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
|