So, I was having an issue with one of my power tubes in my Liverpool with VVR a few months ago. Due to the price of tubes, I figured I would temporarily solve the problem by pulling 2 of EL84s and leaving just the centre two. I compensated my speaker load. I consider the 4 ohm tap now to be the 8 ohm tap and the 8 ohm tap to be the 16 ohm tap.
However, it occurred to me that maybe I am supposed to do more than that? I see in Mark Abbott's schematic that it says to increase the 25W resister (between B+1 and B+2) from 1K to 1.7K if building a 18 watt version of a Liverpool. My first instinct is that this probably makes little difference to me since I'm pretty much running my VVR down below 1/3 anyways. Is this more something I should be concerned about only if I were to crank my VVR to standard plate voltages, or is there another issue at play for the safety of the amp?
I'm hesitant to actually alter the circuit since this is just a temporary measure to save money on tubes. I'll bite the bullet and buy another quad of EL84s at some point...
Question about Pulling 2 tubes in Liverpool
Moderators: pompeiisneaks, Colossal
Question about Pulling 2 tubes in Liverpool
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Re: Question about Pulling 2 tubes in Liverpool
I would not be concerned. BTW, that 25W rating for the 1K seems way overkill. According to the voltages on your attachment that 1K is only dissipating .169 watts.
Re: Question about Pulling 2 tubes in Liverpool
I believe I read discussion about it's power rating on a thread somewhere. Even over-rating to compensate for any potential voltage spikes, from power switches or tube failures, it was likely just a type of resister that Ken had a bunch of in his parts bin... no downside to being over-rated if you already own a bunch of the part.