Help Amp Supply LK-550 Loose tube socket

[rich]

Help   Amp Supply LK-550 Loose tube socket
I want to tighten up the the tube socket, because tube is very loose in socket and you have to push it around to make contact.
I see its on a sub chassis. Do I have to take off the whole sub chassis to get at it?
Thanks for your time.
Rich KF2GG

[Ralph W3GL]

   Short answer:  YES!

    As you needed to actually ask this question, I would suggest
    you contact a professional to take care of the problem with
    that box...

    Either that or run the amp with the two remaining 3-500's that are lit.

    The socket problem is because of insufficient air flow across the filament
    pins under that sub chassis.

   That's not a device for novice fingers... Put the cover back on and bring
    it to the professional that knows about 3500 volt circuity...


    PS;  While I have no connection to the following, Land Air over in Queens
    might be convenient for you and perhaps we  might drop two stones with
    one bird

[K1JJ]

Rich,

Give Amp Supply a call on the phone and ask for tech support - axe them about it.

As long as you unplug the amplifier and discharge the capacitors with a grounding strap, you should be able to get in there and tighten the loose screws supporting the socket.

If the movement is due to the socket pins themselves opening up due to heat, then you will probably need to replace the socket itself. The socket pins are annealed and heat treated to create a springy action. Once they are overheated the spring action dies and you have intermitent filament pin contact.

As Ralph said, the core problem may be due to air flow problems in the first place. You can describe the situation to Amp supply once you see what's in there and they should be able to advise further. Good luck.

Tom, K1JJ

[Ralph W3GL]

    Tom,

     A bit of history...

     Amp Supply has not been around for over 15 or so years...
    
     Denny Had  (Cary Audio in NC), W4USR, retired a couple years back
     and his former service manager at Amp Supply that took care of problems
     with the product line went SK  so there is no one looking after the Amp
     Supply line any more...

     He had a supply of the baffles and modified sub-chassis for the
     LK500 series amps on hand and performed whatever mods to them
     for a fat fee

     The sockets for the three 3-500's each have 4 - 8/32 screws with
     star locks on the nuts so its unlikely the socket its-self is loose
     on the sub-chassis.  

     All the big Amp Supply amplifiers suffered from poor under chassis
     air flow.   They added a baffle and punched a row of holes in the sub-
     chassis to attempt to mitigate the problems in the later units but that
     never fully took care of the air flow problem so they put in a bigger
     fan with higher capacity flow; still lacking the proper cooling.

     I would put money on Riches' problem being filament pin fatigue...


     PS;   I have one of the early unmodified LK500 series amps sitting
             on the shelf to be modified if I ever find the right person willing
             to do the deed...
 
    

[K1JJ]

Hi Ralph,

Hmmm.... that's not the same company that MFJ bought?  Must be some other company.

Yes, I've known Denny since the late 70's. The last I knew he was building and selling those $$$$ tube audiophile amps.

Anyway, I've had the same problem with a commercial 3-500Z amp I had. It had no chimneys and kept melting the solder in the fil pins and ruining the socket pins from heat. I finally went to great pains and build a sub chassis with glass chimneys and new sockets. The amp runs beautifully now and even the plates run cooler.

I have a shelf in my cellar of "dumb-ass" tubes. I call them that cuz I was such a dumb-ass when it came to proper cooling over the years. There are maybe five there with all kinds of black marks and some with holes in the plates. (External anode tubes)   I had tried to keep air to a minimum to reduce blower noise. With some I sucked air OUT of the tops instead of properly blowing air directly in the fils on the way to the anodes at the top.

Bottom line is now all my amps have tremendous air overkill with direct filament air. I have a rule that I should be able to hold my fingers on the fil structure without discomfort after running the tube up to temp. With enuff air it can be done. Haven't lost a tube since.

Hopefully Rich will do some detective work and find what needs to be done with his amp. Direct air on the fil and bottom seals is a good start. Chimneys are the second step for a final  solution.

T

[KM1H]

   Tom,

     A bit of history...

Distorted history

     Amp Supply has not been around for over 15 or so years...

More like 20 years when Denny got caught dipping his wick a second time.
    
