Topics

TEK514 needs new 5V4G tube


Steve Hendrix
 

Okay, it's a "valve" for our limey friends!

Today I was able to do some more troubleshooting with my dad and my sons, on Dad's TEK514. I took along my thermal camera to help track down the short that was blowing the inlet fuse. Turned out i didn't need it, but it helped confirm. One rectifier tube right next to that monster power transformer started getting extra hot within seconds of power-on, and then started arcing and making a nice arc lamp. I've done a bit of searching and it seems the audiophiles like these tubes; the best I could find was AU$55 for a pair on eBay. Dunno how much shipping would be from down under. Fairly simple fix, to swap out a tube - if that's the only problem. But we checked all the electrolytic caps with an ohmmeter and none seemed to be shorted nor open. Looking for any thoughts on a good source for the tube, and/or whether it's a worthwhile fix.

Steve Hendrix


Roy Morgan
 

Steve,

I would strongly suspect a shorted filter cap in that supply.

If you have an external variable B+ supply, bring the voltage up VERY SLOWLY at the tube cathode while monitoring the current. (Scope power off)

Roy Morgan
K1LKY Western Mass

On Jan 26, 2020, at 6:10 PM, Steve Hendrix <SteveHx@...> wrote:

Okay, it's a "valve" for our limey friends!

... One rectifier tube right next to that monster power transformer started getting extra hot within seconds of power-on, and then started arcing and making a nice arc lamp. ...


Richard Solomon <dickw1ksz@...>
 

This may be blasphemy, but you
could replace the rectifier tube with
a couple of diodes.

You may need a small resistance to
adjust for the lower voltage drop in
the diodes.

73, Dick, W1KSZ

On Sun, Jan 26, 2020 at 4:34 PM Roy Morgan <k1lky68@...> wrote:

Steve,

I would strongly suspect a shorted filter cap in that supply.

If you have an external variable B+ supply, bring the voltage up VERY
SLOWLY at the tube cathode while monitoring the current. (Scope power off)

Roy Morgan
K1LKY Western Mass

On Jan 26, 2020, at 6:10 PM, Steve Hendrix <SteveHx@...>
wrote:

Okay, it's a "valve" for our limey friends!

... One rectifier tube right next to that monster power transformer
started getting extra hot within seconds of power-on, and then started
arcing and making a nice arc lamp. ...




Harvey White
 

Considering the cost for a 5V, which IIRC is a rectifier with an indrectly heated cathode (*many* years ago).  You might want to take some silicon rectifiers and put them in, substituting for the 5V4.  You may get a bit hotter B+ out of the combo, and I've heard that some people put some fairly large wattage resistors in series to limit the surge, but I'd certainly consider that fix for AU $45.00.  (which even at the last rate I remember is USD22.00 and that's a big bunch).  I suspect that 1N4006 might be a good candidate.

If you had an octal tube base you could build it into that.

Harvey

On 1/26/2020 6:10 PM, Steve Hendrix wrote:
Okay, it's a "valve" for our limey friends!

Today I was able to do some more troubleshooting with my dad and my sons, on Dad's TEK514. I took along my thermal camera to help track down the short that was blowing the inlet fuse. Turned out i didn't need it, but it helped confirm. One rectifier tube right next to that monster power transformer started getting extra hot within seconds of power-on, and then started arcing and making a nice arc lamp. I've done a bit of searching and it seems the audiophiles like these tubes; the best I could find was AU$55 for a pair on eBay. Dunno how much shipping would be from down under. Fairly simple fix, to swap out a tube - if that's the only problem. But we checked all the electrolytic caps with an ohmmeter and none seemed to be shorted nor open. Looking for any thoughts on a good source for the tube, and/or whether it's a worthwhile fix.

Steve Hendrix



 

Hi Steve,
Is there any reason you can't buy a 5V4G? There are 123 of them on eBay at the moment. Prices start at $12 for them and go up.
I can test it for you to confirm its good if want to send it to me.
Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Richard Solomon
Sent: Sunday, January 26, 2020 4:33 PM
To: TekScopes <TekScopes@groups.io>
Subject: Re: [TekScopes] TEK514 needs new 5V4G tube

This may be blasphemy, but you
could replace the rectifier tube with
a couple of diodes.

