Amp Supply Company

[W1AEX]

I'm just curious if anyone knows (off the top of their head) when the Amp Supply Company stopped producing their line of HF amplifiers. Were they still producing the LK-550 amp in 2005? Everything I can find through searches indicates that these amps were built in the 80's and 90's and I can't verify that they were still being built as late as 2005.

Thanks for any insight you can offer!

Rob W1AEX

[ke7trp]

None of mine say anything past 2003.  Most where built in the late 80s.   After Dentron closed, Amp supply started.  Then it was ameritron.

c

[W1AEX]

Thanks Clark. From what you have told me here and in PM, and from what I have picked up from others, the pieces produced at the end are a real crap shoot. I think I'll steer clear of the item I was looking at!

73,

Rob

[KM1H]

Ive been running a LK-500ZC since 1986, was a dealer for the company, and did some consulting on updating some older designs and the new LK-750 and LK-780. They went under around 1990 when the owner got caught with his secretary with his pants down. He was a prototype for Clinton He pulled the same trick at Dentron with an earlier wife nailing him.  However he is still around fleecing audiophools as Cary Audio Design and making a bundle. I talk to him on the phone a few times a year.

I dont like the NT models unless you stay on one mode and dont QSY much. Ive been converting many to regular Tune models for customers.

The LK-550 isnt my favorite as it can get a bit tempermental on 10/12/15M and the cooling isnt optimized. Its an OK casual amp but I wouldnt run full bore in a contest.

All their amps except the sweep tube model bring big prices on Fleabay and the various versions of the LK-800 go for more than original. Cary will custom build an 800C for you with three 3CPX800A7's and a dual voltage PS giving a good 5KW key down.

Carl

[W1AEX]

The LK-550 isnt my favorite as it can get a bit tempermental on 10/12/15M and the cooling isnt optimized. Its an OK casual amp but I wouldnt run full bore in a contest.

Hi Carl,

Thanks for the added information. I have not come across too many negative comments from owners of these amps. I was kind of surprised when looking at the LK-550 finals that they were not using chimneys. In fact, several owners indicated that a repeating issue was that the tube pins would now and then unsolder themselves when high duty cycle modes were used. I would imagine that the PA compartment would get kind of toasty, even with the "wall of fans"!

Rob W1AEX

[K1JJ]

Hola Rob -

Looks like everyone is building up a linear "Tina-crusher" for this fall.... :-)

The air flow:  I would drill a circle of 3/8" holes around the sockets and add a chimney to each tube. Mount a blower underneath and possibly add cabinet pedestal legs for blower cage clearance.  Or mount the blower on the back and add some ducting to direct the air efficiently to the sockets. Think it out. You might need to remount one of the tubes to provide adjacent chimney clearance.

I have an old Sigma 3000D, a pair of 3-500Z's that would leak out solder from the fil pins. They also used a homo-fan across the tubes. What a bunch of *****. I added chimneys and a squirrel cage blower. Now with the air past the seals and thru the chimneys, the amp runs cool and puts out more power safely.

You can figure out a way to do it, even if it means moving a few parts around, OM.

T

[ke7trp]

You dont need chimneys in that amp and the cooling is plenty.  Look at the picture. The fans are lowered down so air runs across the pins and seal where it counts. 

I have the LK800 here with the Dual volt supply. Its a hoot. This one also has the 17 position! band switch as it was a military version.

My view on these amps is that most are low cost ham amps.  The LK500 is lightweight everywhere. Cheap. Low power. The 550 is a bit better and you get that other tube. The trouble with most is that because of this lightweight design, they fail. Then some nitwit comes along and repairs the amp "his way".  The last one LK500 I had was this way.

C

[WQ9E]

I recall in some amps the pin unsoldering problem was traced to poor socket contacts causing extreme localized heating at the contact point.  So check the socket if you have experienced that problem.   Although a better air cooling system is a good idea it may be masking the root cause of the pin problem.

[K1JJ]

It's a matter of degree. Sure you can get away with most anything, depending on how hard the tube is run. Some ham amps run fans off the side and seem to last fine. I wonder how many commercial amps do it, though.

