• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Amp Supply lk500ZB Help.

Thank's Chris I will check it with a meter after I find the two USA made caps and get it up and running again. I think the only things that have not been replaced or rebuilt in this amp will be the meters and small plate transformer in the last 14 months lol.
 
Russky doorknobs seem to hold up okay.

https://www.ebay.com/itm/4pcs-470pF...845929?hash=item2cdf4bc569:g:9CwAAOSwr6pZ-zZo

They have for us so far, anyway. You may find yourself digging for exotic metric screws to fit these. They will always have to either be cut to length so they won't bottom out in the cap's bushing, or run a nut down a too-long screw and fasten to the cap's bushing that way.

There' s always RF Parts https://www.rfparts.com/580500-7.html

Prices took an ear-popping jump up a few years ago.

73
 
Last edited:
The RF parts or Russian "Doorknobs" are the only real way to go.
Hard to tell from picture those caps appear they are the Plate Blocking capacitors, which block the DC B+ voltage from getting to the (AC) RF Tank circuit.
You may get by with those in a sweep tube amp at lower voltage and power rating, however IMHO there is NO WAY I would ever use a disc type for the purpose in a high power amp.
All the Best
Gary

Old adage get what you pay for!(y)
 
  • Like
Reactions: Dmans
A disc ceramic that's big enough will work fine. That's what Henry was shipping for one customer's amplifier when he called them about it. A big, fat one mind you.

The doorknob is better because it has more metal in it. More metal means lower resistance. Lower resistance means less heat from the current passing through it.

First one problem. Finding a current rating for a ceramic capacitor can be tricky. Figuring out how high the RF circuit current will be is another problem.

The 'more metal' problem can be solved by a higher voltage rating. Not because of the circuit voltages, but because of the capacitor's construction.

The higher voltage rating means you have to put more distance between the two electrodes. But when you do that, you have to make the electrodes larger to obtain the capacitance you need. Larger means more metal.

Using a capacitor rated at 15,000 Volts in a circuit that won't put more than 5000 Volts across it gets you that current rating, and prevents the capacitor from overheating and failing.

Metal is metal. A ginormous disc-style cap that's nearly a quarter inch thick will typically work as well as a doorknob type at the same circuit current.

73
 
  • Like
Reactions: Dmans
Well, yeah. Except for the zero-point-five percent tolerance rating.

10 percent or even 20 is perfectly okay for this kind of application.

Not to mention cheaper, as a rule.

(edit) Just noticed the name "Vishay-Draloric" on the spec sheet. Always associated the name "Draloric" with the big, hollow high-current RF capacitors found in industrial RF-power oscillators. Didn't know Vishay had bought them. Seems like Vishay owns about half the american-made component brand names of the last 50 years.

73
 
Last edited:
  • Like
Reactions: Dmans
Newark does not seem to have anything from 5kv to 15 kV in stock.

cbkidd1,
I have ordered plenty of things from Newark that were not in their US inventory. I have never been in such a hurry that I couldn't wait 5 or 7 days. (Most of these orders are for me not other peoples equipment) Newark was a much better deal about 2 years ago when shipping was a flat $5.99 regardless of the size of the order. Now it is $8.99 ( I believe) so I build a "shopping cart" on their website until it is economically feasible ($40.00+). The do not charge extra for items coming from the UK as long as you are not in a hurry.

Good Luck!

73's
David
 
Pack of 10 Vishay 1000pF 6KV disc caps from Mouser:
https://www.mouser.com/ProductDetail/Vishay-Cera-Mite/564R60GAD10?qs=xrnNvQC1SKQV3fR046g7Jg==

Amazon:
Amazon product ASIN B074Y6DW8S
https://www.amazon.com/Murata-DECB33J102JC4B-Ceramic-Capacitors-6300volts/dp/B00LWNW2VO

DoorKnob style:
https://www.ebay.com/itm/323817252860

Xicon:
https://www.ebay.com/itm/2pk-1000pf-6KV-Capacitors/372235525203

10% tolerance MIL-SPEC:
https://www.ebay.com/itm/CERAMIC-RADIAL-CAPACITOR-1000PF-001uF-6000VDC-6KV-MIL-SPEC-5910-00-893-3070-4PC/190991960289

10% tolerance Murata from Mouser:
https://www.ebay.com/itm/14-High-Voltage-Ceramic-Disc-Capacitors-1000pF-6000V-10-MuRata-DECB33J102KC4B/264339243172

Run 1 of these:
https://www.ebay.com/itm/2x-0-002uF-2nF-2000pF-8kV-8000V-Teflon-Ceramic-HV-Doorknob-Capacitors-FGT-i/192877220453

https://www.ebay.com/itm/High-Voltage-Ceramic-Doorknob-Capacitor-Blue-6KV-2200-pF/230918949389

https://www.ebay.com/itm/2200pF-10kV-High-Voltage-Ceramic-Doorknob-Capacitor-Silver-content-KVI-3/292921242742

BTW, I don't have a LK-500ZB schematic but the LK-500ZC schematic only shows 1 of these being used (C26).

LK-450 (1) 3-500z schematic shows 2 1000pF 5kV caps in parallel:
450 plate.png


LK-500ZC (2) 3-500Z and LK-550 (3) 3-500Z only show 1 1000pF 5kV cap:

plate.png


550plate.png


Personally, I don't like running HV caps in parallel. I prefer to run a single cap of sufficient capacity and voltage.
 
Putting them in parallel increases the current rating, since the circuit current is shared 50-50 between them. The added capacitance alone might be relevant on 160 meters, but won't mean much above 3.5 MHz.

One thing to NEVER do when putting large disc caps in parallel, is to position them alongside each other too closely. The two outer surfaces will arc to each other if they're too close. The epoxy-like outer layer has a breakdown voltage well below the capacitor's breakdown rating. The adjacent side surfaces of two parallel HV disc caps should be separated by a half-inch or more.

You'll never guess how I discovered this pitfall.

73
 
  • Like
Reactions: Shadetree Mechanic

dxChat
Help Users
  • No one is chatting at the moment.
  • dxBot:
    Tucker442 has left the room.
  • @ BJ radionut:
    LIVE 10:00 AM EST :cool:
  • @ Charles Edwards:
    I'm looking for factory settings 1 through 59 for a AT 5555 n2 or AT500 M2 I only wrote down half the values feel like a idiot I need help will be appreciated