Amp supply LK-800 help.

[ke7trp]

I am posting this for a friend.  He has an LK-800ISM like I used to have and he had a failure of the bank of red door knobs caps. They where burnt and no value could be read off them.  He replaced them with a single 500 at 10KV and the power is way down.  Cant fully load.  Anyone know the value of the bank of small red door knobs? 

I seem to remember someone that worked on Amp supply being around this forum.  We cant find any schematics of the ISM model.  It runs three 3cpx800 tubes at 3650 volts.

Thank you

Clark

[N8ETQ]

Hey Clark,

   A regular LK-800 has 2500 pf of fixed loading
padders. See if the thing will fully load on 15M
or 10m.  Manual here: http://www.pj2t.org/ccc/lk800.pdf

73

/Dan

[ke7trp]

Thanks Dan.  That is a different amp.  But maybe he will find the info usefull.

Thanks

Clark

[KM1H]

For what band and any pix?

[ke7trp]

Dont have one at this time

C

[KM1H]

Was this the fixed tuned 2 or 3 band version?
Band 2 is CB

Carl....the guy with Amp Suppy experience

[ke7trp]

There are several versions of the LK800 amp as you probably know. The ISM was the GOVT model.  17 Position band switch.  The one I had used the optional power pack with a 67lb peter dahl,3650 volts on the plates of the three pulse tubes.

While we are the on the amp supply bandwagon..  Carl, Did they make any with a broad band no tune system like the Alphas?  I seem to remember some where like that, Not sure of the models.  I would like to replace my SB220 with one that has this feature so I can move from band to band working DX and not have to tune all the time.  The SB220 has the sharpest tuning and I am growing tired of it.  I only need 1KW for DW work.

C

[KM1H]

The regular ISM model was just for the 13.56, 27.12, 40.68 MHz bands and had nothing to do with the government. ISM means Industrial, Scientific, Medical.

The government ordered several models in the HF and low VHF range and configurations varied. I designed several of them while I was a consultant and some of the customer requirements were different than what hams expect.

The LK-800NT as well as NT versions of the other models had a half assed broadband performance but not something Id want to use with fragile grid 3CX8 series tubes.
Most I get in here are from contesters who want it converted to manual tune and not smoke tubes. The ones with 3-500Z's are OK as long as they are set up for a particular mode per band.

[ke7trp]

Mine had 17 position band switch and ran from below HF up to 32 MHZ.   

So the 3-500 version with No tune was ok?  If it had that option are you locked into no tune?  The only one I know about is the alpha 78 which you can switch from manual to NT.

C

[KM1H]

The only concession to tuning is a small value variable on the Load which is fair on 10M and seperate 80/75M positions. No WARC.

I most always have to make changes to NT's here to suit owners preferences who are mostly casual ops with a set of frequencies they always use.

The LK-550NT which comes with the external Dahl iron doesnt do much more than the LK-500 at 100W drive but makes for a nice AM linear at 450-500W carrier.

I wouldnt use a NT and simply make up cards with settings stuck under the knobs for almost instant QSY; won lots of CW and SSB contests that way and never cooked an amp.

Carl

[ke7trp]

How about this... Is there a way to add a vernier drive to the SB220?  That would fix it.  On 10 meters 1000 watts to 100 is 1/8th of an inch turn on that tune cap.

[KM1H]

You can use one of those Ameritron 6:1 drives which are clones of the Jackson 4511/DAF used on Amp Supply and many others.

There are 2 small holes on a flange to mount a dial plate if wanted.

In the 220 you would need to cut the cap shafts and maybe move them back a bit, never tried it.

Carl

[ke7trp]

Ok.  Thanks Carl.  None of them mount external to the amp?   I used to have one for a collins rig that was external. It was an add on 4 to 1.  Maybe I will search around a bit. 

C

[KM1H]

The 75A4 4:1 was a custom build by Collins into the knob. Jackson had one also but discontinued when the biz was sold.

The Japanese had a panel mount in the 70-80's Im sure youve seen but dont know how long it would handle the torque

[ke7trp]

I ordered a $12 used part used in a heathkit to experiment with. Its shallow, and uses 1/4 in and 1/4 out.

C

[ke7trp]

I guess the guy got the info he needed from the PDF. Thanks Dan!

C