[Amps] B&W PT2500

Sat Aug 27 11:51:16 EDT 2022

With the Commander down, this seemed like a good time to fire up the
PT-2500A. It's the B&W version.

20 meters:
Standby Vp = 3300 volts
Loaded Vp = 2800 volts
Ig = 250 mA
Ip = 760 mA
Po = 1180 watts

73,
Steve, N2IC

On Sat, Aug 27, 2022 at 9:18 AM Fern Rivard via Amps <amps at contesting.com>
wrote:

> 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 at 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 at 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 at 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 at contesting.com>  On Behalf Of gudguyham--- via
> >> Amps
> >>> Sent: Thursday, August 25, 2022 11:48 PM
> >>> To: Bob Gibson<w5rg at yahoo.com>;amps at 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 at 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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