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Re: [Amps] B&W PT2500

Subject: Re: [Amps] B&W PT2500
From: Fern Rivard via Amps <>
Reply-to: Fern Rivard <>
Date: Sat, 27 Aug 2022 15:00:26 +0000 (UTC)
List-post: <>
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.

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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.


     ... 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,


-----Original Message-----
From: Amps<>  On Behalf Of gudguyham--- via
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

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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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