Tube amp question

Started by October 10, 2018
I see lots of tube amps with the tubes mounted such that they point
down. This means all the heat rises up into the chassis. This seems
counter-intuitive to me. All those components baking all the time. Is
it just for convenience?
Eric
et...@whidbey.com wrote:
> > > I see lots of tube amps with the tubes mounted such that they point > down. This means all the heat rises up into the chassis. This seems > counter-intuitive to me. All those components baking all the time. Is > it just for convenience? >
** It is certainly not ideal, plus the tubes can overheat when mounted this way too. Octal types with plastic bases are prone to "bias creep" when the plastic base begins to become conductive. .... Phil
On Wednesday, October 10, 2018 at 1:59:46 PM UTC-7, et...@whidbey.com wrote=
:
> I see lots of tube amps with the tubes mounted such that they point > down. This means all the heat rises up into the chassis. This seems > counter-intuitive to me. All those components baking all the time. Is > it just for convenience? > Eric
You don=E2=80=99t appreciate the effort being made to improve the euphoniou= s presence in these vacuum tube electronics. This orientation is applicabl= e in the Northern Hemisphere. It is to optimize the curvature in the paths= of the electrons due to the Lorentz forces induced by the earth=E2=80=99s = magnetic field, and to match that curvature with the helicity of the windin= gs of the grid wires. This was commonly done in other vacuum tubes: color= monitors with cathode ray tubes had opposite magnetic field compensations = for the two hemispheres for improved convergence and image quality. The next technological improvement will be to replace the copper wiring wit= h silver, just as they did on the Manhattan Project. Of course, the silve= r will be carefully annealed to be oxygen-free and single-crystal.
On Thu, 11 Oct 2018 07:08:19 -0700 (PDT), "jfeng@my-deja.com"
<jfeng@my-deja.com> wrote:

>On Wednesday, October 10, 2018 at 1:59:46 PM UTC-7, et...@whidbey.com wrote: >> I see lots of tube amps with the tubes mounted such that they point >> down. This means all the heat rises up into the chassis. This seems >> counter-intuitive to me. All those components baking all the time. Is >> it just for convenience? >> Eric > >You don&#2013266066;t appreciate the effort being made to improve the euphonious
presence in these vacuum tube electronics. This orientation is applicable in the Northern Hemisphere. It is to optimize the curvature in the paths of the electrons due to the Lorentz forces induced by the earth&#2013266066;s magnetic field, and to match that curvature with the helicity of the windings of the grid wires. This was commonly done in other vacuum tubes: color monitors with cathode ray tubes had opposite magnetic field compensations for the two hemispheres for improved convergence and image quality.
> >The next technological improvement will be to replace the copper wiring with
silver, just as they did on the Manhattan Project. Of course, the silver will be carefully annealed to be oxygen-free and single-crystal. I knew it! Instead of OFHC copper they will use OFHS silver. Eric
On 10/10/2018 22:05, etpm@whidbey.com wrote:
> I see lots of tube amps with the tubes mounted such that they point > down. This means all the heat rises up into the chassis. This seems > counter-intuitive to me. All those components baking all the time. Is > it just for convenience? > Eric > > --- > This email has been checked for viruses by AVG. > https://www.avg.com >
Not sure ... I know that a lot of Fender guitar amps have their tubes mounted "upside down" - but the output pentodes are all fitted on ceramic bases. I have one which I use on a daily basis and it seems to be OK to me in spite of being more than 40 years old. I have noticed on certain other makes that the screen grid resistors unsolder themselves and fall off when they get very hot, although I don't suppose that was one of the design criteria. AT
Abandoned Trolley wrote:

> > > > Not sure ... I know that a lot of Fender guitar amps have their tubes > mounted "upside down" - but the output pentodes are all fitted on > ceramic bases.
** Some use white ceramic sockets - but most use plastic or phenolic bases.
> I have noticed on certain other makes that the screen grid resistors > unsolder themselves and fall off when they get very hot, although I > don't suppose that was one of the design criteria. >
** Really has to be a faulty tube or a big problem in the biasing to make that happen. ... Phil
>"Is it just for convenience? "
They want the knobs at the top. It is most logical to mount them to the chassis as it IS convenient and that also provides shielding. They could build 2 chassis' and put the "sub' chassis lower so as to facilitate this but the hot air would still go up. Same difference. With the sometimes very high impedances involved shielded triax could make for problems with capacitance. To the tube itself it doesn't matter, what would matter is mounting it horizontally, which I would not recommend and most would agree.
In article <0b1e7a77-5647-4fdd-b910-d087c7537ff8@googlegroups.com>, 
jurb6006@gmail.com says...
> > To the tube itself it doesn't matter, what would matter is mounting it
horizontally, which I would not recommend and most would agree.
> >
It all depends on the tube. Some tubes specify that for horizontal certain pins have to be in a certain position.
On 18/10/2018 01:33, Phil Allison wrote:
> Abandoned Trolley wrote: > >> >> >> >> Not sure ... I know that a lot of Fender guitar amps have their tubes >> mounted "upside down" - but the output pentodes are all fitted on >> ceramic bases. > > > ** Some use white ceramic sockets - but most use plastic or phenolic bases.
++ I appear to be "blessed" with the ceramic variant
> > >> I have noticed on certain other makes that the screen grid resistors >> unsolder themselves and fall off when they get very hot, although I >> don't suppose that was one of the design criteria. >> > > ** Really has to be a faulty tube or a big problem in the biasing to make that
happen. ++ Not completely certain about that - at the time the solution seemed to be to just double the power rating of the resistor - AT
> > > > ... Phil > > > --- > This email has been checked for viruses by AVG. > https://www.avg.com >
Abandoned Trolley wrote:


> > >> Not sure ... I know that a lot of Fender guitar amps have their tubes > >> mounted "upside down" - but the output pentodes are all fitted on > >> ceramic bases. > > > > > > ** Some use white ceramic sockets - but most use plastic or phenolic bases. > > > ++ I appear to be "blessed" with the ceramic variant > > > >
** No fooling..........
> > >> I have noticed on certain other makes that the screen grid resistors > >> unsolder themselves and fall off when they get very hot, although I > >> don't suppose that was one of the design criteria. > >> > > > > ** Really has to be a faulty tube or a big problem in the biasing > > to make that happen. > > > ++ Not completely certain about that - at the time the solution seemed > to be to just double the power rating of the resistor - AT >
** Other makes may use EL34 tubes instead of 6L6GC, which draw much higher screen currents particularly when the output stage is overdriven. Typically, 1000 ohm resistors are used for each screen resulting in them running very hot with peak signal currents of about 80mA to 100mA. 5 watt wire wound types are normally used, but even they get hot enough to de-solder themselves if there is a loose socket connection to the plate pin of the EL34. .... Phil