However, chimneys are a good idea with any 4-400A, 4-1000A, 3-500Z, 3-1000Z type series tube.  Pressurized, forced air is  what Eimac recommends in their data sheets. The most efficient and encompassing way to do this is with a chimney.

I've run tests with a fan blowing air from ONE direction across the tubes and found the glass 180 degrees opposite the side facing the fan to be significantly hotter.  I've also tested the difference between air blown directly on the fils compared to air that comes in from one side and found the same general results. An even 360 degree air flow on all tube parts is ideal. This means the best air flow is forced through the bottom onto the seals and then follows a smooth, 360 degree flow up across the full glass envelope out the top.

But again, in the other extreme, I know some who don't run anode air at all on 4X1's (except for the pins) and they seem to last a long time when run modestly.  I sometimes wonder which is worse-  even thermal expansion, even though very hot OR uneven thermal expansion when air comes in from one side only - I dunno.  I'm not sure the seals like one side of the tube structure being hotter than the other.


I did recently lose an external anode final because I had uneven fil and seal cooling as described above. Adding the air directly onto the fils and bottom seals kept them cool all around. That costly mistake shook me up and since I've gone overboard with cooling - always using chimneys and strong air flow on all rigs here.

T  

[ke7trp]

Agreed.  Better yes, But on that amp thats going to be used on SSB or light AM as designed. Its fine the way it is.  If your going to put more power out of that unit and use it for heavy max carrier AM, Then it probably should be modified. It was never intended for that though.

On my new Transmitter, We used 304Tls and they do not require Chimneys. They are pyrex and are made to run hot. Just a fan blowing across the seals is all that is needed.  The 4-400s are not using Chimneys either. Just a blower under the deck.  Some builders wont run Chimneys. Lots of BC rigs ran 4-400s with no chimneys and that is probably the reason.

I cant wait for the winter to come around so I can hear you guys again Tom!

[W1AEX]

The air flow:  I would drill a circle of 3/8" holes around the sockets and add a chimney to each tube. Mount a blower underneath and possibly add cabinet pedestal legs for blower cage clearance.  Or mount the blower on the back and add some ducting to direct the air efficiently to the sockets.

Hi Tom!

Yah, I've used a variation of that FB design on the 4-400 x 833's PB rig. I drilled holes around the tube socket for the 4-400, pressurized the lower chassis with a squirrel cage fan, and had a large fan pulling air out of the back of the upper chassis area directly behind the tube. I never had a failure with that setup, and I used to run that final at 3KV and 300ma and see +600W output while pounding away with the 833 modulators. My 4-400 tubes were all broadcast pulls (free!) from WDRC, so they had a lot of PB hours on them!

[K1JJ]

Clark: Nice looking rigs in that second pic. Excellent cosmetics.

Yes, the "radiation cooled" tubes like the 304TL, 750TL, etc need no air on the anode glass area, though some pin/seal cooling is a good idea.

Yep, I'm having 75M withdrawals now too. Can't wait to give it a go again out west for youse guys.



Rob: WDRC?  They  used to be about 1/2 mile away when I lived in Windsor as a Novice. They came thru my electronic devices big time. I had a tunable crystal set and that's all I could hear.   Maybe big boss jock Dick Robinson modulated your tubes. Though that was in the 60's.... :-)

That was a good way to get tubes years ago. I once lived in Colo and called the local AM BC's. I ended up building a quad 4-400A linear as a result of one lucky call to KIMN? I believe.

T

[WA1GFZ]

I heard Dick bought his school back last year when they went dark.
He had a voice like there was 10 pound weights on his BA. (and it hurt)

[K5UJ]

I looked at that 3 x 3-500 amp supply amp once and was disappointed that they did not have the tubes in chimneys.  you can maybe get by on heavy duty cycle modes with a pair and a fan on the side but I think with three or more you have to come up from the bottom for equal cooling on all tubes.   I run a pair on AM at around 250 to 300 w. with a side fan blasting 180 CFM and had no problem with babbling away (except for pissing off the other guys on frequency) but I would not want to run three that way.  There was something else I didn't like but I can't remember what it was now.  Might have been something with the power supply.   Anyway, I decided to build my own--another one Tom!      You can't get a strapping amp these days, or if there is one out there for sale, they want an insanely high amount of money.   Not too long ago there was some kind of hb RF deck on eBay, I think it was a pair 8877, no power supply, and it was around $4 or $5K!  nuts.

