Re: [Amps] B&W PT2500

[Fern Rivard via Amps <amps@contesting.com>]

I've owned both the PT-2500 by Viewstar (pair of 3-500Z) and the rather 
rare PT-3000 by Viewstar which used a single 8877 tube and both had no 
difficulty in easily putting out 1500 watts on all bands.
Fern  VE7GZ


On 27/08/2022 8:46 a.m., gudguyham--- via Amps wrote:
> The originally designed and manufactured  PT2500 was by the company Viewstar in Canada!!  They weren’t bound by the same limits.  Even Henry 
> built amps with high power capability running 3-500’s at 3800-4000 volts.  The PT2500 has around 3500 volts on the plate and with that kind of high voltage 
> there is no problem making 1500 watts output.  Even an sb220 with 2950 on tne plate can make 1200 watts output.  If your PT2500 only does 1100 watts maximum 
> you’ve got some issues going on.  Admittedly they are not known for the best input networks for solid state radios but if you can forward the drive to the 
> cathode effectively you’ll get 1500 watts pretty easily.  Viewstar couldn’t compete in that market so B&W bought them.  IMHO they flipped 
> just as badly as Viewstar.
>
>
> Sent from the all new AOL app for iOS
>
>
> On Saturday, August 27, 2022, 10:23 AM, Steve London<n2icarrl@gmail.com>  wrote:
>
> You are correct - the PT-2500 has a pair of 3-500Z's. It was designed and
> built in the era when the USA power limit was 1000 watts DC input. Hence,
> the HV is not high enough for 1500 watts output, regardless of the drive.
> Mine is good for about 1100 watts output with 70-100 watts drive, depending
> on the band. Except on 10 meters, the input SWR is low enough for my solid
> state radio to not cut back.
>
> 73,
> Steve, N2IC
>
> On Sat, Aug 27, 2022 at 7:26 AM Joe Subich, W4TV<lists@subich.com>  wrote:
>
> > The PT2500 is (I think) 2 x 3-500Z.  The gain is already marginal
> > if trying to reach 1500W out with 100W drive.  Now, if one were
> > working with ceramic/metal tubes or solid state devices that reach
> > 1500 W (or their 1 dB compression point) at 30W (as many do), a
> > 2 or 3 dB attenuator is a very good idea for many reasons.
> >
> > 73,
> >
> >      ... Joe, W4TV
> >
> > On 2022-08-27 12:47 AM,w5cul@sbcglobal.net  wrote:
> > > For an input SWR when using a solid state amplifier against a PT2500
> > Amplifier, why not use something like this?  It will provide a 50hom load
> > to the transceiver input  regardless of the band exercised.  They offer
> > 1db, 2db on up of attenuation, and are matched at 50ohms to the Transceiver
> > input of the amp all the way to 1Ghz or better. The point being here the
> > transceiver will always see a ~50ohm load.  Just a thought.
> > >
> > https://www.ebay.com/itm/370603866564?hash=item5649b639c4:g:s2sAAOSwLzdWRTy4
> > > Thank you,
> > >
> > > Mike
> > > W5CUL
> > >
> > > -----Original Message-----
> > > From: Amps<amps-bounces@contesting.com>  On Behalf Of gudguyham--- via
> > Amps
> > > Sent: Thursday, August 25, 2022 11:48 PM
> > > To: Bob Gibson<w5rg@yahoo.com>;amps@contesting.com
> > > Subject: Re: [Amps] B&W PT2500
> > >
> > > Bob, I’ve got two of these amps in my shop now.  You should be aware
> > that the stock open frame relay is 120vdc and most radios can’t handle this
> > switching voltage/current.  You’ll need a buffer of some sort.  Personally
> > I like installing a soft key internally.  You can use a Harbach SB220 soft
> > key kit or a similar one completely assembled.  I have completely assembled
> > soft key units.  Don’t try to key this amp without one!  Also, be aware
> > that this amp does not have adjustable input networks like many other amps
> > do.  Keep in mind that these amps were designed around being used with tube
> > type radios with adjustable pi-networks.  Therefore the input networks only
> > needed to be “good” as to present an “ok” swr to a tube exciter.  Using
> > this amp with a solid state radio you may find that the input swr is less
> > than stellar.  If it’s a bit high for a solid state radio they will fold
> > back and your power output will be low.  Check your input swr!  If it’s
> > poor there’s not much you can do about it except use the radio tuner.  The
> > input circuits are buried and inaccessible.  Way before it’s time, this
> > amp has a grid trip circuit which is factory set for 400ma.  Lou
> > > Sent from the all new AOL app for iOS
> > >
> > >
> > > On Thursday, August 25, 2022, 11:38 PM, Bob Gibson via Amps <
> > amps@contesting.com> wrote:
> > > I have bought a B&W PT2500 amplifier and I looking for blower for the
> > unit. If anyone happens to have a part number or where to find one..Please
> > let me know..Also has anyone done any kind of a mods to one..20 meter
> > output is low..
> > >      73s Bob W5RG
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