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September 29, 2020, 06:59:58 AM

Author Topic: Mcandmars ramblings \ build thread...  (Read 29335 times)

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Offline ZacharyP

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Re: Mcandmars ramblings \ build thread...
« Reply #135 on: July 27, 2015, 03:48:18 AM »
I stuck with the original values, but switched to Nichicon KX series just because.

I tried modelling the power supply circuit in PSUDII and for reasons i don't fully understand increasing the values of some of the caps actually made the ripple worse.  Specifically the first two 220uf caps that form the voltage doubler, changing those values had odd side effects, and dramatically increases the current load of the transformer.  It may be as much as quirk with the software more than anything else.

The ripple level at the following 100uf caps seems the most important to me as its directly supplying the output stage of the tube via a choke plate load, while and also feeding into the 8k / 22uf resistor down stream supplying the CCS plate load for the driver stage.  Personally i wouldn't want to lower the value, and i don't think there is much to be gained if anything by playing about with the 22uf cap due to the CCS load.

My main source these days is the Bottlehead DAC, and according to the datasheet for the DAC chip it can happily drive loads down to 1k so i don't see that being an issue.  Now that i am looking for it i went back and looked at all the various amps i know of using 6C45 tubes and almost all of them are using 20k pots.  Now i know why :)

Thanks for replying.  Always good to learn something new.

Offline johnsonad

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Re: Mcandmars ramblings \ build thread...
« Reply #136 on: August 31, 2016, 02:58:51 PM »
I wanted to thank you for your thread.  I have stripped my SEX amp of the Stax module having moved it to another amp and wanted to set it up for speaker use.  Your thread put me on track for the mods I was looking for. 


Aaron Johnson

Offline i luvmusic 2

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Re: The quest for silence...
« Reply #137 on: October 28, 2017, 07:18:42 AM »
Part 4: Headphone jack resistors / Power supply chokes,

As suggest by Doc.B adding two 120ohm resistors in series with the headphone jack greatly reduced the background noise/hum on the amp making it almost silent. Refer to heater supply 100r resistors above.

Installing the two C3X chokes in place of the 680ohm resistors in the main power supply removed the remaining 10% of background hum.  Having listened to the amp at length with various headphones i cannot hear a thing, just a lovely black background which makes a world of difference to the clarity/detail. Really happy with the result ;D

Specs for the C3X are 10Henries, 50mADC, 500ohms. They both measured ~470ohms on my meter however the power supply voltages measured before/after were all within three volts of each other.

As for physical placement, it would be possible to locate them to the side of the tube sockets on standoffs but i wanted to leave a bit of room around that area to replace the two capacitors in the future.  The only other place i could find was the front edge of the chassis so they sit below the headphone socket and power switch.  Obviously there are no issues with hum from their placement.

For the bracket i used a piece of steel strip i had, crudely bent to shape in a vice to fit around the various components and held in place by the volume pot.  I lucked out as i had a washer under the volume pot to space the knob flush with the top plate that happened to be exactly the same thickness as the steel strip so it all just fell into place.  Gave the bracket a quick sand/spray with clear coat to prevent rust and called it a day.

Which of the Hammond Choke  is equivalent to the C3X?Thanks!

Offline Paul Birkeland

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Paul "PB" Birkeland

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Offline mcandmar

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Re: Mcandmars ramblings \ build thread...
« Reply #139 on: October 15, 2019, 02:21:06 PM »
My eBay search spat these out recently which caught my interest, never seen any 6DN7 tubes with a metal base like that.  Might have to source a pair for the collection ::)