Yaqin MS-22b Phono Amp

And the last series :
 

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Greetings to the magnanimous legend: Mr. Les a.k.a. Hi-Q!

Hello Sir,
I am a great admirer of all the work you've done to share your technique of modding the Yaqin MS's with the world, it's all really amazing and incredibly generous. Thank you for it all!

I just obtained the modding tek PDF and am about halfway through the list of supplies--as I am here in the States, I'm searching on the Allied website and finding that a few of the components are possibly no longer carried (the site says "contact your local distributor office" and does not allow placing the items into the cart. Here in rural New Mexico, I'm nowhere near any distribution office!) and many more are back-ordered.

I was going to ask you if some of Allied's in-stock components would be appropriate stand-ins; but to be honest, I am an absolute newbie into the electronics modification world and am fairly apprehensive about the process to begin with. :boggled: The prospect of obtaining a replacement board, even a bare one, is a thrilling one. Of course, a fully-loaded board would be even more awesome--but either way, I am absolutely on board with the idea (pun intended!:D). Would it be alright to message you my contact and/or mailing info for when they're available? Any idea of the timeline thereof?

Cheers!
<V>
 
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Well I may be able to help you with some parts, will be a lot cheaper than sending the whole unit and the reason why there is a guy in the States doing the conversions. With regard to the replacement boards, we have had a problem with mechanical fit (5mm too short), possible to overcome but art work is being changed for another batch of boards. I did successfully fit the very first board to a UK MS23 and the owner is very satisfied, the RIAA plots came out really well. I have a couple of the early boards spare if you want one, you will have to drill two countersunk 3.5mm holes in the side rails, 5mm below the existing ones closest to the rear panel. The boards use special tube sockets so I will provide these with each board plus the five 2 pin plugs that mate with the present sockets feeding the signals in and out, plus of course the LED one. The other big problem with these early boards is an accidental short circuit across pins of V3 and some tracking being too close to the fixing points. These I can remodel and fix as required. But for those prepared to wait just a little longer, we should soon have some boards you can fit without any of these track problems.
 

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That does not sound like a problem for me....:)
How do i get that beta board?

Peter

Hi Muimui, there are plans being made right now for a replacement printed circuit board which will be available either bare or fully built and tested.
To save me a lot of re-typing, check out the new pdf and zip to page 46.
:)
http://goo.gl/YxMgRN

Hi Les,
Are you still working on a new board? I would like to do you mod but a new PCB would makes it much easier of course.

Thanks for all your work.

Peter
 
I did the Lesbox modification to my brand new MS-23B. All went fine and it sounds great. The only thing is that i have is the overheating problem described on page 45 of the manual. So that resistor is on order.
It was an easy job. The only thing a bit more hard to see on the picture was where and how to place the EQ's. But looking at the diagram itself did the trick.

Thanks Les for this great mod and explanation.

Peter
 
Hi Ciao, Like others, I have tried ECC81 and ECC82 as well as ECC83 just as an experiment. The effects of different types can be heard and some prefer an alternative to the ECC83. I am myself quite happy with the use of three ECC83's in the amplifiers I have made, whether they are MS22-B conversions or hard wired examples. I suppose it is all down to ones personal preference.
Although all of them can be used, the LesBox CF circuit is designed specifically for 12AX7/ECC83, where V3 plate current is just over 1mA, with R26/25 at 150Kohms. The circuit as is can be successfully supported with a compact PSU designed around this cheap transformer:
10W Tube Preamp EI Transformer MINI transformer 2*110V to 0-6V 1A 0-200V 2mA | eBay
Seeing that a (more) traditional CF circuit would have used a medium-gain tube like the ECC82/12AU7, I swapped V3 for it but observed that the B+ line immediately sagged to below 200Vdc and the transformer above heated up. I realized that an ECC82/12AU7 gobbles up more than 10mA each tube half as CF (with R25/26 correctly set to somewhere between 22K and 56K), which is above the maximum 20mA said transformer can handle.
The original PSU of the wretched MS-22 as well as all the other PSU designs for the LesBox provide ample current for the B+ line, even for V3 with ECC82/81. This is one subtle detail to watch out for V3 tube rollers.
An ECC82/12AU7 would have provided an output impedance better than 400ohms; what is the output impedance of the LesBox with the ECC83 as is?
 
Have a sample of 10 of the new boards but cannot release them until I know they fit OK and that will also enable the instructions to be verified/completed. I have offered a free built and tested board, plus fitting, for anyone in the UK as a guinea pig but nobody with an MS22 or MS23 has yet taken up the offer. I don't want to release the boards until I know they fit OK mechanically, the electrical tests are fine and no doubt will be better when fitted into an enclosure.
Les
 

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Just received my Lesbox conversion with one of the new boards. Very many thanks Les! My system needs setting up after some building works carried out but can't wait to try the MS23b with the new board. Have to say Les is top man, turn around from sending the MS23 to it being returned was les than a week and included very helpful documentation including circuit diagram of work carried out. Will post review after listening, although I'm sure I won't be disappointed.
Kirt
 
We are on hold at the moment as one of the converted MS23's is having problems with hum on the Right channel. It was fine at my place, in fact it was the quietest one I have ever done, so waiting for its return for analysis. The cost of parts works out at around just under $125, that's with the board and free labor including testing. The alternative is to supply it as a part kit, i.e. Board, valve holders and heatsink for $30. Postage costs have to be added of course, the lighter we can make the parcel then the cheaper it will be.
BUT at the moment I have to address the Right Channel hum condition so all work stops until then.