Hong Kong Lowther Jazz 6L6 SET amp

[Westendboy]

Hi James, have you checked your inbox

[Jazid]

Hi Keith,

Apologies for the delay, following a request from an AoS member (Lawrence) to check for hum as he uses sensitive speakers I have listened and there is low level hum audible from about 1-2ft from the amp. Bear in mind I use higher sensitivity AN-E (allegedly 95dB/m). This is perfectly normal and acceptable in a modestly priced valve amp. However I settled down to listen and got lost in the music because it is so damned good, and when eventually I went to turn it off an hour later the hum had become louder and was now just about audible from my listening position. I don't know if it was always like that as I rarely get a chance to listen for more than a short session, so it could be just how it is. Either way clearly this ain't going to cut it with sensitive horn speakers, and I don't think it right that the amp should hum more when warm anyway so I played around swapping different valves - no change, and then popped the back off and uncovered some suspect solder joints which have all been re-soldered, but still no change. I am now going to re-cap the power supply as it gets hot in there so it might help and can't hurt. This amounts to 5 capacitors none of which I had in stock so I am waiting on RS. Rest assured the capacitors I have selected are all better spec than the originals (which were already decent quality). Where apropriate I have modestly increased capacitance, though obviously not for the 47uF after the rectifier!

When this is done and properly soak tested I shall report back, it could be that the hum is a design issue and remains, it could be tired electrolytics, it could be something else, I just can't say at the moment, but I will not release it until I feel secure that is is behaving correctly, so sorry for the inevitable delay - its for your benefit chaps After that I have promised first dibs to Lawrence and his Hornings, Keith you are next in line to pop over for a listen, and Karl from LH is third in line.

Whoever gets this amp is a lucky bugger I swear!

[Westendboy]

That’s fine James, good luck with your investigations!

[Jazid]

Just a quick update, I ordered caps from RS because they were in stock, and it appears that four were in stock and delivered and installed, but one IS technically in stock but in ... Japan! Anyway by the end of the week... Further progress, the earthing was suspect and I have improved safety there and implemented proper star grounding so hopefully things will look up. I'll document the tweaks in due course although muggins forgot to take 'before' pictures. Duh!

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[Jazid]

Back up for sale as I MUST shift stuff. Modestly upgraded in so far as the PSU caps are better than original, star earthing is way better than stock. There is still low level hum, less now than as written above and really nothing to concern anyone at the price point, I think it's due to the transformer orientation, and I'm not about to alter that. It is solid, valves are solid, absolutely as described in my original post, sweet little amp. Available for postage as an extra cost - I'll pack it well for sure, or for properly socially distanced collection from W14 West London if you are passing on work. Pics of innards available to interested parties via email - PM me your contact and I can send.

[anubisgrau]

PM sent

[Lawrence001]

Think it sold within minutes on the Wam to a former owner.

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