Modifying the Lowther Club HK Jazz 6L6 ($449 SET amp) - diyAudio
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Old 26th February 2012, 03:33 AM   #1
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Default Modifying the Lowther Club HK Jazz 6L6 ($449 SET amp)

I recently purchased a Jazz 6L6 direct from Lowther Club HK and have been quite impressed with this little amp especially given its modest price.
Even unmodded and with the Chinese valves it arrived with it delivers very smooth, relaxing sound especially at the low volume levels I tend to do most of my listening at.

I'm hoping to improve its sonics even further and have ordered an assortment of NOS tubes which I'm sure will do the trick, along with some Obbligato premium gold film caps to replace the 0.33uF WIMA coupling caps, because I've never been a big fan of WIMAs and find them somewhat veiled.

I've worked with valve circuits before but my knowledge of electronics is quite rudimentary so I mainly limit myself to simple mods like replacing caps/resistors etc and simple circuit changes.
Lowther Club HK were kind enough to send me a schematic of the amp and I'd love it if some of the more knowledgeable folk on the forum could take a look and gauge if there are any fairly simple changes I can make to improve things even more.

Cheers, thanks for reading guys.



Here's a photo of the amp:

Click the image to open in full size.


The specs and further details are listed here:

Lowther Club Home


Here's the schematic:

Click the image to open in full size.
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Old 14th September 2012, 08:10 PM   #2
julcat is offline julcat  Mexico
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any news about you mod??
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Old 14th September 2012, 08:41 PM   #3
DF96 is offline DF96  England
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SET usually means single-ended triode, but here it seems to mean single-ended tetrode - otherwise known as pentode mode.

If changing the coupling cap then keep the same value, to avoid LF loop stability problems.
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Old 10th April 2014, 01:00 PM   #4
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hows the mod project. with 90db S/N this amp is right up there with the cary amps which come in at 90db as well. I'm thinking of ordering one as well.
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Old 16th April 2014, 08:50 AM   #5
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Man... the price is very attractive.

Here are some that I can propose:
- replace 240k 6L6G grid leak resistor with grid choke
- change 100k pot to a stepped attenuator
- bypass 680u/50v with good quality film cap, or change to BlackGate
- bypass 22u/400V and 220u/450v with good quality film cap
- change output transformer. :P
- change 5H choke to amorphous choke
- regulate the 6L6 grid supply. Zener used tends to sound noisy. YMMV.
- change to Mundorf SIO or Gold-IO perhaps for coupling?
- change to interstage transformer coupling
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Old 16th April 2014, 01:53 PM   #6
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Quote:
Originally Posted by tubeworld View Post
Man... the price is very attractive.

Here are some that I can propose:
- replace 240k 6L6G grid leak resistor with grid choke
- change 100k pot to a stepped attenuator
- bypass 680u/50v with good quality film cap, or change to BlackGate
- bypass 22u/400V and 220u/450v with good quality film cap
- change output transformer. :P
- change 5H choke to amorphous choke
- regulate the 6L6 grid supply. Zener used tends to sound noisy. YMMV.
- change to Mundorf SIO or Gold-IO perhaps for coupling?
- change to interstage transformer coupling

These three seem low effort and are great ideas....but can you use a grid choke on a 6l6....I normally see them on input tubes mainly due to their very low current capacity....any grid choke recomendations? thanks

- replace 240k 6L6G grid leak resistor with grid choke
- bypass 680u/50v with good quality film cap, or change to BlackGate
- bypass 22u/400V and 220u/450v with good quality film cap
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Old 16th April 2014, 03:29 PM   #7
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Location: Jalan Kayu, Singapore
It's better to use grid choke than grid leak resistor on output tube. Maybe you mixed up with plate load choke. Grid choke does not carry DC but only AC. It is good for the driver/input tube where it sees higher impedance -> easier to drive, it also present a low DCR for the output tube grid.

There are several vendors that has grid choke. Check the vendors below the line:
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Old 16th April 2014, 04:12 PM   #8
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yes...I am confused...thought that grid and anode chokes only pass DC...thus the benifet since it wont effect audio signal which is AC.

so I need to do more homework on this.

AudioKarma.org Home Audio Stereo Discussion Forums
Attached Images
File Type: jpg Grid-Choke-1.jpg (44.9 KB, 149 views)

Last edited by speakerfritz; 16th April 2014 at 04:21 PM.
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Old 16th April 2014, 04:50 PM   #9
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Quote:
Originally Posted by tubeworld View Post

Here are some that I can propose:
- replace 240k 6L6G grid leak resistor with grid choke
- change 100k pot to a stepped attenuator
- bypass 680u/50v with good quality film cap, or change to BlackGate
- bypass 22u/400V and 220u/450v with good quality film cap
- change output transformer. :P
- change 5H choke to amorphous choke
- regulate the 6L6 grid supply. Zener used tends to sound noisy. YMMV.
- change to Mundorf SIO or Gold-IO perhaps for coupling?
- change to interstage transformer coupling
...then make some measurements and notice that you have ruined frequency response, got higer THD and have less money .
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Old 17th April 2014, 12:25 AM   #10
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speakerfriz - that pic you got is spot on.

artosalo - that's where all the fun is, no? :P
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