|
I've completed sorting through hundreds of CMOS chips (the old Motorola 4000-series) and fixed my extra Trac TE144 keyer.? It was good to actually fix something, for a change.? BTW, if any of you need one of these chips (or two or three) email me off-list and I can send some to you.? I have lots of them!
Getting to the meat & potatoes of this current post:
Some of you know that I have been struggling with an R-4B that defies my attempts at repair.? I have used $25 worth of freeze spray, swapped tubes, replaced parts -- including the entire Board 11 (see Garey's CD) and the SSB/CW AM switch and double-checked the wiring.? I have replaced components around V5 and T10, T11.? I have not replaced Board 3, though I did replace C163 (wasn't the problem, obviously).? Checked all resistor values on Board 3.
When the receiver is first powered up, everything behaves normally.? Switching from AGC off to either fast or slow doesn't change the AGC voltage at TP2, which I set to around -1.35V.? S meter stays on S1 with no signal.
As the receiver warms up. the meter stays on S1, with -1.35V on TP2, with the AGC off. Voltage will remain stable with AGC off and goes down when AGC is turned on. Voltage starts slowly drifting towards 0V as it warms up.? The meter goes upscale with AGC on.
If I set the bias to -1.35V per the procedure (with AGC on) when cold, voltage gradually heads toward 0.? R87 is at about 40% up from full anticlockwise -- i.e., around what is normally expected.? To get the TP2 voltage back up to -1.35 after warmup, R87 needs to be nearly max.? If I set the sensitivity with AGC off, it stays stable but the voltage will go more positive if I turn the AGC on.
On the air, the receiver sounds pretty normal with the voltage set with AGC off but, of course, deflection of the meter is less with the signals on the air.
All of the components of Board 11 can't be the problem because I swapped the entire board with a good one that I had.? Ditto for the switch.? R40 sets to S9+40 with -15.0V and stays there.? I checked D10 and D13 both for leakage and with freeze spray (Thank the stars I don't have to change D13!!!)
I'm running out of ideas...
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
|
Wow, poor Steve..
Sounds like you have replaced everything, what a tricky one.
The one thing that I know pulls the AVC line is gassy tubes.? I don't know how much the gas changes with warmup, maybe Richard or someone does?
I might try pulling tubes on the AVC bus and watching the AVC lines during warmup where you are seeing the problem.? The voltage won't be right but
just look for drift.
73,
Gary
WB6OGD
|
Based on my limited experience, knowledge and baloney quotient, I offer the following:
Anytime I have a difference in cold vrs warmed up as regards to performance, I suspect:
First of all tubes:? Even a good tube will "drift" when warmed.? If the inner surface?around the getter is silvery, then it may mean the insides of the tube are not pristine?as the getter material is exhausted.? The tube life is dependent on many things, cleanliness?of the insides is one of them.
Capacitors:? As they age, the ability to hold and pass on charge varies.? Generally, I have found, the warmer a cap, the better it works.
Resistors: If a circuit changes current boldly when it warms, then a marginal resistor could be at fault.? Drake did not spend a lot of money on the quality of their resistors.
Lastly, Soldered connections:? Another current sensitive issue, with cold being the least current and warm?the greater current.
I suppose I should include transistors as well as they are affected by temperature changes,? In either state, they may function, but at different points on the curve.
I hope you can resolve this dilemma.? As you have done in the past, your findings are valuable to those of us who insist on fixing these radios.? As none of us have an infinite time frame to do so, sharing the results of our victories is a valuable tool in keeping the old stuff working.? Now if anyone has a solution for creaky knees, I would be interested to know. ?this as well.
David Assaf III W5XU, VP8RXU ?
On Fri, Jan 5, 2024 at 9:51?AM Steve Wedge, W1ES/4 via <w1es= [email protected]> wrote: I've completed sorting through hundreds of CMOS chips (the old Motorola 4000-series) and fixed my extra Trac TE144 keyer.? It was good to actually fix something, for a change.? BTW, if any of you need one of these chips (or two or three) email me off-list and I can send some to you.? I have lots of them!
Getting to the meat & potatoes of this current post:
Some of you know that I have been struggling with an R-4B that defies my attempts at repair.? I have used $25 worth of freeze spray, swapped tubes, replaced parts -- including the entire Board 11 (see Garey's CD) and the SSB/CW AM switch and double-checked the wiring.? I have replaced components around V5 and T10, T11.? I have not replaced Board 3, though I did replace C163 (wasn't the problem, obviously).? Checked all resistor values on Board 3.
