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Old 25th January 2004, 11:52 AM   #11
Morse is offline Morse  United States
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Hi EC8010, Sy;

I like the ideas I've seen so far for cutting back on the turnon thump. Here are a couple of other suggestions for helping Morfeas improve his amp (not just turnon thump); what does everyone think of them?

1. Put the smaller cap first in that CLC bridge - maybe even add a smaller first leg to his CLC filter just to take it easy on his PS trafo. Charging those enormous HV caps has got to be stressing his trafo!

2. Put an NTC (Negative Temperature Coefficient) thermistor inline with the B+ (in front of the caps) to help limit the current flow.

3. Drop the size of the filter caps and rely more on inductance to provide filtering.

4. Use a hybrid or indirectly heated valve rectifier instead of ss - obviously this won't work with the enormous current draw of those caps at startup. A 5AR4 has a textbook max lead cap size of 40uF IIRC, for example - I'd keep it under 30uF personally.

Just ideas. Good luck Morfeas!
All the best,
Morse
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Old 25th January 2004, 12:27 PM   #12
morfeas is offline morfeas  Greece
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@EC8010: hope so. I didnít get that big bang at the lab with 89db speaker. But my main speakers are 100db.

@Sch3mat1c: žF (microfarad)

@SY: unfortunately the PT is one. So Iím going to try it on the secondary AC HV line.

@Morse: there is a thermistor on the primary of the PT. PT is 630VA. No space available on the chassis for an extra tube.

Thanks to all for the replies.
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Old 25th January 2004, 01:30 PM   #13
SY is offline SY  United States
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It's best to use the current limiter on the primary side. They don't tend to like high voltages. If it causes the filaments to warm a bit more slowly, that's probably OK (that's the way Eico did it in some of their classic tube amps with SS rectification). The main thing is to not do the sort of hot switching you've got set up now.
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Old 1st February 2004, 08:37 AM   #14
morfeas is offline morfeas  Greece
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Default All OK

Problem solved.

Moved the relay just after the bridge with 4k7 in parallel.

Thanks to all.

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