You may need a small resistance to
adjust for the lower voltage drop in
the diodes.

73, Dick, W1KSZ

On Sun, Jan 26, 2020 at 4:34 PM Roy Morgan <k1lky68@...> wrote:

Steve,

I would strongly suspect a shorted filter cap in that supply.

If you have an external variable B+ supply, bring the voltage up VERY
SLOWLY at the tube cathode while monitoring the current. (Scope power
off)

Roy Morgan
K1LKY Western Mass

On Jan 26, 2020, at 6:10 PM, Steve Hendrix
<SteveHx@...>
wrote:

Okay, it's a "valve" for our limey friends!

... One rectifier tube right next to that monster power transformer
started getting extra hot within seconds of power-on, and then started
arcing and making a nice arc lamp. ...







--
Dennis Tillman W7PF
TekScopes Moderator


Chuck Harris
 

Electrolytic caps get into a condition where they
become lower voltage versions of themselves.

An ohmmeter tests at 1.5V in most cases, and 9V in
VOM's. Using one to test a 400V capacitor is less
than worthless.

-Chuck Harris

Steve Hendrix wrote:

Okay, it's a "valve" for our limey friends!

Today I was able to do some more troubleshooting with my dad and my sons, on Dad's TEK514. I took along my thermal camera to help track down the short that was blowing the inlet fuse. Turned out i didn't need it, but it helped confirm. One rectifier tube right next to that monster power transformer started getting extra hot within seconds of power-on, and then started arcing and making a nice arc lamp. I've done a bit of searching and it seems the audiophiles like these tubes; the best I could find was AU$55 for a pair on eBay. Dunno how much shipping would be from down under. Fairly simple fix, to swap out a tube - if that's the only problem. But we checked all the electrolytic caps with an ohmmeter and none seemed to be shorted nor open. Looking for any thoughts on a good source for the tube, and/or whether it's a worthwhile fix.

Steve Hendrix




Steve Hendrix
 

At 2020-01-26 09:01 PM, Dennis Tillman W7PF wrote:


Is there any reason you can't buy a 5V4G? There are 123 of them on eBay at
the moment. Prices start at $12 for them and go up.
I can test it for you to confirm its good if want to send it to me.
Odd, I already looked. Out of the first hundred or so hits, I found only two, and both were way more expensive than that. I'll have another look, and try some different search terms so i don't get 4WD nuts etc. Thanks for the pointer.

Steve Hendrix


Steve Hendrix
 

At 2020-01-27 12:07 AM, Chuck Harris wrote:


Electrolytic caps get into a condition where they
become lower voltage versions of themselves.

An ohmmeter tests at 1.5V in most cases, and 9V in
VOM's.  Using one to test a 400V capacitor is less
than worthless.
I was wondering about that, because I rarely use electrolytics anywhere above about 24V in my work. But would a shorted cap cause the rectifier tube ahead of it to arc over? I suppose it's possible that extra heat generated in the tube could soften or melt some of the internal structures, causing spacing to shrink as something bends. In that case, it seems to me that the tube is now bad, but the root cause of a shorted cap still needs to be fixed. Would you suggest replacing all the big electrolytics first? Since Tek seemed to like stocking only 20uF caps (which were called 20mF in those days), they used as many as 6 in parallel in some places. The physical connection methods used are beautiful artwork, but makes it a bit tricky mechanically to replace the caps as they're used as standoffs to hold everything else.

Steve Hendrix


Chuck Harris
 

When presented with a dead short, a 5V4 will make
quite a light show as it strips the coating off its
cathode. An already gassy 5V4 will make a similar
light show. Rarified air not being as good of an
insulator as a hard vacuum.

Capacitors that are old enough to have a 5V4 are usually
old enough to have corrosive electrolyte that will slowly
eat the oxide dielectric layer from the aluminum foil
plates. A 514 is definitely old enough to have this
problem. Most, if not all, twist lock electrolytics are
old enough to have this problem.

The safe answer is to rebuild the oxide layer (reform) the
capacitors before applying full voltage to the capacitors.

