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Audio/Video Hardware => Valves/Tubes => Topic started by: charles on November 28, 2018, 05:53:09 PM

Title: Restoration of Leak 12 Point One mono-blocks
Post by: charles on November 28, 2018, 05:53:09 PM
In he past I restored some Leak TL12 point one valve amplifiers and some I use on a regular basis.

A couple of weeks ago I obtained two Leak 12 point one mono-blocks.

One must be very careful when restoring these Leaks because its value lies in originality.

These sets are basically original as one can get, with original components such the body, tip spot resistors.

These sets need some restoration because of some small rust spots underneath the chassis, etc.

These are the open frame transformer models (circa 1948 -1953) that are the more sought after models.

One has to replace some electronic components but keep the replaced components.

The Leak 12 point one is probably one of the most collectible vintage valve amplifier.

I just hope I have the time to do this restoration.

I will later post some photographs.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: 2wice on November 28, 2018, 06:09:08 PM
Awesome Charles!
Looking forward to the progress pics.

Thanks for sharing.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: peterc on November 28, 2018, 06:21:46 PM
Great find Charles.

Looking forward to following your project

Peter
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Des Miles on November 29, 2018, 08:45:03 AM
Going to be an awesome project! Looking forward to seeing pics of the restored amps.

Just as an aside, our American friends call those old tip spot resisters, " dog bone resisters " and some restorers actually replicate them using modern resistors.

https://www.radiomuseum.org/forum/replicating_old_dogbone_resistors.html

Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on November 29, 2018, 04:43:57 PM
Thank all of you for the encouragement regarding the restoration process.

Regarding the body, tip, spot resistors. Most of the time these resistors keep their value.
This is my experience regarding the other Leaks that I restored in the past.

I will test them to see if the values drifted. I try to keep most of the original resistors.

I have a complete and in good cosmetic condition a spare Leak chassis minus the oil capacitor bank,
output-and mains transformers that I am going to use for one of the mono-blocks and to test all the
transformers.   
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: El Sid on November 30, 2018, 11:24:07 AM
Photos please Charles!  :sd:
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: afroaudio on December 02, 2018, 01:16:46 PM
Here we go gents.....

(https://farm5.staticflickr.com/4836/45231010885_255af17a93_c.jpg) (https://flic.kr/p/2bUUKHg)1 (https://flic.kr/p/2bUUKHg) by Bregtje Cals (https://www.flickr.com/photos/111114546@N05/), on Flickr

(https://farm5.staticflickr.com/4856/46092531952_33b1367f92_c.jpg) (https://flic.kr/p/2de3gUL)2 (https://flic.kr/p/2de3gUL) by Bregtje Cals (https://www.flickr.com/photos/111114546@N05/), on Flickr

(https://farm5.staticflickr.com/4859/45231010645_2c88ff84ff_c.jpg) (https://flic.kr/p/2bUUKD8)3 (https://flic.kr/p/2bUUKD8) by Bregtje Cals (https://www.flickr.com/photos/111114546@N05/), on Flickr

(https://farm5.staticflickr.com/4832/45231010515_8df4677b91_c.jpg) (https://flic.kr/p/2bUUKAT)4 (https://flic.kr/p/2bUUKAT) by Bregtje Cals (https://www.flickr.com/photos/111114546@N05/), on Flickr

(https://farm5.staticflickr.com/4863/46092531502_b851df7fbf_c.jpg) (https://flic.kr/p/2de3gM1)5 (https://flic.kr/p/2de3gM1) by Bregtje Cals (https://www.flickr.com/photos/111114546@N05/), on Flickr
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: King_Julian_S on December 02, 2018, 01:23:23 PM
 
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Family_Dog on December 02, 2018, 02:28:18 PM
It looks like those transformers have cooked, Charles?

-F_D
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on December 02, 2018, 03:15:16 PM
Johnathan thank you for the photos.

Eric, these amplifiers stood for many years probably under a carport.

The output transformers look much better.

If necessary, the mains transformers can be rewound.

The coming week I will start measuring the mains transformers.


 
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: marantz123 on December 02, 2018, 04:07:50 PM
Gorgeous !!! ...and in very very capable hands for restoration for future generations to enjoy...on our shores. Good luck Charles, n plenty pics and step-by-step stuff..please.  :thumbs:
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Ampdog on December 03, 2018, 05:58:01 AM
Ach NO!!!

What a way to spend Christmas for a hard-working man! :(  :sweat:

(You will watch that directly heated rectifier?)
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: fredeb on December 03, 2018, 11:53:19 PM
Wow Charles ! Where do you find all these treasures ?

Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on December 04, 2018, 12:41:40 PM
All over the country

Sometimes it takes lots of time and effort to locate a wanted item.