When the receiver is first powered up, everything behaves normally.? Switching from AGC off to either fast or slow doesn't change the AGC voltage at TP2, which I set to around -1.35V.? S meter stays on S1 with no signal.
As the receiver warms up. the meter stays on S1, with -1.35V on TP2, with the AGC off. Voltage will remain stable with AGC off and goes down when AGC is turned on. Voltage starts slowly drifting towards 0V as it warms up.? The meter goes upscale with AGC on.
If I set the bias to -1.35V per the procedure (with AGC on) when cold, voltage gradually heads toward 0.? R87 is at about 40% up from full anticlockwise -- i.e., around what is normally expected.? To get the TP2 voltage back up to -1.35 after warmup, R87 needs to be nearly max.? If I set the sensitivity with AGC off, it stays stable but the voltage will go more positive if I turn the AGC on.
On the air, the receiver sounds pretty normal with the voltage set with AGC off but, of course, deflection of the meter is less with the signals on the air.
All of the components of Board 11 can't be the problem because I swapped the entire board with a good one that I had.? Ditto for the switch.? R40 sets to S9+40 with -15.0V and stays there.? I checked D10 and D13 both for leakage and with freeze spray (Thank the stars I don't have to change D13!!!)
I'm running out of ideas...
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
|
Thanks, Gary.
Yeah, I swapped out tubes already but one at a time.? I have cleaned out the sockets and used a Proxabrush with DeOxIt in all the sockets.
I've changed four more resistors and thought I had a "Eureka!" moment but it didn't happen.
To completely discount the tubes, I think it's now time to replace all of the tubes at once.? I'll let y'all know if that did it.? You're in the right direction and I have had gassy 12BE6's mess things up in the past...
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Friday, January 5th, 2024 at 11:23 AM, wb6ogd <garywinblad@...> wrote:
Wow, poor Steve..
Sounds like you have replaced everything, what a tricky one.
The one thing that I know pulls the AVC line is gassy tubes.? I don't know how much the gas changes with warmup, maybe Richard or someone does?
I might try pulling tubes on the AVC bus and watching the AVC lines during warmup where you are seeing the problem.? The voltage won't be right but
just look for drift.
73,
Gary
WB6OGD
|
I may have found the problems.? Note the use of plural here. I'm going to let it sit for an hour before I declare "Victory!".
I did what I should have initially done when confronted by such a bizarre issue: Shotgun all of the tubes at once and work backwards.? When I "shotgunned" all of the tubes, the problem seems to have gone away.? So far, I am fairly sure that at least three different tubes contributed to this, as Ray Magliozzi used to say, "Woe and Intrigue".
First of all, I discovered that a former owner had put a 6AU6 into V2's position.? Fair enough: it uses the same basing as the 6HS6 but doesn't have nearly the gain and its curve is quite different.? In fact, I have owned so really early stuff (an R-4 and a T-4) that used a 6AU6 at that location.? This seems to have affected the gain but not impacted the AGC.
V3 (12BE6) seems to be a contributor.? These are famous for going gassy and when they do, tube testers don't always find them until they're really bad.? So V3's replacement is staying in.??
V5 (12BA6) looks like it was a contributor.? Again, I had swapped it out by itself and didn't see much of an improvement.
Right now, I've replaced V4 and V9 with the original tubes and V9 pulled things down very quickly V4 was also contributing.
SO Gary, thanks for your suggestion!? I had swapped one tube at a time and kept having trouble.? There were .multiple bad tubes that were contributing but one of the 12BA6's was the worst offender.
Ronnie can finally get his receiver back!
73,
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Friday, January 5th, 2024 at 1:36 PM, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:
Thanks, Gary.
Yeah, I swapped out tubes already but one at a time.? I have cleaned out the sockets and used a Proxabrush with DeOxIt in all the sockets.
I've changed four more resistors and thought I had a "Eureka!" moment but it didn't happen.
To completely discount the tubes, I think it's now time to replace all of the tubes at once.? I'll let y'all know if that did it.? You're in the right direction and I have had gassy 12BE6's mess things up in the past...
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Friday, January 5th, 2024 at 11:23 AM, wb6ogd <garywinblad@...> wrote:
Wow, poor Steve..
Sounds like you have replaced everything, what a tricky one.
The one thing that I know pulls the AVC line is gassy tubes.? I don't know how much the gas changes with warmup, maybe Richard or someone does?
I might try pulling tubes on the AVC bus and watching the AVC lines during warmup where you are seeing the problem.? The voltage won't be right but
just look for drift.
