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Old 20th February 2012, 12:13 PM   #1651
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For $8 it's worth a try. With so much power to burn, you can sometimes get lower noise by using multiple parallel parts (eg 10x 100R). This will surely help reduce the noise contribution from the wire-attach junction, which plays a major part in the sound of resistors, I suspect. Andy has some recommended types, all wirewounds I believe. Parallel pairs of Welwyn W24 (vitreous enamelled wirewound 14W) are the minimum standard, cheap enough to use as a reference.

The thick film types can sound terrible - not recommended.

Inductance will certainly not upset the Filament Regulators. It may make the circuit more inclined to pick up EMI though, and this is potentially a serious problem. Keeping the wiring in tight loops will help.
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Old 20th February 2012, 12:16 PM   #1652
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Great, thanks!!
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Old 20th February 2012, 12:39 PM   #1653
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I just tried out some of these Russian types as cathode resistors (other values, same type)

90 x 2 Ohm 10W 2% Aluminium Wire Wound Resistors / NOS | eBay

They seemed to sound better than the Welwyn types, so that's good. The 5cm long ones are 10 watts. Otherwise I've been using Dale wirewound surplus stock from the USA which are great sounding.

eBay - The UK's Online Marketplace

Welwyn is a pretty good option.

Agree thick films are dreadful - worst of all. Ceramic are middle of the road, aluminium clad a little better but not great.
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Old 21st February 2012, 03:25 AM   #1654
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I have my raw supply firing up and have the following number without load. Please do comment if the voltage is at the spot.

B+ 237v
Filament 1. 25.11v
Filament 2. 25.12v

Albert
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Old 21st February 2012, 05:09 AM   #1655
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Hi Albert, I think these look OK.

For the Filament, you can connect the dummy load of 1.5-ohm and the 10-ohm bias resistor (in series).
Please check that you have 0.5R [R1] in the rectifier line, and total 2-ohm [R2+L1] in the C1 to C2 line.
Make sure you have a heatsink on the Regulator.

With the dummy load connected, expect about 17 to 19V of raw dc. Adjust the regulator's trimmer to get 1.5V across the 1.5R - should correspond to 11.5V across the output of the regulator.
when this adjustment is correct, check the raw dc at C2 again. Should be 16.5V to 17.5V. If it is more than 17.7V, then add some resistance to R2 to lower it.
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Old 21st February 2012, 02:33 PM   #1656
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Quote:
Originally Posted by Rod Coleman View Post
Hi Albert, I think these look OK.

For the Filament, you can connect the dummy load of 1.5-ohm and the 10-ohm bias resistor (in series).
Please check that you have 0.5R [R1] in the rectifier line, and total 2-ohm [R2+L1] in the C1 to C2 line.
Make sure you have a heatsink on the Regulator.

With the dummy load connected, expect about 17 to 19V of raw dc. Adjust the regulator's trimmer to get 1.5V across the 1.5R - should correspond to 11.5V across the output of the regulator.
when this adjustment is correct, check the raw dc at C2 again. Should be 16.5V to 17.5V. If it is more than 17.7V, then add some resistance to R2 to lower it.
Rod,

Thanks for the fast reply.
I'm now in the middle of reforming the main chassis for the reason that I don't have room for sinking the Sala's reg. I thought I have to place the 1660 at inside the chassis. Sala's reg., big heatsink, 26 & resistors will be on the top.
Will report asap

Albert
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Old 26th February 2012, 07:02 PM   #1657
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Default Input transformer?

Hello!

I just built a 26 preamp with 5:1 Audionote transformers and the sound is simply amazing. It smokes the 6sn7 or 5687 setup with the same output transformers on every level.

I want to go all DHT on my 300B monoblocks and have some 46 tubes that I will use as a driver. But what to choose as input tube? I probably also need 1:2 input transformers to get enough gain so can somebody give me any clues on what kind of specifications I must look for? Are the Audionotes any good?

Vidar
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Old 26th February 2012, 10:16 PM   #1658
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I use 26 with plate choke into 46 (battery grid bias) into a Hammond 126C with end bells taken off into a 300B. Very good sound and enough volume since it's all 1:1 ratios.

Input tubes? another 26 or a VT67. But do you really want 4 stages? For a bit more gain, maybe 4P1L for the 46?

Andy
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Old 27th February 2012, 05:09 PM   #1659
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Thank you for the response.

The preamp with 5:1 transformers is just to (damn) good to change at the moment so I need three stages on the monoblocks. Never heard of VT67. I´ll check it up.

Is there somebody who has recommendations for input transformers?

Vidar
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Old 27th February 2012, 05:23 PM   #1660
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Default 26 is up running

Hi,

I have my 26 running and seems quite healthy.
Raw filament after rectifier, I have 0.5 ohm, 470uf, 25mH + 2 ohm, 30,000uf - I have 17.6v on this point, but the 2 ohm 10w is hot at 58c after 3 hour, then to Rod's reg. 11.5v n 10v at 10 ohm. This 10 ohm is a group of 10 100 ohm 5w dale wirewound, the temperature within these 10 are vary from 75c to 105c after 3 hours. This is what I'm a bit worry about. Is there any way I could even out the temperature ??
On Hv, I have 182v to Sala's reg. and 150v supply to 26, 145v on plate of 26. Since I have a very big heatsink for the Sala's reg. so the temperature is only around 30c after 3 hour. The square wave didn't look too good and will do some experiment this couple days.
Will upload some pics later.

Albert
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