>On Fri, Apr 05, 2002 at 07:00:44AM -0800, Richard wrote:
>> - Filament/bias transformer failure is more common because the
>> transformer is not fused. So, with the stock biasing scheme, a shorted
>> tube can destroy the fil. transformer in minutes. Changing the stock
>> config from V-cutoff bias to R-cutoff bias will prevent a repeat
>> performance. [see SB-220 circuit improvements article on my Web site]
>
>Some of these improvements have already been made to this amplifier. You
>have an excellent site, btw.
>
? Tnx.
>> Original 220 filter caps typically fail in c.20-years, so it's probably
>> time to change them.
>
>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.?
>> Good means <200uA leakage at 400V - plus c. 200uF per..
>
>I'm not sure about the leakage, but they did give 200uF per, actually
>closer to
>270uF per. In actuality, they probably aren't "good". I'm certainly not
>going
>to re-use them.
>
>> >At this point, my main question is what is the best
>> >path to determining and resolving the problem with the plate transformer.
>>
>> Unsolder one HV secondary wire, apply 120/240V. If it trips the
>> breaker, there's a shorted winding. If this eventually happens to mine,
>> I would phone Peter W. Dahl and order a custom replacement with a tapped
>> secondary in lieu of a tapped primary since it makes for a more efficient
>> transformer design.
>
>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'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.
>...
good luck, with your Heath, Heath
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
end
|