73,
Gary
WB6OGD
|
sounds like some good sleuthing there Sherlock! ? ?I am interjecting here from experience about heater to cathode leakage. ?This sounds like what may be happening here. ?Few tube testers have this test and it may of increasing importance as the available pool of tubes decreases. ?I will continue to consider this and perhaps contrive ?a tester or see what might be available. ?What is your thinking? ?73. John w4bfs
toggle quoted message
Show quoted text
On Jan 5, 2024, at 3:45 PM, Steve Wedge, W1ES/4 via < w1es@...> wrote:
I may have found the problems.? Note the use of plural here. I'm going to let it sit for an hour before I declare "Victory!".
I did what I should have initially done when confronted by such a bizarre issue: Shotgun all of the tubes at once and work backwards.? When I "shotgunned" all of the tubes, the problem seems to have gone away.? So far, I am fairly sure that at least three different tubes contributed to this, as Ray Magliozzi used to say, "Woe and Intrigue".
First of all, I discovered that a former owner had put a 6AU6 into V2's position.? Fair enough: it uses the same basing as the 6HS6 but doesn't have nearly the gain and its curve is quite different.? In fact, I have owned so really early stuff (an R-4 and a T-4) that used a 6AU6 at that location.? This seems to have affected the gain but not impacted the AGC.
V3 (12BE6) seems to be a contributor.? These are famous for going gassy and when they do, tube testers don't always find them until they're really bad.? So V3's replacement is staying in.??
V5 (12BA6) looks like it was a contributor.? Again, I had swapped it out by itself and didn't see much of an improvement.
Right now, I've replaced V4 and V9 with the original tubes and V9 pulled things down very quickly V4 was also contributing.
SO Gary, thanks for your suggestion!? I had swapped one tube at a time and kept having trouble.? There were .multiple bad tubes that were contributing but one of the 12BA6's was the worst offender.
Ronnie can finally get his receiver back!
73,
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Friday, January 5th, 2024 at 1:36 PM, Steve Wedge, W1ES/4 via < w1es@...> wrote:
Thanks, Gary.
Yeah, I swapped out tubes already but one at a time.? I have cleaned out the sockets and used a Proxabrush with DeOxIt in all the sockets.
I've changed four more resistors and thought I had a "Eureka!" moment but it didn't happen.
To completely discount the tubes, I think it's now time to replace all of the tubes at once.? I'll let y'all know if that did it.? You're in the right direction and I have had gassy 12BE6's mess things up in the past...
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Friday, January 5th, 2024 at 11:23 AM, wb6ogd < garywinblad@...> wrote:
Wow, poor Steve..
Sounds like you have replaced everything, what a tricky one.
The one thing that I know pulls the AVC line is gassy tubes.? I don't know how much the gas changes with warmup, maybe Richard or someone does?
I might try pulling tubes on the AVC bus and watching the AVC lines during warmup where you are seeing the problem.? The voltage won't be right but
just look for drift.
73,
Gary
WB6OGD
|
By the way the Antique Radios website has an interesting forum going on on this very subject
toggle quoted message
Show quoted text
sounds like some good sleuthing there Sherlock! ? ?I am interjecting here from experience about heater to cathode leakage. ?This sounds like what may be happening here. ?Few tube testers have this test and it may of increasing importance as the available pool of tubes decreases. ?I will continue to consider this and perhaps contrive ?a tester or see what might be available. ?What is your thinking? ?73. John w4bfsOn Jan 5, 2024, at 3:45 PM, Steve Wedge, W1ES/4 via ??< w1es@...> wrote:
I may have found the problems.? Note the use of plural here. I'm going to let it sit for an hour before I declare "Victory!".
I did what I should have initially done when confronted by such a bizarre issue: Shotgun all of the tubes at once and work backwards.? When I "shotgunned" all of the tubes, the problem seems to have gone away.? So far, I am fairly sure that at least three different tubes contributed to this, as Ray Magliozzi used to say, "Woe and Intrigue".
First of all, I discovered that a former owner had put a 6AU6 into V2's position.? Fair enough: it uses the same basing as the 6HS6 but doesn't have nearly the gain and its curve is quite different.? In fact, I have owned so really early stuff (an R-4 and a T-4) that used a 6AU6 at that location.? This seems to have affected the gain but not impacted the AGC.
V3 (12BE6) seems to be a contributor.? These are famous for going gassy and when they do, tube testers don't always find them until they're really bad.? So V3's replacement is staying in.??
V5 (12BA6) looks like it was a contributor.? Again, I had swapped it out by itself and didn't see much of an improvement.