Some like to do this by using a variac, but although it
is better than brute force turning the juice on, it isn't
optimal. The problem with using a variac is the voltage
is lower (good), but the power available to heat the
capacitor is just as high as always. And, a most tek tube
scopes have thermal relays that turn on the HV, which wont
reliably switch at lower than full voltage.

Optimal is to reform the same way the factory did in the
first place, which is to apply full voltage through a
1-10K power resistor for 1 hour.

-Chuck Harris

Steve Hendrix wrote:

At 2020-01-27 12:07 AM, Chuck Harris wrote:


Electrolytic caps get into a condition where they
become lower voltage versions of themselves.

An ohmmeter tests at 1.5V in most cases, and 9V in
VOM's.  Using one to test a 400V capacitor is less
than worthless.
I was wondering about that, because I rarely use electrolytics anywhere above about 24V in my work. But would a shorted cap cause the rectifier tube ahead of it to arc over? I suppose it's possible that extra heat generated in the tube could soften or melt some of the internal structures, causing spacing to shrink as something bends. In that case, it seems to me that the tube is now bad, but the root cause of a shorted cap still needs to be fixed. Would you suggest replacing all the big electrolytics first? Since Tek seemed to like stocking only 20uF caps (which were called 20mF in those days), they used as many as 6 in parallel in some places. The physical connection methods used are beautiful artwork, but makes it a bit tricky mechanically to replace the caps as they're used as standoffs to hold everything else.

Steve Hendrix




Colin Herbert
 

You could try lashing up a solid-state substitute with a couple of diodes and a series voltage dropper resistor having an appropriate wattage. It may be a "lash-up", but it would probably serve to prove the point and keep the scope working until a proper replacement can be found.

"Ask Jan First" has some at 27 Euro plus shipping:

http://www.fragjanzuerst.de/eindex.htm

Also Langrex in the UK have some Russian-made ones at £14.50:

https://www.langrex.co.uk/?s=5V4G&post_type=product

Good Luck, Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Steve Hendrix
Sent: 26 January 2020 23:10
To: TekScopes@groups.io; TekScopes@groups.io
Subject: [TekScopes] TEK514 needs new 5V4G tube

Okay, it's a "valve" for our limey friends!

Today I was able to do some more troubleshooting with my dad and my sons, on Dad's TEK514. I took along my thermal camera to help track down the short that was blowing the inlet fuse. Turned out i didn't need it, but it helped confirm. One rectifier tube right next to that monster power transformer started getting extra hot within seconds of power-on, and then started arcing and making a nice arc lamp. I've done a bit of searching and it seems the audiophiles like these tubes; the best I could find was AU$55 for a pair on eBay. Dunno how much shipping would be from down under. Fairly simple fix, to swap out a tube - if that's the only problem. But we checked all the electrolytic caps with an ohmmeter and none seemed to be shorted nor open. Looking for any thoughts on a good source for the tube, and/or whether it's a worthwhile fix.

Steve Hendrix


Dave Trainor
 

A method to deal with that used by some ham radio restorations is to use a
Dremel tool with a tiny cut off wheel and slice the can open about 1/2²
from the terminal end, clean out the inside, and clean out the terminals
now exposed on the inside.

Now you can easily place a new snap mount type cap on the terminals and
solder it in place. You can leave it that way - or you can place the
cleaned out can over the top and use some silver aluminum furnace duct
tape sold at the big box Home Depot stores and if you are careful with the
tape and positioning and were careful with the Dremel to make a nice cut -
it looks almost like a new can cap.

Its not as hard as it sounds, and keeps original appearance.
Especially for the ones that are used as you say to mount other parts by
having a specific base design and terminals. Essentially you are putting a
new cap in the old case.

Hope this help - good luck getting it going - and yes I agree the tube is
probably bad now. If the cap is shorted on the output it will draw
current, way too much current thru the rectifier and certainly could cause
the tube to self destruct, do the same thing with a solid state diode say
rated 500ma, and draw a couple amps thru it, it will get hot and release
its magic smoke. Same thing with a vacuum tube rectifier.

