Hi, so I’ve just completed a 5e3 build using the classictone PT and OT (PT on 355-0-355 and 240v taps). I’m looking to wrap up the build but the plate dissipation that I’ve calculated is a tad over 14w - 14.37w. I’m using 2 x NOS RCA 6V6GT, NOS Raytheon 12AY7 in V1 and 12AX7 in V2, sounds great. See below voltages and calc, should I try a 270ohm cathode resistor or is it ok as is? Any help is greatly appreciated, thanks.
Wall voltage: 236vac
HV: 697vac
V1-V4 heaters: 6.44vac
5y3 heater: 4.96vac
B+: 365vdc
B+1: 325vdc
B+2: 237vdc
Plate to cathode = 328vdc (plate 350vd - cathode resistor drop of 21.73vdc)
Cathode resistor measured r = 248ohms
21.73 / 248 = 0.87621A
0.87621 x 328 = 28.74w
28.74 / 2 = 14.37w per tube
Help needed with 5e3 plate dissipation
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Governator
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martin manning
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Re: Help needed with 5e3 plate dissipation
Note that your plate dissipation is about 5% less than you calculated due to the screen current, but still a bit hot at 13.6W. I think I would try a 270Ω to make those NOS tubes last a little longer.
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Stevem
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Re: Help needed with 5e3 plate dissipation
With your voltages having each output idling at 24 ma (70 percent) would be the hottest you would want to go, a life giving 60 % would be 21 ma.
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Governator
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martin manning
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Re: Help needed with 5e3 plate dissipation
70% is a reasonable idle dissipation for push-pull amps, as explained here: https://www.aikenamps.com/index.php/idl ... 70-percent
Cathode biased amps can be biased hotter due to the nature of their transient behavior, and most people seem to prefer setting them around 90-95%
Cathode biased amps can be biased hotter due to the nature of their transient behavior, and most people seem to prefer setting them around 90-95%
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Governator
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Re: Help needed with 5e3 plate dissipation
Hi, so I’ve finally had a chance to swap out the cathode resistor for a 270ohm. Here are the voltages:
Plate to cathode = 330vdc (plate 352vdc - cathode resistor drop of 22.3vdc)
Cathode resistor measured r = 269.5ohms
22.3/ 269.5 = 0.082745A
0.082745 x 330 = 27.306w
27.306 / 2 = 13.653w per tube
What are your thoughts, is this ok to leave? Thanks for the help.
Plate to cathode = 330vdc (plate 352vdc - cathode resistor drop of 22.3vdc)
Cathode resistor measured r = 269.5ohms
22.3/ 269.5 = 0.082745A
0.082745 x 330 = 27.306w
27.306 / 2 = 13.653w per tube
What are your thoughts, is this ok to leave? Thanks for the help.
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martin manning
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Re: Help needed with 5e3 plate dissipation
You're down to 13W on the plates if we assume the tubes are matched and that 5% of the cathode current is going to the screens. If they don't red-plate you could leave it, or try 300Ω.
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Stevem
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Re: Help needed with 5e3 plate dissipation
If you assume that when/ if you play the amp dimed the V+ will sag some 15 volts or more then you could leave it idling where it is, but if it was my wallet that shelled out the bucks for those RCA tubes I would be idling them cooler!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Help needed with 5e3 plate dissipation
Cathode bias is fundamentally different to fixed bias, can’t just run the power valves cooler without detrimentally altering circuit operation.
What’s the point spending big money on holy grail valves, but then hamstringing their ability to perform by changing a classic design so as to induce a greater degree of dynamic bias shift (Aiken’s ‘squish’)?
The most efficacious way to reduce anode dissipation is to plug a guitar in, turn up the volume and play; HT sag and power transfer to the speaker will achieve that, as well as facilitating enjoyment of your creation
What’s the point spending big money on holy grail valves, but then hamstringing their ability to perform by changing a classic design so as to induce a greater degree of dynamic bias shift (Aiken’s ‘squish’)?
The most efficacious way to reduce anode dissipation is to plug a guitar in, turn up the volume and play; HT sag and power transfer to the speaker will achieve that, as well as facilitating enjoyment of your creation
Last edited by pdf64 on Fri Mar 26, 2021 6:21 pm, edited 1 time in total.
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Stevem
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Re: Help needed with 5e3 plate dissipation
So are you really saying that idling them at let's say 12.8 watts would be a issue , because I can't see that by any means!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Governator
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Re: Help needed with 5e3 plate dissipation
I also have a Fluke that tongs DC mA, see below pics:
On one side I get 38mA, and 42mA on the other. Thoughts?
On one side I get 38mA, and 42mA on the other. Thoughts?
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Re: Help needed with 5e3 plate dissipation
Unfortunately the photos aren't very helpful in working out exactly what is being measured?
But it would be unusual for any 2 valves in shared conditions to have zero discrepancy in their anode or cathode currents.
At face value, the discrepancy seems as low as could reasonably be expected.
But it would be unusual for any 2 valves in shared conditions to have zero discrepancy in their anode or cathode currents.
At face value, the discrepancy seems as low as could reasonably be expected.
https://www.justgiving.com/page/5-in-5-for-charlie This is my step son and his family. He is running 5 marathons in 5 days to support the research into STXBP1, the genetic condition my grandson Charlie has. Please consider supporting him!
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Stevem
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Re: Help needed with 5e3 plate dissipation
I agree, those two output tubes are as closely matched as you should need them in terms of IDLE conditions, the more important question for me is how that may spread even more when they are driven and also how that spread may change between the outputs as frequency they are driven by changes!
That by far determines how good the amp sounds to your ear when driven hard and especially into the clipping range!
That by far determines how good the amp sounds to your ear when driven hard and especially into the clipping range!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!