Right now, I've replaced V4 and V9 with the original tubes and V9 pulled things down very quickly V4 was also contributing.
SO Gary, thanks for your suggestion!? I had swapped one tube at a time and kept having trouble.? There were .multiple bad tubes that were contributing but one of the 12BA6's was the worst offender.
Ronnie can finally get his receiver back!
73,
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with??secure email.
On Friday, January 5th, 2024 at 1:36 PM, Steve Wedge, W1ES/4 via ??< w1es@...> wrote: Thanks, Gary.
Yeah, I swapped out tubes already but one at a time.? I have cleaned out the sockets and used a Proxabrush with DeOxIt in all the sockets.
I've changed four more resistors and thought I had a "Eureka!" moment but it didn't happen.
To completely discount the tubes, I think it's now time to replace all of the tubes at once.? I'll let y'all know if that did it.? You're in the right direction and I have had gassy 12BE6's mess things up in the past...
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with??secure email.
On Friday, January 5th, 2024 at 11:23 AM, wb6ogd < garywinblad@...> wrote: Wow, poor Steve..
Sounds like you have replaced everything, what a tricky one.
The one thing that I know pulls the AVC line is gassy tubes.? I don't know how much the gas changes with warmup, maybe Richard or someone does?
I might try pulling tubes on the AVC bus and watching the AVC lines during warmup where you are seeing the problem.? The voltage won't be right but
just look for drift.
73,
Gary
WB6OGD
|
If the Richard you mean is me I don't have the answer but I have had problems with gassy tubes affecting the AVC. In may case the slow AVC was too fast. Gary Barrell told me it was probably a gassy tube but the tubes tested OK on a TV-7 gas test. When I changed tubes the problem went away. Don't remember which tube. The AVC is very high impedance so very slight conductivity will affect it. The TV-7 test circuit will indicate tubes which are very gassy but not those with only a slight amount of gas. I think this is true for most tube testers. About the only way to tell is to change the tubes and maybe more than once. These tubes may work fine in other circuits.
toggle quoted message
Show quoted text
On 1/5/2024 8:23 AM, wb6ogd wrote: Wow, poor Steve..
Sounds like you have replaced everything, what a tricky one.
The one thing that I know pulls the AVC line is gassy tubes.? I don't know how much the gas changes with warmup, maybe Richard or someone does?
I might try pulling tubes on the AVC bus and watching the AVC lines during warmup where you are seeing the problem.? The voltage won't be right but
just look for drift.
73,
Gary
WB6OGD
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
On 2024-01-05 14:08, Richard Knoppow wrote: problem went away. Don't remember which tube. The AVC is very high
impedance so very slight conductivity will affect it. The TV-7 test This reminds me of a similar problem I had with my KWM-2. Very high impedance in the T/R circuit. It would take a second or two to go back into receive. Problem was a leaky capacitor. My Heathkit cap checker said it was fine. - Jerry, KF6VB
|
A couple of comments: The getter in receiving tubes (including TV sweep tubes) should be silvery, when it starts to be worn it becomes sort of white or cloudy. Heavily used tubes may show this around the edges of the getter on the inside of the envelope.
The resistors Drake used were carbon composition resistors, quite generally used at the time. The stability depends on exactly how they were made. The best of them were made by Allen-Bradley and sold under that name and also by Ohmite, exact same resistor. But, even those change with age. Typically a carbon composition resistor will drift up in value. The higher the original value the more it will drift. Probably any resistor of 100K or more will be found to have shifted a significant amount but even very low value resistors, like the 15 ohm cathode resistors in the T4XB will change, some actually drift low. Any composition resistor with visible seams or mold marks on the sides should be suspect. I don't know who made these but they seem to far less stable than the AB or Ohmite ones.
Modern resistors are carbon or metal film types which have much different construction. If made correctly these have excellent long term stability. They also do not have a voltage coefficient of resistance as do the composition type. While they are reputed to have higher reactance in fact they have LESS reactance than CC types, can be proved by measuring them. The reactance of the spiralled part is not significant and is very low Q. Carbon has a negative temperature coefficient, metal can have anything depending on the kind of resistance meterial used and the arrangement of the coatings (many resistors have more than one deposit of resistance material). I don't know about modern oxide composition resistors but they seem to be stable and can handle quite high power.
