Here is some food for thought. In both my SB-220 and my HL-2200, I added a 10
ohm 10 watt resistor directly below the stock RFC and prior to the bypass
capacitor to ground. Its purpose is to protect the power supply from plate to
grid shorts. It seems that this resistance may have 'reduced' resonances in
the RFC circuit by accident. If someone is doing some measurements, you might
check what a 10 ohm resistor in series with the RFC does to the resonances.
73
.... Bill K3HZP
---------- Original Message ----------
From: "jim.thom jim.thom@telus.net" <jim.thom@telus.net>
To: amps@contesting.com
Subject: [Amps] QRO Technologies HF2000 plate choke, cont.
Date: Sun, 14 Nov 2021 14:07:18 -0800
Date: Fri, 12 Nov 2021 11:45:57 -0800
From: Jim Brown <jim@audiosystemsgroup.com>
To: amps@contesting.com
Subject: Re: [Amps] <
Message-ID:
<95d62c19-7d9e-f068-5fda-28d08e167c73@audiosystemsgroup.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
On 11/8/2021 4:18 PM, jim.thom jim.thom@telus.net wrote:
> I have heard of at least 5 of the ameritron chokes blowing up in the last
> 7 months....and they were ALL on 17m band... go figure.
<MFJ has never been known for their quality control, regardless of which
<of their brand names are involved.
<73, Jim K9YC
## The ameritron choke is supposed to series resonate at 11.6 mhz...and
also 27.1 mhz. 225 uh, 4 kv, and 1.5 amp. 17m band is the last place it
should blow up, wtf ?
## W8JI makes a more precise version, looks identical. However, it's
rated for 245 uh, and series resonates at 11.7 mhz...and 16.3 mhz...per
his CTR website. He may have stated the 16.3 mhz resonance incorrectly.
## 2 more blow ups with the ameritron choke last week.... again on 17m.....
go figure.
## The RF choke from RF parts, ameritron, MFJ catalog and alpha are
all identical..and all come from mfj.
## I bought 2 x of these chokes from RF parts a while back, and measured
225 uh and 224 uh. I will have to test em for series resonances...using
the original JI test method. Dead simple..and works.
## Stuffing the MFJ choke into a L4B would be a snug fit.... with not a
lot of clearance between top of choke..and top steel lid... like 7/16".
## I measured the OEM drake choke in the 80-10m L4B. It's 154 uh...and
doesn't seem to resonate anywhere. It works on all 3 x warc bands +
11m. This was all into a dummy load. It's gotta resonate somewhere.
Jim VE7RF
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