How to bias an HT Club 40 MKII - found the answer

Discussion - HT Venue amplifiers. Inspiration from Studio to Stage.
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cnumb262
Posts: 5
Joined: Sat Oct 12, 2019 9:12 pm

Fri Oct 18, 2019 1:53 am

I have had this amp for a few weeks and it sounds great. I want to try some different EL34 tubes to see how they sound. I am very used to biasing Marshalls and similar amps, but can't quite understand the MKII.

I do see a couple of adjustment screws with 2 leds net to each. The leds are green and red, both right now are shining the green ones. There is also a 3 prong connector next to the leds. All of this seems like the bias on teh MKII can be set without dropping the chassis - which is a great feature. Unfortunately, I can't find any documentation on how to hook up my meter and what each adjustment screw does.

Any instructions will be appreciated.

Thanks, in advance

*** I meant to add that I dropped the chassis down and looked for a bias pot, but there are none mounted on the board. As I was putting the chassis back in I noticed the cutouts with the adjustment screws and leds.
Last edited by cnumb262 on Tue Jan 07, 2020 11:56 pm, edited 1 time in total.

cnumb262
Posts: 5
Joined: Sat Oct 12, 2019 9:12 pm

Sat Jan 04, 2020 11:37 pm

I did figure it out. The MKII is set up nicely. There are 2bias pots which are accessible directly from the chasis without having to remove it. If you turn the amp upside down the bias pot is the one on the left (facing the amp) and the balance pot is the one on the right. Make sure of 5 things.

1) Have the amp set to the cleanest channel (green on the footswitch or no light on the front panel with no footswitch)
2) Have all the volumes turned totally down
3) have an instrument cable plugged into the input
4) Have the amp set for 40 watts (not the 4W)
5) Turn the power on and take the amp out of standby (let it warm up in standby for a few minutes to get the tubes ready)

I used a bias right to verify the settings (~25 mvdc on each tube) and the leds built into the system give a very good indication. Out of spec and they turn red, as the adjustment approaches optimal they start to turn green and the get brighter. When they hit the brightest, that is the sweet spot. Keep turning and they will turn off. I checked with my VOM and the green lights are very accurate.

Remember, bias adjustment is an optimal range. This is an analog system and any number of elements in the path will impact the bias. I like the tubes to be close, but not exactly the same. To my ear it is a nicer sound - i like the distortion better.

After playing around a little I found that I had to tweek each until they were both bright green. I took them too far, until they turned off, and then backed them off until I got the first indicator of bright green. There is a range in the pot when it will stay bright green. I liked the sound when I was at the upper edge of that bright spot.

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