The instability of capacitors depends on the type of cap. Old type paper caps are not stable with time because of degradation of the paper dielectric. This varies with the paper used (it was special paper) and the effectiveness of the sealing of the element from external moisture. Heat in a capacitor can be generated by series resistance, that is, the dielectric has some resistance which can dissipate power. This is especially noticeable in electrolytic caps. A capacitor also has parallel resistance, usually known as leakage. Parallel resistance comes from anything that reduces the insulation of the cap. All electrolytic caps have some parallel resistance due to the nature of the dielectric. Modern ones use different chemistry than the old ones and have less leakage, but all have some. This passes some DC. Since one purpose of a capacitor is to block DC leakage makes it less effective for this function. Leakage, since it is resistance, also dissipates some power causing the cap to become warm. If there is a lot of leakage the cap can get quite hot and, since it originates with the dielectric the heat can cause the cap to expand and the dielectric, which is usually a paste, to boil out. These caps can explode if they get hot enough.
A paper cap with high leakage can also get warm but usually there is not enough to cause it to expand. However, caps used where blocking DC is important, such as grid coupling caps or cathode bypass caps, can cause malfunction of the circuit. In audio circuits leaky coupling caps can cause serious distortion since they change the operating point of the tube or transistor they are used with.
Old paper caps will generally need replacement due to changes in the value or the series resistance. Series resistance generally goes up.
Ideally, a capacitor of any sort should have infinite parallel resistance and zero series resistance. Some modern plastic film caps come close.
Mica and ceramic caps have a set of vices all their own. Mica was and is very widely used, especially for RF, because it has very good properties and is quite stable. The most common problem with mica is due to the type of construction. A great many caps are of the silver plated type. In these the mica dielectric is plated with a coaging of silver which forms the electrodes. These are inherently very stable and, since both the thickness of the mica and of the plating can be controlled very accurately they can be made with very close tolerances. The problem comes from the casing. If the casing allows moisture to enter it will cause the silver to oxidize forming crystals or whiskers. Eventually, this cause partial shorts changing the value of the capacitor and making it unstable in value. Same problem happens with plated crystals. This so called "silver mica disease" is common for capacitors made around the 1950s with Bakelite housings but does not seem to be a problem with later caps which are coated with epoxy by dipping. One should watch out for the symptoms of silver mice disease but not shotgun mica caps since most are perfectly stable.
The main problem with ceramic caps comes from a lack of understanding that they are not all the same. There are several types of ceramic dielectric; in general, the kinds with low dielectric contstant, called K in ceramic types, are very stable, rivaling mica but high K types have problems with ageing, temperature coefficient, voltage coefficient and sensitivity to mechanical deformation, i.e. they are microphonic. The caps used as temperature compensation are of the Low K veriety and are generally stable. The K value affects the size of the cap: low K can be quite large where High K can be very small for the a given value and voltage. The trade off is in stability, High K are NOT stable and should not be used where stability is a requirement. Other than that they are very long lived although their values may drift somewhat (I mean Hi K). In general, ceramic caps should not be shotgunned (with a few exceptions). Look out for mechanical damage around leads.
There is a great deal of tutorial information about capacitors on the web, mostly at manufacturer's sites. Worth doing some reading.
I seem to have written an essay. Didn't mean to. Sometimes my fingers just run away.
toggle quoted message
Show quoted text
On 1/5/2024 8:36 AM, David wrote: Based on my limited experience, knowledge and baloney quotient, I offer the following:
Anytime I have a difference in cold vrs warmed up as regards to performance, I suspect:
First of all tubes:? Even a good tube will "drift" when warmed.? If the inner surface?around the getter is silvery, then it may mean the insides of the tube are not pristine?as the getter material is exhausted.? The tube life is dependent on many things, cleanliness?of the insides is one of them.
Capacitors:? As they age, the ability to hold and pass on charge varies.? Generally, I have found, the warmer a cap, the better it works.
Resistors: If a circuit changes current boldly when it warms, then a marginal resistor could be at fault.? Drake did not spend a lot of money on the quality of their resistors.
Lastly, Soldered connections:? Another current sensitive issue, with cold being the least current and warm?the greater current.
I suppose I should include transistors as well as they are affected by temperature changes,? In either state, they may function, but at different points on the curve.
I hope you can resolve this dilemma.? As you have done in the past, your findings are valuable to those of us who insist on fixing these radios. As none of us have an infinite time frame to do so, sharing the results of our victories is a valuable tool in keeping the old stuff working. Now if anyone has a solution for creaky knees, I would be interested to know.
?this as well.
