Futterman OTL ferrite bead specification - diyAudio
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Old 13th March 2004, 12:12 AM   #1
jwan is offline jwan  Canada
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Lightbulb Futterman OTL ferrite bead specification

Hi all,

I am building a Futterman H3aa OTL amp. Does anyone knows about the ferrite bead specification/value that used for suppress the high frequecny/ocillation in all signal path for 6LF6 tubes in this amp.

I don't know what reange of high frequency should be suppress so I cannot find the right ferrite bead.

Moreover, anyone knows about this amp's power supply shematic/specification?

Thanks a lot.

God bless

joseph
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Old 14th March 2004, 12:37 AM   #2
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Hi,

Quote:
I don't know what reange of high frequency should be suppress so I cannot find the right ferrite bead.
The ferrite beads aren't mentioned in the component list I have seen but I assume they're there nonetheless.
Their purpose is to keep out RFI and EMC so you're probably looking at a frequency range of 500 kHz+.

The ones I've seen on a similar OTL_ actually it's a clone but using PL519s instead_ were only about a cm long and fitted on the input grids (g1).

Quote:
Moreover, anyone knows about this amp's power supply shematic/specification?
Have you taken a look here:

FUTTERMAN.

Cheers,
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Old 15th March 2004, 12:50 AM   #3
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I once have repaired an Futterman OTL 6LF6 based.
On a former repair job clearly ferrite beads where added all over the place to try to cancel oscillations I assume.

I took them all out, made everything original and added 10k grid resistors to all the 6LF6.

Never heard of any (oscillation) problem with that amp since then.

Dick.
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Old 15th March 2004, 02:37 AM   #4
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Hi,

Quote:
On a former repair job clearly ferrite beads where added all over the place to try to cancel oscillations I assume.
While you can replace a gridstopper with a ferrite bead with similar results and even better, doing the opposite isn't recommended on sweeptubes such as the LF6 and KG6s.

Without actual measurements you don't really know what you're doing, ferrite beads need to be placed on the right spot for best results.

This somewhat reminds me of people sticking ferrite clamps on powercords randomly creating all kinds of odd resonances in the process...

Cheers,
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Old 15th March 2004, 07:17 PM   #5
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most ferrite beads or clamps work way outside the audiobandwith, and yes it's very crucial they are on the right spot.

For measurements you need pretty fancy stuff, a normal oscilloscoop is not capabel of doing this.

But for the normal tube stuff we make a gridstopper can cure a lot of weird problems.

Dick.
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