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Multi-Way Conventional loudspeakers with crossovers

Telefunken TFK6006 50ohm Lpads
Telefunken TFK6006 50ohm Lpads
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Old 20th December 2018, 06:56 AM   #1
Raccoon1400 is offline Raccoon1400  Canada
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Default Telefunken TFK6006 50ohm Lpads

A customer brought me a pair of Telefunken TFK 6006 speakers needing repair. They are a 4 way design.

I discovered one of the two L-pads in each speaker is toasted. The reset switch doesn't seem to hot either. The L-pads are 50ohm, which seems to be unusual.

What are my options for replacement?
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Old 20th December 2018, 09:53 AM   #2
Lojzek is offline Lojzek  Croatia
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This is how Visaton l pads measure. Check your own and ask additional information at the stores.
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File Type: png Visaton Lpads.png (36.6 KB, 111 views)
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Old 20th December 2018, 10:05 PM   #3
Galu is offline Galu  Scotland
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Here are links to the Visaton L-pads mentioned by Lojzek:

LC 57 | Visaton

LC 95 | Visaton
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Old 21st December 2018, 05:47 AM   #4
Raccoon1400 is offline Raccoon1400  Canada
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Quote:
Originally Posted by Lojzek View Post
This is how Visaton l pads measure. Check your own and ask additional information at the stores.
I can't quite make sense of this diagram? It is showing two Lpads of different resistances? Or maybe each L-pad has a different resistance on each side of the center tap?

I suppose if I use a lower resistance L-pad I just won't be able to turn the mids down as much, right? (It is the mid level controls)
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Old 21st December 2018, 06:19 AM   #5
Raccoon1400 is offline Raccoon1400  Canada
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Maybe I'm not quite understanding what an Lpad is. Maybe these aren't actually Lpads. There are three terminals but only two are connected.

What I am sure of is whatever it is, it is very dead.

Here's a picture. (There were two wires connected to the open pot but one broke off)
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File Type: jpg IMG_4556[1].jpg (1,018.8 KB, 86 views)

Last edited by Raccoon1400; 21st December 2018 at 06:31 AM.
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Old 21st December 2018, 08:55 AM   #6
Lojzek is offline Lojzek  Croatia
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Quote:
Originally Posted by Raccoon1400 View Post
I can't quite make sense of this diagram?

Visaton schematic shows that an L-pad is consisted of 2 variable resistors. The one between terminals 3(IN) and 2(out) can have a resistance from 8 ohms to 0, and the one between 2 and 1(common) can have any resistance from 0 to 40 and infinitely high. The knob turned completely to the left would have maesured like this: 8 ohm (from 3 to 2) and 0 (from 1 to 2). The more you turn to the right the lesser becomes the first value and the larger the second one thus making the drive unit louder.
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Old 21st December 2018, 12:52 PM   #7
Galu is offline Galu  Scotland
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Yours are not L-pads, they are variable resistors (rheostats).

Ceramic Casing 25W 50ohm Variable Resistor Wire Wound Rheostat: Amazon.co.uk: Business, Industry & Science

You need something like the above. Connect to middle (wiper) termnal and one outer terminal.
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Old 22nd December 2018, 12:58 AM   #8
ICG is offline ICG  Germany
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Location: I had a Déjà Moo - I've seen that BS before!
You should replace the L-pads with normal voltage divider, it sounds a LOT better, these darn things eat a lot of details.
Try different combinations, R1+R2=~40 Ohm, usually R1 (serial) is a low value (probably 1-5,6 Ohm), the R2 (parallel to -) is in praxis the much less critical in value (22-39Ohm ca.).
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Old 22nd December 2018, 02:08 AM   #9
Galu is offline Galu  Scotland
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How old are these speakers?

It was common to use 50 ohm rheostats to control levels in vintage speakers.

This usually pre-dates the introduction of variable, constant impedance L-pads.

The photograph clearly shows that rheostats were used and not L-pads.

If you simply want to renovate these speakers to original spec, then use 50 ohm rheostats.
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Old 22nd December 2018, 07:03 AM   #10
Raccoon1400 is offline Raccoon1400  Canada
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Quote:
Originally Posted by ICG View Post
You should replace the L-pads with normal voltage divider, it sounds a LOT better, these darn things eat a lot of details.
Try different combinations, R1+R2=~40 Ohm, usually R1 (serial) is a low value (probably 1-5,6 Ohm), the R2 (parallel to -) is in praxis the much less critical in value (22-39Ohm ca.).
The customer doesn't want to spend too much on these, and I have to redo a bad refoam job too. So I think this is the way I'll go as it is also the cheapest way.
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