David Assaf III
W5XU, VP8RXU
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Thank you, great article... WD4AGG
On Friday, January 5, 2024 at 04:49:16 PM CST, Richard Knoppow <1oldlens1@...> wrote:
? ? A couple of comments: The getter in receiving tubes (including TV
sweep tubes) should be silvery, when it starts to be worn it becomes
sort of white or cloudy. Heavily used tubes may show this around the
edges of the getter on the inside of the envelope.
? ? The resistors Drake used were carbon composition resistors, quite
generally used at the time. The stability depends on exactly how they
were made. The best of them were made by Allen-Bradley and sold under
that name and also by Ohmite, exact same resistor. But, even those
change with age. Typically a carbon composition resistor will drift up
in value. The higher the original value the more it will drift. Probably
any resistor of 100K or more will be found to have shifted a significant
amount but even very low value resistors, like the 15 ohm cathode
resistors in the T4XB will change, some actually drift low. Any
composition resistor with visible seams or mold marks on the sides
should be suspect. I don't know who made these but they seem to far less
stable than the AB or Ohmite ones.
? ? Modern resistors are carbon or metal film types which have much
different construction. If made correctly these have excellent long term
stability. They also do not have a voltage coefficient of resistance as
do the composition type. While they are reputed to have higher reactance
in fact they have LESS reactance than CC types, can be proved by
measuring them. The reactance of the spiralled part is not significant
and is very low Q. Carbon has a negative temperature coefficient, metal
can have anything depending on the kind of resistance meterial used and
the arrangement of the coatings (many resistors have more than one
deposit of resistance material). I don't know about modern oxide
composition resistors but they seem to be stable and can handle quite
high power.
? ? The instability of capacitors depends on the type of cap. Old type
paper caps are not stable with time because of degradation of the paper
dielectric. This varies with the paper used (it was special paper) and
the effectiveness of the sealing of the element from external moisture.
Heat in a capacitor can be generated by series resistance, that is, the
dielectric has some resistance which can dissipate power. This is
especially noticeable in electrolytic caps. A capacitor also has
parallel resistance, usually known as leakage. Parallel resistance comes
from anything that reduces the insulation of the cap. All electrolytic
caps have some parallel resistance due to the nature of the dielectric.
Modern ones use different chemistry than the old ones and have less
leakage, but all have some. This passes some DC. Since one purpose of a
capacitor is to block DC leakage makes it less effective for this
function. Leakage, since it is resistance, also dissipates some power
causing the cap to become warm. If there is a lot of leakage the cap can
get quite hot and, since it originates with the dielectric the heat can
cause the cap to expand and the dielectric, which is usually a paste, to
boil out. These caps can explode if they get hot enough.
? ? A paper cap with high leakage can also get warm but usually there
is not enough to cause it to expand. However, caps used where blocking
DC is important, such as grid coupling caps or cathode bypass caps, can
cause malfunction of the circuit. In audio circuits leaky coupling caps
can cause serious distortion since they change the operating point of
the tube or transistor they are used with.
? ? Old paper caps will generally need replacement due to changes in
the value or the series resistance. Series resistance generally goes up.
? ? Ideally, a capacitor of any sort should have infinite parallel
resistance and zero series resistance. Some modern plastic film caps
come close.
? ? Mica and ceramic caps have a set of vices all their own. Mica was
and is very widely used, especially for RF, because it has very good
properties and is quite stable. The most common problem with mica is due
to the type of construction. A great many caps are of the silver plated
type. In these the mica dielectric is plated with a coaging of silver
which forms the electrodes. These are inherently very stable and, since
both the thickness of the mica and of the plating can be controlled very
accurately they can be made with very close tolerances. The problem
comes from the casing. If the casing allows moisture to enter it will
cause the silver to oxidize forming crystals or whiskers. Eventually,
this cause partial shorts changing the value of the capacitor and making
it unstable in value. Same problem happens with plated crystals. This so
called "silver mica disease" is common for capacitors made around the
1950s with Bakelite housings but does not seem to be a problem with
later caps which are coated with epoxy by dipping. One should watch out
for the symptoms of silver mice disease but not shotgun mica caps since
most are perfectly stable.
? ? The main problem with ceramic caps comes from a lack of
understanding that they are not all the same. There are several types of
ceramic dielectric; in general, the kinds with low dielectric contstant,
called K in ceramic types, are very stable, rivaling mica but high K
types have problems with ageing, temperature coefficient, voltage
coefficient and sensitivity to mechanical deformation, i.e. they are
microphonic. The caps used as temperature compensation are of the Low K
veriety and are generally stable. The K value affects the size of the
cap: low K can be quite large where High K can be very small for the a
given value and voltage. The trade off is in stability, High K are NOT
stable and should not be used where stability is a requirement. Other
than that they are very long lived although their values may drift
somewhat (I mean Hi K). In general, ceramic caps should not be
shotgunned (with a few exceptions). Look out for mechanical damage
around leads.
