First rate Mullard 5-10 stereo home build

Dandy

Addicted Member
Someone I know only slightly has very kindly passed on to me a superb home built stereo amp from the late 50s or early 60s. The amplifier is a stereo Mullard 5-10 with a huge separate power supply that could also supply power to a tuner, a preamp and a small office block! When I first saw pictures of it, I could see that the power supply was good by looking at the size of the PT and two chokes, and I guessed that the OPTs would be nice too from what I could make out. But, when I got it, I was amazed to see two beautiful matching Partridge C-core transformers under green plastic covers. The units have been in storage for a decade, or more judging by the grime covering the peeling grey-green paint. I believe it may have been built to supply music to a company recreation hall.

I had been advising the owner to restore the amp, before he decided whether to keep it and offered to help. But in the end he simply sold it to me for a very modest price.

I'm a great fan of EL84 amps of this era and have restored and bought quite a few, but this is likely to be the best I've ever heard. I did the obvious checks and cap replacements before first running it and repaired a few issues that may have led to it being put away in the first place. The most serious issue was that the Belling Lee connectors on the cable between the power supply and amp had a broken ground pin, so the whole amp was only grounded via the RCA plug connected to a flimsy later ss phono box. I found this out by getting a kick from it as I removed one of the RCAs! These connectors are obsolete, but I'll try and source a replacement. In the meantime, I've just added a connection between the busbars of the power supply and the amp.

With input direct from a CD player it is incredibly loud and detailed. I've replaced the essential electrolytic and coupling caps, but not begun a thorough service. I also removed a loose brass screw from under the tagboard, wondering what mischief it might have caused over the years...

Anyway, here are some pics. Feeling thankful.
IMG_0584.JPG IMG_0585.JPG IMG_0586.JPG IMG_0582.JPG IMG_0583.JPG
 
That really does not look home made,especially the amplifier portion.The componentry,layout and especially the ''style'' of the build screams Made in England.
I'm thinking maybe Leak,Pye or perhaps even Mullard themselves.

Edit: If it was indeed home made,likely the builder was involved in the manufacturing industry.
 
wow, if thats a kit it looks like one designed by and assembled by a military radio man. Spectacular build quality on that.

If factory made, that comment still holds. I'm sure you've seen some pro made amps that were a complete mess inside.
 
I've replaced the essential electrolytic and coupling caps, but not begun a thorough service. I also removed a loose brass screw from under the tagboard, wondering what mischief it might have caused over the years...

Anyway, here are some pics. Feeling thankful.
View attachment 1011562 View attachment 1011563 View attachment 1011565 View attachment 1011572 View attachment 1011568

Great scroe! Nice transformers and separate power supply to boost! I think you are even more fortunate finding that lose screw before it goes haywire.
 
Thanks for the comments. I'm still pinching myself. I've just learned that the guy who made it worked for many years in the design office at Rolls Royce. So arts and gadget are right. Sadly he is no longer here to tell more, but he gave it to his brother, who gave it to the person who sold it to me...

The decals on the side, not shown on the pictures, are definitely put on by hand, rather unevenly and not with the beautiful symmetry of the internal layout.

Fairlane, thanks for the 'Bad Ass' comment. I have been wondering whether to strip and repaint the chassis, but I think maybe I should keep it battle scarred. It falls into the category of 'heritage'. The power supply is more battered than the amp. Maybe because it is very heavy and was knocked about in storage?

Apologies for the radial 47uf, 100v caps. They are just in for safety as one of the originals only measured 12uf. . I have some 10uf 450v caps on order to replace the 8uf originals used for additional filtering. In the long run I think I might spend more on some high quality components. Not sure what to do about the carbon comp resistors. Metal film all the way, or only replace those that have drifted?
 
Yeah, he absolutely built the sh** out of that amp. That's how you do it.

Other than safety recapping (the electrolytics and any leaky coupling caps), I would clean it as much as possible, and leave it absolutely as is otherwise.

Regards,
Gordon.
 
Awesome find! I have always wanted a pair of partridge transformers, and the C core transformers by partridge are rare.

Are they Partridge P4014? If so they are 8k 43% ul taps.

I have seen stereo Millard 5-10 amplifiets that look identical to yours, with the c core transformers at the back and the inputs at the front. But if I'm not mistaken the ones I've seen had point to point wiring with 2 small tag boards, unlike yours which has 2 huge boards.
 
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Beautiful amp!

Looks like the first day of Christmas came early this year.

I admire how overseas, people would invest in an expensive low powered amp. It speaks to a different way of thinking.

As for re-painting, my philosophy is it's only original once. A careful job polishing the old paint wouldn't hurt anything though.
 
Awesome find! I have always wanted a pair of partridge transformers, and the C core transformers by partridge are rare.

Are they Partridge P4014? If so they are 8k 43% ul taps.

Yup. Couldn't be happier. Although 20% taps give a bit more power, these are plenty loud enough. They are also painfully revealing of poor sources.

Re tag boards, one small tag board for a mono amp is the way the Mullard book does it. http://www.r-type.org/articles/art-003e.htm
 
Yup. Couldn't be happier. Although 20% taps give a bit more power, these are plenty loud enough. They are also painfully revealing of poor sources.

Re tag boards, one small tag board for a mono amp is the way the Mullard book does it. http://www.r-type.org/articles/art-003e.htm

Yes, I'll post some pictures of the stereo Mullard amplifier I'm speaking of when I get home, looks identical to yours, although I don't have much other information on it than that. For these Mullard amps, the transformers make or break it, and in your case, they make it!
 
The wiring in the power supply reminds me of Harry Joyce's work with Hiwatt guitar amps.
 
Thanks for your kind comments. The battle scars will remain, though I have noticed that the top layer is not the original paint job, and the second paint job left the original livery exposed. I've tried to show this in the next post.

The beautiful thing about the layout of the amp is the orderliness. Each resistor is orientated the same way, so you can see at a glance the two parallel channels and easily follow the physical layout from the schematic. The fact that the tube sockets are exposed means that continuity checks and voltage or current measurements can be taken easily.
 
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