a bit of fun this morning

M

murray johnson

Guest
Royd Abbot brought round a couple of amps that he wanted checking over so I've been having a look/play this morning.

The first was a rather scruffy Nait (original type). At some point someone had cut the mains lead off this so I had to remove what was left of the old one from inside & make up a new one.

P1010056.jpg


This was actually a pretty straightforward job. While I had it upstairs I was interested to see what the power output was. I remember Naim being very coy about this when the amp came out (I had one in 1983!) I measured it at about 12 Watts into 8 ohms.

As I had owned one previouslyI was interested to see how this one sounded. I don't have & couldn't be arsed to make an RCA to Din adaptor to try the line stage (not yet anyway) so I stuck with the phono input. While my normal cartridge is away for a rebuild I've been trying various ones that I've found lying about. My current favourite is a high output Eroica MC. I normally don't like high output MC's but the Eroica is sounding lovely. Very lush, colourful & organised. If the current ones are anything like this one (probably quite old, don't know) then they are a bargain because this is a great little cartridge.

I tried the Nait first with some bookshelf speakers I've been playing with & it worked pretty well. Its not a forward shouty sounding amplifier. It does remind me a bit of the Olive series stuff we heard at Effem's last bake-off but if anything it is better balanced and less obviously 'tailored' than those were. It does still sit on the harmonics of instruments a bit and doesn't play any very high stuff (in an am radio sort of way)

I then switched over to the horn speakers and the 12 watts sounded far more generous & colourful there. Its never going to be a match for some pushpull EL84's (ie Leak Stereo 20 or HiFi World KEL84)but it was tidy & enjoyable enough. You have to say that they used good quality bits in these, no noisiness in the pots & no audible signs of age. Made a good job of replaying the Brahms Piano Concerto No1 I threw at it. All in all quite pleasant although speakers ideally need to be an easy load and on the high side of 90 dB/W.

P1010058.jpg


Once it was up & running i turned my attention to the Audiomaster 11a valve amp. This looks to me like a full on version of the Mullard 5-20 circuit. Huge Partridge mains & output transformers. A Partridge choke inside. All hard wired with PIO caps in the power supply & signal path. They don't make them like this any more.

Here it needs a little TLC

P1010059.jpg


Here it's had some

P1010060.jpg


A view underneath

P1010062.jpg


A view from the rear

P1010061.jpg


With the valves in. The original input valves EF86 & ECC83 are Mullards, the GZ34 is a Brimar. I've put in a matched pair of Sovtek EL34's.

P1010063.jpg


I had to make up a new mains lead for this one too. The first check is the fuses which seemed ok. Then I tried firing it up without the rectifier to check the heaters work. They don't so thats where I'm up to. I must see what's actually getting to & coming out of the mains transformer. Will post more when I get further.

 

TIU

Artist and daft as a brush
Wammer Plus
Dec 17, 2005
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HiFi Trade?
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Send it to me Murray, I know a local expert on amps!

Good job so far.That Audiomaster is certainly old as it took a round pin mains plug. Must date back to the 60's?

 
M

murray johnson

Guest
there or thereabouts. One of the capacitors says Dec 1957.

 
M

murray johnson

Guest
Doh! This power amp is of the type which powered a separate pre-amp and which was switched on and off by the on/off switch on that. There is an 8 pin socket on the back that would have connected to an umbilical from the pre.Putting a link between two of the pins on this socket means it now comes on when you plug the mains in.

Ok heaters work, ht supply works but one of my EL34's is drawing excess current and 'warms' its cathode resistor more than it should.

Still, its progress!

Perhaps this thread should move to the DIY section.

 
M

murray johnson

Guest
I'm out & about all week, will have to have another go at it next weekend.

 

Defiant

Wammer
Wammer
Apr 8, 2006
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Surrey
You actually plugged that in?
shock.gif.7732780fe7e208b945ce79ca96402fca.gif


Just the thought scares the crap out of me - I'd be the one in the next room stood on a thick rubber insulating sheet
42.gif.6d63386a5269ceda16cdf2e3fe89de81.gif


 

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