Author Topic: Restoration of Leak 12 Point One mono-blocks  (Read 2623 times)

Offline charles

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #30 on: December 18, 2018, 08:52:14 AM »
The Leak uses an EF36/EF37A (low microphonic pentode) valve in its first amplification stage.

I just tried another one in place of the original one.

I measured the total harmonic distortion, it was 0.06%
higher as previously measured.

The one valve has more distortion than the other one.

Offline Ampdog

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #31 on: December 18, 2018, 11:53:04 AM »
Charles,

Just refreshment: The input valve, particularly if a pentode, adds negligible distortion to the total compared to the output valves. It might be that the particular EF37 has low Gm (thus gain), thus there is lower overall NFB. I would rather consider that.

Check the spectrum if you can: Mostly 3rd harmonic (unlikely) does mean it might be the pentode. Mostly 2nd harmonic, likely output stages because of lower NFB.

[But 0,06% (at maximum output?) is lower than spec - so why worry?)]
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline charles

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #32 on: December 18, 2018, 03:44:33 PM »
Ampdog,

Just to be more clear.

Original measurement: THD at rated output with original valve: 0.19%
Second measurement: THD at rated output with replacement valve: 0.25% 

You are correct regarding the Gm of the second valve. Tested it with an AVO valve tester
Ia: correct  Gm: 1.5 mA/V, should be 1.8 mA/V

I still have to check all the coupling capacitors, etc. The THD will probably be much lower after
this exercise. This was just to check its current performance.

I will later conduct an extensive spectral analysis on the amplifier.

I want now to start with the second one that need much more restoration work.

Offline afroaudio

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #33 on: December 21, 2018, 07:49:38 AM »
Charles asked me to upload this photo of the first amp he has restored..

20181215_101657 by Bregtje Cals, on Flickr

Offline Family_Dog

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Re: Restoration of Leak 12 Point One mono-blocks
« Reply #34 on: December 21, 2018, 07:57:34 AM »
Good stuff! Any under-chassis views?


-F_D



-Eric

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Offline charles

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #35 on: December 21, 2018, 08:25:17 AM »
Jonathan, thank you for uploading the photo, it is appreciated.

I will at a later stage post a photo of the under-chassis view.

The second Leak chassis:

Removed the wiring loom, components and hardware from the chassis.

One can remove the whole loom, component board, valve sockets and other hardware as one unit.
The workmanship those days was excellent.

Now to clean the under-chassis from rust will take some time. 

Offline HB

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #36 on: December 21, 2018, 08:30:45 AM »
Good stuff! Any under-chassis views?


-F_D
Sis!! :banned:
When You Come to a Fork in the Road, Take It!            [Yogi Berra]

Offline CAD

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Re: Restoration of Leak 12 Point One mono-blocks
« Reply #37 on: December 21, 2018, 09:45:16 AM »
Good stuff! Any under-chassis views?


-F_D

Eric and his up skirt view requests ,some things just never change  ;D
Light travels faster than sound. This is why some people appear bright until you hear them speak.

Offline Family_Dog

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Re: Restoration of Leak 12 Point One mono-blocks
« Reply #38 on: December 21, 2018, 11:02:12 AM »
 :nfi: What can I say? I'm addicted to such beauty!   :angel:


-F_D



-Eric

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Offline HB

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #39 on: December 21, 2018, 12:42:42 PM »
:nfi: What can I say? I'm addicted to such beauty!   :angel:


-F_D
Isn't leak Scottish? :point:
When You Come to a Fork in the Road, Take It!            [Yogi Berra]

Offline Ampdog

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #40 on: December 21, 2018, 06:53:35 PM »
Leak?  Scottish!!

He was born in West London, went to school in Southall, and built his first hi-fi set at the age of 14 (rather a late starter). That was a crystal set (no valves to distort, so must have been hi-fi ....)

Charles,
While the other lads are playing 'peep-at-girlie's ......', lets get back on track - er - Leak. I presume you have done the preliminary tests for leaking coupling caps; other than that they play no role in distortion matters. (In fact, contrary to popular belief, coupling caps are quite unimportant in hi-fi pursuits. But lets not start that now - don't want to spoil the Christmas spirit - both figuratively and literally.)

But you measured the distortion "as 0,06% - higher than previously?"  Never mind. (also the EFs work at a quite lower current than valve testers use; different Gm then. Again, never mind.)

Hoping you will take time off for "Christmas spirit" (now we can go 'Scottish'). Down here, I still suffer with some small but persistant bit of hum on a Hallé - darn things, in the presence of a 500VA power transformer. C-core pesting and such.  Perhaps to mount the 4 Kg 10 cm cube thing on a wall-wart far away ...
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline charles

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #41 on: January 12, 2019, 08:35:26 AM »
It took me a long time to remove all the rust from the chassis. Now finished with a coat of primer paint.   

One has to be very careful with this operation in order not to damage the paint and lettering of the top part.

An original 12 point one paintwork, even with marks and scratches are worth more to collectors. 

It took some time to clean the loom, component board and other components.

Now for the re-assembly operation.
« Last Edit: January 12, 2019, 08:38:42 AM by charles »

Offline Family_Dog

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Re: Restoration of Leak 12 Point One mono-blocks
« Reply #42 on: January 12, 2019, 08:45:17 AM »
Charles, you do know it is obligatory to post pics...  ;)

Many of us can't read but we do understand photos.


-F_D



-Eric

That Guy in South Africa...
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Offline charles

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #43 on: January 12, 2019, 12:08:33 PM »
Family_Dog, I will do so.

Offline Ampdog

Re: Restoration of Leak 12 Point One mono-blocks
« Reply #44 on: February 03, 2019, 06:17:58 AM »
Er ......  just to be clear here, CHARLES:

I believe F_D means pictures of the amplifier - not yourself .....   :-\
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)