I think a small linear or even a switch mode power supply (however, be aware
of the switching freq. noise) for the heather will do the job easily. No
fiddling around with variacs, perfect control and inrush current limiting.
Gl, Carel
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of David H Craig
Sent: Sunday, December 20, 2009 3:48 AM
To: Jack Parker; Robert Briggs
Cc: amps@contesting.com
Subject: Re: [Amps] Re GS-35B hours..
I concur with this 100%. Each of my GS35bs had a variable transformer
on the primary side of the filament transformer and it has a profound effect
on performance. I use test-points on my Fluke to determine the filament
voltage at the "socket" (really brass band clamps). During peak line-load
times I have found drops as low as 11.9vdc (from the set 12.6-12.8v normal).
With fine adjustment the variac brings the voltage back to nominal range &
output increases to what it should be. It also eliminates the need for a
filament soft-start.
For setting it, I use the same procedure as the commercial guys use-
turn it up to max output & then down to a slight reduction, then just back
up to full-output. It works- output goes back up to normal. Though thus
far (since 2006) I have not yet "softened" a GS35b despite hard use, but I
also suspect it will buy a bit more output during a GS35b output decline.
After all, at 12.6V nominal at 2.6 amps, theere isn't a lot of wattage on
the filament of a tube capable of 1500W+ output.
73 Dave N3DB
----- Original Message -----
From: "Jack Parker" <vhfplus@gmail.com>
To: "Robert Briggs" <vk3zl@bigpond.com>
Cc: <amps@contesting.com>
Sent: Saturday, December 19, 2009 11:20 AM
Subject: Re: [Amps] Re GS-35B hours..
> One thing that users of external anode power tubes might consider is
> filament voltage. My experience in commercial FM broadcast rigs is that
> running a PA tube at it's rated filament voltage from day one is a
> guaranteed way to shorten tube life.
>
> After installing a new tube in a transmitter, and operating it for a few
> days to a week at full rated filament voltage, I would watch transmitter
> output power and reduce filament voltage until output power began to
> decrease. At this "knee" I would increase filament voltage a couple of
> tenths of a volt and operate the tube at that voltage, which generally was
> a
> half a volt, or so, below the "rated" voltage. I experienced increases in
> tube life of at least 50 percent based on comparisons to tube log records
> when the tubes were installed and run at full voltage for the life of the
> tube.
>
> This procedure worked well with 4CX5,000 and 4CX10,000 tubes in
> Continental
> FM transmitters. Determining whether this procedure is valid with a GS-35B
> would be an interesting experiment but I would not be surprised if is
> applicable to the Russian tube.
>
> 73,
>
> Jack, W6NF
>
> On Fri, Dec 18, 2009 at 7:04 PM, Robert Briggs <vk3zl@bigpond.com> wrote:
>
>> G'day all....I note the comment that 500 hours is probably the useful
>> life for the GS-35B....I have two amplifiers which are turned on and run
>> daily.I use CW only, 160 meters..My original 35B amplifier was put on
>> air in March 2006....That tube still runs perfectly...Say 300 days per
>> year 3 hours switched on and running say 1 hour CW output that tube
>> hasn't missed a beat....My newest GS-35B amplifier put on air last may
>> 2009 is also switched on for at least 3-4 hours a day and once more
>> shows no sign of losing emission....I think either amplifier won't need
>> a tube change for many years....
>>
>> I don't run either tube hard, using 3500 volts on the original amplifier
>> and running it to 1100 watts output.It is capable of much more but why
>> flog a willing horse...The newest amplifier has a deficient voltage
>> doubling HT supply (AL-80B Transformer) and I run it to 1kw output
>> CW....The GS-35B is a willing worker and with a robust power supply is
>> quite capable of the US legal limit..I have found no vices with the
>> tube...Best advice I have from my own experience is to make sure the
>> tube is tuned and loaded properly both input and output and all is
>> sweet....
>>
>> Bob..VK3ZL..
>>
>>
>>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|