[Amps] SB-200 power supply diodes

[Carl]

Very correct Gerald. Even Dentron and Amp Supply used 2.5A and 3A diodes as 
does Ameritron from the beginning with the AL-80 series with 1N5408's.

I do a fairly large SB-200/220 repair business and 6M conversions and they 
are the only amps with perennial diode problems. The 600ma ratings are 
marginal to start and when you toss in cap leakage and tube arcs its often 
time for lots of smoke as well as transformer failures.

Carl
KM1H


----- Original Message ----- 
From: <TexasRF at aol.com>
To: <w7ry at inbox.com>; <4cx250b at muohio.edu>; <amps at contesting.com>
Sent: Sunday, March 27, 2011 9:00 AM
Subject: Re: [Amps] SB-200 power supply diodes


> Think about this again. The SB200/220 both use a voltage doubler capacitor
> filter hv supply. We know that peak currents in these type supplies can be
> five  to ten times the average current.
>
> So, with a .6 to .7 ampere average, those diodes are taking a 3 to 6 
> Ampere
> hit 60 times every second.
>
> For the miniscule added cost it makes a lot of sense to use 1N5408 diodes.
> Reaming the mounting holes for the larger lead size is a trivial  effort.
>
> If 1N5408 diodes had been available when those amplifiers were  designed 
> no
> doubt they would have been used. Especially so when you consider the
> equalizing capacitors and resistors would not be needed. I would remove 
> them now
> as the parts that are not there can't fail. Who knows what those resistor
> values  might be after upwards of 50 years use?
>
> 73,
> Gerald K5GW
>
>
>
>
>
>
>
> In a message dated 3/26/2011 11:25:25 A.M. Central Daylight Time,
> w7ry at inbox.com writes:
>
> Agreed  Jim!  3 amp diodes are an overkill on the SB-200 and  SB-220.
>
> 73
> Jim  W7RY
>
>
> --------------------------------------------------
> From:  "Jim  Garland" <4cx250b at muohio.edu>
> Sent: Saturday, March 26,  2011 6:24 AM
> To: <amps at contesting.com>
> Subject: Re: [Amps] SB-200  power supply diodes
>
>> Kathy,
>> I'd advise replacing the diode  string in your SB-200 with 1N4007 diodes
>> instead of 1N5408. Not that  there's anything wrong with the 1N5408, but
>> the
>> holes in the  circuit board will have to be drilled out to make them fit.
>>  The
>> 1N4007 will be a perfect fit, and with  a 1A/1000V rating,  will be more
>> than
>> adequate for an SB-200. You should probably  also replace the elderly
>> electrolytics in the amplifier while you have  it apart.
>> 73,
>> Jim W8ZR
>>
>>> From: Kathy  Bookmiller <wb2aio at yahoo.com>
>>> Subject: [Amps] SB200  diodes
>>> To: amps at contesting.com
>>> Message-ID:  <795630.36304.qm at web59714.mail.ac4.yahoo.com>
>>> Content-Type:  text/plain; charset=iso-8859-1
>>>
>>> Thanks to everyone for  their replies. I'm going to order them from
> Mouser
>> and replace  them
>>> all as that is the consensus of the replies I received both  on-list and
>> off. Did take a run over
>>> to my local RS store  and they had some that were close to the 1n5408s 
>>> in
>> spec, but only a  3
>>> pack of them, so will order them all from Mouser.? That seems to  be the
>> norm for RS. It
>>> seems about every time I go in  there for some parts, they'll have them
> in
>> those drawers  in
>>> the back, but only one or none is inside the  compartment.
>>> While waiting for them to show, maybe I'll finally  get into my old
>>> NCL2000
>> that is loosing
>>> it's  drive and has been sitting on the repair bench for a year:) That 
>>> is
>>  how I ended up buying
>>> the SB200 when it showed up on Craigslist  here last summer, while
> waiting
>> for a new set of
>>> tubes to  show up.
>>> So I'll spend the weekend looking for the odd band fill  in the WPX
>>> contest
>> and checking the
>>>  capacitors in the SB200 and cleaning off the board of the old  diodes.
>>> 73,
>>> Kathy
>>  *************
>>
>>  _______________________________________________
>> Amps mailing  list
>> Amps at contesting.com
>>  http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>>
>>  -----
>> No virus found in this message.
>> Checked by AVG -  www.avg.com
>> Version: 10.0.1204 / Virus Database: 1498/3529 - Release  Date: 03/25/11
>>
> _______________________________________________
> Amps mailing  list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps