Nobsound 300b Monoblocks - HELP NEEDED!

[Wakefield Turntables]

A pair of these monoblocks landed in the listening room. They each have three valves to each monobloc. 300b x1 6H8C ×1 Soviet Union 5U4C ×1. Now the problems start. Douk audio in their wisdom left no markings for the position of the 6H8C or the 5U4C, so I could very easily plug them in the wrong way around. There are no markings on the amp. To add insult to injury my allen keys are worn down and useless and I don't have the right drill bit to have a look at the PCB. You couldn't make it up! . So my question dear AOSer's, do any of you own a pair or know the correct position of the 6H8C or 5U4C valves? The 300b just sits in the middle, that's the easy bit. So, basically, HELP!

[Edward]

Judging from the ebay listing the taller valves (the 5U4C) sit at the rear and the shorter valves (the 6H8C) sit to the front of the 300b. Download the 7th image of the listing so you can zoom in on the valve type. The other images show the orientation.

I hasten to add I don't have this amp nor direct knowledge - just going on the ebay listing.

[Wakefield Turntables]

I did just as you said several hours ago. They are now working, nothing has blown up yet. Thanks for your reply.

[Edward]

Interested to know what your impressions are once you have tuned into them.

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[willbewill]

Interested to know what your impressions are once you have tuned into them.

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+1

[Wakefield Turntables]

Might write a few words tonight if I get time from decorating today.

[Wakefield Turntables]

These 300b are off back to China. These amps hum like a complete bugger. So, I've got the valves in the correct positions. The amps exhibit no hum from the Tx when fired up but as hum like a complete bugger when you attach them to a passive speaker, this is with no pre-amp connected. I've had several different mains leads from cheap walwart jobbies to some expensive Furutech foo shielded monsters. All hum. Both units work, I've had them playing music. This is a HUGE disappointment. Any ideas why they should hum so badly? I'm going to wait to see if any forum members can come up a quick fix, else, it's reboxing them and back to nobsound. I'm very very annoyed.

[Pharos]

Short the I/P to make sure that you are not putting hum into them. (Short = 0V.)

[Wakefield Turntables]

I've powered one amp up (altough this phenomen happens with both units) and just attached the speaker cable from the speaker to the amp. No other cables. I've just tried powering up from the wall socket and still same old hum, I thought it might be the extension I was using.I'm not sure what I/P means Dennis.

[Wakefield Turntables]

Here's a little video demonstrating the problems. I'm beginning to think it might be an internal grounding problem, but on BOTH amps . The hum is a hell of a lot louder than on the video. I'm certain it's not Tx hum.