ARC veterans, asking for your input

Randy Myers

Randy Myers

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Hey you Audio Research veterans, I need your opinions please. I have a VT-50 amplifier. It is in wonderful shape and sounds fantastic. It was recently refurbished and retubed by ARC.

I just purchased and installed Gold Lion KT88 power tubes, and love the improvements in sound to my ears.... biasing the power tubes is not that difficult.

My question is about the smaller tubes, the 6922's... if I want to replace these tubes is biasing required? I have read a very convoluted process document from ARC about retubing the amplifier. I am not sure if doing this full process when replacing the smaller tubes is required or not. I have heard both. Some people have said it is important while others have said that the process is only to assure the tubes are matched.

So I am looking for you ARC veterans to tell me if I can safely replace the 6922 tubes or if I have to go through this complicated process. If I do then this would be a deal breaker for me. I can do the power tube biasing, but I do not believe I can to the full convoluted process that is described in the document I downloaded.

If I can simply purchase new 6922 tubes, such as a matched set of Gold Lion versions, and insert them in the amp without any other process I might do this. If not, and this full process is required I might have to rethink about if the VT-50 can be a long term amplifier for me. It is one heck of a good sounding amp though!
 
Hey Jozua, I am pretty certain ARC will say that the amplifier has to be sent to them for retubing :)...
 
This is a long term concern for me. I really like the sound, especially with the Gold Lion KT88 tubes. I also know that the 6922 tubes do not have to be replaced often, but if I want to try some Gold Lion tubes for example... if it were a simply a matter of picking up a quad match set then we might be off to the races....
 
From an audiogon discussion:

You can't just drop in new 6922 tubes in the VT50 amp. The new 6922 tubes need to be biased.

And you MUST have closely matched 6922 tubes. Especially the driver tubes. Not only matched pairs for each channel but each section of the dual triode tube must be closely matched. If each section of the tube is not closely matched you will never be able to bias the input and driver tube for each channel. (Behind each channel side panel there are 3 bias trim pots.)

The VT50 is no where near as hard to bias as VT100 MK 1 and Mk 2 but it still can be a pain if you do not start out with closely matched 6922 tubes.

You may complain about ARC tube pricing but you would probably be surprised how many 6922 tubes they go through to get closely matched triode sections let alone matched pairs.

https://forum.audiogon.com/discussions/arc-vt-50-damage-repair-advice
 
Ok, so this sounds like that process has to be done... and from looking in my amp I do not see these extra trim pots, so it appears some disassembly work has to also be done. What a pain.

Granted these tubes do not require replacing often but it does sound like the amp has to go to ARC to do this. This tells me it is probably not going to be my long term solution. I do not know if I will be able to afford a VT80 in the foreseeable future so I might have to consider a PrimaLuna as an alternative. We will just have to wait and see how this all unfolds.
 
Randy

If the output tubes are matched and biased correctly my gut feel is you just need to buy closely matched driver tubes.

There is no need to get seriously stressed about it or to sell the amp due to the above uncertainties. Rather spend time finding the correct interconnects & speaker wire as in my experience the ARC amps have incredible resolution when correctly set up.

If still in serious doubt, ask a expert technical guy to check the amp after replacing the valves.

Take care.

Jozua
 
Appreciate the input!

So if I wanted to try a different 6922 tube in the ARC what would be recommended? I like what the Gold Lion KT88 did to the sound over the tubes ARC provided in their retuning... these were not bad but the Gold Lion stepped it up a bit.
 
Randy

There are really only three brands in current production and you have one of them in the amp, the EH/Sovtek. That only leaves you with the Gold Lions or the JJ's. The JJ's are not going to be better and the Gold Lions are a toss up since they are made in the same factory by the same company as the EH's. A tightly matched quad of NOS tubes from Andy at VTS would be your only other option and the cost would be based on what you get, but they would last for years. The most reasonable would be the Matsushita's that were built in a Mullard tooled factory and sound very similar. Really good tubes for about $40 a piece. Call Andy on the phone and talk to him, he won't steer you wrong ask Mike.
 
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