I have been listening to this amp for one to two hours each day for the past week. There was some distortion but after a while I noticed that it seemed to be at concentrated around certain mid-range frequencies so today I replaced the dodgy Wharfdale Delta 10 speakers I had been using with my much smaller Vaf DC1 speakers. All the distortion vanished and while not as efficient, the Vafs sound so much smoother and cleaner than the Wharfdales. It sounds OK but I will reserve a final judgement on it's sound quality until after I run my main speakers off it.

Well I think it is finished after I added the same rectifier capacitor fix that Stephe made on the Nobsound 6P1. The data sheet for the 5U4G tube specifies a max cap of 40uf but a 150uf was supplied and specified in the instructions. My local b&m components shop, Jaycar (https://www.jaycar.com.au/) only had 10uf or 47uf 450v caps so I got two 10uf and wired them in parallel. I also added the bleed resistor. While not loud, I believe hum has increased and I suspect the designer specified the higher value cap to reduce hum. I was also having problems with the right 6J8P tube that would intermittently cause the right channel to cut out - wiggling the tube would fix it. I decided to reflow the solder over the pins I could easily access and that seemed to fix it. Listened to the amp for about an hour and it is OK on my test speakers. I will need to put it into my main system to gauge it's sound quality or lack there of. My modified filter capacitors:

One final look inside?:

Today I replaced the cables from the RCA inputs to volume control to tubes with a new cable bypassing the volume control. Fitted the base plate and timber façade. I played it for around 20 minutes and it sounds OK, nothing fantastic (Although this was with my test speakers - a pair of ancient Wharfedale Delta 10 bookshelf speakers I was given due to blown tweeters. I replaced them with cheap non-original tweeters). One thing I did notice was after I turned it off after using it for 20 minutes - a short time later I started it again and this time the music had a scratchiness in the high frequencies. I switched it off again and let it completely cool down and the scratchiness was gone? Just another issue I will need to solve:

Today I wired up the new potentiometer (volume control) and was getting sound from both channels except one was full volume and the other barely audible. I tried some contact cleaner on the volume control and now both channels are the same volume but extremely quiet. So I just bi-passed the volume control and success! I was using the volume control on the DVD player and found that a quiet to moderate levels it sounded OK. However distortion was noticeable at higher volume levels. This got me wondering if the inputs require a fixed resistor in place of the potentiometer? There is some low level hum from the left channel (you need to put your ear near the speaker to hear it) but no issues with the right channel.

I had a poke around in the FU50 to try and work out why there was no sound. I was assuming it was related to the volume potentiometer as both channels were not working when I eventually noticed I had failed to installed a wire on the left channel (indicated in pink below):

What was really annoying is that I had been highlighting every wire and component on the amps layout diagram as I installed them yet I failed to notice I had not highlighted that line for that wire. I double checked and the same wire on the right channel was there. Once installed, I had a working left channel but the right was still silent. I removed the volume pot and it does seem to be flaky as I get inconsistent resistance readings from it. Fortunately they supplied two in the kit so I only need to buy some new cable.

Fitted the remainder of the resistors and caps (think I am proud of two or three solder joints) and put the base cover and timber front onto it then plugged in the tubes. Connected some speakers and a DVD player as the CD source, turned everything on - amps VU meters light up and all tubes glow. No sparks or smoke 🙂. Hit play on the DVD player and - nothing 🙄. No sound and the VU meters needles don't move. Looks like I will need to play around to see what the issue is.

Wiring completed including adding a safety ground. Next is to add the remainder of the resistors and caps:

Been slowly building the FU50. I do have some concerns with the lack of a safety ground on the case. The replacement Nichicon caps are longer than those supplied so I may have to get creative when mounting them. They are positioned right next to the main transformer and I couldn't imagine the heat from that would be good for them.

Wiring exposed:

Starting to add components:

Caps are normally +- 20%. Looks like a fun kit!

Just ordered a set of Nichicon electrolytic replacement caps from Mouser, my first order with them. I will use the two supplied polypropylene caps (branded Wurth but are they???) as they measured quite well. Note, I added a pair of 2.2uf 400v caps as both YouTubers added them across the VU meters input pins. These are not shown in the instructions so I am assuming they were added to reduce interference on the speaker outputs. The YouTubers also added a 10k potentiometer to adjust the VU meters input. My kit came with 1.5k resistors so once again I am assuming these fixed resistors will place the VU meters at the correct setting.

I checked the values of all the components and surprisingly, all the resistors were either spot on or very slightly off by 1% or less. The capacitors however were all over the place. There are two of each cap so comparison was easy, For example: Specified value 33uf - measured 37.4uf & 28.8uf Specified value 150uf - measured 144.1uf & 147.7uf I also used Google translate to convert the instructions Chinese text to English so some interpretation is needed to read them:

My FU50 kit arrived today, two weeks from ordering to arrival. The box was reasonably well packed although the foam layer in the bottom of the box was in three pieces. All the major parts came covered in bubble wrap and none of the transformers were dented (which was an issue highlighted in two YouTube videos). So far I have only given the main components a cursory look but they all seem new and in good condition. The main transformer is 230v so I should not need a bucking transformer (I checked my mains power - 242v during off-peak & 238v during peak). Later on I will check all the resistor values and order a complete set of replacement caps as I don't trust what was supplied.

A couple of years ago I assembled an EAR834 clone phono stage. the quality of the kit was surprisingly good, but you need to replace some of the parts which were a mix of very decent to low quality. The EAR was not point to point wiring but simply plugging components into a high quality board which had the components printed on it, hence a doddle to build really. As a phono stage, it sounds amazing, especially after replacing the supplied tubes.

More recently I built Jerry Curtis’ great little SEP “spud” amp. That one is point to point wiring. What a little gem that is! It kills my A50 dead!

Please let us know about your kit and what the quality is like. There are some gems out there.