[W1AEX]

I looked at that 3 x 3-500 amp supply amp once and was disappointed that they did not have the tubes in chimneys. 

I agree with you Rob, however, it would appear that they had a lot of "confidence" in their design. Look at the output ratings they published in their manual! 1500 watts continuous rating for RTTY, which isn't too bad at 500 watts per tube, but 900 watts of AM? It's unclear whether they mean 900 watts of carrier or 900 watts PEP, which would be strangely low, so who knows how the typical owner interpreted this. I would imagine quite a few tube pins unslobbered themselves if someone attempted to run 900 watts of AM carrier!

Rodger, I have heard the same stories about fatigued connectors on the tube sockets causing a poor connection and enough heat to unsolder the filament pins. A good reminder to check that if it happens.

Rob W1AEX

[K1JJ]

Another thing to consider about fil pins unsoldering -  The fil socket clips are usually annealed to produce the spring action. If the tube pins get hot due to poor cooling they may cause the socket clips to lose their spring action and in turn, make the contact even poorer as discussed in previous posts. It's almost like a thermal runaway situation.

After my Sigma 3000D 3-500Z fil pins dripped solder, I replaced the sockets. The clips seemed weak. That, however, didn't solve the problem since the fils dripped solder again.  The chimneys did the trick and they never dripped again since.


BTW, I repaired the fil pins using a torch. The heating and soldering must be done very quickly or glass/seal damage will occur. Using a long time duration big soldering iron seems more risky to me.

T

[ke7trp]

I cant get past the idea of Drilling holes in the deck. That seems wrong. The 4-400 has holes in the base so air runs up through the base and out those holes.  Look at the picture of my RF deck above. Drilling holes like that is just going to put less air through the tube.

C

[K1JJ]

You must use chimneys when using the drilled holes.  I've tried both ways - no holes and holes.  Much depends upon the socket design and the way it is mounted.  Sometimes there is not a lot of air that flows thru the tube base holes and the anode glass gets starved when the socket is mounted directly on the chassis without holes.. I had this happen with 4X1's and it required huge blower pressure to get decent  air for the anode area.

The Tron suggested the holes  saying he used it in the past for several transmitters. I added the holes and the air increased dramatically to the anode area, but still had a good path thru the seals/base to keep them cool. The air noise was much less too because of the lower back pressure restriction.

Anyway, for my present 4X1 modulated by a pair, instead of drilling holes, I simply sub-mounted the sockets slightly, creating a 1/4" gap for air to flow uniformally around, inside the chimney. This gap can be adjusted using washers that stand the socket off from the chassis. By experimentation, a certain gap vs: tube base holes air ratio can be found that cools both areas FB.

There's many ways to pull this off using chimneys.

T

[ke7trp]

The tube was not designed to use chimneys.  I guess thats what is telling me that its not needed.  Its designed to use a simple socket that blows air from the bottom of the socket up through the pins, and out those holes. BC transmitters used this meathod.

On the T368 they used a metal chimney. Probably because in that transmitter, ONE single tube is producing 500 to 600 watts OUTput of class C am at 100% mod.  Its really quite amazing that the transmitter will run this much all day and all night with one tube. If you look at the ratings of the 4-400, Its spot on with the data sheet.

On the ham amps that use fans blowing across the pins and tubes, Its simple economics. It is enough for the low duty cycle and power output of the tubes. 

On that LK550, You have three tubes that are running way way below maximums with low plate volts.  Costs where cut.

One idea I really do like is seen on the heathkit chipewa amplifier. They had a hollow pipe that went up between the tubes and blasted the plate cap heatsinks with air. I might add that to my RF deck one day.  This has to really lower the plate and seal temp.