But 5V4G tubes are not hard to find. I would personally find a tube and
not use solid state, you will increase voltages with modern diodes because
there is a higher voltage drop with the tube. If the caps are good a 5V4G
will last a very long time.

73 - Dave N8ZFM


On 1/27/20, 6:12 AM, "TekScopes@groups.io on behalf of Steve Hendrix"
<TekScopes@groups.io on behalf of SteveHx@...> wrote:

At 2020-01-27 12:07 AM, Chuck Harris wrote:


Electrolytic caps get into a condition where they
become lower voltage versions of themselves.

An ohmmeter tests at 1.5V in most cases, and 9V in
VOM's. Using one to test a 400V capacitor is less
than worthless.
I was wondering about that, because I rarely use electrolytics anywhere
above about 24V in my work. But would a shorted cap cause the rectifier
tube ahead of it to arc over? I suppose it's possible that extra heat
generated in the tube could soften or melt some of the internal
structures, causing spacing to shrink as something bends. In that case,
it seems to me that the tube is now bad, but the root cause of a shorted
cap still needs to be fixed. Would you suggest replacing all the big
electrolytics first? Since Tek seemed to like stocking only 20uF caps
(which were called 20mF in those days), they used as many as 6 in
parallel in some places. The physical connection methods used are
beautiful artwork, but makes it a bit tricky mechanically to replace the
caps as they're used as standoffs to hold everything else.

Steve Hendrix




--
This message was scanned by ESVA and is believed to be clean.
Click here to report this message as spam.
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Hi Steve,
I was looking on the US eBay. I have seen evidence that some other countries have different listings. I don't know why and I may have been partially confused by the language difference. Here are a few examples of what I saw today
312970721548 $19.00 2 QTY JAN CHS 5V4G rectifier tubes - TV-7A/U tested SYLVANIA / KEN-RAD
161828569368 $12.55 1PCS - 5V4G (5V4) Vacuum Tube - NOS
163911281558 $14.40 5C4S ☆1pcs☆ (5Ц4С,5V4G, 6Z30, 5Z4G) KENOTRON NEVZ 1956 NOS FIGURED FLASK
114066265864 $15.00 (Make Offer or Buy It Now) Strong Emerson by Sylvania FAT BOTTLE Black Plate Bottom D Getter 5V4G Tube

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Steve Hendrix
Sent: Monday, January 27, 2020 3:00 AM
To: TekScopes@groups.io; TekScopes@groups.io
Subject: Re: [TekScopes] TEK514 needs new 5V4G tube

At 2020-01-26 09:01 PM, Dennis Tillman W7PF wrote:


Is there any reason you can't buy a 5V4G? There are 123 of them on
eBay at the moment. Prices start at $12 for them and go up.
I can test it for you to confirm its good if want to send it to me.
Odd, I already looked. Out of the first hundred or so hits, I found only two, and both were way more expensive than that. I'll have another look, and try some different search terms so i don't get 4WD nuts etc. Thanks for the pointer.

Steve Hendrix





--
Dennis Tillman W7PF
TekScopes Moderator


Dave Trainor
 

Steve, make sure you fix the issue with your filter caps before you plug
in a new 5V4G tube or you will repeat the destruction of your new tube.
The tube failed for a reason, be sure you correct that first. Sure you
know that, but had to say it.

73 - Dave N8ZFM

On 1/27/20, 3:58 PM, "TekScopes@groups.io on behalf of Dennis Tillman
W7PF" <TekScopes@groups.io on behalf of @Dennis_Tillman_W7pF> wrote:

Hi Steve,
I was looking on the US eBay. I have seen evidence that some other
countries have different listings. I don't know why and I may have been
partially confused by the language difference. Here are a few examples of
what I saw today
312970721548 $19.00 2 QTY JAN CHS 5V4G rectifier tubes - TV-7A/U
tested SYLVANIA / KEN-RAD
161828569368 $12.55 1PCS - 5V4G (5V4) Vacuum Tube - NOS
163911281558 $14.40 5C4S ☆1pcs☆ (5Ц4С,5V4G, 6Z30, 5Z4G) KENOTRON NEVZ
1956 NOS FIGURED FLASK
114066265864 $15.00 (Make Offer or Buy It Now) Strong Emerson by
Sylvania FAT BOTTLE Black Plate Bottom D Getter 5V4G Tube

