Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: FL 2100Z 572B Filament Brightness  (Read 3860 times)
VE3XKD
Member

Posts: 51




Ignore
« on: October 05, 2011, 07:23:09 PM »

Hi

I have picked up a non-working FL 2100ZB that the previous owner stated 'had some problems'. I checked out all of the voltages, and they seem fine. However I notice that the L2, the Choke in the filament supply, had melted insulation and when the Amp is powered on, one tube lights up quite brightly, and the other quite dimmly.  Swapping the tubes around shows that it is not a tube issue but some kind of socket or power supply issue. It looks like someone has previously used a soldering iron on the tube sockets, I am wondering if anyone can help me understand why one tube would glow more brightly than the other. BTW, I tried two sets of tubes, and both sets exhibit the same issue, in the same sockets so I assume that there may be something wrong with the delivery of the filament voltage. Both tubes show about 6.5 volts across the filament pins, but is it possible that the choke wires may have been unsoldered and reversed and that this might cause the problem?
Logged
K8AXW
Member

Posts: 4002




Ignore
« Reply #1 on: October 06, 2011, 09:27:39 AM »

To verify what you are saying:  Let's say the filament of V1 is bright, the filament of V2 is dim.

If you swap the tubes, the V1 tube in the V2 socket is NOW dim?  You measure 6.5VAC on the pins of both tubes?

Did you inspect the insides of the tube "dim" tube socket for black or gray scale or burning??

Did you pull the "dim" tube and squeeze the socket pins slightly and then try it again?

Are you sure the voltages on both tube filament pins are identical?

Reversing the choke wires wouldn't cause this. 



Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #2 on: October 06, 2011, 10:01:06 AM »

The first most likely cause sounds like it would be that the tube (thermionic valve to you over there) sockets are in need of replacement. 

The solder tracks of someone else attempting to resolder the connections is the big clue -- when one finds a tube socket where it appears that the tube heat desoldered connections, simply resoldering the connection is not the cure -- the solder most likely melts due to the heat loss of a high resistance connection in the socket.  The filament pins, with all the current they can carry, are typically the ones that can heat to solder melting temperatures. 

Sometimes one can tighten the socket pins to get a tighter friction grip on the tube pins and this looks like a cure.  From experience, I would call that a "fix" - worth it in an emergency to keep running - but not a "repair" in the sense that the problem is very likely to come up again.  I like to replace the entire set of tube sockets when this is encountered and have never had a callback for the service shop from doing it that way. 


73
Logged
G3RZP
Member

Posts: 4965




Ignore
« Reply #3 on: October 06, 2011, 12:18:17 PM »

I believe your northern neighbours call them 'tubes', too. The original poster is from Canada...

You may well be right about tube sockets. The ones in my 30L1 were shot to hell.....
Logged
W8JI
Member

Posts: 9296


WWW

Ignore
« Reply #4 on: October 06, 2011, 01:15:29 PM »

Usually if socket pins are bad, the filament will be intermittent or varying in brightness.

If it was my amplifier I would disable the HV by removing BOTH HV AC wires and tape them up real good over plastic wire nuts.

Then, only after I was 100% sure HV was off, I would wiggle on the tubes and see if the brightness changed.

The odds of a perfect stable pin resistance are zero. My bet is the sockets are wired wrong.
Logged
N2EY
Member

Posts: 3926




Ignore
« Reply #5 on: October 06, 2011, 02:20:40 PM »

Sockets are bad. Replace them before you do anything else. Wiring is probably bad too.

73 de Jim, N2EY
Logged
K8AXW
Member

Posts: 4002




Ignore
« Reply #6 on: October 07, 2011, 10:00:59 AM »

The filament wiring should be checked, for sure!  I'm betting bad pin contacts. 

It has been my experience that after squeezing the pin contacts and the brightness returns to normal, the socket will have to be replaced.  The pin squeezing thing is just a temporary fix 'just to find out.'
Logged
VE3XKD
Member

Posts: 51




Ignore
« Reply #7 on: October 07, 2011, 10:30:20 AM »

Poblem Solved. It was the filament pins of the tube socket. I sprayed them with contact cleaner, Q-Tips, followed by another spray of more contact cleaner to get any residual cotton out of the way and then squeezed them slightly. Both tubes now light equally.

Many thanks for all the tips and kind help. Will let everyone know how it works when it gets all put back together.

73 VE3XKD
Logged
N2EY
Member

Posts: 3926




Ignore
« Reply #8 on: October 07, 2011, 01:56:46 PM »

Poblem Solved.

I would still replace the sockets, as suggested by K8AXW, KE3WD and possibly others. The contacts may have lost their springiness.

Remember that each of the filament contacts is carrying over 4 amps continuously, so if the connection is the least bit imperfect it can cause all sorts of trouble.

73 de Jim, N2EY
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #9 on: October 07, 2011, 03:25:26 PM »

Replace the sockets and here is why:  

You have evidence that some of the contacts got so hot due to voltage drop across them that they melted the solder underneath.  


That kind of heat, coupled with time, will also most likely soften the temper of the metal that the socket contacts are made from.  Bending or otherwise making those contacts tighter is very likely to prove to be only a temporary fix as the softened metal will soon be right back the way it was when the filaments were not lighting well.  

Have seen it on the repair bench numerous times, complete with all the evidence of someone continuing to try to make the contacts be, well, contacts again.  Eventually such "fixes" result in something happening to the amp that the owner can't fix with the toothpick and that's how they end up on our testbenches $$$.  

My all-out favorite is still the guy who soldered two 3-500Z's into their sockets...


73
Logged
K8AXW
Member

Posts: 4002




Ignore
« Reply #10 on: October 07, 2011, 09:22:45 PM »

XKD:  You're description of the solder joints on the pins could have been the previous owner trying to solve the problem thinking it was poor solder connections.  Since the wire going to the filament pins is probably pretty heavy it required a lot of heat to resolder them. 

This reheating probably just made the pin problem worse.  As 3WD said, "replace them."  It just might save you a LOT of grief later!
Logged
N2EY
Member

Posts: 3926




Ignore
« Reply #11 on: October 08, 2011, 05:21:50 AM »

K8AXW and KE3WD are absolutely right. Replace the sockets! I'll just add this:

What you did may "fix" the problem for a time. But ultimately the contacts may fail again, and when they do, take a tube and/or other stuff with them. Good 4 pin tube sockets are both readily available and inexpensive, good 572Bs are neither.

73 de Jim, N2EY
Logged
VE3XKD
Member

Posts: 51




Ignore
« Reply #12 on: October 09, 2011, 02:59:13 PM »

All

Thanks for the recommendations. I get about 600 watts out on all bands when driven by my TS 940 (Bird wattmeter and dummy load) except 160 and 10, where it's about 450 watts. i will replace the sockets as soon as I can find some on the web.

73

VE3XKD
Logged
W8JI
Member

Posts: 9296


WWW

Ignore
« Reply #13 on: October 09, 2011, 06:05:43 PM »

I'm still very surprised that a socket can cause a consistent steady low voltage, rather than an erratic brightness.
Logged
K8AXW
Member

Posts: 4002




Ignore
« Reply #14 on: October 10, 2011, 08:40:32 AM »

Tom I think he said the voltage was steady at both tubes but one tube filament was dim.... which indicated high resistance between the tube socket and tube pin.
Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!