started to work on the basket case 4-1000 amp

[Opcom]

A start's been made on rebuilding/finishing the basket case 4-1000 amp picked up earlier this year
http://amfone.net/Amforum/index.php?topic=36305.msg278945#msg278945

The amp is a mess and I pulled everything out of the rack.

The power supply stuff was all mounted to a 3/4" thick wood base that was just sitting in the bottom of the rack. I think I'd rather bolt things into the cabinet itself.
Found out the choke is rated 0.68A, very nice.
The rectifier filament transformer is a Langevin rated 2.5V at 20A. 866's take 5A each, so what rectifier tube uses 2.5V/10A each? Curious.
The small, old swivel casters are shot. They have flat spots on the wheels and were probably never intended to be used on a 200 lb amp.
The whole thing runs on 120VAC including the plate transformer. That's Ok I guess - a 20A outlet would be best but no reason it can't use a 15A one.

The RF deck layout is OK, but the filament wiring underneath is ugly so that needs re-done. The OM had apparently used salvaged items with pigtails on them and just joined the pigtails. I should redo that.

The old B&W 850A tank coil has the coil support plastic rotted off. I cut some strips of plexiglass from an old damaged oscilloscope graticule and put them in place. A good glue for them can be made from styrofoam cups and acetone. It goes on thick like goop and dries tough like nylon. Might have some pics of the coil repair later when the coil's done.

[N2DTS]

Does not look like it was ever finished, no sign of any grid tuning.

Those plate tune and load caps look like what I have in my 4x150 rig.

[Opcom]

You are right, I don't think it ever was finished, the thoughts of the two others that looked it over were that the builder got to preliminary "JS" testing and figured out it was an engineering mess and put it aside. There is/was evidence the HV was tested or had been on.

The plate tuning cap is the same one as in the Johnson Thunderbolt. Rated 2000-2500V, I think - apparently good for more as it didn't look arced. Would be fine for the 4X150 voltages, that is certain.

The HV supply is probably no more than 3500V on the bleeder, don't know how much under a 600mA load. The design may have some issues. It was partly dismantled so there's no way to tell unless it is rebuilt. The filters measure 3.75uF each and look like the usual 3-4KV size/type. No markings but they'd have to be OK for 4KV or would have crapped out before.

I'm going to put the HV supply back together as it probably was and try to test it with an electronic load or maybe a resistor bank.

A thought looking at the transformer (pics in other topic) is the secondary CT has a nice big insulator just like the ends. I wonder if it can stand a bridge. The Elenco Commander with a 4-1000 and ran 6KV and was about the same size if not shorter. I can't find any pictures of the insides of the RF and power sections of the Commander. The schematic and manual is attached, for the sake of amusement. Nice to look at but I don't want to go there, not personally ready for 5-6KV work.

[Opcom]

Elenco Commander schematic 2 versions - what every 4-1000 amp wants to be!

Anyway back to the thing, it deserves a chance. More later after some tests on the power supply. If the volts are too low for the 4-1000 to be efficiently cathode-driven then other tubes might be fine, like two 3-500 or 4-400's whatever is lying around and whatever sockets are available. Three or so 4X150/250 in AB1 would work and the drive is low voltage so a 50 ohm load could be put there eliminating tuning. Not picky. Sockets cost as much as tubes these days!

[Opcom]

I found a 200pF air variable cap rated 7KV (0.175" spacing) to replace the small 300pF air variable that was arcing at higher plate voltages (the other tests using pulsed voltage http://amfone.net/Amforum/index.php?topic=37370.0 ).

I also found a 0.08" spacing 1000pF transmitting cap for loading. I am not convinced a 4-section receiver type cap can take the output very well, and the one in there is trashed.

Back to the plate tuning cap, is 200pF enough? When I was testing things at low voltage before, I never used the whole 300pF.

The voltage will probably be 4500-5000.

Should add a little inductance as in this topic
http://amfone.net/Amforum/index.php?topic=32440.0

A 150 Ohm NI resistor has been put from the filament RF side to GND for testing as it lowers the 4-1000 cathodes 110 Ohm impedance down to where the match is OK.

I still face the issue of no room for a decent plate tuning cap or loading cap - the original builder had the plate tuning cap between the tube and the front panel. I want to move the tuning cap to the space over the loading cap, removing a meter to do it. Recall just under 6" space from the front panel to the tube chimney. Not the best design. Can't move the loading cap under the chassis unless I want to redo the entire thing underneath too.

haha this will also leave me with meter hole where a tuning cap shaft has to come through etc... and have to move the grid current meter, but there should also be room for an extra meter or two with the little tuning cap gone so I won't skimp on meters if possible.

It won't be pretty but I hope it will be like an old military truck - ugly but strong. Assuming it does work when done it'll need a name 8-)  Here's a pic of the ugly thing just in case. Little 300pF air variable tuning cap is there in plain sight - same cap as used in the Johnson Thunderbolt @ 2500V.

[Opcom]

The basket case seems to be a 'layout' copy of the Kilowatt amplifier in the Eimac Amateur Service Newsletter AS-10, K9LKA article "The 4-1000A in Grounded Grid". of which Bill Orr W6SAI was the editor. But the amp was apparently by Larry Kleber K9LKA. The "Kilowatt" in this case means DC input, so it's the higher old ratings and should be good on AM.

The 'short' loading cap it 'should' have seems to be:
1500pF, 0.03" spacing, 1KV
cardwell PL-8013
or
B&W 51241 (usually unobtanium)

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note: possibly modern replacement is the Johnson 154-30-1
1500V
18-1000pF
0.030 spacing
63 plates
'M' 5 23/64" (not stated what M is, probably length)

Johnson 154-30-1 was found at
http://cardwellcondenser.com/johnson-capacitor-division/type-e-154-series/type-e-154-series-single/
I would rather have a used one, probably can not afford new parts for this amp. Prices are not listed. if you have to ask...