What about the input VSWR?
That amp is notorious for frying input circuits as well as that 40/80/160M
toroid coil, especially in high duty cycle modes. Bandswitching a toroid at
those impedance transformations is not a good idea; they work OK as the L
coil in a pi-L.
Once fried it should be replaced.
You can also test one tube at a time by stuffing a rag in the empty hole and
using 20M. I run 40W drive to make the A-B comparisons.
Carl
KM1H
----- Original Message -----
From: "Gerald Williamson via Amps" <amps@contesting.com>
To: <steve@nr4m.com>; <amps@contesting.com>
Sent: Monday, March 02, 2015 4:08 PM
Subject: Re: [Amps] high drive/low output QRO HF-2500
Steve, do you suppose one of the two tubes is not working?
73,
Gerld K5GW
In a message dated 3/2/2015 12:44:00 P.M. Pacific Standard Time,
steve@nr4m.com writes:
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.
Suggestions?
73 de Steve, NR4M
On 2/20/2015 01:53, Carl wrote:
Same problem on all bands?
Carl
KM1H
----- Original Message ----- From: "Steve Bookout" <steve@nr4m.com>
To: <TexasRF@aol.com>; <amps@contesting.com>
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.
Steve
On 2/20/2015 00:31 , TexasRF@aol.com wrote:
90W drive; how much reflected?
73,
K5GW
In a message dated 2/19/2015 5:22:23 P.M. Central Standard Time,
steve@nr4m.com writes:
Hello all,
Took a QRO HF-2500 out of storage and put it on my 40 meter mult
station.
Tuned by the book (because I never can remember how to tune this
thing
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
only,
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.
Ideas?
73 de Steve, NR4M
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73 de Steve, NR4M
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