Help using 100v Line speakers

[EF80TVVALVE]

Hi, I'm hoping some members can help me understand 100v line speakers. These are not something I have used before and I am a bit unsure on matching them to the amplifier. Firstly we will start with the speakers themselves, they have appeared on the forum a few times, I bought them to fix up and use with a 20w Mullard amplifier with 100v taps. They are made by GEC, each cabinet houses 5 speakers and 5 transformers. The overall DC resistance of each cabinet (5x Tx in parallel) equals close to 44Ohm.

These ones do not have tapped primaries, they have two connections marked A and B. The secondaries are numbered 1 to 4. The DC resistance of the speakers measures around 5ohm and the DC resistance of the primaries measure 210ohm. My question is how do I set these up to work correctly with the 20w amplifier? I don't want to cause any damage to either so I'm hopimg some members with more experience on this topic can help shed some light on this.

[peter_sol]

Just connect the leadafrom the speaker to the 100v line out of the amp
job done.

[Trevor]

yes i agree in the first instance
but why so many transformers i suspect that the centre speakers will be tapped at a higher power level this will effect the polar response pattern
Something i picked up from a Briggs handbook
years ago
Trev

[samjmann]

From what I can recall the minimum impedence that the amp should be looking into is : line voltage squared/amp power in watts. ie 100X100/20=500 ohms.
This was measured using a line impedence meter that injected a 1KHz tone into the 'network' then gave the minimum load impedence to give full power. There's a lot of free info on some PA sites on all of this. Chances are if you connect up it will work OK as described in the previous post. When I measured systems I often found mismatches that were way out, but I never recall the amp being damaged. Hope this helps. SJM.

[Hartley118]

Just think of the power amp as a voltage source. At its maximum output, the amplifier will be giving 100V. Each speaker will then draw it's rated power. As Trevor says, the power input to each speaker in the line source column will be arranged to give the right directional polar diagram.

Martin

[Refugee]

They actually consist of five individual 100V line speakers with volume taps on there individual transformers.
The way they used to be used was to run the amplifier so that the output was 100V and any speakers that needed less power were set to lower taps.
Those speakers had at some time been tuned to a particular listening room and were most likely bought from new with the facility do do just that.
They more usually have a single transformer. The volume taps are always on the secondary.

[EF80TVVALVE]

Thanks for all of the help. I just wanted to be sure I wouldn't run the risk damaging them or the amp. This particular pair do sound very nice, I've been reading about 100v systems and they seem to receive a fair bit of stick regarding reproduction quality espacially bass response. If anything with this pair the bass reproduces very well and has a lot of headroom. The only niggle I have found with them is at really high frequency they are a bit deaf, although it really is dependant on the mix of the record too. Easy to get around by setting the volume with the bass cut to drive the HF a bit better and then 'fill in' the bass to the appropriate level. Does anyone habe any info on GEC BCS series equipent or speakers? From what I can see they were all PA equipment

[dseymo1]

Yes, almost always PA or sound reinforcement applications - the advantages being lower loss over long cable runs and the facility to set up a chain of speakers with different ( or variable) outputs. Low frequency response is mostly determined by the transformers used, which were often designed down to a price for speech and background music use. The larger columns like yours are sometimes ported and include better transformers, as they were used for incidental music, dances etc. HF is more to do with the drivers themselves and the phase effects due stacking them. You might find it interesting to temporarily isolate one driver and run it from a low-impedence source, just to see what difference there is.

[OscarFoxtrot]

If your amp also has a 70 volt output tap, you can run the speakers from that and they'll run at half the speaker rated power, so a lot less risk of overloading.

I'd be surprised if, intended for a valve amp, the columns were more than 10 watts each. a 20 watt amp would be typical for a small hall.

[Refugee]

These speakers are certainly more posh than the ones I converted from 100V to low impedance for use on noisy camp sites in the 1980s.
They had a single transforms about 2/3 the size of one of the type we see here to drive the entire cabinet.
They must have been installed in a posh establishment in there day.

[PaulR]

Originally Posted by OscarFoxtrot

If your amp also has a 70 volt output tap, you can run the speakers from that and they'll run at half the speaker rated power, so a lot less risk of overloading.

I'd be surprised if, intended for a valve amp, the columns were more than 10 watts each. a 20 watt amp would be typical for a small hall.

I would like to try running a 100v line speaker from my Clarke and Smith tuner amp which has a 75v output for a vintage themed church summer fair later in the year. Am I right in assuming it will be safe?

[OscarFoxtrot]

You need to check the wattages but yes, it is safe, it's an established way of providing large numbers of low powered speakers.

Stick to below about 80% of am power though.

[PaulR]

Thanks - I imagine the amp is no more than 8 - 10 watts so will look to see whether the speaker has a tap lower than that.

[OscarFoxtrot]

If it's an 8812 that's 12 watts output.

If necessary you can use a tapped transformer attenuator to further change the speaker volume/wattage eg
https://www.cybermarket.co.uk/shop/p...-controls.html

the attenuator needs to be rated at the speaker wattage not the amp wattage.

Or you could use an 100V output transformer with 8 and 16 ohm taps as a stepdown autotransformer. Input to the 16 ohm, output to the 8 ohm, [do I have that the right way round) and that will halve your speaker wattage. You get what is probably a good enough frequency response, and the power/sizing is easy - just pick one rated at enough or more output power. Tape off the primary leads - those will have hundreds of volts on them.

[PaulR]

Hi yes it is an 8812. I am pretty sure that the speaker has a lower tap than that so all should be OK. I could use an ordinary speaker but I just fancy trying the line output

[OscarFoxtrot]

10 classrooms at 1 watt (don't know what that is in Badminton Courts)

[PaulR]

It is odd that you never see the matching speakers for sale whilst the radios and record players turn up quite often

[OscarFoxtrot]

I suspect the radios etc were taken home by teachers, but the speakers get lost in building renovations.

[PaulR]

I seem to remember that the schools were quite nicely wired for them. There were sockets in every classroom with individual volume controls and two speakers in the hall, again with a volume control set into the wall. Our local school still has the fittings but no equipment of course.