Hello. Has anyone tried them on the MC240? Thanks
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Russian 6p3s-e for MC240 good ?
- Thread starter psychoaudio
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I have seen two versions of this tube;
An older non-"E" type that uses the Dumet-style construction. These are very low-rated tubes that won't survive long under any conditions, and are best avoided.
The now more common -"E" type using (although this exact tube has been offered with several other base variants) coin-base construction. Generally referred to as the 5881/ 6L6WGC. This is a mechanically and electrically very rugged little guy, but does NOT survive in applications calling for and needing a true 6L6GC type. It will work very well in a McIntosh MC-240, which is a rather conservatively designed amplifier, sounds good and will give good service. I used these myself for a couple of years. (I own a pair of '240s)
My personal recommendation would be the JJ 7027A. An excellent tube in all respects, but, as with all modern tubes, only buy tested tubes from a reputable seller.
An older non-"E" type that uses the Dumet-style construction. These are very low-rated tubes that won't survive long under any conditions, and are best avoided.
The now more common -"E" type using (although this exact tube has been offered with several other base variants) coin-base construction. Generally referred to as the 5881/ 6L6WGC. This is a mechanically and electrically very rugged little guy, but does NOT survive in applications calling for and needing a true 6L6GC type. It will work very well in a McIntosh MC-240, which is a rather conservatively designed amplifier, sounds good and will give good service. I used these myself for a couple of years. (I own a pair of '240s)
My personal recommendation would be the JJ 7027A. An excellent tube in all respects, but, as with all modern tubes, only buy tested tubes from a reputable seller.
I don't think that tube has a high enough plate voltage rating to use in a 240. I would more inclined to go the other way and plug in some 6550s.
While 6550s may “work” in a 240, the amp wasn’t designed for them, esp wrt filament current needs. A quad of 6550s will increase filament needs by ~ 3A, not a trivial increase.
My experience with 6p3se is that it’s nearly a 6L6GC but with plate dissipation closer to 25W vs the 30W rating of the GC. In the 240 this isn’t a problem. As a point of comparison, the original MC30 (240 circuit is pretty much a clone) used 1614s as finals and these are just “selected” metal 6L6s with slightly higher ratings.
The “official” max voltage rating of the 6p3ce is somewhat obscure. I’ve used them in typical GC apps at 450-500V wo issue. Years ago I read a review of a guitar amp that used 6p3ces running at 550V. There were no problems during the review period.
My memory is fuzzy, but doesn’t the MC240 run 600V?
No, the schematic shows 430V and my experience is 425-475V depending on line voltage and how hot finals are biased. This range applies to all vintage Mac “consumer” amps I’ve encountered. Don’t know about MC3500 and MI200 is far higher than 500V.
I’m probably just remembering the voltage doubler capacitors’ original voltage rating then, maybe they were rated 600V. Thanks for the correction/clarification. I do remember cautions against using (vintage) 6L6G & 6L6GB based on voltage but that might also be unnecessary?
All of those types are really not up to the rigors of the Mac amps. But I’ve also seen those and other lower rated 6L6 types apparently surviving fine in them. So you probably could get away with using them . . .while keeping vigilant. I stick with GC types either NOS or new mfg.
last time I measured plate voltage was in the 435VDC range. Also depends on what the AC mains line in is measuring.
Yes I have heard that comment for years. Like many was afraid to give it a try. The implication being the higher heater current will draw more current from the PT, running it hotter and creating a higher risk for PT failure.
Was really surprised to learn the resulting test data does not support the claim. Just before Covid hit in 2020 decided to try various Output valves with a complete measurements on current draw, power, THD using an MC30 (very similar circuitry to the 240). Plugged in some 6L6s, 6550s, KT88s and took a full set of measurements.
pretty interesting results. Should also note if a person tries the larger power tubes they need to change the bias resistor (ie bias different on 6550 vs. 6L6GC).
AC mains input and Idle power was monitored with each tube change. Was very interested to see there was no significant change in power draw. and what was really interesting was PT temp did not change either which makes sense since the power draw did not change on the amp.
The amp was run into a load to get full power and THD measurements with each set of tubes.
The THD measurements at 30 and 40 watts power output were the same or slightly lower than with the 6L6 bottles.
See attached.
Attachments
It’s good you had a positive experience successfully rolling 6550s into your MC30s. It's also good you have hard data confirming proper performance. While it’s a fact that the basic signal circuitry of the 30 is quite similar to one channel of the 240, there are enough significant differences in implementation between the two that I’d still be cautious extrapolating 100% from from one to the other.
Since the OP is concerned specifically with the use of the 6p3ce, getting into the weeds of tube rolling details beyond that probably isn’t appropriate. So condensing things greatly, I have a question: Why would one want to run 6550s in a 240 that’s been optimized for 6L6s when various plug-n-play 6L6 types are readily available AND when running 6550s requires soldering to change the bias? Esp when your measurements indicate mostly equal performance between the two types. Seems like a lot of work for a couple of additional watts of output.
Since the OP is concerned specifically with the use of the 6p3ce, getting into the weeds of tube rolling details beyond that probably isn’t appropriate. So condensing things greatly, I have a question: Why would one want to run 6550s in a 240 that’s been optimized for 6L6s when various plug-n-play 6L6 types are readily available AND when running 6550s requires soldering to change the bias? Esp when your measurements indicate mostly equal performance between the two types. Seems like a lot of work for a couple of additional watts of output.
The whole point of running the 6550s is not for more power. You need a higher B+ to get more power from 6550s. In the 240 the 6550s are working easy. Not taxed at all so they should last considerably longer than the 6L6 varieties.
Having moved from the MC240 to the MC75s I can say that there is also a large difference in tube price from the 6L6GC / 7027A to the 6550A/KT-88. The top vintage ones command ridiculous money.
Although I do understand the logic in moving to the more durable tubes, I think that the biggest difference is if you’re using them hard where the 6L6GC has a reputation for “wearing out” more quickly if you use it hard than if you’re running it at lower outputs.
I might be wrong, ... as my tube gear hasn’t run hard in 40-50 years.
Although I do understand the logic in moving to the more durable tubes, I think that the biggest difference is if you’re using them hard where the 6L6GC has a reputation for “wearing out” more quickly if you use it hard than if you’re running it at lower outputs.
I might be wrong, ... as my tube gear hasn’t run hard in 40-50 years.
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Tube rolling for extended life is new reason to roll (for me). I’d guess that rolling 6550s into a 6L6 position would accomplish that goal all else equal. In the good ol days I would have been more inclined to roll in the US mfg 35W 6L6 variants like 7581A or 7027A if extended life was a priority. But good NOS examples of those types are getting expensive and harder to find. So new mfg 6550s are probably as good a choice as any out there now if extended final life is a goal. OTOH, IME the life of finals in vintage Mac unity coupled amps has been one of their strong points and I’ve never felt the need to improve it. YMMV
would agree. Finding NOS stock on some JAN valves is pretty tough.
