Chokes are 200 henry , from ebay seller in Hong Kong.
I see you are in San Marcos I was there last weekend, my sister just retired and moved there from Boston.
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Hi Ed, The final adjustment should be made with the B+ applied, and the anode/plate current confirmed at the correct value. Woth low-current filaments like the 2P29L, this is even more important than 300Bs, say.
At current around 650mA you should expect about 1V of forward voltage drop across the SIC.
yes, they're not cheap but are great diodes and sound amazing
I ended up producing a PCB to hold 6 SIC diodes for the preamps. You don't need a heatsink in this case.
Ale
Got it.
Thank you Rod, your support for your product is superb
Your are first class )
After returning to my voltage measurements I kept finding one tube that was problematic and was always changing , once hot it would draw substantial less current.
Luckily I bought 4 and of the 4 I have two that match up well.
Just an update on my new 4P1L SIC diode stage. This time I used my amorphous core NP Acoustics large plate choke, rated 40mA and 180H. This is up a level in clarity from my no-name plate choke, which in itself was pretty good. But this is better, in fact I think the cleanest and most detailed stage I've built so far. It doesn't quite have the lush sonorities of the 26 and 01A but it's more solid. I'm going to leave this in my system for now, though my 26 stage with smaller NP amorphous plate choke and SIC bias is going to be hard to resist.
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Nice! I've been here for ~18 years, moved from South Austin, so still close to home.
Thanks to the suggestions here I left out the resistor at the top of the SIC diodes - turned out it wasn't doing anything useful and the sound was better with just the diodes. I A-B'd the 4P1L with my large NP Acoustics plate choke against the 26, and I'm slightly preferring the 26. It has more "life" and makes the 4P1L, which is otherwise very detailed and neutral, sound just a touch two-dimensional. I've been running the 26 at 7mA without any obvious ill effects.
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I have a 4P1L using the K & K audio board (great build quality) and Rod Coleman Regs for each tube.
Issue I am having: the f- and f+ is always rising to 2.7 V which it too high and not the 2.1 the data sheet dictates. Anyone incountered this? I dropped the supply voltage down to 13.5V in a attempt to lover the f voltage and still 2.7.
Should the tubes also be making a chime noise during warmup?
Might be the way too high f voltage. I only ran them a few min because of the high voltage.
Issue I am having: the f- and f+ is always rising to 2.7 V which it too high and not the 2.1 the data sheet dictates. Anyone incountered this? I dropped the supply voltage down to 13.5V in a attempt to lover the f voltage and still 2.7.
Should the tubes also be making a chime noise during warmup?
Might be the way too high f voltage. I only ran them a few min because of the high voltage.
I'm sure Rod will come in here, but 13.5v seems far too high as a supply voltage. I think it depends which vintage of Coleman regs you have. Around V4 you needed approx 7v headroom which puts the supply voltage at around 9v. We're now on V7 and I think the ideal headroom is a bit below that. So I'd try 9v supply just to start with, not more. You also need to use the onboard trimmer to set the voltage correctly once the supply voltage is in the right range, with your voltmeter between pin 7 and pin 1+8. I assume that's how it's connected for 2.1v. If you have a bench voltage supply you can bring the voltage up gradually and you should come to an area (probably around 7-9v supply) where the filament voltage stabilises and goes up more slowly. This is the area where the reg should be working correctly. The voltage continues to rise, but more slowly.
Have you fully read Rod's instructions for use of the reg? His instructions are a model of completeness and clarity.
Have you fully read Rod's instructions for use of the reg? His instructions are a model of completeness and clarity.
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Yes, 13.5V supply is very high - unless you have a filament bias resistor.
Is the filament connected in parallel mode for 2.1V?
If you send me some email, I can send the debug test points - if there is anything wrong, it will show up there.
When a DHT filament warms up, it slackens its tension, and this can chime on the supports.
Silly mistake - connection in parallel is between pin 8 and pin 7+1. Sorry!
I can see that some of you uses diodes as bias for your tubes, it seems to me that the reason must be to get a low value of cathode impedance in the absent of an cap.
But you lose the ability to adjust to a precise current. I was thinking of another solution, se schematics below. Please tell me if you think it will work.
The dynamic resistant is roughly R (in ohm) = 25/I cathode (in mA)
But you lose the ability to adjust to a precise current. I was thinking of another solution, se schematics below. Please tell me if you think it will work.
The dynamic resistant is roughly R (in ohm) = 25/I cathode (in mA)
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