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Re: [Amps] SB220 step start blows fuses

To: "Warren Volz" <>, "amps" <>
Subject: Re: [Amps] SB220 step start blows fuses
From: "Jim W7RY" <>
Date: Mon, 18 Sep 2017 17:44:52 -0500
List-post: <>

Hard telling what took out all of the semiconductors. Could have been hooked up wrong at one time too.

Thanks for letting us know and glad you got it all working!

Jim W7RY

-----Original Message----- From: Warren Volz
Sent: Monday, September 18, 2017 1:51 PM
To: amps
Subject: Re: [Amps] SB220 step start blows fuses

Just to close this out, as various people suspected the QSK circuit was
broken. I ended up replacing 4 components (Q7, Q6, Q4, U1) on the W7RY
QSK board and now the amp is working. I believe that a HV arc took out
these components prior to me (used QSK board).

Thanks everyone for the help!

-Warren KD5YPH

On 07/12/2017 12:40 am, Warren Volz wrote:

Well I have a major update!

The amp shipped with 2 3-500zs that are "not full output" according to the seller. Since the amp was in shambles I didn't have a way to test them until now.

One of the 3-500zs is unmarked and missing the phenolic spacer below the glass envelope. The other is clearly labeled as a Eimac. I tested each tonight with the HV plugged in. The unmarked worked without issue but the Eimac arced right after turning the amp on!

So, I guess I'm in the market for a new 3-500z. Based on what I see online, there isn't really a way to fix this gassy tube but I'm going to let it sit with no HV and filament voltage for ~30-60 min to see if that has any impact.

Tonight I also removed the fan and oiled the bearings + the surrounding fiber. The fan is a lot louder than I expected, but with the oil it's slightly quieter.

Thank you all for your help!


On Jul 11, 2017, at 6:35 PM, Warren Volz <> wrote:

Again thank you all for the advice and guidance.

Replacement fuses showed up today so I'm being a little more
adventurous. As multiple people pointed out the dim bulb tester I have
as built won't work unless I can find at least one 300W bulb.

So, I remove the dim bulb tester and tried each tube in the amp. Good
news is that both filaments light up just fine! To me that rules out the
filament supply and paints a target on the HV supply as many of you have

The amp as I received it was a pile of parts, and so I have no reference
in terms of working/not working prior to my mods. Both the QSK and the
RM220 were used pulls off of an auction site. The RM220 is squarely in
my sight now since it had a burned out metering resistor when I got it.
When I checked previously the diodes were all ok. Also, all components
(caps + resistors) on the filtering board are new.

I'll likely try reconnecting the HV primary without the plates connected
to see what that does next.

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