[Amps] SB220 step start blows fuses

Carl km1h at jeremy.qozzy.com
Wed Jul 12 21:12:12 EDT 2017

BTW, running filaments only does nothing except burn 50 watts. The anode 
needs to run at least at a bright red to degass.

When the tube arcs even in the CW position it is usually a hard short but 
the only way is to test it at 1000V or less which will not sustain a gas 


----- Original Message ----- 
From: "Warren Volz" <warren at warrenvolz.com>
To: "amps" <amps at contesting.com>
Sent: Wednesday, July 12, 2017 2:40 AM
Subject: Re: [Amps] SB220 step start blows fuses

> 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!
> -Warren
>> On Jul 11, 2017, at 6:35 PM, Warren Volz <warren at warrenvolz.com> 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
>> suggested.
>> 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.
>> -Warren
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps

This email has been checked for viruses by AVG.

More information about the Amps mailing list