[Amps] high drive/low output QRO HF-2500
Steve NR4M
steve at nr4m.com
Wed Mar 4 11:26:27 EST 2015
Happy 'Hump day' to all,
I did a little investigation based on suggestions from members of the group.
In preparation for running the amp with only one tube, and then the
other tube, figured I would do some simple resistance checks of the
tube. I was looking for an open filament. I pulled both tubes out to
check one against the other. (I really do hate putting these tubes back
in their sockets...)
Trying to understand the Svetlana pin out info for this tube. /Assuming
/in their 'bottom view' that the gap in the pin symmetry is at the six
o'clock position. That is, pin 1 (G1) is at 7 o'clock and pin 7 (H) is
at 5 o'clock. I also located the 3 connected pins for the cathode (K)
at pins 2, 4 and 6. This, then, seems to make sense to me.
First tube I pulled measured an open across pins 7 and 3 (H) I am
supposing 'H' is the designation of the filament.
The second tube showed 1.4 ohms across the same two pins. Therefore, I
believe the first tube has an open filament. This would explain the
'not working correctly' vs catastrophic event of a short somewhere.
I have a couple of spare tube I got several years ago. I do not know
their pedigree, but supposed to be NOS.
Any issues with freely mixing tubes, or is the performance of this tube
such that a pair of tubes MUST be matched, or at least recommended, to
be matched for getting the operating bias/quietens current of each tube
the same?
Comments welcomed.
73 de Steve, NR4M
On 3/2/2015 21:28, Carl wrote:
> 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 at contesting.com>
> To: <steve at nr4m.com>; <amps at 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 at 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 at nr4m.com>
>>> To: <TexasRF at aol.com>; <amps at 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 at 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 at 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
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>
>>>>
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>>>
>>
>>
>> --
>> 73 de Steve, NR4M
>>
>>
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>
>
--
73 de Steve, NR4M
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