674 as a parafeed 4:1 output posted by MaciekP on May 27, 2004 at 10:15:21:
I would start with something more like 2-4uF. The maximum measured output (just prior to transformer saturation) for a parafeed 6N1P driven LL1674 connected 4:1 is 4.5vRMS at 20Hz. I didn't measure it at a higher frequency.
- Re: LL1674 as a parafeed 4:1 output - Dave Davenport 17:56:10 05/27/04
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