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tried to DIY the "Carnhill Red"  varnish with some food coloring,

what do you think, to light, too dark?

used an old 1166 term board with half the secs removed as we only need 600 ohms,

in back is REDDI box with transformer connections brought out to tag strip for easy hookup, so we have a test bed for different iron,

notice dual chamber bobbin, stock 1166 will run flat out to 100 K Hz, but it is low ratio, when you increase ratio to 4:1, the extra pri turns means the bumps will move to a lower freq,

a dual bobbin makes 4 windings out of 2, so we have a 4 section pri instead of 2, this puts the bumps back up above 100 k Hz so your dog will not get annoyed,  :D

that is a cathode cap bypass switch on the left, it will save your Sony 7506 bones from popping a speaker when you play the 6 string bass,

 

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more winding and now we have a VTB-2291 wired as 2400:600,

gonna plug and play to get the funk because we have no gap, laced up 1 x 1,

that is a string of Edcor EI 75 that the coil is sitting on for your amusement only,

we have some industrial style core brackets scaled down to audio,

looks a bit more serious than the old U bracket, got to mix it up now and then,

tapped out some 6-32's for the terminal boards,  bake and dip,

ready to rock,
 

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here is an inductance graph of the Carnhill VTB2290 vs the VTB2291,

both wired 2400:600

no unbalanced DC in the coils,

now when you run them with 10 ma DC, the 2291 graph will sink below the 2290 graph (green line) , and the 2290 graph will stay in the same place due to being butt stacked,

i tried the ungapped 2291 in the Reddi circuit with a bass git and it did not distort in a pleasing sort of way, it worked but the 2290 is a better choice here,

Henries will affect the attack of a bass string, when you first hit the string, there is a very low freq pulse that may or may not make it through the transformer, so you can shape the envelope of the note with the inductance,
 

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here is an OPT done on Telefunken snap in lams

sounds great in the Reddi with bass guitar,

sec-pri-sec  winding, 4:1

only thing left to try is a gapped nickel core OPT for the Reddi,

need some bib nickel lams = big $$$  :p

 

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My tube di pcb in production :D
Will be ready on next week. Will show results!
 

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CJ said:
here is an inductance vs low frequency graph for the DIY 2290 wired for a 2400 ohm primary,

Does the the rise in inductance at low frequencies follow some well established formula for this type of material? I am thinking if there is a way to deduce the inductance at 10Hz or 20Hz from the measurement on my Agilent meter at 100Hz. It clearly varies with core material but are the variations for each material well known?

Cheers

Ian
 
dirty1_1garry said:
My tube di pcb in production :D
Will be ready on next week. Will show results!

Nicely done.

I've done a set of PCB's as well.  It was my first set, designed in Eagle.  Pretty fun!  I have them out to a few guys now for testing.  I did mine as a separate PCB for the audio and one for the PSU.  This way they can fit in a number of different applications. 
 
Ian, inductance graphs will vary depending on turns, applied voltage, core size, gap or no gap,

but we can look at graphs for various chokes and transformers to get a rough idea,

here is a V72 choke with 20 volts applies and about 20,000 turns,

EI 625 core with a 3 mil gap, Silicon Steel, 4 ma of  DC>

 

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Hey CJ - I'm thinking this should be my next project and it looks like a doodle to do. Apart from the fact I've never dealt with tubes but understand the "they can kill you" thing very well..
For parts could we get together a little BOM? I know a fair few people who would like to try this out - and it have a really I large improvement in my recordings which is the most important thing.
 
I got mine up and running last night.  Sounds great.  I am using one of CJ's custom transformers and my case and PCB's I designed for it.  The case is a little bigger then my normal PSU cases to give me more room between the audio  and the AC.  I am running the heaters off of DC for now.  I will test both options probably.  But it sounds great.

Great project!

 

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HA! I have one of those ply wood boards from CJ in my shop too!!!

I'd love to see a few more photos of yours - looks like one of the photo links is dead...

I had been eyeing your tube PSU cases as an enclosure for mine as well - I would buy a pair of them if you were able to drill out some front/back plates... I'm not really geared up to do that very well...

I have a prototype of one of these built with Ian's boards and CJ's transformers, its great - just didnt have time to case them up before leaving for tour...

what dimensionally is different between this and your normal PSU enclosure?

 

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