Re: Qualified Opinions? 1-4



I'll roll the dice.


¥ wrote:

I was looking back on some old notes I'd taken a few years ago.
Unfortunately, I neglected to write down the source!

My question is -does anyone here agree or disagree with the following
statements, as is;

1.] "...Fixed Bias Output: Most modern amps are this type (vs. Cathode
Biased):

There is no change in the operating level of the tubes while the amp is
being played, therefore, no singing sustain characteristic."


Agree.





2.] "...How much idling current the output tubes want to see; +/- 35mA.
> Louder, thicker, more easily over-driven.
< cleaner and thinner."


This is a mixed bag, and too general.

I would agree, with exception.

The +/- 35 ma makes it so.

Without that, I would agree.




3.] "...To thicken tone in most 2 ch. amps: Bridge the channels as follows-

Plug the guitar into #1 input of one channel, then run a patch cord from
the #2 input of the channel the guitar is plugged into over to the #1
input of the other channel. Now, adjust volume and tone controls of
both channels, to your taste. This will increase the signal that the
power tubes get from the pre-amp".

Providing the number of stages in each maintain equal phase relationship, I agree.

Old Marshall JMP four pluggers for example.






4.] "...For owners of Fender R.I. 5F6a Bassman amps:

Chances are, you'll want to reverse the the leads on your speakers as
they came from the factory.

Why? So the amp "plays forward" like the originals. Jensen (P10R) chose
to label their speaker terminals the opposite of today's standard. What
is today's standard?

Hook a flashlight battery to a speaker and see if it moves FORWARD. If
it does _not_, reverse the leads going to the speaker terminals. Now
look at the speaker terminals: The one going to the (+) side of the
battery is your your positive and the one going to the (-) side of the
battery is your your negative.

Check w/ a battery to make certain. When you find the (+) terminal by
today's standards, it should go to the sleeve of the plug, & the (-)
terminal should go to the pin in the middle of the plug..."

Thank you.

Here again, I agree, with exception.

The only reason for doing the battery trip is to insure that all speakers move in the same direction
as a group, and that when proper battery output polarity is applied, they move forward.

THIS, is the only standard to follow for the sake an applied standard to unite all speaker
applications to the same phase relationship.

However, without the same type of standard applied to the amplifiers, you can experience an
incorrect speaker phase relationship function.

For example, there was a bass player who was using a GK-400RB on a SWR stack with an old SVT parked
right up against each other. For some reason there was not a hell of a lot of expected low end
coming from this system.

Every thing was check out by the road crew as I had instructed with a nine volt battery. All the
speaker cones move in the correct direction with the + terminal applied to the tip of each speaker
cabinet speaker wire from the back of both amps. Yet, there was no bottom end from this rig.

So, I told one of the crew to revers the wires on the wire on the SVT, and MARK THAT CABLE.

Sure enough, the bottom appeared big time.

For some reason the GK and the SVT were out of phase with each other.

I never did get both heads together on my bench to check the phase relationship of BOTH amps
together at the same time.

For that, you need a dual trace scope run in chopped mode.

It is interesting to watch the trace relationships change between them, as you sweep the full
bandwidth too.

None sweep with 100% zero degree phase shift throughout their bandwidth.


Regards,

mvm

--


Regards,

Rich Koerner,
Time Electronics.
http://www.timeelect.com

Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers
.

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