[Amps] Choosing a Plate Transformer
Jeff Blaine
keepwalking188 at yahoo.com
Tue Mar 10 15:33:59 PDT 2009
Scott,
The max ratings per the "spec sheet" (if you want to call it that...)
are 2500v @ 600ma as a max operating range. But Gary is right, these
things don't come together if you are respecting the plate disipation
limit. Somehow in his message, the "1" in the 1500 number came out as
!500 instead causing my confusion...
I have a pair of GI7B with custom heat sinks (the stock sinks are not
very efficient) - so it's a more or less optimized setup for allowing
running near the high end of the anode dis max. Coupled with that is a
variac + tx arrangement that lets me run the voltage from about
1700-3100 on the plates.
In my configuration, there is a definate fall-off in efficiency below
about 2000v (loaded), and again at about 2600v. So if you want to
consider this range a "sweet" spot...
Next, the gain of the tube increases with voltage. The grid drive
remains constant. So at the lower voltage, the limiting factor tends to
be hitting the grid max current. And at the higher end, the limiting
factor tends to be the the anode disipation limit (which heavily assumes
the cooling arrangement can keep up).
I've not yet got a proper set of characterization data to prove it yet.
But I feel that the amount of heat coming off the amp is greater when
using the higher voltage than the lower voltages - although I cannot get
the math to reflect it (the efficiency should be somewhat less if this
were to be true). And it is much easier to glitch the tube when tuning,
or in the event you overdrive the tube, at the higher voltage.
From an efficiency standpoint, my net is around 63-69% on 20/40/80.
It's less on the higher bands. Not sure what band you are setting up
for. And of course, these numbers are specific to my configuraiton.
From my notes, a typical 80m setting is something like 2500V plate @
600 ma plate (for the pair). 65w drive. 1020w out (average power).
1500w in. 550w plate dis approx. The max power I have seen out of a
pair, under any circumstances, is 1400w and then the tube will glitch
easily (probably due to excess grid drive which is theorized to cause
the grid to deform as it's heated (or overheated) but I don't have any
data to back that theory).
One thing I can say is that using a tuned input with toroids has a HUGE
HUGE effect on the efficiency (say 50% without, and 65% with!). So
whatever your plans are, be sure to allow for fitting a tuned input.
Hope it helps.
73/jeff/ac0c
KB0NLY wrote:
> Hmm, ok. Well just telling you what everyone else runs them at.
>
> 73,
>
> Scott
>
>
> ----- Original Message -----
> From: "Gary Schafer" <garyschafer at comcast.net>
> To: "'KB0NLY'" <kb0nly at mchsi.com>; "'Jeff Blaine'"
> <keepwalking188 at yahoo.com>; "'RICHARD GEORGE'" <k6kwq at msn.com>
> Cc: <amps at contesting.com>
> Sent: Tuesday, March 10, 2009 1:26 PM
> Subject: RE: [Amps] Choosing a Plate Transformer
>
>
>
>> I know the minimum i'm shooting for, 2500v 600mA. This will be to run
>> a
>>
>>>> single GI7B
>>>>
>
> 2500 volts at 600 ma = 1500 watts input. You said it! :>)
>
> 73
> Gary K4FMX
>
>
>> -----Original Message-----
>> From: KB0NLY [mailto:kb0nly at mchsi.com]
>> Sent: Tuesday, March 10, 2009 1:50 PM
>> To: garyschafer at comcast.net; 'Jeff Blaine'; 'RICHARD GEORGE'
>> Cc: amps at contesting.com
>> Subject: Re: [Amps] Choosing a Plate Transformer
>>
>> But I don't have 1500w input?
>>
>> 73,
>>
>> Scott
>>
>>
>> ----- Original Message -----
>> From: "Gary Schafer" <garyschafer at comcast.net>
>> To: "'Jeff Blaine'" <keepwalking188 at yahoo.com>; "'RICHARD GEORGE'"
>> <k6kwq at msn.com>
>> Cc: <amps at contesting.com>
>> Sent: Tuesday, March 10, 2009 12:41 PM
>> Subject: Re: [Amps] Choosing a Plate Transformer
>>
>>
>> I think that the GI7B has a 350 watt plate dissipation. 1500 watts input
>> at
>> 60% efficiency = 900 watts out. 1500 -900 = 600 watts of plate
>> dissipation!
>>
>> The tube will cook.
>>
>> 73
>> Gary K4FMX
>>
>>
>>> -----Original Message-----
>>> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
>>>
>> On
>>
>>> Behalf Of Jeff Blaine
>>> Sent: Tuesday, March 10, 2009 12:03 PM
>>> To: RICHARD GEORGE
>>> Cc: amps at contesting.com
>>> Subject: Re: [Amps] Choosing a Plate Transformer
>>>
>>>
>>> Hi Richard,
>>>
>>> I'm curious what you base that on?
>>>
>>> 73/jeff/ac0c
>>>
>>>
>>> RICHARD GEORGE wrote:
>>>
>>>> !500 watts input to a single GI7B. That is going to be awfull hard on
>>>>
>>> the
>>>
>>>> tube.
>>>>
>>>>
>>>> ----- Original Message -----
>>>> From: "KB0NLY" <kb0nly at mchsi.com>
>>>> To: <amps at contesting.com>
>>>> Sent: Tuesday, March 10, 2009 8:30 AM
>>>> Subject: [Amps] Choosing a Plate Transformer
>>>>
>>>>
>>>> I'm thinking about slowly scrounging parts to build another amp in the
>>>> future, it will be a ways off so in no hurry, and i was wondering how
>>>>
>>> one
>>>
>>>> chooses a plate transformer.
>>>>
>>>> I know the minimum i'm shooting for, 2500v 600mA. This will be to run
>>>>
>> a
>>
>>>> single GI7B.
>>>>
>>>> I was thinking about using those Far Circuit boards for constructing
>>>>
>> the
>>
>>>> doubler and rectifier. It looks like the average factor is 2.8.
>>>>
>> Which
>>
>>>> means for 2500v i would need a transformer with a secondary of at
>>>>
>> least
>>
>>> 893
>>>
>>>> volts (rounded up). But what should i do on the current capacity
>>>>
>> side,
>>
>>>> should i look for something as high as a 1 amp transformer? Most of
>>>>
>> the
>>
>>>> ones i am finding on eBay for example are 500mA or smaller. I could
>>>> probably get away with .500 mA.
>>>>
>>>> The question is, does one loose ampacity with the double circuit, or
>>>>
>>> does
>>>
>>>> the current remain constant? I can't seem to find any notes in the
>>>>
>>> handbook
>>>
>>>> articles on the subject of choosing a transformer. This is why the
>>>>
>> last
>>
>>> amp
>>>
>>>> i built i used a donor FL-2100B so i wouldn't have all the questions
>>>>
>> on
>>
>>>> constructing the power supply. But the next time around i want to
>>>>
>> build
>>
>>> the
>>>
>>>> power supply from scratch and learn more about HV supplies!
>>>>
>>>> The 6M amp i just built is working great by the way. It will do 500w
>>>>
>>> but i
>>>
>>>> keep it around 400w. I checked into a net this weekend that a nearby
>>>>
>>> club
>>>
>>>> holds on 6m, they were suprised how loud i was as i'm usually the most
>>>> distant and sometimes one of the weekest for them to hear.
>>>>
>>>> 73,
>>>>
>>>> Scott KBØNLY
>>>>
>>>> www.kb0nly.net
>>>>
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