Lumley Reference Monobloc Amplifiers

AbbieKitten

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Jun 30, 2021
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Hi everyone

Anyone familiar with Lumley Reference Valve Monoblock amplifiers

I have a question about the bias screws

The instructions book we have says there is a bias adjustment screw behind each valve, however ours only has one central screw.

We are unsure as to how the bias adjustment works on our amps.

Thanks in advance.
 

insider9

Well-known member
I'm not familiar with your amp but I would advise caution as doing the wrong thing with a valve amp can lead to untimely passing. Link below might be helpful overall.

 
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AbbieKitten

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Nothing wrong with that of indeed any Lumley. There must also be a selector switch to move from valve to valve. Which model do you have?
Nothing wrong with that of indeed any Lumley. There must also be a selector switch to move from valve to valve. Which model do you have?
Interesting link Insider - yes the sockets for the multimeter are there on the back (1pair - a black and a red) and then as you suggest Al ears, there is a 5 position rotary switch to select valves. When vertical the switch is off - 2 clicks to the left selects valve 1, back a click towards vertical selects v2, first click beyond vertical to the right v3, and one further click to the right selects v4. All as it says in the manual - but then it says as each valve is selected there is a Bias Adjusting Screw (a simple slotted screw) set into the top of the amp base immediately behind each valve. On our model there is just one screw set centrally in the top of the amp base. Tried biasing the valves assuming you select a valve, and then that single screw adjusts the one you've chosen and so on. Went along all 4 of them to start with and noted the reading ( really low around 30) and then turned up v1 to around 45 to 50. Trouble is when selected v2, that had now gone up to around 55 - and so had the others by more or less similar amount ! It's like the selector isn't selecting a single valve exclusively :- and they are a pair of monoblocks and they both behaved the same. Just wondered if anyone knew there must be a trick to this particular model of Lumley Reference 120 monoblock. Maybe the one with the 4 valve adjusting screws is an older or newer model than ours ?
Grateful - really grateful for any informed assistance guys - thanking you in advance
 

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