Re. #1855

Dear Leak 12.1 lover (Henniet..),

A normal working Leak TL12.1 should NOT hum to the extent that you described (i.e. audible within 1-2 meters).

Noise including hum from TL12.1, eg from my pair of TL12.1, is hardly audible within 1 metre from a sensitivity 85 dB Rogers BBC LS3/6 variant speaker, and noise is hardly audible within 3 inches from a 82 dB LS3/5A, i.e. sound should be CLEAN even without any AC supply filter.

AC supply filter or cleaner will NOT erase the noise problem that is resident inside the amp!

BTW, re. #1850: Have you got rid of the abnormality in sensitivity (EF36 vis-a-vis EF37A) in your pair of amps?

Don't waste your money. Got the help from an experienced tech to restore your amps straightly.


最後修改時間: 2025-12-06 22:00:50

師兄其實我係求其響淘寶搵，其實你可以響淘寶再睇下其他牌子或者有啲更好嘅方案啱你。

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Thanks, do you have a link to the shop?

試試呢樣嘢。

I have a new challenge.
One of the amps that was recently restored and capacitors replaced has a problem. The problem is that I can hear a buzzing noise coming from the transformer. It is a mechanical noise. It is audible from about 1 to maybe 2m from the amp. At first when the amp is switched on it is quiet but after after few minutes the noise starts to appear.
Is this a problem? Can I keep on using the amp?
Can it be fixed?

600 & 620 Ohm wire-wounded resistors

600 is vintage
620 is current production

Yes, according to the official schemetics, it is 600 Ohm 5-7 Watt wire wounded.

In reality you can find 620 Ohm which is also good and it can extent the life of KT66s.

最後修改時間: 2025-12-02 17:19:41

Hi
Please confirm the specification of the cathode resistor. Is the following correct?:
600ohm, wire wound, 5 to 10 watts?
Is this correct?

This easy-to-access "tag-board" (same as LEAK TL12.1's tag-board, just when a replacement is needed. I have some stocks)






最後修改時間: 2025-11-22 12:55:56

Thanks for sharing. South Africa is a very different world and happy to know you and your world.

Are there electronic components shops around your town/city, or you must buy from online shops?

If you can source your own supplies, try the restoration by yourself, given one of the purposes of LEAK TL12.1 having easy-to-access "tag-boards" is for EASY repair/restoration!

I know some idiots in electronics could do restoration themselves. Just read the users manual of a good multi-tester 萬用錶 for measuring AC/DC voltage, ohmage of resistors/coils, capacitance of caps - Just junior secondary school physics is sufficient (if can remember the lessons).

You probably need courage and carefulness in handling high voltage e.g. over 100/200V AC, over 400-500V DC more than electronics knowledge. Skills can be grown with more and more practices in using a soldering gun!

Back to your concerns about EF36 vis-a-vis EF37A in your TL12.1s, it should be absolutely clear in mind that two normal working EF36/EF37A tubes should give very similar performance (except that EF36 is more sensitive to RF interferences) to the extent that none should be "softer" (except when one of the tubes is in fact weak and out of its spec).

Get two new-old-stock (NOS) EF37A tubes to replace them.

最後修改時間: 2025-11-22 06:14:14

I have 2 pairs. I am referring to the bottom picture which shows one of a pair. The top picture is a different pair and not part of this question. Referring to the bottom one it looks different now because it was recently recapped and some resistors were replaced. The recap was not done by me because I do not have the skills. But I have since found a solution to the imbalance problem. A very strange thing. I found if I use EF36 in the pair the balance is restored. But with EF37A there is an imbalance. The technician can’t explain it either.

I am in South Africa.


最後修改時間: 2025-11-21 19:43:48

Re. #1845 (and #1816 & 1819)

Are your pair of TL12.1 (of which one unit has "softer") the same as you shown before (pictured below)?

Obviously they are very different internally and need to be restored to be the same. Where are you based? USA/UK/? ?






最後修改時間: 2025-11-20 20:37:06

四/五十年前的老機器，零件愈原裝，毛病愈多，誤差愈大，聲音愈差。
既已拆下舊電容，為何不順道測量一下電阻呢？

I could also mention the amps had a full recap but some of the resistors are still orginal. The tubes is fine. But weirdly one amp plays softer than the other. Anyone ever encountered this problem?

Hi
Has anyone ever encountered an imbalance in volume between their Leak 12.1 amps? I have a problem with one amp playing softer than the other one. I have swopped the valves between the amps but the problem remains.

Thank you kindly for the reply.

This morning I replaced the KT66 with 7581A and my first impressions are favorable.

After listening for 2 hours I find the sound is clean, chimey, delicate, focused and well balanced. Bass is slightly less (compared to GEC KT66).

I will say the GEC has a slightly warmer & natural tone.

The differences are small.

They are new production Tung-Sol 7581A.

I can live happily with them.

Other tubes are:
Mullard EF37A
Mullard ECC33 (yellow print)
Mullard GZ32

最後修改時間: 2025-09-01 17:51:45

Re. 1841

As checked the Duncan tube data sheet, 7581A has exactly the same pin-outs as KT66 (including G3 internally connected to cathode), and 7581A anode Va and Vg2 tolerance a are slightly better than KT66's. It should be a good substitute for KT66.

On added benefit is 7581A's heater current is 0.9A vis-a-vis KT66's 1.27A, i.e. it consumes lesser current.

Soundwise, you should compare by your ears and let us know your findings.

最後修改時間: 2025-09-01 14:03:27

According to the tube data sheet for 7581A it is "unilaterally interchangeable" with the 6L6GC. Should be good in Leak 12.1?

Hi
Can I use the 7581A tube in my Leak 12.1 instead of KT66?

I've been using 7581A in my Quad II amps without any problems.

7581A is said to be (from internet);

"an upgraded 6L6GC tube but willprovide more headroom than typical 6L6GC tubes. The 7581A power tube has a plate dissipation rating of 35W, as opposed to the 6L6GC and 7581 rating of 30W."

我又八卦建議一下

很不錯的

這種東西工廠用了廿幾年，我2019年開始就冇回到中國工廠

2017年最後一次安裝這種輪，在一些測試儀器底架下，質地不錯，好穩定，水平調教暢順

應該適合這個重型喇叭底座，如果高度適合都建議使用

嘩這位主人家好多有趣嘅玩具呀