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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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5th Jan 2018, 6:26 pm | #21 |
Pentode
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Re: A pair of Leak TL12s
I checked inside the output transformer, there were two dry joints which i soldered again.
This made a slight difference on the output volume but i still have the same issues. |
5th Jan 2018, 6:37 pm | #22 |
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Re: A pair of Leak TL12s
Sorry if this one's really obvious, but the plug which selects the transformer secondary is supposed to be the shorting type (pins connected to one another). It looks a lot like the trailing lead type (pins not connected). I don't imagine the wrong type could have been used could it ?
Cheers, GJ
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5th Jan 2018, 8:21 pm | #23 | ||
Pentode
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Re: A pair of Leak TL12s
Quote:
As you said i checked all the anode and cathode voltages and they were fine except for the EF86! The heat voltages were fine but at pin 1 i get 150v which is supposed to be around 70v and at pin 6 i get 190v again supposed to be around 132v. So i thought lets replace R15 and R7 and R6 just to be sure, same thing voltages measures the same give or take a few volts. Cant think what could be doing that. Quote:
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5th Jan 2018, 8:39 pm | #24 |
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Re: A pair of Leak TL12s
The point is, are the two pins of the selector electrically joined together?
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5th Jan 2018, 8:57 pm | #25 |
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Re: A pair of Leak TL12s
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5th Jan 2018, 9:01 pm | #26 | |
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Re: A pair of Leak TL12s
Quote:
Check the cathode voltage and measure the voltage between cathode and control grid. I'm assuming basic things like the valve lights up and that the anode, screen grid, cathode and grid leak resistors are of the correct value and fitted in the correct position.
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5th Jan 2018, 9:20 pm | #27 |
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Re: A pair of Leak TL12s
A thought that occurs to me is that digital meters can give different readings to analogue meters, as they don't load the circuit so much. How do the EF86 readings compare with the other amp?
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5th Jan 2018, 9:26 pm | #28 | |
Heptode
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Re: A pair of Leak TL12s
Quote:
The cathode voltage is next to check. This is a low impedance point and the reading will not be much affected by the type of meter used. If this is also higher than it should be there is probably a high resistance in R3 or R4 or a bad connection. These are 2.2k and 100 ohms respectively, and R4 is one of the resistors that looks "wrong" in your photo's... it looks like it is a 100Kohm or perhaps 10kohm. (It actually looks identical to R13 which is and should be 100kohm) Those circuit references are the ones in this diagram: http://44bx.com/leak/Leak/Circuits/TL12Plus3.gif If the cathode voltage is low, try another valve and carefully examine the contact pins in the valveholder to see if any of them are broken. Last edited by DangerMan; 5th Jan 2018 at 9:32 pm. |
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5th Jan 2018, 9:36 pm | #29 |
Dekatron
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Re: A pair of Leak TL12s
If I'm looking at the right schematic the screen feed is 1meg and the voltage measurements were done with a 20k OPV meter.
Lawrence. |
5th Jan 2018, 10:18 pm | #30 | |
Pentode
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Re: A pair of Leak TL12s
Quote:
Well that was a great learning experience, so easy to make a simple mistake and for it to cause all those issues! It doesn't help that i'm colour blind and struggle with the colours, i have to use the DMM and double check everything. Thanks to Josef for getting me to check the Output transformer and Yourself and Station X! Finally! Last edited by vishalk; 5th Jan 2018 at 10:20 pm. Reason: added more |
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5th Jan 2018, 10:39 pm | #31 |
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Re: A pair of Leak TL12s
Good to know it's fixed. Checking and analysing voltage readings every time for me!
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5th Jan 2018, 10:45 pm | #32 |
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Re: A pair of Leak TL12s
Excellent! A good outcome... and we've all made the same mistake at some time.
Now sit back and enjoy the music, which always sounds so much sweeter after such a struggle. Pete |
6th Jan 2018, 12:33 am | #33 |
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Re: A pair of Leak TL12s
Haven't we just ! As Bohr said "An expert is the man who has made all the mistakes in a narrow field" .
Cheers, GJ
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6th Jan 2018, 7:55 am | #34 |
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Re: A pair of Leak TL12s
"a great learning experience, so easy to make a simple mistake" Yep, as I said in post #15. I did it on a early build and have done it once or twice since. The crazy thing is you can miss it time and again whilst rechecking your work.
Good to hear you got it fixed, A.
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6th Jan 2018, 11:28 am | #35 |
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Re: A pair of Leak TL12s
Cant we just, I'm having the same problem with another which I will deal with when I'm feeling better.
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6th Jan 2018, 6:08 pm | #36 | |
Pentode
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Re: A pair of Leak TL12s
Quote:
Good thing was i now know for next time if i have high anode and screen voltages it means the valve isn't passing enough current, but also to check voltages, correct values and bad connections Very happy it's working, that's whats amazing about this forum and the helpful members on here. You can get help to repair and diagnose! Brilliant |
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6th Jan 2018, 6:13 pm | #37 |
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Re: A pair of Leak TL12s
If you have LOW anode and/or screen voltages, it's generally the result of capacitors going leaky.
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6th Jan 2018, 10:38 pm | #38 |
Pentode
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Re: A pair of Leak TL12s
Amplifiers are ready for battle! So which one do you think will sound better?
Bought new valves (ebay recently did a 20% off everything) so bought some brand new matched Bugera EL84's and GZ34. The EF86 and ECC81 are matched NOS. Should be able to do some listening tomorrow. |
6th Jan 2018, 11:32 pm | #39 |
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Re: A pair of Leak TL12s
Harold Leak would have been disappointed if they sounded any different . Back in the 1950s/60s high-end amplifier manufacturers worked to a standard of high-fidelity which was supposed to be demanding enough to make the amplifier 'disappear' sonically. In practice the only thing which was sonically significant was whether it could deliver enough power to drive the chosen speakers to sufficient volume in the room in which they were used.
It was absolutely agreed that speakers sounded different. And record cartridges did too. But the best electronics at a given power level were sold against other criteria - reliability, affordability, even looks (Leak were very proud of their tidy wiring) and, in this case, system architecture. If you wanted just one amp driving a mono system you could buy a single TL/12 Plus. If you wanted stereo then a Stereo20 would be cheaper than two TL/12s and would occupy less space. But their specifications were essentially the same. So there might be more difference between two Stereo20s (mostly due to different levels of matching between the valves) than between a Stereo20 and two TL/12s. Cheers, GJ
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7th Jan 2018, 1:03 am | #40 | |
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Re: A pair of Leak TL12s
Quote:
And for this logical reason... any small differences in the "raw" amplifier will be reduced by the negative feedback factor (the loop gain), as he and his team fully appreciated at the time. That's what makes them so good.. as well as the quality of the output transformers which was integral to the designs and permitted them to work properly, of course. Pete Last edited by DangerMan; 7th Jan 2018 at 1:13 am. |
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