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Re: [Amps] high drive/low output QRO HF-2500

To: Carl <>
Subject: Re: [Amps] high drive/low output QRO HF-2500
From: Steve NR4M <>
Date: Mon, 02 Mar 2015 20:43:55 +0000
List-post: <">>
Hi Carl, and others,

My apologies for taking so long to get back you everyone on this. 'Life' got in the way.

I got the amp moved over to another position and put the output into a dummy load.

Driving it with an Omni 6, I got the same output on 40 as I did into an antenna driving it with a K3.
The 4 square on 40 showed a 1.2:1 SWR and the dummy load a 1:1.

On 20 meters, I tuned it up gradually to several levels of input, doing it by the manual. At 100 watts input from the rig, I got 1250 watts out to the Bird wattmeter.. The input is 2100w + (2500 volts @.850 ma) That's 59% efficiency if I don't count the 100 watts drive. It tunes up easily, but I am not seeing the gain I once did. 40-50 watts input used to give me 1500 easily. It's as if I lost 3-4 db of amp gain.

I used 20 meters as a second tune-up band as I don't remember using any toroid inductors for the 20 meter tank circuit. The 40 meter toroid part of the tank circuit looks like a 'grilled cheese sandwich', with the plastic having heated and drooped down around the 40 meter toroid. Regarding the 40 meter toroid: On 40 (and 20) it tunes up at the approximate settings, per band, given in the manual, so I am not looking at the cosmetic issues of the 40 meter toroid. It seems to have the correct inductance to resonate with the described capacitor settings.


73 de Steve, NR4M

On 2/20/2015 01:53, Carl wrote:
Same problem on all bands?


----- Original Message ----- From: "Steve Bookout" <>
To: <>; <>
Sent: Thursday, February 19, 2015 7:40 PM
Subject: Re: [Amps] high drive/low output QRO HF-2500

The K3 that is driving it shows 1.2 or 1.3 to 1 standing wave.


On 2/20/2015 00:31 , wrote:
90W drive; how much reflected?
In a message dated 2/19/2015 5:22:23 P.M. Central Standard Time, writes:

    Hello all,

    Took a QRO HF-2500 out of storage and put it on my 40 meter mult

    Tuned by the book (because I never can remember how to tune this
without the book...) and the output is low at about 1050 watts. This
    is with about 90 watts of drive.  When last used it was used on 15
    but always got plenty of power out.  Efficiency looks fine at
    about 62%
    (700ma @ 2400 volts)

As I recall, this amp used to drive full output with 35, or so, watts.

    Power doesn't drift, and tunes up easy.  It's just acting more
    like an
    SB-220 than the amp it is.

    Plate and load cap settings appear correct per the manual.


    73 de Steve, NR4M
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73 de Steve, NR4M

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