Just curious if anyone has tried either of these tubes in a Mark III, perhaps with a 5R4 to drop the B+ voltage? I guess the reason is the same as why climb a mountain - because it's there!
+3
Bob Latino
hawaii.ken
kygeezer
7 posters
6CA7EH or 6P3C-E in Mark III?
kygeezer- Posts : 51
Join date : 2012-11-30
kygeezer- Posts : 51
Join date : 2012-11-30
That should be 6P3S-E
hawaii.ken- Posts : 157
Join date : 2012-01-31
Bob Latino- Admin
- Posts : 3262
Join date : 2008-11-26
Location : Massachusetts
This is just my opinion but .... If you use any modern made 6CA7's in a Mark III, they will probably have a short life. The B+ with a GZ34 tube rectifier in a Mark III is about 475 to 500 VDC on today's 120 volt mains. Using a 5R4 or a 5U4 rectifier will drop the B+ to *maybe* a range that a 6CA7 can deal with ?
As to the bias "range" that hawaii.ken mentioned, he is correct that a Mark III that is normally set up to bias KT88 or 6550 tubes may not have enough range to bias a 6CA7. You can, however, alter the bias range on a Mark III to more favorable bias range for a 6CA7 by pulling the 1000 ohm main bias resistor and replacing it with a larger value like a 5K or 7.5K.
Bob
Jim McShane- Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago
"The 6P3S-E max anode voltage is only 250V so should not be used."
I wouldn't pay much attention to that spec, it's doubtful that it's a maximum spec anyway. You can use the 6P3S-E anywhere you'd use a 6L6GC. I burn in the 6P3S-Es I sell at 465 volts on the plate and screen. I've sent hundreds to people who use them far above 250 volts. There have been zero failures.
The 250 volt number is found on a Cyrillic language data sheet, and I suspect it's a translation error or such.
I wouldn't pay much attention to that spec, it's doubtful that it's a maximum spec anyway. You can use the 6P3S-E anywhere you'd use a 6L6GC. I burn in the 6P3S-Es I sell at 465 volts on the plate and screen. I've sent hundreds to people who use them far above 250 volts. There have been zero failures.
The 250 volt number is found on a Cyrillic language data sheet, and I suspect it's a translation error or such.
hawaii.ken- Posts : 157
Join date : 2012-01-31
Thanks for the info, Jim.
BNR_1- Posts : 111
Join date : 2013-06-11
Bob Latino wrote:
This is just my opinion but .... If you use any modern made 6CA7's in a Mark III, they will probably have a short life. The B+ with a GZ34 tube rectifier in a Mark III is about 475 to 500 VDC on today's 120 volt mains. Using a 5R4 or a 5U4 rectifier will drop the B+ to *maybe* a range that a 6CA7 can deal with ?
As to the bias "range" that hawaii.ken mentioned, he is correct that a Mark III that is normally set up to bias KT88 or 6550 tubes may not have enough range to bias a 6CA7. You can, however, alter the bias range on a Mark III to more favorable bias range for a 6CA7 by pulling the 1000 ohm main bias resistor and replacing it with a larger value like a 5K or 7.5K.
Bob
Hi Bob:
Can the stock (factory issued) PT handle the additional current draw from a 5U4 rectifier considering the higher voltages at today's AC outlets? Isn't the 5U4 rated at 3 amps while the 5AR4 and 5R4 rated at 2 amps.
Thanks you
Bob Latino- Admin
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Location : Massachusetts
I have used 5U4's in stock ST-70's with no issues. The B+ is lowered somewhat and you might lose a watt or two
but they appear to work just fine in an original ST-70 even at today's somewhat higher line voltages ..
Bob
GP49- Posts : 792
Join date : 2009-04-30
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The 5U4 was the stock rectifier in the Mark II, with the same power transformer and EL34 tubes. The added filament draw is a non-issue.
BNR_1- Posts : 111
Join date : 2013-06-11
GP49 wrote:The 5U4 was the stock rectifier in the Mark II, with the same power transformer and EL34 tubes. The added filament draw is a non-issue.
Hi GPA:
Far from an expert on the subject matter but doesn't the Mark II have 3 less tubes than the ST70? Would that factor into the equation at least from the filament draw?
Thank you
Last edited by BNR_1 on Wed Jun 19, 2013 4:15 pm; edited 1 time in total (Reason for editing : My comment appeared to be written by GPA49 and not me.)
GP49- Posts : 792
Join date : 2009-04-30
Location : East of the sun and west of the moon
BNR1 wrote:
Far from an expert on the subject matter but doesn't the Mark II have 3 less tubes than the ST70? Would that factor into the equation at least from the filament draw?
