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Old 20th February 2012, 09:47 AM   #441
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Quote:
Originally Posted by Nelson Bass View Post
It takes a very good DHT regulator to outperform ac supply. I've done experiments with classic and exotic 3-pins voltage regulators and they suck the life out of music. I'll try tentlabs DHT supply in the future. Rods solution looks nice too!!
AC does sound better than those 3-pin regulators but there exists something totally different. AC still sounds bad!
I'm not an advertiser here, nor I am receiving any credits from Rod.
There is no need for you to re-invent the wheel. I am a coil winder and have experimented with the most insane solutions, go back several pages and just read what I've done here...
I have listened to anything you could imagine of. Rod's circuit gave me something else but not perfect. With this simple mod it surpassed all my expectations.
Do not lose your time but only if you would like to experiment different flavors. If you want to go to the end, there is no reason to lose your time.
I've already done it for you...
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Old 20th February 2012, 09:47 AM   #442
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Originally Posted by Rod Coleman View Post
You're right about the 3-pin regulators - they are useless for filament heating. But ac-heating is also bad-sounding, compared to the possibilities of Direct-Heated Triodes.
The first test to make with a filament regulator is to compare to ac. If your new regulator does not sound better in every possible way than ac, then you have a failure.
I AGREE!
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Old 20th February 2012, 11:15 AM   #443
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Placebo effect don't live here !
PLEASE don't start to tell that all sound the same Please
We are well skilled DIY's....
you are free to use mox ....
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Last edited by nicoch58; 20th February 2012 at 11:19 AM.
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Old 20th February 2012, 11:22 AM   #444
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Quote:
Originally Posted by nicoch58 View Post
Placebo effect don't live here !
PLEASE don't start to tell that all sound the same Please
We are well skilled DIY's....
you are free to use mox ....
No placebo effect here!
Everybody is free to do whatever he wants.
We are all well skilled DIYers, I also agree on this!
I just wanted to pass my 2 cents here. Nobody is perfect, we're all here to cooperate towards illusionary perfection. But please let's keep this thread up to the high level it deserves.
Greetings from Athens!
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Old 20th February 2012, 12:11 PM   #445
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Och! thanks....
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Old 22nd February 2012, 12:51 PM   #446
needsp is offline needsp  United Kingdom
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Hi All

Firstly Iíd like to praise Rodís filament heater supplies. Iím using 300B version in a couple of SE amps, and there are unbelievably good. I went from an unregulated dc supply, then tried some dedicated CCS regs from DIY HiFi Supply- much better than the dc supply- to Rodís circuit. Thereís nothing subtle about the improvement they bring, and, if you can accommodate them you should! (You should also try his shunt cascode driver topology, which, if anything, is even more amazing- but I digress.)

Secondly, Iím quite open to the idea that changing the MOX resistor in the regulator for a carbon type. Generic carbon film resistors sound much better generic metal films IMO (unless high tolerance is a circuit requirement), despite many theoretical reasons for the reverse to be true.

But Iím a bit confused about the graphite rod business. Iíve done a bit of research, and it seems weíre dealing with two different materials. Graphite rods (for electrolysis etc) seem to be made solely from graphite, which is compressed into a rod-

Graphite & Carbon Technical Data

But these materials have resistivities in the range ~7 (medium grade) to ~ 15 (fine grade) ohm.mm2.m-1 which means than even a narrow, 3 mm diameter rod would have to be ~20- 40 cm long to make a 0.82 ohm resistor! Which suggests the material Peter used was in fact a pencil lead- made form a baked mixture of graphite and clay. I.e. a graphite /ceramic mixture- as used in carbon composition resistors- which he hates the sound of!

Whatever. If we want to try suitable resistors made up of either carbon composition, or carbon film ( I think these use pure carbon rather than a mixture, but I may be wrong), choice is a bit limited. High wattage, low ohmic types arenít made, and even values below 10 R are rare. I think Iím going to try carbon films- 4 x 3R3 1W types in parallel-

MULTICOMP|MCF 1W 3R3|RESISTOR, 1W 5% 3R3 | Farnell United Kingdom

For composition types we could try 4 of

OHMITE|OA33GKE|RESISTOR, CARBON, 3.3OHM, 1W, | Farnell United Kingdom

but these are pricey (especially in the UK)

Comments? Please be gentle if Iíve missed something here

Paul
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Old 22nd February 2012, 01:24 PM   #447
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Glad you're enjoying the 300Bs, Paul, and thank you for the recommendation.

Peter's experiments have set me down this route, too.

The R1 current sense resistor in the Filament Regulator Kits is a Wirewound - 0,82 for 300B. This value is not critical, since the trimmer is there to accommodate differences.

Please note that the Wirewound I supply is FLAMEPROOF, that's to say that it won't set fire to anything even if you short the whole regulator out or something similar. The action of the regulator prevents short circuits, so this is a vanishingly unlikely event, but please be warned.

about 30 minutes ago I set up a 300B regulator with 2x 1,5-ohm carbon film 1W resistors. RS 7078558. They are notable straight away for running very cool, even at 1,3A (about 0,6W each). I'll run them steady for a while, then look at the noise, and maybe try them in my 300B-SE amp.

If you want to try Carbon comp, then the low-cost way to go is Farnell 0,5W 6,8-ohm - parallel 8 pcs. These are only about 10p (~6 cents) a copy.

I think that the challenge with Carbon/graphite rods will be the lead-attach. We need a good grip, but without shattering the rod. Preforming on an undersized rod might be one route.
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Old 22nd February 2012, 01:52 PM   #448
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For experimenters wanting to try out the Carbon Rod-type resistor, please note that the current-sense resistor R1 has alternative mounting points to accommodate LONG resistors, up to 45mm, or even more. The picture shows a 75TL regulator (6,25A) sporting the Welwyn W23 at R1.


.
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File Type: jpg 75TL.jpg (192.7 KB, 1005 views)
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Old 22nd February 2012, 02:00 PM   #449
djn is offline djn  United States
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Hi Rod, we just now are getting settled in our new house and so I have time to start back up on the GM70 amp project. I am thinking of putting some of the PS (including the GM70 filliment PS) in a separate chassis. Is there going to be an issue with running a foot or so of umbilical chord to the main amp?
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Old 22nd February 2012, 02:04 PM   #450
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You're doing the right thing, for sure!

Keep the transformer/caps/rectifier in the PSU chassis, and run the raw dc to the signal chassis. The regulator should be within about 150-250mm (6-10") of the tube socket. Put 1000uF/35V on the PCB supply input terminals, and let us know how it sounds!
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