? ? There is a great deal of tutorial information about capacitors on
the web, mostly at manufacturer's sites. Worth doing some reading.
? ? I seem to have written an essay. Didn't mean to. Sometimes my
fingers just run away.
On 1/5/2024 8:36 AM, David wrote:
> Based on my limited experience, knowledge and baloney quotient, I offer
> the following:
>
> Anytime I have a difference in cold vrs warmed up as regards to
> performance, I suspect:
>
> First of all tubes:? Even a good tube will "drift" when warmed.? If the
> inner surface?around the getter is silvery, then it may mean the insides
> of the tube are not pristine?as the getter material is exhausted.? The
> tube life is dependent on many things, cleanliness?of the insides is one
> of them.
>
> Capacitors:? As they age, the ability to hold and pass on charge
> varies.? Generally, I have found, the warmer a cap, the better it works.
>
> Resistors: If a circuit changes current boldly when it warms, then a
> marginal resistor could be at fault.? Drake did not spend a lot of money
> on the quality of their resistors.
>
> Lastly, Soldered connections:? Another current sensitive issue, with
> cold being the least current and warm?the greater current.
>
> I suppose I should include transistors as well as they are affected by
> temperature changes,? In either state, they may function, but at
> different points on the curve.
>
> I hope you can resolve this dilemma.? As you have done in the past, your
> findings are valuable to those of us who insist on fixing these radios.?
> As none of us have an infinite time frame to do so, sharing the results
> of our victories is a valuable tool in keeping the old stuff working.?
> Now if anyone has a solution for creaky knees, I would be interested to
> know.
>? ?this as well.
>
> David Assaf III
> W5XU, VP8RXU
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
On 2024-01-05 15:45, R W Gould via groups.io wrote: Thank you, great article...
WD4AGG *** Thanks from me too. I saved it. - Jerry, KF6VB
|
??? I seem to have written an essay. Didn't mean to. Sometimes my fingers just run away. And it's very welcome. Thanks. Regards Guillermo - LU5WE. On 1/5/2024 8:36 AM, David wrote:
Based on my limited experience, knowledge and baloney quotient, I offer the following:
Anytime I have a difference in cold vrs warmed up as regards to performance, I suspect:
First of all tubes:? Even a good tube will "drift" when warmed.? If the inner surface?around the getter is silvery, then it may mean the insides of the tube are not pristine?as the getter material is exhausted.? The tube life is dependent on many things, cleanliness?of the insides is one of them.
Capacitors:? As they age, the ability to hold and pass on charge varies.? Generally, I have found, the warmer a cap, the better it works.
Resistors: If a circuit changes current boldly when it warms, then a marginal resistor could be at fault.? Drake did not spend a lot of money on the quality of their resistors.
Lastly, Soldered connections:? Another current sensitive issue, with cold being the least current and warm?the greater current.
I suppose I should include transistors as well as they are affected by temperature changes,? In either state, they may function, but at different points on the curve.
I hope you can resolve this dilemma.? As you have done in the past, your findings are valuable to those of us who insist on fixing these radios. As none of us have an infinite time frame to do so, sharing the results of our victories is a valuable tool in keeping the old stuff working. Now if anyone has a solution for creaky knees, I would be interested to know.
??this as well.
David Assaf III
W5XU, VP8RXU
|
well, it was not my intention to draw people from addressing the problem, but it appears that intended helpful comments based on nearly 60 years of radio repair experience was not taken as intended.?? I will no?longer be a source of intended help where the intention is reversed.
Sorry.
David Assaf III W5XU, VP8RXU ?
>? ??? I seem to have written an essay. Didn't mean to. Sometimes my
> fingers just run away.
And it's very welcome. Thanks.
Regards
Guillermo - LU5WE.
>
> On 1/5/2024 8:36 AM, David wrote:
>> Based on my limited experience, knowledge and baloney quotient, I
>> offer the following:
>>
>> Anytime I have a difference in cold vrs warmed up as regards to
>> performance, I suspect:
>>
>> First of all tubes:? Even a good tube will "drift" when warmed.? If
>> the inner surface?around the getter is silvery, then it may mean the
>> insides of the tube are not pristine?as the getter material is
>> exhausted.? The tube life is dependent on many things, cleanliness?of
>> the insides is one of them.
