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Old 23rd February 2014, 12:00 AM   #51
mach1 is offline mach1  Australia
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Quote:
. New Year Special Offer:
APPJ PA0901A amp + Gold Lion (Genalex) Re-issue ECC83(Made in Russia) + Shuguang EL84 =USD190 + shipping cost
Black and Silver colors are available.

*** The special offer is valid until 31st, Jan., 2014.
Do you have any of these left?
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Old 26th February 2014, 05:07 PM   #52
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Hello,

Yes, only one set left.

Thanks,
Tony.
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Originally Posted by mach1 View Post
Do you have any of these left?
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Old 22nd March 2014, 10:26 PM   #53
0mr is offline 0mr  Romania
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Default about components

Hello,
Can anybody tell me please if the received product appj is like the initial released version miniwatt n3? I'm talking about the pcb quality and components. The capacitors used are from nichicon and rifa? Who is the manufacturer of the output transformers? Thank you and best wishes!
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Old 25th March 2014, 05:52 PM   #54
0mr is offline 0mr  Romania
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Originally Posted by Musik007 View Post
Hello,

Yes, only one set left.

Thanks,
Tony.
Hello,

Is it still available?
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Old 6th April 2014, 08:59 AM   #55
Welcome is offline Welcome  France
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Quote:
Originally Posted by 0mr View Post
Hello,
Can anybody tell me please if the received product appj is like the initial released version miniwatt n3? I'm talking about the pcb quality and components. The capacitors used are from nichicon and rifa? Who is the manufacturer of the output transformers? Thank you and best wishes!
Yes, the capacitors are "from" Nichicon and Rifa. This is what they are branded as, but are actually fakes. They still do their job, though.

My amp died. Symptoms were: tubes didn't light up, but the power supply light did. No sound, obviously. The cause: The primary psu capacitor (270µF/400V) had ever-so-slightly swelled up and lost its ability to hold a charge. After replacement, the amp worked as new again.

It would seem that others have had this same problem. I suggest everyone replace this capacitor asap instead of waiting for it to die. The type is snap-in, 10mm pitch, dimensions are 25 mm diameter, 40 mm lenght. There is absolutely no space for bigger caps, and the value in question may be hard to find at this size. I went with 100µF/400V instead, which has worked perfectly. The original capacitor, given its shoddy quality, could probably never actually store 270µF.
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Last edited by Welcome; 6th April 2014 at 09:06 AM.
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Old 8th April 2014, 11:58 PM   #56
0mr is offline 0mr  Romania
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Thank you for your answer. Are you sure that the caps are fake????? I didn't even know that chinese would make fake discrete components of well known brands. Nichicon are not even so expensive. I just had a doubt that they use rifa and nichicon in mass production at that price point, as advertised and in pictures. I also heared that the potentiometer is a mess, even if it's alps. I'm thinking to buy one and change all the caps and potentiometer. If there is no space for a bigger cap i can fit one outside the case. I also want to use a socket saver to protect the board and the smd res/caps that are around the sockets from excessive heat.
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Old 11th April 2014, 08:19 PM   #57
Welcome is offline Welcome  France
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Are you kidding? Every single component from any sort or reputable brand is being faked these days. Nichicon in particular has had a counterfeit warning on the front page of their website for years.

While trying to figure out the faults in this, I compared all the components in this amp to real parts from the various manufacturers and they all looked suspicious and not the same quality as the real thing. The easiest way to tell is usually the printing, which can be faded, off-center, wrong font, etc. Also sizes and even shapes differ.

The amp is really brilliant, and there is no need to modify it. Out of the box, it's the best amp I've ever used. And I've used quite a few. Properly sized caps are widely available and fitting one outside of the chassis will be greatly detrimental to the functionality of the circuit. You may even render it unusable. It uses an SMPS and you don't screw around with those.

There's nothing wrong with the potentiometer. It does its job well. It may be somewhat uneven at the start, but that's normal and usually not a big deal (it takes a LOT of unevenness between channels to be audible). A different potentiometer will definitely not fit in here, and resorting to bypassing it and instead using an external pre-amp is criminal - aesthetically speaking. This tiny amp works really well on its own, and the main reason for its appeal is its way of making uglier, bigger stereo systems a thing of the past.

The thing runs hot, but it's a tube amp - that's normal. The SMD components are in no danger here. The only thing that needs sorting out are the electrolytic capacitors. I've put hundreds of hours into this thing, and it has shown no sign of dying (apart from literally dying... but that was just once! Knock on wood.).