Some good news regarding the Leak 12 point one.

I have put one of the mains transformers in the spare Leak chassis and
started to measure it.

One must first measure the primary resistance, secondary HT winding resistance and others
and also do an insulation test before applying power to it.

Powered it up: All voltages present.

Bear in mind this is without a load.

This is a relief, now for the second mains transformer.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: AudioEars on December 04, 2018, 07:16:34 PM
I am following your endeavour like a favourite mini series
Cant wait  for your next update / "episode"
I wish you luck and may the resoration angels guide you to a smooth path to success
Kind regards
AudioEars
 
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: peterc on December 05, 2018, 06:56:48 AM
Good luck Charles, lovely project.

Peter
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on December 05, 2018, 02:41:14 PM
Thank all of you for the encouragement regarding the restoration process.

Tested the second mains transformer.

Powered it up: All voltages present.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Family_Dog on December 05, 2018, 04:01:21 PM
That's good news, I was a bit concerned about how they looked in those pics.

To this day I have never even held a Leak 12 in my hands but it sounds like a fun project and I should guess easier to work on than the Quad IIs of the same era.


-F_D
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: El Sid on December 05, 2018, 04:01:37 PM
Great stuff Charles! So both mains transformers have passed the insulation tests and are making the right voltages?
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on December 05, 2018, 06:05:18 PM
^^^^

That is correct.

Size wise, one Leak mono-block is about the size of two Quad II amplifiers.

These mono-blocks have some rust spots underneath the chassis so it may be a better option to remove the wiring loom
and components from the chassis to restore the chassis.

An easy option is to use the spare chassis and populate it with one mono-block's OTF, MTF and Oil Capacitor Block.

This spare chassis will be my test jig to test all the OTF's, inductors and other components.


 
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Family_Dog on December 05, 2018, 07:50:25 PM
I would concur with the above, remove the wiring harness and do it properly. Will make for a very professional quality product when you've finished.


-F_D
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: KNL on December 06, 2018, 04:13:26 PM
Great news on the transformers, looking forward to future posts..
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: VALVAGLO on December 06, 2018, 11:39:45 PM
@ Charles,   Never mind the voltages and such,  What does it sound like?

Just pulling your leg.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Ampdog on December 09, 2018, 05:46:52 AM
Hi Charles,

Apology that I do not always respond to your restoration projects as enthusaistically as others. They don't know: We two setlle that sort of thing at a Sea Food restaurant together with a botlle of .........  ? Much better restoration job after that!

But this matter of using original components af far as possible. Obviously - until they are no longer obtainable. Is my question irrelevant:  Would e.g. H.J.Leak not have used a 'more modern' version of say the dotted resistors if he had lived today, Why do using better modern parts change the 'intrinsic value'?  I can understand Great-Gran's wash table which he used to dunk Marie-Antoinette's head in; it does not need to still be fully operational and all that. But (and I am asking honestly): When guys restore ancient cars, do they go scavenging the boxes and surroundings for the same rusted possibly half-stripped bolts and nuts used in the time in pursuit of originality?  (Not that I have noticed)

In other words, between Gran's toilet table and the restored Ford XYZ, is there not a difference in the intrinsic value?  "Here; I got this Model T with all the original bolts, but unfortunately it does not run ..."  I always ask: "Would the designer not have used newer exact same components if he were to 'restore' his product 60 years hence?"

I am not making a statement one way or the other; I am not a judge with experience in thi field. But in this field you read up more than I do (I hope you do!), so in what actually lies the "value" of a restored say 1938 Excelcior amplifier?  (For that matter, how is the 'value' of any ancient something actually determined?)

Not trying to go off on a different tangent, but it always puzzled me: What are the end requirements regarding any valuable piece of restored "ancientry"?
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on December 09, 2018, 07:20:54 PM
Regarding the original components.

One has to test each resistor to check if it changed its value significantly or is it within the say 10% to 20 % applicable tolerances.
Then keep it. If changed make sure, if possible, that it is the same value, same type, size, etc.

The cathode bypass capacitors have to be changed as well as the coupling capacitors..

The oil capacitor bank is so reliable that in most instances it stays.

I have some 12.1's that has most of its original components and it still has a 0.1 % THD at rated output.

Very important when replacing the components, keep the original components.   

Bear in mind that lots of these 12 Point One's have been serviced in the past, so some of the original components
have already been replaced with modern ones.

The first ones were produced at the end of 1948. These Leaks are very old valve amplifiers. 

The market determine the value of a collectible vintage valve amplifier.

"What are the end requirements regarding any valuable piece of restored "ancientry"?"
At a later stage I will try to answer your question.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on December 12, 2018, 02:53:30 PM
Fitted the MTF, OPT and Oil Capacitor Block onto the spare Leak chassis.