     Denny Had  (Cary Audio in NC), W4USR, retired a couple years back
     and his former service manager at Amp Supply that took care of problems
     with the product line went SK  so there is no one looking after the Amp
     Supply line any more...

He was still building a few LK-800C's to order about 2 years ago, its been about 6 months since we last spoke. Bill Edwards, K4BWC, was the Service Mgr who later started Omega Electronics. I was a consultant to AS for the LK-750 and 780 and Bill and I were good friends for 25 years.  I have been doing the full line of Dentron and Amp Supply amps for decades and Billy and I often swapped parts and customers who didnt want to ship.


     He had a supply of the baffles and modified sub-chassis for the
     LK500 series amps on hand and performed whatever mods to them
     for a fat fee

     The sockets for the three 3-500's each have 4 - 8/32 screws with
     star locks on the nuts so its unlikely the socket its-self is loose
     on the sub-chassis.  

     All the big Amp Supply amplifiers suffered from poor under chassis
     air flow.

Thats a bunch of bull. Ive been running a LK-500ZC since 1986 and never had any problems and that includes a decade of serious contesting. Ive had many of them and the 550 in here and never a socket or tube problem from air flow. The LK-800 uses a premium EBM-Papst fan under the tube chassis and it produces so much air in the H position that the L position is fine for most use with a simple resistor change.

Most of the air hype is due to the CBers who use those amps and Bill did a lot of work for that bunch.


   They added a baffle and punched a row of holes in the sub-
     chassis to attempt to mitigate the problems in the later units but that
     never fully took care of the air flow problem so they put in a bigger
     fan with higher capacity flow; still lacking the proper cooling.


All the ones Ive seen after 1986 production have that mod


     I would put money on Riches' problem being filament pin fatigue...


Certainly possible but I wouldnt condemn a companys products on heresay or an occassional problem. Heath also had an identical problem yet the air was adequate as long as the fan was running at speed and the intake wasnt blocked.

Way too many hams want silent amps and dont want to run the AS fans on the H position. Early models were single speed with a series resistor that I always lower the value to give adequate air for all but serious contesting. I also add a 2 speed switch to many.


     PS;   I have one of the early unmodified LK500 series amps sitting
             on the shelf to be modified if I ever find the right person willing
             to do the deed...
 
    

Tom, MFJ bought Ameritron.

Carl

[rich]

Thanks for all your help. I of course knew what to do not to kill myself.
I'am always careful going into any amp. I pulled the tubes out and found that the tube that was loose had thinner pins on the end of it.
So I switched the tubes around and that fixed the problem. Into a dummy load 100watts in gets 1600 out.
Thanks all Rich

[K1JJ]

Good, Rich.

OK on poor tube pin contact due to a thinner set of fil pins on one tube. If that tube goes intermitent again, you could always coat the tube fil pins with solder to build them up thicker for better socket pin contact.

When my 3-500Z lost it's fil pin solder due to excessive heat, I was able to solder the pins and leads back again. What I did was put a small aluminum clamp/clip heatsink on one pin and then heat the pin end with a propane torch. I was able to fix both pins without seal damage. The key is to clean/sand the pin well and put the heat on quickly and for a short second or two. Add the solder at the same time. It's better to have a short blast of heat than a long drawn-out session which may work it way into the glass seals and break.

Another possibility to to add the solder to the socket pins instead, though I think the tube pins are a better place for mating contact geometry.

T

[W3SLK]

I thought the SB-220's were famous for 'lack-of-air' around the pins of the 3-500Z's???

[KM1H]

Only when the builder didnt pay attention to the line that specifically said how/where to position the fan. Also when they dont lube it for 30 years.

[Opcom]

Agreed about neglect, and you guys probably know better, but I have never bought leenyars that do not have a cooling system that I think is equivalent to, or better than, the tube manufacturers' reccommendations. That might be why I have not bought any leenyars. The NCL-2000 is an exception as it was offered for $75. Its cooling is OK for SSB all day, but only about 1/2 rate for long sessions on AM or as part of an RF generator. OK for Heathkit as 3-500's cost $100 so if you burn one big deal. 8122's cost $400.