Its neat to see all the ways you can build a cooling system. Lots of neat ideas have come along!


C

[K1JJ]

I have Eimac labeled chimneys here that were designed for the 4-400A.  It's probably optional to use them based on how hard the 4-400A's will be run.

Anyway, check out my old quad 4-1000A amp, Quadzilla. It has since been converted to Fabio, the single 4X1 plate modulated by a pair. Those four chimneys sure make the tubes look bigger and kinda cool, no?  


T

Second pic: Some serious plate color needing a lot of air... the air is sucked in from outside the house to make things quiet and get a headstart on cooler air.  

[ke7trp]

I was speaking of the data sheet. They designed the tube to be used with no chimney.  That 4-1000 setup looks awesome. The chimneys make the tubes look huge Tom. Thats one hell of a rig!

C

[K5UJ]

Rob, thanks for the amp specs.  by the context I think the 900 w. is a p.e.p. figure but it is odd that they de-rate for AM but not the 100% d.c. modes.  since I have never seen one in operation I don't know how much air the stock amp moves through the RF deck.  Manufacturers of cw/ssb amps often de-rate based on the plate supply and cooling for high duty cycles.   Here, I see they give an ICAS current for the plate transformer.  I'd like to know what the CCS current spec is.  That might reveal something about the basis for the power out specs.   Without knowing how the amp runs with the stock fan and what if any cooling the p.s. gets and what the manual says I can't say much else.

BTW, another thing to watch as far as heat is concerned is the parasitic suppressors.   They should be about 2 inches from the anode caps and in the air flow, or the straps to them from the plate caps should be so they don't get too hot and have the resistors cook or their solder melt.

[ke7trp]

Its 900 AM input for carrier.  50 to 60 percent probably.  Who knows with these things. They are lightweight Ham amps built for a ham friendly budget.

C

[KM1H]

I dont understand all the fussing and pure mis information about the LK-500.

1. Most 3-500 amps using under about 3000V do not use chimneys and work fine. Eimac has blessed this since 1969. Mine still has the original 1986 tubes and has been beat hard in award winning DX and WPX contests in both modes....look at old QST/CQ results.

2. There is nothing cheap about it. Peter Dahl transformers and the same meters, filter and tuning caps, bandswitch, as Alpha and other good brands. Its way above Heathkit or Kenwood quality. Resale prices speak for themselves.

3. They werent cheap when new either. The basic LK-800A was $2995 in the late 80's

If I were going to beat on it for AM Id cut out the side panel and replace the holes with a less restrictive mesh, especially the LK-550 which has plenty air flow but its all backed up from egress restriction.

Carl

[K1JJ]

Clark -

Thinking more about it, I would say your arrangement with the air blowing thru the bottom holes is a better approach than using a single side fan. The next best thing to a chimney.

One thing to keep in mind is the plate cap seal area gets little air without a chimney. The chimney causes the air to "hug" the envelope and when using a heatsinked type plate cap there is more cooling at that point. Your upper air-tube idea would be a good addition to cooling the top seal.


Carl: Sure, as we discussed before, we can get away with most any cooling, depending upon how hard the tubes are run. It's all about what you want to do. However, I think it's hard to deny that a chimney, with it's form contouring of the air around the tube, will permit one to run air more efficiently, maybe with slightly less air flow to do the same job on the upper half.  I still find one side of the tube is hotter than the other when using a side fan as many amps use.

Again, most anything will work - it's just a matter of some guys wanting to make it easier to balance air flow. I had a heck of a time getting my air balanced with multi-tube amps. The way to see is to do a touchy-feely on all the glass, seals amd plate caps after a good full power key-down. (high voltages turned off, of course)  When using chimneys,  I can usually touch any of these areas without getting uncomfortable. When one side is getting favored, or the top plate cap has little air, I see a big difference in temperature gradient.  When done in moderation, side fans  won't hurt a tube, but if you have the chimneys available, I think it's simply additional insurance for mistakes and running the amp very hard in AM service. (and for the anal-minded amongst us... )  

T