Puzzling Pentode Problem, 1951 radio...

[Jan Panteltje]

On a sunny day (Fri, 7 Aug 2020 16:07:07 -0700 (PDT)) it happened Tabby
<tabbypurr@gmail.com> wrote in
<678b12d0-1a06-4bd1-8571-fec3442c126co@googlegroups.com>:

On Friday, 7 August 2020 07:20:45 UTC+1, Jan Panteltje wrote:
On a sunny day (Tue, 4 Aug 2020 01:23:48 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
d3e571d2-2bfb-4ed5-9fdf-2129f25e726co@googlegroups.com>:

I got an early roundie, prefer radios generally though

Yea.
*IF* the output tube in that radio is considered \'total loss\'
then MAYBE:
Perhaps there is some cathode material coming lose and shorting the grid if the tube gets hot.
In such a case burning it out might help,
say a hundred volt between cathode and grid with a 25 W Edison type bulb in series for a second.

I have revived many old CRTs like this:
Heater on, few hundred volt on the grid + versus cathode -
via a light bulb for a few seconds to revive the cathode,
but that was for low light cases, cathode contamination.

Sparking out a short could work for some cases perhaps.

Isn\'t that what CRT rejuvers do? The result doesn\'t last, but worse it damages the picture quality when it deteriorates again.

No, those apply high voltage DC between grid (Wehnelt) and cathode wit hheater on,
then after a second or so high current starts running that burns any crap that accumulated on the cathode.
The current is limited by a light bulb that at the same time shows the thing works again.
For a color CRT it is done 3 times for the R, G and B gun.
I have never seen any comebacks if it worked (had a TV repair shop for many years).
People are happy with the cheap fix, not everybody has the cash to buy a new set.

run a rather high grod current for
Tubes keep getting harder to find though. Refiring the getter can also fix some.


New tubes are 20$ on ebay..

For the price of 2 tubes you have a very good PLL transistor radio,
inclusive rechargable batteries, power adaptor, and sometimes
even a turnable ferrite antenna, even a wire antenna.

Lol. I\'ve got a far better tranny radio than that. Unfortunately they\'re obsolescent these days.

Curious? I have some radio experience, I like the Tecsun,
even received weather data with it on long wave (audio fed into laptop),
HAM radio SSB, it has an antenna attenuator, narrow band setting, FM stereo you can switch on and off (less noise in mono).
and covers most of the normal radio bands,.
For higher bands I have a Baofeng portable 2 meter, 70 cm transceiver.
For a bit higher I have the rtl_sdr sticks that can do anything from say 20 MHz to 1.5 GHz:
http://panteltje.com/panteltje/xpsa/index.html
Even done GPS with it:
http://michelebavaro.blogspot.com/2012/04/spring-news-in-gnss-and-sdr-domain.html
scroll down for panteltje
My site:
http://panteltje.com/pub/run_50_outside_2728000.gif

So now there are many other things I use that rtl_sdr stick for...
The Tecsuns plus Baofeng plus RTL_SDR stick are together still < 100$
and fit in you hand.
The RTL_SDR stick can of course also receive digital TV.

So much for boat anchor spectrum analyzers and what not.
Oh I forgot the RTL_SDR stick also receives ship AIS data here:
http://panteltje.com/pub/xgpspc_ships.gif
and of course tracks the airplanes:
http://panteltje.com/pub/xgpspc_5_planes.gif

Handy little things, also reads my weather station, see bottom of picture.
https://www.ebay.com/itm/272411458376

Does not get much better than that, helps if you can write some code.


Honesty requires that I mention I heard of the RTL_SDR sticks in this newsgroup.

I will not go into the power transistor TX stuff I have...

 

[Tabby]

On Saturday, 8 August 2020 08:01:34 UTC+1, Jan Panteltje wrote:

On a sunny day (Fri, 7 Aug 2020 16:07:07 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
678b12d0-1a06-4bd1-8571-fec3442c126co@googlegroups.com>:
On Friday, 7 August 2020 07:20:45 UTC+1, Jan Panteltje wrote:
On a sunny day (Tue, 4 Aug 2020 01:23:48 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
d3e571d2-2bfb-4ed5-9fdf-2129f25e726co@googlegroups.com>:

I got an early roundie, prefer radios generally though

Yea.
*IF* the output tube in that radio is considered \'total loss\'
then MAYBE:
Perhaps there is some cathode material coming lose and shorting the grid if the tube gets hot.
In such a case burning it out might help,
say a hundred volt between cathode and grid with a 25 W Edison type bulb in series for a second.

