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Re: [Amps] B&W PT2500

To: Steve London <>, "Joe Subich, W4TV" <>
Subject: Re: [Amps] B&W PT2500
From: gudguyham--- via Amps <>
Reply-to: "" <>
Date: Sat, 27 Aug 2022 14:46:20 +0000 (UTC)
List-post: <>
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 <> 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.

Steve, N2IC

On Sat, Aug 27, 2022 at 7:26 AM Joe Subich, W4TV <> 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, 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.
> >
> >
> >
> > Thank you,
> >
> > Mike
> > W5CUL
> >
> > -----Original Message-----
> > From: Amps <> On Behalf Of gudguyham--- via
> Amps
> > Sent: Thursday, August 25, 2022 11:48 PM
> > To: Bob Gibson <>;
> > 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 <
>> 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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