Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on September 03, 2016, 06:19:18 am

Title: Combination cathode bias and fixed bias - Question for Tubeswell
Post by: kagliostro on September 03, 2016, 06:19:18 am

Ciao Tubeswell

at DIYItalia a guy has posted a link to an old your's thread of 2008, this one

http://music-electronics-forum.com/t7531/ (http://music-electronics-forum.com/t7531/)

I would like to know if you have experimented further with this architecture

THANKS

Franco

Obviously if someone has something to say he is welcome

p.s.: some schematic that adopt the mixed Cathode Bias + Fixed Bias

(http://i.imgur.com/XpahP2p.png)

(http://i.imgur.com/zY3Tonr.gif)

(http://i.imgur.com/WRfYEPq.gif)

Title: Re: Combination cathode bias and fixed bias - Question for Tubeswell
Post by: tubeswell on September 04, 2016, 01:19:40 pm

Hiya Franco.


Crikey those old threads are embarrassing.  :sad2:


In short, no I didn't take it any further in the end.


The Vox AC50 is another example FWIW.

Title: Re: Combination cathode bias and fixed bias - Question for Tubeswell
Post by: kagliostro on September 04, 2016, 01:50:36 pm

Quote

..... are embarrassing.

Absolutely no, why ? In south of Italy they say nessuno nasce imparato (no one is born learned)

At DIYItalia we have a guy who has experimented this tecnique and he say he has very positive results

(Despite that I'm not able to follow exactly what he say, so, as I know you, I've think to ask)

Thanks anyway

Ciao

Franco

p.s.: The Vox AC50 ..... I've looked at that schematic a lot of times, I never noticed that particular, Thanks

Title: Re: Combination cathode bias and fixed bias - Question for Tubeswell
Post by: sluckey on September 04, 2016, 03:42:35 pm

Several of the Magnatone M series amps use a combination of fixed and cathode bias. The resistor is typically 100Ω and has no bypass cap which also adds a measure of degenerative feedback in addition to the global NFB loop.

My M10A is an example...

     http://el34world.com/charts/Schematics/files/magnatone/magnatone_m10a.pdf (http://el34world.com/charts/Schematics/files/magnatone/magnatone_m10a.pdf)

Title: Re: Combination cathode bias and fixed bias - Question for Tubeswell
Post by: kagliostro on September 04, 2016, 04:20:00 pm

I see, never put attention to that

Thanks Steve

Franco