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Steve
Hendrix
Sent: Monday, January 27, 2020 3:00 AM
To: TekScopes@groups.io; TekScopes@groups.io
Subject: Re: [TekScopes] TEK514 needs new 5V4G tube

At 2020-01-26 09:01 PM, Dennis Tillman W7PF wrote:


Is there any reason you can't buy a 5V4G? There are 123 of them on
eBay at the moment. Prices start at $12 for them and go up.
I can test it for you to confirm its good if want to send it to me.
Odd, I already looked. Out of the first hundred or so hits, I found only
two, and both were way more expensive than that. I'll have another look,
and try some different search terms so i don't get 4WD nuts etc. Thanks
for the pointer.

Steve Hendrix





--
Dennis Tillman W7PF
TekScopes Moderator




--
This message was scanned by ESVA and is believed to be clean.
Click here to report this message as spam.
http://h0stname/cgi-bin/learn-msg.cgi?id=BB68C2867B.74696


Stephen Hanselman
 

I’v got to figure out where I left my spread sheets, but I’m fairly certain I have the tube probably NOS. If I do it will be cost of shipping

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Jan 27, 2020, at 12:58, Dennis Tillman W7PF <@Dennis_Tillman_W7pF> wrote:

Hi Steve,
I was looking on the US eBay. I have seen evidence that some other countries have different listings. I don't know why and I may have been partially confused by the language difference. Here are a few examples of what I saw today
312970721548 $19.00 2 QTY JAN CHS 5V4G rectifier tubes - TV-7A/U tested SYLVANIA / KEN-RAD
161828569368 $12.55 1PCS - 5V4G (5V4) Vacuum Tube - NOS
163911281558 $14.40 5C4S ☆1pcs☆ (5Ц4С,5V4G, 6Z30, 5Z4G) KENOTRON NEVZ 1956 NOS FIGURED FLASK
114066265864 $15.00 (Make Offer or Buy It Now) Strong Emerson by Sylvania FAT BOTTLE Black Plate Bottom D Getter 5V4G Tube

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Steve Hendrix
Sent: Monday, January 27, 2020 3:00 AM
To: TekScopes@groups.io; TekScopes@groups.io
Subject: Re: [TekScopes] TEK514 needs new 5V4G tube

At 2020-01-26 09:01 PM, Dennis Tillman W7PF wrote:


Is there any reason you can't buy a 5V4G? There are 123 of them on
eBay at the moment. Prices start at $12 for them and go up.
I can test it for you to confirm its good if want to send it to me.
Odd, I already looked. Out of the first hundred or so hits, I found only two, and both were way more expensive than that. I'll have another look, and try some different search terms so i don't get 4WD nuts etc. Thanks for the pointer.

Steve Hendrix





--
Dennis Tillman W7PF
TekScopes Moderator



Steve Hendrix
 

Wow! The collective knowledge and willingness to help here are amazing! It will be a week or two before I can act on all this, other than to get some parts ordered and on the way.

I'm thinking I like the idea of cutting off the tops of the caps and just soldering a "modern" electrolytic in place of the old cap. Never having cut open an electrolytic before, I'm not sure what to expect. How much messy gunk am I going to get into? Will the metal on the inside be reasonably receptive to solder, on the terminals I need to contact? Anything else I should know, before trying my hand with a Dremel?

Steve Hendix


David Holland
 

Not too bad. They're not liquid. More like damp. Stinky too. There may
be (solid) tar as well.

Nothing solderable inside. I usually cut near bottom. Clean out guts.
Drill through holes to permit new radial caps leads to be poked through the
holes and then soldered to the terminals outside. Leave the terminals
attached (obviously)

I then reattach the top part with aluminum tape as previously mentioned.

On Mon, Jan 27, 2020, 9:32 PM Steve Hendrix <SteveHx@...>
wrote:

Wow! The collective knowledge and willingness to help here are amazing! It
will be a week or two before I can act on all this, other than to get some
parts ordered and on the way.

