>Mike Willis wrote:
>
>>The relay is across the transformer primary, an AC one which activates
>>after about
>>a second. So far so good.
>
>>For the EHT short problem, I have a resistor in series with the EHT.
>
>The problem I was thinking of was when you get a trouble in the
>transformer or bridge or HV caps; then the mains limiting resistors
>don't get switched out.
>
>In message <19980316102421.AAC10088@[205.231.11.72]>, Rich Measures
><measures@vc.net> writes
>
>>> If there is a fault which draws high primary current and
>>>stops the HV output rising to the value that shorts out the resistors,
>>>they sit there with most of your line voltage across them until they go
>>>bang.
>>
>>That is the idea. The resistors act as fuses in the event of a major
>>circuit fault. If all's well, the 7w resistors barely get warm during the
>>c. 1 second step-start.
>
>I guess you can't mistake the fault indication, but I find it easier to
>replace a fuse :-)
>
If a circuit fault blows the mains fuses, replacing the fuses will not
fix the fault, and will result in blowing yet another pair of fuses. If
there is a circuit fault, the fix is going to require plugging in one's
soldering iron. . Fuses for a TL-922 go for $15 each from Kenwood. 7w
resistors go for around $1.50 each.
>>
>>>I guess it's more difficult with a single transformer as you need
>>>to let the auxilliary supplies build up to operate the relay.
>>>
>>- Two or more transformers act like a single transformer when the
>>primaries are in parallel.
>
>Indeed - I was thinking of the difference between a commercial amp with
>one transformer for all supplies and home brew system where the
>auxilliary supplies are often separate.
There is virtually no difference between the values needed for
stepstarting a single transformer and stepstarting two transformers,
providing that the total VA ratings are similar.
>
>>
>>>Having suffered once, I now use a fixed timer which gives a few seconds
>>>delay - if there's a fault then the line fuse blows.
>>>
>>A fixed timer changes only the capital investment.
>
>True, but it's only pennies.
>
A fixed timer costs more than the stepstart circuit in Figure 1, which
uses the existing hv filter as the timing capacitor.
cheers
Rich...
R. L. Measures, 805-386-3734, AG6K
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|