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[Amps] SB-220 Transformer Problem

To: <amps@contesting.com>
Subject: [Amps] SB-220 Transformer Problem
From: halbritt@harm.org (Heath Albritton)
Date: Fri, 5 Apr 2002 14:31:38 -0800
On Fri, Apr 05, 2002 at 01:58:41PM -0800, Richard wrote:
> >I concur.  I don't feel bad for ordering the new caps, I just feel bad about
> >the fact that I assumed that they were bad to begin with.  There is also the
> >heat issue with the bleeder resistors that the Harbach part solves.
> >
> ?  How much $ does he get for Caps and equalizer Res.?

He gets $125 for the pack which can be found on his SB220 page:
http://www.harbachelectronics.com/reference/harpg3cart.htm There is also a
larger image of the pack: http://www.harbachelectronics.com/pictures/fb-220.jpg

The pack includes the caps, a PCB, bleeder resistors, and a frame.  Given that
I haven't run the amp yet, I can't attest to the performance, but I'm sure they
work fine.  However, I am very pleased with the fit and finish of the whole
pack as a unit.  He uses Cornell-Dubilier 480v 210uF computer grade caps which
he also sells independent of the pack for $75/8.  When looking for
replacements, the cheapest caps that I was able to find were about $64/8.
Given the quality of the pack, in my opinion, the price delta of $50 is worth
it.

> >That was one of the "various things" that I tried which resulted in more
> >smoke and a tripped breaker.  Did I mention the smoke? 
> 
> ?  Yes. The transformer is history.  

I'm not surprised.

> > I'll plan on making a 
> >call to Mr. Dahl and see about getting a replacement, though I'm not sure
> >what the circuit should look like with a tapped seconary vs. a tapped
> >primary.  Making that change might be beyond my expertise.
> >
> ?  I would order a 1200/800 Vrms secondary; dual 120V, 60Hz-only primarys on
> a core that will fit. Potting is worth the money on a HV transformer.  You
> should be able to switch secondary taps with the extant SSB-CW switch
> Provided you don't hot-switch (the LV-HV switch needs to go closest to the
> mid-point on the FWD, which is what Kenwood did on the TL-922) -   Dahl's E-I
> cores are good.  Grade-5 Hypersil® cores are a bit better, but they do not
> fit well in the rectangular space available.  Dahl's transformers typically
> have low winding R, so a step-start is advisable.  No-load anode potential
> should be around 3500VDC/2400VDC.  P-out should be c. 300w more than stock on
> SSB.  However, more V =s more VHF gain, so the parasite suppressors need to
> be improved and glitch protection is not a bad idea.  

Parasitic suppressors have already been installed and I'm definitely going to
adding glitch protection.  As a result of this post, someone has offered me an
original unused transformer which would end up costing less than half as much
as a new Dahl unit.  I wonder if it would really be worth it for the extra 300W
or so to go with the new Dahl transformer.  I welcome opinions.

> good luck, with your Heath, Heath

Heh, I shall need it.


Thanks,

Heath Albritton (KG6GTX)

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