#26 pre amp

[Magz]

Originally Posted by Vbenonisen

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

Which Audionote 5:1 are you using? They have quite a few ranging from pure copper wire to pure silver wire, with various core materials.

[Vbenonisen]

I have the cheapest copper version with double C-cores. Boy do I wish for the most expensive silver version.....Heaven knows what that must sound like.

[andyjevans]

Albertli -

Regarding temperatures, in filament bias the 10 ohm resistors get hot. 100 degrees is not tragic - I think I was getting something like that. I mounted them on top of the chassis so there would be air around them. You can barely touch them - they run hot!! Mine are rated 50 watts (four 10 ohms in series/parallel)

andy

[vgeorge]

Originally Posted by albertli

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

Nice result Albert.
Check voltage across these resistors when temperature changes as I assume you are using them in a series parallel configuration. A more detailed description would be helpful, both channels react the same, which ones are hotter etc.
Regarding square waves on the scope, I could get them in a better shape, as well as removing a ringing at 70kHz from the ll1660, by using a 4,7k with 100nF acroos the output of the 1660, before the AVC I use at the output. I want to do more listening tests before I can comment as to this change is better or not but on the scope looks better.

[vgeorge]

FYI I get 85c at my resistors.

[mogliaa]

I have same resistor stack as Andy mentioned and got about 80C

[euro21]

Originally Posted by albertli

The square wave didn't look too good

My #26 preamp (220V SSHV2, Rod C. regulator, filament bias -11R-, 6mA cascode CCS, 2*0.22uF teflon coupling ) -3dB bandwith 2Hz-230kHz!
100kHz square wave rise- and fall time only 1us!

[albertli]

Originally Posted by andyjevans

Albertli -

Regarding temperatures, in filament bias the 10 ohm resistors get hot. 100 degrees is not tragic - I think I was getting something like that. I mounted them on top of the chassis so there would be air around them. You can barely touch them - they run hot!! Mine are rated 50 watts (four 10 ohms in series/parallel)

andy

Andy,

Thanks and I'm going to have the 10 100 ohm 5w re-arranged. Will report.

Albert

[albertli]

Originally Posted by vgeorge

Nice result Albert.
Check voltage across these resistors when temperature changes as I assume you are using them in a series parallel configuration. A more detailed description would be helpful, both channels react the same, which ones are hotter etc.
Regarding square waves on the scope, I could get them in a better shape, as well as removing a ringing at 70kHz from the ll1660, by using a 4,7k with 100nF acroos the output of the 1660, before the AVC I use at the output. I want to do more listening tests before I can comment as to this change is better or not but on the scope looks better.

George,

The voltage across 2 groups L/R are quite the same. They are 9.6v/9.63v respectively, and I'll tune them back up to 10v after the configuration. The temperature different only happens amount/ within the 10 resistors at the same group.
Will try your zobal mod and report asap
Thanks

Albert

[albertli]

Originally Posted by euro21

My #26 preamp (220V SSHV2, Rod C. regulator, filament bias -11R-, 6mA cascode CCS, 2*0.22uF teflon coupling ) -3dB bandwith 2Hz-230kHz!
100kHz square wave rise- and fall time only 1us!

Would love to know more, so I could learn more.
Are you with transformer coupled ???
Thanks

Albert