I have revived many old CRTs like this:
Heater on, few hundred volt on the grid + versus cathode -
via a light bulb for a few seconds to revive the cathode,
but that was for low light cases, cathode contamination.

Sparking out a short could work for some cases perhaps.

Isn\'t that what CRT rejuvers do? The result doesn\'t last, but worse it damages the picture quality when it deteriorates again.

No, those apply high voltage DC between grid (Wehnelt) and cathode wit hheater on,
then after a second or so high current starts running that burns any crap that accumulated on the cathode.
The current is limited by a light bulb that at the same time shows the thing works again.
For a color CRT it is done 3 times for the R, G and B gun.
I have never seen any comebacks if it worked (had a TV repair shop for many years).
People are happy with the cheap fix, not everybody has the cash to buy a new set.

I\'m confused, that sounds the same thing as you described doing.


NT

 

[Jan Panteltje]

On a sunny day (Sat, 8 Aug 2020 18:20:16 -0700 (PDT)) it happened Tabby
<tabbypurr@gmail.com> wrote in
<eff2a241-73a5-4ad9-8c9d-441556957ebdo@googlegroups.com>:

On Saturday, 8 August 2020 08:01:34 UTC+1, Jan Panteltje wrote:
On a sunny day (Fri, 7 Aug 2020 16:07:07 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
678b12d0-1a06-4bd1-8571-fec3442c126co@googlegroups.com>:
On Friday, 7 August 2020 07:20:45 UTC+1, Jan Panteltje wrote:
On a sunny day (Tue, 4 Aug 2020 01:23:48 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
d3e571d2-2bfb-4ed5-9fdf-2129f25e726co@googlegroups.com>:

I got an early roundie, prefer radios generally though

Yea.
*IF* the output tube in that radio is considered \'total loss\'
then MAYBE:
Perhaps there is some cathode material coming lose and shorting the grid if the tube gets hot.
In such a case burning it out might help,
say a hundred volt between cathode and grid with a 25 W Edison type bulb in series for a second.

I have revived many old CRTs like this:
Heater on, few hundred volt on the grid + versus cathode -
via a light bulb for a few seconds to revive the cathode,
but that was for low light cases, cathode contamination.

Sparking out a short could work for some cases perhaps.

Isn\'t that what CRT rejuvers do? The result doesn\'t last, but worse it damages the picture quality when it deteriorates
again.

No, those apply high voltage DC between grid (Wehnelt) and cathode wit hheater on,
then after a second or so high current starts running that burns any crap that accumulated on the cathode.
The current is limited by a light bulb that at the same time shows the thing works again.
For a color CRT it is done 3 times for the R, G and B gun.
I have never seen any comebacks if it worked (had a TV repair shop for many years).
People are happy with the cheap fix, not everybody has the cash to buy a new set.

I\'m confused, that sounds the same thing as you described doing.

Yes of course, because that is what I did
As to your statement \"The result doesn\'t last, but worse it damages the picture quality when it deteriorates
again\" in this context makes no sense,
You have a set where the picture is so dimm (old BW sets often went that way after many years) that the only option
is to replace the picture tube (if obtainable), or buy a new set.
Or you can burn the contamination on the cathode away in a few seconds giving the set a new life for years.
Customer happy, has money left for pizza or whatever.
Sure after years the set will detoriate again by the same mechanism.
If you do the reviving carefully there is no damage to the CRT.
Turning to your UL41 (?) I would not use this method with a high current such as in the CRT wehnelt case.
You could first measure grid-cathode cold (ohm meter),
If that is OK try again with heater on, (negative meter on grid, else you conduction!)
Look for shorts.
If any shorting grid-cathode then zap it if cold with a bit of voltage, maybe 20 V and few kOhm series resistor
(those grids can be easily damaged though) to see if the short burns out.
repeat metering.
*Use brain* to get a picture what is happening in the space between cathode and grid and on the surface of the cathode.
Again grids are fine wire so no high current stuff allowed like a CRT,
All this IF the tube is in your opinion total loss.


