[Top] [All Lists]

Re: [Amps] SB 220 Exploding Resistor

To: "Jim Thomson" <>, <>
Subject: Re: [Amps] SB 220 Exploding Resistor
From: "Carl" <>
Date: Wed, 20 Jan 2016 17:48:09 -0500
List-post: <">>
Date: Mon, 18 Jan 2016 14:13:10 -0700
From: John Lyles <>
Subject: [Amps] SB 220 Exploding Resistor
Message-ID: <>
Content-Type: text/plain; charset=windows-1252; format=flowed

If you get a strong enough wirewound resistor, this can suffice as the
surge current limiting resistor for a spark over in a tube. With 250
amps at the beginning of the overcurrent (2500 V/10 ohms) spike, there
is enough magnetic field to break a wirewound R as the windings have
mechanical force between turns. I have always used bulk carbon for
series R, like Kanthal Globar makes. They are exactly the right part for

Finding them through distribution might be a problem, though. Has anyone
else used these?


## The energy absorbing types are the AS series. The SP series is what is used in dummy loads, etc. I have used these real small globars back in the 70s... for the parasitic suppressor in several amps, but I don’t remember if they were type AS or SP. Dunno if Globar will sell you just 1-2 of them ?
SP types are rated for  350 deg C.
AS types are good for  250 deg C

## There is no issue using wire wounds for a glitch R.... provided they are sized correctly.
2500 /10 ohms  =  250A.
3000 / 10  ohms =  300A

##  2500 / 50 ohms = 50A
     3000 / 50 ohms =  60A

## A single 50 ohm @ 50 watt WW works quite well..and does not implode. However, I use a HV fuse in series with the 50 ohm glitch Resistor..... to interupt the peak fault current...asap.

##  I have also tried paralleled  100 ohm  @  50/100 watt  wirewounds.

## Ameritron sells the globar type AS glitch resistor.... forget the value they use. If its real low, like 10-15-20-25 ohms, you could always series 2-5 of them. But I believe they are not cheap. I believe
they only sell one value.

## I have also tried the bigger, tubular type SP resistors for a glitch R, and they work good. But these were obtained surplus. I have also tried large tubular type AS, and they work very well.

## But the wire wounds are cheap to buy new, and in any value and wattage you want. Readily available. 50 ohms will limit fault current to a low value.... and is not high enough to cause heat issues, when used on high duty cycle modes. Also, the V drop across 50 ohms, with 500-1000 ma of plate current is not an issue either.

##  You will not implode a 50 ohm  @  50 /100 watt WW any time soon.
## surplus globars show up on the market from time to time..and also work good. I bought several 50 ohm, 90 watt CCS type SP globars, same as used in a heath dummy load, these also work
excellent for glitch use.  I believe ameritron also sellls em.

Jim   VE7RF

That 250A "assumes" the 2500V is a constant. In an amp with a wimpy transformer the B+ tanks.

Ive used a 12 Ohm 15 W for decades since I picked up a few hundred new ones at an auction.

RCA recommended 15 Ohms minimum for the 8122 at 2500V and 10uF output C. In the NCL-2000 the resistor is 15 @ 10W and in over 50 years Ive never seen one blow. It is listed as a special surge current rated in the parts list and Im pretty sure it is a WW.

Amps mailing list
<Prev in Thread] Current Thread [Next in Thread>