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-   -   Yaqin 300b (http://www.diyaudio.com/forums/tubes-valves/121231-yaqin-300b.html)

tocaco3 12th April 2008 07:03 PM

Yaqin 300b
 
Does anyone have any bad experiences with the Yaqin 300B? I bought one recently and although it sounds good I'm kind of worried about the staff that I read here and elsewhere about Chinese amps bought from EBay, like the Yaqin Mc10? and others.

zoukidouki 18th March 2009 01:39 AM

I bought one six months ago. Everything was find until last monday, a big white smoke came from underneath the ampli and a lot of blue sparks in the head of the 274B. After removing some screws I can tell that 2 caps of 10uF under 450v are gone. Is anybody else have had this problem yet?
Cheers

planet10 18th March 2009 03:27 AM

This amplifier should be somewhat similar to the Grant Fidelity 300B.

Are the cathode resistors big metal clad ones sitting on the circuit boards?

dave

zoukidouki 18th March 2009 05:27 PM

The problem with yaqin bought from ebay from a non official seller or even from an official is that you will have to ship back an 28Kg amplifier. Mean that you will never do it and nothing prove that you will have it back. So you better do some DIY and go thank to this forum...
There is a 50 Ohms/50 Watt resistor and a 100KOhms resistor on parallel of each 10uF/450V Caps.

planet10 18th March 2009 07:08 PM

What happens on the GF version of this amp, is that the metal clad resistors -- not being heat sinked -- get REALLY hot, and prematurly expire -- so far everytime by spraying their guts all over the inside of the amplifier.

We have been mounting better quality 25w metal clads to the bottom plate & replacing the caps. This is best done before the caps go.

dave

zoukidouki 19th March 2009 02:58 AM

Hi Dave,

Thank you for answering me. I don't understand you mean what by GF.
You advise me to replace he 50W resistors by a 25W? I don't understand why? Do you have a diagram of this amplifier, if yes can you please send me an email with this schematic attached
Thank you very much.

planet10 19th March 2009 06:52 AM

Quote:

Originally posted by zoukidouki
Hi Dave,

Thank you for answering me. I don't understand you mean what by GF.
You advise me to replace he 50W resistors by a 25W? I don't understand why? Do you have a diagram of this amplifier, if yes can you please send me an email with this schematic attached
Thank you very much.

GF = Grant Fidelity.

Does your amp look like the attached?

We replaced the 100w (not heatsinked) Rs with 25W ones (heatsinked to the bottom panel).

dave

PS: what is the tube complement of your amp?

zoukidouki 19th March 2009 02:46 PM

Hello Dave,

This is the address where I found the schematic of the 300B. The two caps that have burned are C14 and C15, the first ones just after the filament of 274B.
I don't really understand your answers so this schematic should make it easier to understand each other.
http://img529.imageshack.us/my.php?i...nms300bxo9.jpg

planet10 19th March 2009 05:57 PM

2 Attachment(s)
Your amp is a bit different Schema wize, althou the topology is the same, so it is possible layout is the same. I don't know for sure which caps they are in the schema... i do know the physical location, and it would have helped if i had attached the picture i intended.

dave


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