A pair of 545s - at last!

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TrevorTron
Berichten: 5
Lid geworden op: 26 apr 2024, 19:48

Hello all, new member here from Scotland.
After searching for at least 15 years I finally found a pair of (affordable) RH545s. I know from personal experience how good the smaller ones sound so it seemed the logical progression.
They were sold as "not working", I got the two speaker boxes and a basket full of bits! Oh, and a pile of A3 sheets of paper resembling a service manual.
Once I had established that everything was there, I checked a few random electrolytics with my Atlas ESR meter and they all returned surprisingly excellent readings. (I don't recall ever having to replace a blue Philips-branded elco).
I then re-fitted the boards (while checking for any obvious problems) and checked one box at a time using a variac to ramp up the voltage gradually.
One of them showed very little sign of life - no Power or Auto LED but the Roll Off LED did light when the knob was turned.
The other speaker did a bit more. I heard the familiar click of the relay (I use 541s daily for background music in my workshop!) and when fed with a signal I got distorted sound from the mid & hi freq drivers. When I switched off the power at the mains the sound became clearer and the LF came to life briefly as the big caps discharged. I put the power on again and the distorted sound was back. As I looked (and felt/smelt) around for anything obvious, the sound gradually got clearer and clearer, and after about 5 minutes I was rewarded with possibly the nicest sound I have EVER heard from a speaker box of this size. Obviously it will need further investigation to establish why it takes so long to 'warm up' but for the moment I am one very happy bunny!
So with a reasonably 'working' unit I decided to do some board swapping to locate the fault with the dead speaker.
First up was the power amp - perfect! It fired up straight away and sounded just as good.
I was then going to swap the board that lies flat, but noticed some differences which I will illustrate later when I take more photos.
So I took the front panel section from the sick speaker and tried that in the 'good' one. I noticed someone has written "Poor" on it - and they were correct! Hardly any sound (very distorted) and a worrying background 100Hz hum, I stopped in case it caused more damage.

More tomorrow as I am tired and will start making mistakes!
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HermanH
Berichten: 6818
Lid geworden op: 22 mei 2015, 21:39
Locatie: Omgeving Breda

Great job sofar.

As it's Kingsday today I guess not many freaks will read this post and comment. Probably tomorrow when they are sober again.
Met een kleinere auto neem je minder mee
pjottr
Berichten: 1145
Lid geworden op: 11 jul 2018, 23:57

Nice :clap:
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fastfolkert
Berichten: 1145
Lid geworden op: 26 jul 2017, 23:12
Locatie: NE-Fryslân en Twente

Hi Trev, interesting find and I will closely watch this topic!
(and good to have someone from Caledonia on this forum ;) )
Mancave op zolder met hifi uit de 70's-90's waaronder Quad, NAD, ARCAM, Meridian, Mission, Cyrus, B&W, DUAL en Philips natuurlijk!
TrevorTron
Berichten: 5
Lid geworden op: 26 apr 2024, 19:48

Well so far so good!

I have had one box singing on all 3 drivers, but there is a bit of 100Hz background hum from the bass unit so I guess some new caps will be going in soon. But.... WOW!! I absolutely LOVE it!! Everything I expected and some! I just cannot wait to get them playing as they should and have them in my listening room forever.

The other one is now working on LF and MF, nothing from the tweeter. There was nothing to start with but I found two cracks on the front (controls) circuit board and a broken capacitor. Once they were addressed we had life - but still nothing from the tweeter. (It is a slow overall process as I have to jump back & forth between these and 'paying' jobs!).
I did manage to rule out the power amps as both boxes performed the same when the amplifier sections were swapped.

What I have also discovered is that it is not a 'matching' pair. There is a significant difference in serial numbers. There are some minor differences on the 'bottom board' connections and only one (presumably the later one) has a woofer protection circuit. If all goes well I will probably update the older one with this 'insurance policy', it makes sense does it not?
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Older one, note the black wire which is not present on the other box.
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mae
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Berichten: 7333
Lid geworden op: 17 nov 2013, 02:42
Locatie: Randstad
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TrevorTron schreef: 06 mei 2024, 23:19 What I have also discovered is that it is not a 'matching' pair. There is a significant difference in serial numbers. There are some minor differences on the 'bottom board' connections and only one (presumably the later one) has a woofer protection circuit. If all goes well I will probably update the older one with this 'insurance policy', it makes sense does it not?
A significant difference would be in the first 5 digits of the serial number, usually. Do you have the serial numbers handy? With a bit of luck I can draw some conclusions from them or at least show you how to derive the revision and production date.

Also, I'm trying to estimate the total production.
TrevorTron
Berichten: 5
Lid geworden op: 26 apr 2024, 19:48

[/quote]
A significant difference would be in the first 5 digits of the serial number, usually. Do you have the serial numbers handy? With a bit of luck I can draw some conclusions from them or at least show you how to derive the revision and production date.

Also, I'm trying to estimate the total production.
[/quote]

I did try to attach images of the serial numbers but could not for some reason. Here they are.
I appreciate your assistance in researching their history.
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