This chassis was already fitted with some replacement components so I did a spot check on most of the resistors. I still have to check all the
capacitors.

I used a variac to slowly reform the oil capacitor block (these are four capacitors housed in a big metal enclosure).

Some good news, according to preliminary tests the amplifier produced an output.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: 2wice on December 12, 2018, 03:40:51 PM
Nice one Charles.

Hope to see some more photos soon.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on December 13, 2018, 04:45:47 PM
Amplifier could not produce rated output.

Found the fault. A previously replacement electrolytic cathode bypass capacitor had the wrong value.

Replaced it with the correct value capacitor.

Amplifier output now correct.

I still have to check the coupling capacitors for leakage.

Measured also the THD and output power.

I will post some photographs of the restored amplifier.

Now for number two. 
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: fredeb on December 14, 2018, 07:04:37 AM
Progress seems fast Charles - well done !
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: mygoggie on December 14, 2018, 11:59:18 PM
Photos will be excellent! Love the thread so far!
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles 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.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Ampdog 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?)]
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles 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.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: afroaudio on December 21, 2018, 07:49:38 AM
Charles asked me to upload this photo of the first amp he has restored..

(https://farm5.staticflickr.com/4892/45679165534_2891bfd48e_z.jpg) (https://flic.kr/p/2cAvEty)20181215_101657 (https://flic.kr/p/2cAvEty) by Bregtje Cals (https://www.flickr.com/photos/111114546@N05/), on Flickr
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Family_Dog on December 21, 2018, 07:57:34 AM
Good stuff! Any under-chassis views?


-F_D
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles 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. 
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: HB on December 21, 2018, 08:30:45 AM
Good stuff! Any under-chassis views?


-F_D
Sis!! :banned:
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: CAD 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
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Family_Dog on December 21, 2018, 11:02:12 AM
 :nfi: What can I say? I'm addicted to such beauty!   :angel:


-F_D
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: HB 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:
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Ampdog 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 Hall - 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 ...
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles 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.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Family_Dog 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
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on January 12, 2019, 12:08:33 PM
Family_Dog, I will do so.
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Ampdog 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 .....   :-\
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: El Sid on February 03, 2019, 02:19:40 PM
Either way - we wait patiently....   ;)
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: afroaudio on February 04, 2019, 12:15:57 PM
Charles asked me to upload these photos of the very nice chassis restoration he has done:

(https://farm5.staticflickr.com/4841/46255816304_3e8203e054_c.jpg) (https://flic.kr/p/2dtt9Ed)20190202_183338 (https://flic.kr/p/2dtt9Ed) by Bregtje Cals (https://www.flickr.com/photos/111114546@N05/), on Flickr

(https://farm5.staticflickr.com/4841/46255816504_889a5eda89_c.jpg) (https://flic.kr/p/2dtt9HE)20190202_183356 (https://flic.kr/p/2dtt9HE) by Bregtje Cals (https://www.flickr.com/photos/111114546@N05/), on Flickr

(https://farm8.staticflickr.com/7835/46255816374_e631e2e815_c.jpg) (https://flic.kr/p/2dtt9Fq)20190202_183348 (https://flic.kr/p/2dtt9Fq) by Bregtje Cals (https://www.flickr.com/photos/111114546@N05/), on Flickr
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Family_Dog on February 04, 2019, 01:41:13 PM
This makes me so eager to build another valve amp, but already I am barely using the ones I have already built. Restorations such as this are always an enjoyable and satisfying process!


-F_D
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Chingy on February 04, 2019, 02:56:56 PM
This makes me so eager to build another valve amp, but already I am barely using the ones I have already built. Restorations such as this are always an enjoyable and satisfying process!


-F_D
Eric, you have no space, send some of the valve amps to me, then you can build more  :whistler: :mates:
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: Family_Dog on February 04, 2019, 03:24:05 PM
Sounds like a plan.... but wait! Valves are not shock-resistant and will break when the courier drops them, leading to their magic smoke escaping and therefore a subsequent loss of performance. Oh well...   :Ooooooh:

-F_D
Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: charles on February 04, 2019, 06:25:06 PM
afroaudio thank you for the uploading of the photos, it is appreciated.

The next step is to replace the loom and other components that will take some time to complete.

Title: Re: Restoration of Leak 12 Point One mono-blocks
Post by: marantz123 on February 05, 2019, 10:33:06 PM
This makes me so eager to build another valve amp, but already I am barely using the ones I have already built. Restorations such as this are always an enjoyable and satisfying process!


-F_D
Barely using them...FD...I understand why u throwing stuff out..man..that couldnt be an easy decision. Was offered a pair of decent looking Sansui L75 recently...just had to walk away...gotta be strong ..dunno how u guys do it.