Directly grounding the grids increases the stage gain which may lead to
instability on the highest bands. This also adds more stress to the
bandswitch.
Adding another 100-150W wont sound any louder at the other end.
Many years ago, maybe 1992-3, I picked up a SB-221 with a blown transformer
and bandswitch and did a bit of experimenting. With an outboard PS
delivering 3200VDC under a 900ma load I was able to get 1700-1800 out
160-10M with 100W drive. The switch was a JVC 9000 series similar to Amp
Supply and others. The 221 and late 220's came with the wide spaced Tune cap
which was also offered as an upgrade by Heath. The grids were left as built.
Cooling was with a 8" diameter muffin fan with a 2 speed switch on the front
panel, I dont know if the Harbach fan has enough cfm to cool graphite tubes
at that power. Increased air also generates more noise.
That amp is still around, I saw it on Fleabay late last year.
Carl
KM1H
----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <amps@contesting.com>
Sent: Wednesday, June 09, 2010 6:24 AM
Subject: Re: [Amps] Peter Dahl / Harbach SB-220 transformer
> Strikes me as the only good way to get more out of an SB-220 - avoids
> stress on the bandswitch and tune cap due to higher voltage. I wonder
> if anyone has ever combined this with directly-grounded grids, which
> W8JI and others advocate for increased power gain.
>
> With the original grid circuitry, my SB-220 gets just about 1.2 KW out
> on 80 and 40, decreasing to about 900 watts on 10, all with 100 watts of
> drive.
>
> 73, Pete N4ZR
>
> The World Contest Station Database, updated daily at
> www.conteststations.com
> The Reverse Beacon Network at http://reversebeacon.net, blog at
> reversebeacon.blogspot.com
>
>
> On 6/8/2010 9:56 PM, James wrote:
>> Carl, It's an upgrade. I have the Dahl installed. The original supplied
>> something like 900 mils, the Dahl 1.3 amps with the same 3.2 kv...but
>> less
>> sag.
>> Now you don't HAVE to cut the safety screen... some people just let it
>> bow,
>> it's just a little taller.
>> This is important, however, you can't just drop the xfmer in. The
>> mounting
>> bracket will catch on the lips of the chassis. You have to unbolt the
>> side
>> and slide it in that way. You also have to drill new holes.
>> Now the 220 was a 1 kw amp. I could get 1.3 If I drove the snot out of
>> it.
>> This was on a Kenwood sw2000 meter (and yes meters lie.) After the Mods..
>> new caps, diodes, bleeders, and xfmer..I could get 1.6 kw out. Jim KB4RMN
>> ----- Original Message -----> ----- Original Message -----
>>
>>> From: "Bill VanAlstyne W5WVO"<w5wvo@cybermesa.net>
>>> To: "[Amps]"<amps@contesting.com>
>>> Sent: Monday, June 07, 2010 10:45 AM
>>> Subject: [Amps] Peter Dahl / Harbach SB-220 transformer
>>>
>>>
>>>
>>>> I'm interested in hearing from anybody who is knowledgeable about the
>>>> SB-220 replacement transformer by Peter Dahl that Harbach is
>>>> offering --
>>>> specifically, wehether it has significantly higher power capacity than
>>>> the
>>>> OEM Heathkit transformer and/or a higher voltage output. They also say
>>>> you
>>>> have to cut a hole in the inside top cover to accommodate its size,
>>>> which
>>>> is not a big deal for me -- but if it isn't a SIGNFICANTLY more
>>>> powerful
>>>> transformer, there's no real reason for me to shell out the bucks for
>>>> one.
>>>> I guess the short form of the question is: Is this transformer a
>>>> replacement or an upgrade?
>>>>
>>>> Bill W5WVO
>>>> _______________________________________________
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>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
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>>
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