If it does not work buy a nice Tecsun

Simple physics, if tube dies then smash it, do a post-mortem, look at the grid cathode space, it is very small in those tubes,
I sure took several apart in my youth.

What was that great tranny you had?

 

[Tabby]

On Sunday, 9 August 2020 08:18:12 UTC+1, Jan Panteltje wrote:

On a sunny day (Sat, 8 Aug 2020 18:20:16 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
eff2a241-73a5-4ad9-8c9d-441556957ebdo@googlegroups.com>:
On Saturday, 8 August 2020 08:01:34 UTC+1, Jan Panteltje wrote:
On a sunny day (Fri, 7 Aug 2020 16:07:07 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
678b12d0-1a06-4bd1-8571-fec3442c126co@googlegroups.com>:
On Friday, 7 August 2020 07:20:45 UTC+1, Jan Panteltje wrote:
On a sunny day (Tue, 4 Aug 2020 01:23:48 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
d3e571d2-2bfb-4ed5-9fdf-2129f25e726co@googlegroups.com>:

I got an early roundie, prefer radios generally though

Yea.
*IF* the output tube in that radio is considered \'total loss\'
then MAYBE:
Perhaps there is some cathode material coming lose and shorting the grid if the tube gets hot.
In such a case burning it out might help,
say a hundred volt between cathode and grid with a 25 W Edison type bulb in series for a second.

I have revived many old CRTs like this:
Heater on, few hundred volt on the grid + versus cathode -
via a light bulb for a few seconds to revive the cathode,
but that was for low light cases, cathode contamination.

Sparking out a short could work for some cases perhaps.

Isn\'t that what CRT rejuvers do? The result doesn\'t last, but worse it damages the picture quality when it deteriorates
again.

No, those apply high voltage DC between grid (Wehnelt) and cathode wit hheater on,
then after a second or so high current starts running that burns any crap that accumulated on the cathode.
The current is limited by a light bulb that at the same time shows the thing works again.
For a color CRT it is done 3 times for the R, G and B gun.
I have never seen any comebacks if it worked (had a TV repair shop for many years).
People are happy with the cheap fix, not everybody has the cash to buy a new set.

I\'m confused, that sounds the same thing as you described doing.


Yes of course, because that is what I did
As to your statement \"The result doesn\'t last, but worse it damages the picture quality when it deteriorates
again\" in this context makes no sense,
You have a set where the picture is so dimm (old BW sets often went that way after many years) that the only option
is to replace the picture tube (if obtainable), or buy a new set.
Or you can burn the contamination on the cathode away in a few seconds giving the set a new life for years.
Customer happy, has money left for pizza or whatever.
Sure after years the set will detoriate again by the same mechanism.
If you do the reviving carefully there is no damage to the CRT.

That is far from the only option.

Firstly there\'s what I call cooking. Crank the filament up to 8 or 9v and let it sit for an hour. Usually emission is then better at 6.3.

After seeing the results of many rejuves I opted for boosting heater voltage as the primary way to improve CRT emission. It works very well. I once had a CRT with zero emission - I presume it had been left on unattended long term in a business setting - and got it back to normal by giving it +66%. It ran yellow rather than orange-red. Kept it for 10 years, it got used regularly and was still good after the 10 years.

Anode boosting I could not recommend, though I\'ve seen it done, presumably by backstreeters.

Then there are at least 2 methods used by some CRT testers, one of which you describe above.

Re results of rejuve, whatever you\'re doing must be different to what I\'ve seen. I typically saw brightness restored for anything from 1 month to a handful of months. And when it dimmed again the picture smeared badly, something that never happened before rejuve.

Turning to your UL41 (?) I would not use this method with a high current such as in the CRT wehnelt case.
You could first measure grid-cathode cold (ohm meter),
If that is OK try again with heater on, (negative meter on grid, else you conduction!)
Look for shorts.
If any shorting grid-cathode then zap it if cold with a bit of voltage, maybe 20 V and few kOhm series resistor
(those grids can be easily damaged though) to see if the short burns out.
repeat metering.
*Use brain* to get a picture what is happening in the space between cathode and grid and on the surface of the cathode.
Again grids are fine wire so no high current stuff allowed like a CRT,
All this IF the tube is in your opinion total loss.

It would be fine on a transformer coupled input, that would short the grid current harmlessly. With 17uA it would need 100k max to get it down to 1.7v excess grid voltage, which is perhaps tolerable. No doubt it\'ll get worse. But I would not expect to see audio transformer coupling on a U series radio

For the 2nd set I could buy another, make an SS one or sub a UL84 & adaptor.. Dunno what I\'ll do.


> If it does not work buy a nice Tecsun

I have precisely zero interest in buying any transistor radio.


NT

 

[Jan Panteltje]

On a sunny day (Sun, 9 Aug 2020 00:44:24 -0700 (PDT)) it happened Tabby
<tabbypurr@gmail.com> wrote in
<f5777309-c708-4c54-8257-a7f3e9527158o@googlegroups.com>:

After seeing the results of many rejuves I opted for boosting heater voltage
as the primary way to improve CRT emission. It works very well.

Well you are using the tube out of spec.
I have seen cases like that, CRT lighting as a lightbulb.


>I have precisely zero interest in buying any transistor radio.

You never answered the question I had to your statement that you had far superior tranny radios?
What radio?
Was just bull?

 

[Tabby]

On Sunday, 9 August 2020 11:38:33 UTC+1, Jan Panteltje wrote:

On a sunny day (Sun, 9 Aug 2020 00:44:24 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
f5777309-c708-4c54-8257-a7f3e9527158o@googlegroups.com>:

After seeing the results of many rejuves I opted for boosting heater voltage
as the primary way to improve CRT emission. It works very well.


Well you are using the tube out of spec.
I have seen cases like that, CRT lighting as a lightbulb.


I have precisely zero interest in buying any transistor radio.

You never answered the question I had to your statement that you had far superior tranny radios?
What radio?
Was just bull?

I don\'t bull. If you\'ve not realised that you\'ve not been paying attention. Yes there\'s more than one contender, yes one of mine is one of them. I\'m not much into tranny radios. The internet has obsoleted them, and really that\'s a good thing. Listening to round the world shortwave was never too entertaining or informative. I don\'t care whose is better or why.

Valve radios I still like some. Unfortunately I\'m not impressed by the Pye. Yes it has some clever ways of being cheap, but that\'s all. I dislike the sound. The cabinet is a fine example of missed opportunity. The thing is packed with an excessive number of power resistors all running hot. What\'s to like?


NT

 

[Wond]

On Fri, 07 Aug 2020 16:07:07 -0700, Tabby wrote:

On Friday, 7 August 2020 07:20:45 UTC+1, Jan Panteltje wrote:
On a sunny day (Tue, 4 Aug 2020 01:23:48 -0700 (PDT)) it happened Tabby
tabbypurr> wrote in
d3e571d2-2bfb-4ed5-9fdf-2129f25e726co@googlegroups.com>:

I got an early roundie, prefer radios generally though

Yea.
*IF* the output tube in that radio is considered \'total loss\'
then MAYBE:
Perhaps there is some cathode material coming lose and shorting the
grid if the tube gets hot. In such a case burning it out might help,
say a hundred volt between cathode and grid with a 25 W Edison type
bulb in series for a second.

I have revived many old CRTs like this:
Heater on, few hundred volt on the grid + versus cathode -
via a light bulb for a few seconds to revive the cathode,
but that was for low light cases, cathode contamination.

Sparking out a short could work for some cases perhaps.

Isn\'t that what CRT rejuvers do? The result doesn\'t last, but worse it
damages the picture quality when it deteriorates again.

Tubes keep getting harder to find though. Refiring the getter can also
fix some.


New tubes are 20$ on ebay..

For the price of 2 tubes you have a very good PLL transistor radio,
inclusive rechargable batteries, power adaptor, and sometimes even a
turnable ferrite antenna, even a wire antenna.

Lol. I\'ve got a far better tranny radio than that. Unfortunately they\'re
obsolescent these days.


NT

I too would like to know which _transistor_ radio is \"far better\"! Or
perhaps you were thinking _transformer_?