I'm thinking I like the idea of cutting off the tops of the caps and just
soldering a "modern" electrolytic in place of the old cap. Never having cut
open an electrolytic before, I'm not sure what to expect. How much messy
gunk am I going to get into? Will the metal on the inside be reasonably
receptive to solder, on the terminals I need to contact? Anything else I
should know, before trying my hand with a Dremel?

Steve Hendix



Sent via mobile annoyance thing. Please pardon any typos.


Chuck Harris
 

I do it much the same way. Copper, or steel wouldn't last
very long in the electrolyte before it corroded away, so it
is only aluminum in the can.

A hack saw works fine too... if you are careful.

-Chuck Harris

David Holland wrote:

Not too bad. They're not liquid. More like damp. Stinky too. There may
be (solid) tar as well.

Nothing solderable inside. I usually cut near bottom. Clean out guts.
Drill through holes to permit new radial caps leads to be poked through the
holes and then soldered to the terminals outside. Leave the terminals
attached (obviously)

I then reattach the top part with aluminum tape as previously mentioned.

On Mon, Jan 27, 2020, 9:32 PM Steve Hendrix <SteveHx@...>
wrote:

Wow! The collective knowledge and willingness to help here are amazing! It
will be a week or two before I can act on all this, other than to get some
parts ordered and on the way.

I'm thinking I like the idea of cutting off the tops of the caps and just
soldering a "modern" electrolytic in place of the old cap. Never having cut
open an electrolytic before, I'm not sure what to expect. How much messy
gunk am I going to get into? Will the metal on the inside be reasonably
receptive to solder, on the terminals I need to contact? Anything else I
should know, before trying my hand with a Dremel?

Steve Hendix



Sent via mobile annoyance thing. Please pardon any typos.



Mlynch001
 

I restore those can type caps by putting them in a lathe, cut the rolled edge off, remove the guts, save the metal grounding ring and solder lug ring from the old cap, clean out the inside, 3D print a spacer to hold the required radial cap centered with airspace around the outside (this keeps the new cap from flopping around inside the can), 3D print a bottom plate of suitable dimensions to hold the old solder lug, place the new cap inside with the leads protruding from the appropriate holes, re-roll the lower edge of the can to secure the assembly and then solder the leads. Makes a perfect OEM original looking replacement part with a modern cap inside.

--
Michael Lynch
Dardanelle, AR


Dave Trainor
 

I have had luck then the mallory¹s I have done this with had black tar in
the bottom, with the aluminum foil tape probably point welded to it, then
the solid wet cap above, once all cleaned out I had the pins that were in
tar to protect them able to be soldered to.

It all cleaned out easily. But make sure you leave a lip at the bottom of
the case when you cut so you got a upper and lower area for the final
sealing tape to stick to to reassemble. Cut too close to the bottom and no
place for that end to stick, so I usually stay about 1/2 inch up.

If there is not a term, punching a hole thru for a wire for the new cap is
sure the way to go.

I think you can get longer rated hours in the snap in variety vs a redial,
if I can actually believe the specs as published. Far as I know there are
none made anywhere but Asia now, no matter the name brand of manufacturer.
I try to find the ones with the longest listed expected lifetime hours on
Mouser. And a name that I have at least heard of, Panasonic, Sprague,
Vishay etc.

Loved the explanation from the guy that uses a lathe, and 3d printing and
literally makes a new sealed can, that dude, is dedication in restoration.
Beyond what I could do but - respect your way sir.

73 - Dave N8ZFM


On 1/27/20, 10:04 PM, "TekScopes@groups.io on behalf of Chuck Harris"
<TekScopes@groups.io on behalf of cfharris@...> wrote:

I do it much the same way. Copper, or steel wouldn't last
very long in the electrolyte before it corroded away, so it
is only aluminum in the can.


David Holland
 

On Mon, Jan 27, 2020 at 10:05 PM Chuck Harris <cfharris@...> wrote:

A hack saw works fine too... if you are careful.
If you completely remove the cap (I usually do), a copper tubing
cutter works wonderfully....

One of these things:
https://www.harborfreight.com/tubing-cutter-40913.html (Yeah, I
know, Harbor Freight, but they did have a convenient picture.)

David