=======================================
Yes, but the thread is entitled, "6CA7EH or 6P3C-E in Mark III?" So my reply was regarding the Mark III. However the Dynaco manual for the Stereo 70 does say "The 5U4 or 5U4B can be used in place of the GZ34." This is mentioned as an emergency substitution which implies that the amplifier will not perform to its full specifications with the substitution. But you won't do any damage.
Far from an expert on the subject matter but doesn't the Mark II have 3 less tubes than the ST70? Would that factor into the equation at least from the filament draw?
=======================================
Yes, but the thread is entitled, "6CA7EH or 6P3C-E in Mark III?" So my reply was regarding the Mark III. However the Dynaco manual for the Stereo 70 does say "The 5U4 or 5U4B can be used in place of the GZ34." This is mentioned as an emergency substitution which implies that the amplifier will not perform to its full specifications with the substitution. But you won't do any damage.
BNR_1- Posts : 111
Join date : 2013-06-11
Thanks for clarifying GP
I missed the part of the Mark III in the original posting. My comments to Bob and you were meant for the ST70 amp. My bad. Sorry for any confusion.
I missed the part of the Mark III in the original posting. My comments to Bob and you were meant for the ST70 amp. My bad. Sorry for any confusion.
Roy Mottram- Admin
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Join date : 2008-11-30
6CA7 - in a MK3 or in an ST70 (or any other amp that could use an EL34) definitely yes, they sound great! Not as much power as a KT88 though.
They will bias like an EL34, so keep the bias around 40 - 45 ma per tube.
They will bias like an EL34, so keep the bias around 40 - 45 ma per tube.
GP49- Posts : 792
Join date : 2009-04-30
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New old stock 6CA7s are virtually certain to be closer to the original EL34s, than what is manufactured today as "EL34."
Jim McShane- Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago
With all due respect, how did you reach that conclusion?New old stock 6CA7s are virtually certain to be closer to the original EL34s, than what is manufactured today as "EL34."
As a matter of fact, most EL34 old stock tubes were true pentodes, and 6CA7s were beam tetrodes. So no, NOS 6CA7s are not closer to today's EL34s. While the 6CA7 and EL34 could interchange, they certainly don't sound the same, at least in part due to the internal construction differences.
So what do you think is manufactured today that is so different than the old stock? There is an excellent 6CA7 available in the Electro-Harmonix line (and old Ei 6CA7s were terrific too, but they're gone); and there are a number of very good EL34 tubes out there as well - as well as the outstanding KT-77 Genalex
I'm interested to find out what you meant by your statement, and what you based it on.
GP49- Posts : 792
Join date : 2009-04-30
Location : East of the sun and west of the moon
I'm basing it on failure rates and inconsistency...not just those reported on audiophile boards, but also by personal experience on my own equipment and amplifiers that I serviced while I was in the repair business.
No matter how good a particular tube type from a particular manufacturer might sound, my rule has been: one failure can be a fluke. Two is a trend. Three is disqualification.
No matter how good a particular tube type from a particular manufacturer might sound, my rule has been: one failure can be a fluke. Two is a trend. Three is disqualification.
Jim McShane- Posts : 237
Join date : 2011-10-19
Location : South Suburban Chicago
So you are not talking about "close" meaning construction features or any such hard issues. You just wanted to say that old stock is better quality in your experience/opinion. Okay, fine. But that isn't all that helpful to a person trying to decide which power tube to use in a Mk III.
So I'll try to get back on topic by saying that the 6CA7 beam tetrode is tonally more like a 6550/KT88 than the pure pentode EL34 - regardless of when the tube was made. They share that common construction, and while as Roy said the 6CA7 doesn't have the power the larger tubes have, it can be a very satisfying listening experience.
One other thing to consider - 6P3S-E heaters draw about .6 amps per tube less than the EL34s. That lighter load allows the heater voltage to rise which MAY put the heater voltage higher than you'd like. It's worth checking if you are running 6L6/6P3S-E family tubes in your amp.
So I'll try to get back on topic by saying that the 6CA7 beam tetrode is tonally more like a 6550/KT88 than the pure pentode EL34 - regardless of when the tube was made. They share that common construction, and while as Roy said the 6CA7 doesn't have the power the larger tubes have, it can be a very satisfying listening experience.
One other thing to consider - 6P3S-E heaters draw about .6 amps per tube less than the EL34s. That lighter load allows the heater voltage to rise which MAY put the heater voltage higher than you'd like. It's worth checking if you are running 6L6/6P3S-E family tubes in your amp.
Last edited by Jim McShane on Thu Jun 20, 2013 6:31 pm; edited 1 time in total (Reason for editing : Fix typo)
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