Your journey with lower-watt tube amps -- Can a kit be good enough?

@atmasphere We tested the amp for distortion and found that the left channel had a magnitude more distortion than the right; @5 watts it was 3.5%! So, we opened the amp up and there was a mis-wired tube socket with reversed leads. Green went to blue and vice versa. Someone did not do due diligence. After fixing that, everything was fantastic -- very low distortion and balanced between channels.

@hilde45 +1

Its amazing it did as well as it did initially! It's my surmise the prior owner never played the amp that much due to the error. So it might sound a bit better with some break-in. 

UPDATE: Got my Dynakit ST-35 up and running after a local tech did a bunch of work on it -- firmed up weak soldered joints, replaced wobbly tube sockets with good ones, and added the EFB kit that Atmasphere mentioned. Oh, and added a grounded plug. Also put in NOS Russian military grade EL84 tubes (NOS Reflektor 6n14n-EB Russian EL84/7189A equivalent, c. 1985) We measured distortion on this amp on some sophisticated equipment, and it hits 1% at full power and was about 0.15% at 1W. It will spend most of its time well under 1W. Very nice performance.

Report on initial listening of ST-35: This is one stunning little amp. Played it with my solid state preamp (built around the Burson Audio Buffer) and my Beyma AMT/JBL speakers (97db), using for about an hour -- classical, jazz, vocals, rock. It did amazingly well.

Soundwise, I’d say the grip on the bass is decent-good. Not fuzzy, not super tight, but notes are clear enough and there is full presentation with no gaps. Midrange is really warm and inviting; not quite as delicate and gentle as the KT77 tubes in my Quicksilver, but way more inviting than my KT88 or KT120’s. Really sweet. Highs were never harsh, very delicate and clean. Never bright -- just about perfect. Lots of good toe-tapping, engaging transients, a sense of excitement and a magnetic draw to the music. Put simply: this little amp was kicking some ass.

I’m excited to try this amp on my Fritz Carbon 7 SE Mk. II speakers today.

@hilde45 Nice to hear you hare having success!

I prefer the JJ EL84s. You can get matched pairs at CE Distribution They have a Psvane tube that looks interesting too.

If the power cord is grounded, sometimes you can run into a buzz problem (ground loop) because the audio ground is also the chassis. To get around this you'll have to replace the RCA connectors (not a bad move since they are cheap anyway) and get a phenolic insulator to insulate the filter capacitor can from chassis ground. You that at this link at CE Distribution.

A 1/2 Watt 100 Ohm resistor is then placed between chassis ground and the audio ground.

This operation is a bit tricky since the chassis has to be modified (using a chassis punch) to mount the capacitor on its insulator. But I think you'll find it slightly lower noise.

Does your amp have the carbon composition or metal film resistors on the circuit board? The latter seem to sound better FWIW.

@atmasphere I need to check on your question. No buzz or noise or hum so far. Quiet as a mouse.