If you want DIY, I recommend looking elsewhere. This is not an amp for basement dwelling Frankenstein creators, it's more of a WAF-optimized thing: it even comes in pink! (ps: which I deeply regret not getting.)
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Last edited by Welcome; 11th April 2014 at 08:23 PM.
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Old 12th April 2014, 07:15 PM   #58
0mr is offline 0mr  Romania
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Thank you for the information! I asked about the Nichicon because it doesn't worth to manufacture a fake cap if the original one costs about 20-50 cents. It like manufacturing fake Q&Q low cost watches instead of a 10-50k watch.
About the SMPS i was thinking to bypass it and put a real PS outside the chassis .
I think i'll buy one and just change the caps. I'll also buy a pair of Pioneer SB-B22. I'd rather buy full range speakers but i couldn't find a pair for 150-200$.
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Old 13th April 2015, 08:41 PM   #59
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Hello guys,
A few weeks ago it was my birthday. At that time I was buying on Aliexpress sets of resistors to replenish my stock for repairing the old radio set (tube only) my friends keep feeding me to fix.
I saw this amplifier APPJ 6J1+6P1 Mini tube which use Chinese 6P1 and 6J1 tubes and is sold by many many vendors including Amazon...
I decided it was cheap enough to buy one.
I have it for a couple of weeks now and I'm delighted by it. Of course, 3W is not near enough to properly power the big Cabasse I've in my living room but in the study with a couple of old Grundig two way speakers from the ending 60's it is very very good.
Of course the design exists in many versions with different tubes. A friend of mine provided me with NOS Russian military equivalent of the Chinese’s and these are better.
I've a complain which is due to the case design. The PSU heat can't go away so the case becomes hot after a couple of hours of use. So I made holes in the bottom plate and in the aluminium top plate. It helps a lot. I bet it will help the PSU's condenser survive longer. The gain is around 10 to 15 °Celsius I think
I have a question, though : has anyone a schematics of either the amplifier or the PSU ? Because I bet it will fail one day and as my Chinese is very bad :-( , I won't be able to ask them :-)
Many thanks in advance for your help !
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Old 1st October 2016, 07:43 PM   #60
pcan is offline pcan  Italy
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I just bought this mini-amplifier, a 2011 design but still on sale at a discounted price on all popular web outlets.
First thing I noticed is the absence of any safety marks on the case. I opened it to check the issue, and also to see how they managed to remove the power supply transformer. The PA0901A is built much better than other cheap small tube amplifiers made in China I checked before. The PCB on my amplifier is marked EL84-1-2A 2011.11.11; there may be other versions. Unfortunately on this PCB there are safety code violations. Safety earth is not connected to the chassis. A tiny black wire connects the outlet to a PCB trace, then the trace connects to the signal ground; the signal ground is finally connected to the chassis at the RCA input jacks. A fault current may burn the PCB trace damaging the amplifier and exposing the user to electrical shock hazard. A direct connection from the outlet to the aluminium chassis was easy to add and made this amplifier safer. The second violation is in the mains input filter: the whole mains supply is put across two series-connected 1206 SMD resistors, rated only 150V each. On my 230V supply, a minimum of 3 series connected 1206 resistors are needed. I also added a varistor, to get some protection from power spikes.
The power supply is built around a 230/12.6V switching regulator that provides the DC filament supply (power tubes heaters are conneced in series) and the EL84 bias voltage reference. The control IC is the TOP250YN, wired to a 66 KHz switching frequency. The filament supply is rectified by a fast diode and leveled with a CLC cell. The B+ supply is derived from an auxiliary transformer winding, rectified and leveled with a CLC cell followed by another LC cell. This last cell seems to be a last-minute fix because it is external to the switching PSU metal cage and the capacitor is hot-glued in the nearest free spot, under one of the EL84 sockets. There is no regulation loop on the B+ inside the switching regulator; regulaton is on the 12.6v side only. The EL84 sockets have pin 1 unconnected, this way it is possible to use NOS tubes. On each output tube, the cathode current goes trough a STP4NK60Z MOS, driven by a TL431 IC. Output transformers are sadly underwhelming. The weight is 500g each and they are mounted on a PCB stuffed inside the top portion of the cute aluminium cover. There is no UL tap. To manage the distortion, a global negative feedback is provided, trough a ceramic capacitor to the cathode of the preamp tube.
The electrolytic capacitors on my amplifier have the Nichicon brand and they look genuine (I compared them to real Nichicon capacitors). I only exchanged the main primary-side PSU capacitor because it was of the wrong type. According to the TOP250YN datasheet, on a 50-70W application like this one the capacitor should be between 82 and 150uF. This is also the exact space provided on the PCB. On my amplifier, the manufacturer fitted a gigantic 270 uF snap-in capacitor trough a small adaptor PCB that almost touch the heat spreader. This looks good but is a reliability issue, the capacitor will be toasted by the heat. There is a mention of this failure mode on a previous post in this thread. The original fuse was a 2A slow-blow type; according to the datasheet it should be a fast-acting type.
To summarize my post, I urge the owners of this amplifier, and others APPJ designs with the same case such as the ones based on 6V6 and compactron tubes, to check the outlet ground connection, the two SMD resistors on the hot side of the PCB, and the fuse. Safety first.

Last edited by pcan; 1st October 2016 at 07:55 PM.
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