>>
>> Capacitors:? As they age, the ability to hold and pass on charge
>> varies.? Generally, I have found, the warmer a cap, the better it works.
>>
>> Resistors: If a circuit changes current boldly when it warms, then a
>> marginal resistor could be at fault.? Drake did not spend a lot of
>> money on the quality of their resistors.
>>
>> Lastly, Soldered connections:? Another current sensitive issue, with
>> cold being the least current and warm?the greater current.
>>
>> I suppose I should include transistors as well as they are affected by
>> temperature changes,? In either state, they may function, but at
>> different points on the curve.
>>
>> I hope you can resolve this dilemma.? As you have done in the past,
>> your findings are valuable to those of us who insist on fixing these
>> radios. As none of us have an infinite time frame to do so, sharing
>> the results of our victories is a valuable tool in keeping the old
>> stuff working. Now if anyone has a solution for creaky knees, I would
>> be interested to know.
>> ??this as well.
>>
>> David Assaf III
>> W5XU, VP8RXU
>
>
|
UPDATE
One very bad tube (V5, I think. I should have marked them when I removed them!). Three that weren't great but had passed on the tube tester. V3, V4 and V9.
There is still a change in voltage between AGC off, fast and slow, but these are on the order or 100 mV or thereabouts. Totally within tolerances of the parts.
Thanks to all for the comments and for being the second - nth set of eyeballs and brains on this.
73,
Steve Wedge, W1ES/4
Time flies like an arrow.? Fruit flies like a banana.
Sent with Proton Mail secure email.
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Show quoted text
On Friday, January 5th, 2024 at 7:29 PM, Willy - LU5WE via groups.io <guiye8@...> wrote: I seem to have written an essay. Didn't mean to. Sometimes my
fingers just run away.
And it's very welcome. Thanks.
Regards
Guillermo - LU5WE.
On 1/5/2024 8:36 AM, David wrote:
Based on my limited experience, knowledge and baloney quotient, I
offer the following:
Anytime I have a difference in cold vrs warmed up as regards to
performance, I suspect:
First of all tubes: Even a good tube will "drift" when warmed. If
the inner surface around the getter is silvery, then it may mean the
insides of the tube are not pristine as the getter material is
exhausted. The tube life is dependent on many things, cleanliness of
the insides is one of them.
Capacitors: As they age, the ability to hold and pass on charge
varies. Generally, I have found, the warmer a cap, the better it works.
Resistors: If a circuit changes current boldly when it warms, then a
marginal resistor could be at fault. Drake did not spend a lot of
money on the quality of their resistors.
Lastly, Soldered connections: Another current sensitive issue, with
cold being the least current and warm the greater current.
I suppose I should include transistors as well as they are affected by
temperature changes, In either state, they may function, but at
different points on the curve.
I hope you can resolve this dilemma. As you have done in the past,
your findings are valuable to those of us who insist on fixing these
radios. As none of us have an infinite time frame to do so, sharing
the results of our victories is a valuable tool in keeping the old
stuff working. Now if anyone has a solution for creaky knees, I would
be interested to know.
this as well.
David Assaf III
W5XU, VP8RXU
|
Richard,
YES, you are da man.? I have learned a lot of valuable info from your posts, keep them coming!
73,
Gary
WB6OGD
?
|
Great Steve.? I love it when we find a solution and save an old Drake!
Darn, I sure wish we could? go down to the store and buy a new tube.? I am suspicious of any tube now, they are all as old and creaky as I am.
73,
Gary
WB6OGD
|
Yup, sometimes you gotta savor the victories!
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Show quoted text
Richard,
YES, you are da man.? I have learned a lot of valuable info from your posts, keep them coming!
73,
Gary
WB6OGD ?
|
Whoa David.
Not sure what this refers to but I am pretty sure we all appreciate your insight and help.
In fooling with broken old radios, nobody has an exact answer, we have to work around the problem till we find it, any knowledge and help
is very much appreciated at least by me!
73,
Gary
WB6OGD
|
David, I agree with Gary¡¯s response. ?I liked your comments.
73, Bill KJ5BNE ++++++++++++++++ Bill Blodgett Arlington, Texas
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Show quoted text
On Jan 6, 2024, at 10:05?AM, wb6ogd <garywinblad@...> wrote:
?Whoa David.
Not sure what this refers to but I am pretty sure we all appreciate your insight and help.
In fooling with broken old radios, nobody has an exact answer, we have to work around the problem till we find it, any knowledge and help
is very much appreciated at least by me!
73,
Gary
WB6OGD
|
Gary WB6OGD
David