The 5AR4 has a very low forward voltage drop for a given plate current. Substituting another rectifier may likely cause a B+ voltage sag which may affect performance. That’s probably why Luxman doesn’t give you other choices. Safety wise it’s not an issue.
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Use what the circuit was designed with! Different rectifier tubes have different voltage drops and limits on current draw. Plus different current draws for the heaters - which can overheat power transformers. |
For instance, the 5Y3 (aka the 80) has much less current handling than a 5AR4 (GZ34) or a 5U4. It will quickly red plate (overheat) if used as a substitute! |
I'm not sure what other rectifier tubes are a safe replacement for 5ARA but when I played around with different vintages of 5ARA I found the metal base tubes (mid 1950's) made the largest positive change to my SQ than any other charge I had previously made. They are expensive but I would try one before any other changes. By the way I've used them with ModWright pre, modded Sony CD and Bob Latino VTA ST-70 which I build. |
5ar4 is by a long stretch the best tube rectifier for audio in my experience... all other common alternatives are weaker and less durable
get fresh strong old stock brit euro or usa made ones and be done for this lifetime |
Its not an issue in this case since you have directly heated cathodes, but the 5AR4 also has a controlled warmup time to prevent cathode stripping. At any rate there aren't any good subs for it.
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The reason I asked is that I have a Musical Paradise DAC which states that I can roll all those different tubes. I also have a Modwright LS100 and I checked with Dan, he also confirms it is safe to roll these variants. So, my understanding is that the designer may have one tube that he thinks it sound best, but it is safe and OK to use several other tubes. The synergy with other components is the key.
I am now using a 5Y3 coke bottle in the LS100 and a 5U4G in the DAC, these gives me the best sound to my taste.
From my research on the internet, it is safe to roll a 5R4 substitute the 5AR4. The 5AR4 sound too lean in my system and to my taste. The other tubes gives more air, I feel. |
5U4G sounds better than 5AR4, in my amp at least, but don't risk damaging your amp if it says 5AR4's only.
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The reason I asked is that I have a Musical Paradise DAC which states that I can roll all those different tubes. In a DAC the current draw will be minimal (most rectifiers can handle the output section of an amplifier) so a wider variety of tubes can be used- the outcome will be that the B+ voltage will be slightly lower. |
It’s not an issue in this case since you have directly heated cathodes, but the 5AR4 also has a controlled warmup time to prevent cathode stripping. At any rate there aren't any good subs for it. Do you mean my amp which is based on the Luxman MQ-300 is directly heated cathodes, so, I need to use 5AR4 where it has a controlled warm up? And I can’t use a 5R4 because it doesn’t have the controlled warm up? |
No. I mean that in your amp that quality won't make a difference. Cathode stripping is a phenomena of indirectly heated power tubes. Your power tubes are directly heated (the filament is the cathode literally) so cathode stripping is impossible.
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Late to this thread. Just today, I spoke with the authorized Luxman warranty tech, Mike Garry, about replacing the 5AR4 with a 5UG4 in the MQ-300. He said do not do it. The amp's huge power supplies have an inrush that could be too much for a 5UG4. Or something like that. Glad I asked because I just bought an MQ-300 and I have a stash of nice 5UG4 that I would have tried in it.
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@wrm57
thank you very much. |
Can it be confirmed that the LS100 will accommodate a coke bottle 5u4g in height inside the unit?
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Jokerman1226,
I can confirm that a 5U4G will *not* fit under the cover of a stock LS100. I believe Dan can provide a cover with a hole to accommodate taller rectifiers. I ran a 5U4 in that preamp for a long time, and I just kept the cover off. FWIW, my favorite in that preamp was the 6106, which is the same size as the 5AR4 so the cover will fit.
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