Old 'Scope inductor and cap help please

[Fox's Mercantile]

On 10/11/19 2:57 PM, tabbypurr@gmail.com wrote:

Good advice when being thorough, but time consuming. Just checking Ia or Ik is correct is the quick 'is the stage working' check that gets the job done quickly in most cases. If not obviously you then need to check electrode voltages, Rs Cs etc to determine valve or component failure.

Valves declared fauly by a tester sometimes still work. Grid shorts can make little difference when Rfault is higher than Rin, eg when the valve is transformer fed. And valves sometimes pass on a tester but won't work in the circuit. A tester is very useful but not the ultimate decider.


NT

You persist in posting wrong or misleading information to defend
what you original posted that was wrong and/or misleading.
So typical of you.

Service information usually provides voltages that should be
present at various places. With the exception of RF amplifier
stages, I have never seen "Current through this device should
be..."

Almost all low lever signal stages operate well below the
published Ip in tube manuals.

Again the best way to test tubes is "does it work?"
Replacing capacitors to eliminate shorts and high leakage
will solve a majority of problems. Then any "way out of
tolerance" resistors can be replaced. Then you can check
for defective tubes.
Except the obvious ones, cold (open filament) or red plates.
(Obviously something is seriously wrong.)



--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

 

[Ralph Mowery]

In article <HOCdnQa9L-bgbD3AnZ2dnUU7-R_NnZ2d@giganews.com>,
jdangus@att.net says...

Again the best way to test tubes is "does it work?"
Replacing capacitors to eliminate shorts and high leakage
will solve a majority of problems. Then any "way out of
tolerance" resistors can be replaced. Then you can check
for defective tubes.
Except the obvious ones, cold (open filament) or red plates.
(Obviously something is seriously wrong.)

From what I have seen, tubes are seldom a problem if the filament lights
up and the inside of the glass is silver color and not white. There are
a few exceptions where the tube is ran hard and will get weak. Seems
that the old color TV sets had a bad habit of a couple of tubes in the
horizontal output section getting weak.

 

[Fox's Mercantile]

On 10/11/19 4:46 PM, Ralph Mowery wrote:

From what I have seen, tubes are seldom a problem if the filament lights
up and the inside of the glass is silver color and not white.

Indicating a loss of vacuum, i.e. airleak.
The getter is what initially makes the silver deposit on the inside
of the tube envelope.

There are
a few exceptions where the tube is ran hard and will get weak. Seems
that the old color TV sets had a bad habit of a couple of tubes in the
horizontal output section getting weak.

TV sets were designed to a price point. "Run hard and put away wet"
was a cost savings. And the reason almost every always says "It's
just a bad tube." When in reality, it's almost always capacitors.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

 

On Friday, 11 October 2019 22:17:57 UTC+1, Fox's Mercantile wrote:

On 10/11/19 2:57 PM, tabbypurr wrote:

Good advice when being thorough, but time consuming. Just checking Ia or Ik is correct is the quick 'is the stage working' check that gets the job done quickly in most cases. If not obviously you then need to check electrode voltages, Rs Cs etc to determine valve or component failure.

Valves declared fauly by a tester sometimes still work. Grid shorts can make little difference when Rfault is higher than Rin, eg when the valve is transformer fed. And valves sometimes pass on a tester but won't work in the circuit. A tester is very useful but not the ultimate decider.


NT

You persist in posting wrong or misleading information to defend
what you original posted that was wrong and/or misleading.
So typical of you.

you sure are the bsing hypocrite.

Service information usually provides voltages that should be
present at various places. With the exception of RF amplifier
stages, I have never seen "Current through this device should
be..."

then you lack experience. Some cct diags have it printed on, more often there is a cathode R and a stated voltage or a stated anode voltage. V=IR etc. The size of Rk sometimes gives a rough figure.

Almost all low lever signal stages operate well below the
published Ip in tube manuals.

Again the best way to test tubes is "does it work?"

which is pretty much what I said. If stage current is within normal bounds, it typically does work.

Replacing capacitors to eliminate shorts and high leakage
will solve a majority of problems. Then any "way out of
tolerance" resistors can be replaced.

yup

Then you can check
for defective tubes.

You might. I power it up to check em, and only test tubes when the stage should work but won't.

Except the obvious ones, cold (open filament) or red plates.
(Obviously something is seriously wrong.)

or white getter - those are never going to work!


NT