NL/DE : Restored 1kW Philips audio amplifier from 1955.

This topic has 7 replies, 4 voices, and was last updated April 18, 2014 at 9:03 pm by damo666.

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June 28, 2011 at 8:45 pm #1051198
General Lighting
Moderator
I asked some old boys (from my fathers generation) on an electronics mailing list I am on what a high power audio amp looked like before the 1990s, as it was really only in the 90s with the rave scene that I had ever seen one.

They sent me to a link on an electronics magazine, which led here. Apparently the German dude picked it up for only a few Euros and it was in virtually perfect working order, just needed basic restoration.

EL6471 1kW Großverstärker (Type 102408)
June 28, 2011 at 9:05 pm #1241524
sinner69
Participant
cool pictures….nice tubes! but no fingers into that 3000 volts….
June 28, 2011 at 9:21 pm #1241525
cheeseweasel
Participant
Nice. Any ideas what it would have been used for? Looks like a pretty specialist piece of kit, not something you’d have found at the average rock ‘n’ roll concert or whatever was going on in those days.
June 28, 2011 at 9:30 pm #1241520
General Lighting
Moderator
it was part of a series of similar amplifiers used for fixed public address / sound reinforcement applications in large buildings such as cinémas and theatres. Until my late teens, Philips always made some decent kit..

Amplifiers with valves.
December 26, 2011 at 4:26 pm #1241521
General Lighting
Moderator
just been reading the service manuals on this site and there is also a EL6472 with 2kw audio output… first page of the manual has this on the front

[ATTACH=CONFIG]81182[/ATTACH]

WARNING:

IN THIS AMPLIFIER THE FOLLOWING VOLTAGES ARE PRESENT

+4750 V: anode supply to final stage
+ 700 V: supply voltages of various preamplifier stages.

When the amplifier has been disconnected from the power, you must wait 1 minute before removing the covers or working inside the amplifier.

During this time the high voltage capacitor C11 discharges itself through R13 and R14

SO BE CAREFUL!

to put this into perspective, an industrial mains power supply is 400V and that big electric train in the other video from NL I posted only uses 1500 V. Also it weighs 245 kilos (so about 4 times as much as I do).
December 29, 2011 at 3:43 pm #1241526
damo666
Participant
I’m glad amps that big don’t have to be moved about anymore lol.
January 10, 2012 at 3:14 pm #1241522
General Lighting
Moderator
just below the safety warning it explains how to move the amp (the valves have to be let to cool down and removed and stored in secure packaging) but in them days you normally brought the people to the sound. It can drive not just 100 volt speaker lines but 250 volt lines (this is so telephone cable can be used which is thinner and less expensive). Its not actually as scarey or dangerous as it seems though if the safety rules are followed and by the standards of the time had really good audio quality…
April 18, 2014 at 9:03 pm #1241523
General Lighting
Moderator
whilst looking for other stuff I found the videos of this amp in action. The German dude only had a 250W speaker available so had to use “soft music” for one of the tests

https://www.youtube.com/watch?v=btSg2SX3lUs

this one is the full 1kw (output to the loudspeaker and some dummy load resistors)
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