[Amps] Fw: B&W PT2500

Mon Aug 29 20:24:50 EDT 2022

Pretty weird... Has the plate transformer been replaced? Is is a later 
version?

Let us know what you find...

73, Jim W7RY

On 8/29/2022 9:54 AM, Bob Gibson via Amps wrote:
> Yes..The one I had before was 3800 volts and it put out 1500 watts..But this one I have now does not even come close..Gives me a project..
>
>     73s Bob W5RG
>   
>
>     ----- Forwarded Message ----- From: Jim W7RY <jimw7ry at gmail.com>To: " <amps at contesting.com>Sent: Monday, August 29, 2022, 07:20:23 AM CDTSubject: Re: [Amps] B&W PT2500
>   There is something wrong then.
>
> All the PT-2500s that I have owned, put out 1500 watts easily with a
> pair of 3-500s. And the plate voltage was quite a bit higher than yours.
>
> As other have said, 3800 VDC
>
> 73, Jim W7RY
>
>
> On 8/27/2022 10:51 AM, Steve London wrote:
>> 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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>>>>>
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-- 
Thanks and 73, Jim W7RY