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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

#26 pre amp

Thanks for the replies,

After Kevin’s description of the biasing schemes he has tried I will just stick with the grid bias connection. I’m gonna quit rethinking and start soldering. Hopefully I have learned enough by reading this thread and Kevin’s article that I can get it done.
 
Thanks for the replies,

After Kevin’s description of the biasing schemes he has tried I will just stick with the grid bias connection. I’m gonna quit rethinking and start soldering. Hopefully I have learned enough by reading this thread and Kevin’s article that I can get it done.

Martyh, grid bias which Kevin mentioned, works like charm. Fairly easy to setup. I tried both the biasing methods (cathode and grid with 9V alkaline batteries) and latter is the most sonically superior and least hum. If you check the first page of this thread, I have put the schematic used.
 
Just replaced the RIFA 0.15uf coupling cap of the grid bias circuitry with Mundorf RXF 0.1u. Couldn't believe the magic just this simple mod has done. A whole new life to my 26 pre. Tried few different brands/types of caps including Tantalums but this was the best so far. Hope a better cap like Mundorf silver/oil would do more wonder.

Myrtyh, if you are trying the grid bias, spend some on the coupling cap straightaway. Pretty sure you will not regret.
 
Just replaced the RIFA 0.15uf coupling cap of the grid bias circuitry with Mundorf RXF 0.1u. Couldn't believe the magic just this simple mod has done. A whole new life to my 26 pre. Tried few different brands/types of caps including Tantalums but this was the best so far. Hope a better cap like Mundorf silver/oil would do more wonder.

Myrtyh, if you are trying the grid bias, spend some on the coupling cap straightaway. Pretty sure you will not regret.

Careful there coolzero, some here do not believe that coupling capacitors can affect the sound quality one can achieve. Pure snake oil :D Enjoy. I bet the 26 does sound heavenly!
 
Careful there coolzero, some here do not believe that coupling capacitors can affect the sound quality one can achieve. Pure snake oil :D Enjoy. I bet the 26 does sound heavenly!

:D I know it is subjective but what I hear is what could believe. 26 certainly does not need any of these because it sounds wonderful with anything but I heard a definite change in the character of sound (in a positive way) specially with Mundorf coupling caps every time I use them. This mod was purely unintentional one and just did because I had a pair of RSX in hand. It may complete snake oil technically about changing different type /brands of coupling caps but I could hear a difference most of the times I do that.:confused: Ultimately what we need is best sound possible out of anything, even if it is snake oil;isn't it?:D

Guys..share your thoughts if you wish..seems to be an interesting topic to discuss..
 
Coolzero,

Mighty fine linestage you have there.:)

Regarding the schematic you posted on the first page of this thread, I do not understand the cathode arrangement. The 26 is a DHT, but the drawing shows an IDHT where a filament heats the catode... or am I misunderstanding?

143483d1255440832-26-pre-amp-26-mypre.jpg
 
Coolzero,

Mighty fine linestage you have there.:)

Regarding the schematic you posted on the first page of this thread, I do not understand the cathode arrangement. The 26 is a DHT, but the drawing shows an IDHT where a filament heats the catode... or am I misunderstanding?

143483d1255440832-26-pre-amp-26-mypre.jpg

Sorry for my poor skill of schematic drawing. I didn't have proper software to draw the schematic and barely manage to draw it using a free tool available on the net. Hence don't give much attention to the symbol I used for 26. This final schematic which I used was originated out of valued suggestions provided by Kevin and it proved it's capabilities when I built it.
 
Just replaced the RIFA 0.15uf coupling cap of the grid bias circuitry with Mundorf RXF 0.1u. Couldn't believe the magic just this simple mod has done. A whole new life to my 26 pre. Tried few different brands/types of caps including Tantalums but this was the best so far. Hope a better cap like Mundorf silver/oil would do more wonder.

Myrtyh, if you are trying the grid bias, spend some on the coupling cap straightaway. Pretty sure you will not regret.

Thanks, I’m starting with vitamin Q’s for the inputs. Some people don’t like them but I do. I don’t have nearly the experience substituting parts as the rest of you do but I’ve built whole projects with metal film resistors and modern foil caps and others with carbon resistors and vintage oil caps and the latter gets me much closer to the sound I like. That’s the approach I’m taking this time but since there are only the two input caps it should be pretty easy to experiment. I am hoping though that it sounds so damn good out of the chute I just move on to the next project :D
 
Thanks, I’m starting with vitamin Q’s for the inputs. Some people don’t like them but I do. I don’t have nearly the experience substituting parts as the rest of you do but I’ve built whole projects with metal film resistors and modern foil caps and others with carbon resistors and vintage oil caps and the latter gets me much closer to the sound I like. That’s the approach I’m taking this time but since there are only the two input caps it should be pretty easy to experiment. I am hoping though that it sounds so damn good out of the chute I just move on to the next project :D

Try some carbon film resistors in place of the carbon resistors. It will land you a little closer to a metal film sound, but still give you some of the weight of the sound that the carbons do. I think that we have similar tastes in how music sounds :D
 
I'm sure you intended the -9V reading to be at pin 3, not pin 4.

Sheldon

Thanks Sheldon for the correction. This is the updated diagram.

Anyone who is building this; make sure to use proper, shielded input to grid connections/wiring. Otherwise hum will pick up easily from these points.
 

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How did you come to this conclusion?


Magura :)

Well if you listen to them in the circuit, it would be obvious. Like coolzero said, he prefers carbons to metal films and I can understand why in most cases. I prefer carbon film resistors for a great many applications in a tube amp, as they have a bit more warmth to their tonal balance, with out the heavy warmth of a carbon resistor. Metal films can be a bit lean in their sound, depending upon where they are used in the circuit. I have no idea how the different resistors would sound in a solid state amplifier/preamplifier. I only experiment with tubed circuits. These are not frequency related issues, but are related to the tonal balance.
 
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In which applications do carbon film resistors make a difference in this circuit?


Magura :)

I like them as grid stoppers and cathode resistors(non-inductive types are better for the cathodes) primarily, but bias supplies are also a good place to try them. I normally use Mills wirewounds on the plates, input and in the PS too.
 
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