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   Home   Help Search  
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Author Topic: Al-811  (Read 1419 times)
W4MCX
Member

Posts: 19




Ignore
« on: July 14, 2019, 11:41:03 AM »

Any better replacement fan available for this amp, besides original? Fan is much too noisy!
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KF6OCI
Member

Posts: 125




Ignore
« Reply #1 on: July 14, 2019, 11:54:14 AM »

Check the screws they may not be
tight. Usually a quiet fan.
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KM1H
Member

Posts: 5106




Ignore
« Reply #2 on: July 14, 2019, 12:39:58 PM »

If the amp is reasonably new ask for a replacement.
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W1QJ
Member

Posts: 2948




Ignore
« Reply #3 on: July 14, 2019, 02:49:00 PM »

No amp I ever worked on, owned, used, etc. ever had a more annoying and unbearably loud fan than some amp supply LK500’s on fast speed. 
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K6AER
Member

Posts: 5693




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« Reply #4 on: July 14, 2019, 04:20:55 PM »

Check with Granger.
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K7KBN
Member

Posts: 3677




Ignore
« Reply #5 on: July 14, 2019, 09:33:25 PM »

Check with Granger.

Yeah - she's always got the right answer...wait.
What?
Oh, this isn't the Harry Potter site?  Sorry!   Grin Huh Roll Eyes
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73
Pat K7KBN
CWO4 USNR Ret.
N8FVJ
Member

Posts: 867




Ignore
« Reply #6 on: July 16, 2019, 05:24:33 AM »

Mouser has fans rated by noise in decibels (lower the better). Buy the most quiet fan. Tubes are not dependent upon a lot of air flow for better plate dissipation, just needs air flow to cool the cabinet.
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KM1H
Member

Posts: 5106




Ignore
« Reply #7 on: July 16, 2019, 06:34:51 AM »

Mouser has fans rated by noise in decibels (lower the better). Buy the most quiet fan. Tubes are not dependent upon a lot of air flow for better plate dissipation, just needs air flow to cool the cabinet.

The fan has nothing to do with improving dissipation as glass tubes cool by convection/infrared radiation. The actual purpose of the fan is to keep the plate cap seal and side glass from softening from excessive dissipation of overrated tubes since they are not true to RCA 811A specs and construction. Excessive tuning time is the biggest tube killer in those amps unless 572B's are used and then the transformer becomes the weak link when abused.

Even the Collins 30L1 had a small fan but those RCA tubes lasted for decades when run properly.
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W9IQ
Member

Posts: 3240




Ignore
« Reply #8 on: July 16, 2019, 01:06:42 PM »

Mouser has fans rated by noise in decibels (lower the better). Buy the most quiet fan. Tubes are not dependent upon a lot of air flow for better plate dissipation, just needs air flow to cool the cabinet.

That can lead to problems. Fans are not selected simply by CFM and dB ratings. The primary metric is based on the fan volume vs pressure curve that is published by the fan manufacturer. You need to understand the operating point on that curve to know both the cooling effect (based on air mass) and the dB rating at that point on the curve.

Regardless of the method of heat transfer (radiation, convection or conduction) the result is that the heat must be removed. For any given amp design, the pressure and heat to be removed set the fan requirements - the method of heat transfer is immaterial.

- Glenn W9IQ
« Last Edit: July 16, 2019, 01:14:15 PM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
N8FVJ
Member

Posts: 867




Ignore
« Reply #9 on: July 17, 2019, 06:56:41 AM »

Mouser has fans rated by noise in decibels (lower the better). Buy the most quiet fan. Tubes are not dependent upon a lot of air flow for better plate dissipation, just needs air flow to cool the cabinet.

The fan has nothing to do with improving dissipation as glass tubes cool by convection/infrared radiation. The actual purpose of the fan is to keep the plate cap seal and side glass from softening from excessive dissipation of overrated tubes since they are not true to RCA 811A specs and construction. Excessive tuning time is the biggest tube killer in those amps unless 572B's are used and then the transformer becomes the weak link when abused.

Even the Collins 30L1 had a small fan but those RCA tubes lasted for decades when run properly.

KM1H, re-read my post. My post did not state higher flow fans provide better tube cooling.
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N8FVJ
Member

Posts: 867




Ignore
« Reply #10 on: July 17, 2019, 07:02:21 AM »

Mouser has fans rated by noise in decibels (lower the better). Buy the most quiet fan. Tubes are not dependent upon a lot of air flow for better plate dissipation, just needs air flow to cool the cabinet.

That can lead to problems. Fans are not selected simply by CFM and dB ratings. The primary metric is based on the fan volume vs pressure curve that is published by the fan manufacturer. You need to understand the operating point on that curve to know both the cooling effect (based on air mass) and the dB rating at that point on the curve.

Regardless of the method of heat transfer (radiation, convection or conduction) the result is that the heat must be removed. For any given amp design, the pressure and heat to be removed set the fan requirements - the method of heat transfer is immaterial.

- Glenn W9IQ

The muffin fan as used in the Ameritron AL-811 amplifier is not a blower system cooling external plate tubes that is critical to the blower design with a lot of pressure drop thru the tubes. The muffin fans available from Mouser will provide adequate cooling. 50 CFM is plenty of air flow thru the amplifier cabinet and very quiet 50 CFM fans are available.
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W9IQ
Member

Posts: 3240




Ignore
« Reply #11 on: July 17, 2019, 07:21:45 AM »


The muffin fan as used in the Ameritron AL-811 amplifier is not a blower system cooling external plate tubes that is critical to the blower design with a lot of pressure drop thru the tubes. The muffin fans available from Mouser will provide adequate cooling. 50 CFM is plenty of air flow thru the amplifier cabinet and very quiet 50 CFM fans are available.

It doesn't matter if it is a blower or axial fan. The issue is still the mass of air moved at the system pressure. The axial fan CFM rating is generally given at 0 pressure. There will be a pressure greater than 0 in this application. That is why you need to consult the graph of the fans.

And to complete the picture, the significant difference between a blower and an axial fan is the shape and scaling of the pressure vs volume curve.

- Glenn W9IQ
« Last Edit: July 17, 2019, 07:28:15 AM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9IQ
Member

Posts: 3240




Ignore
« Reply #12 on: July 17, 2019, 09:20:38 AM »

I should also add that generally the lowest noise for the axial fan will be reached at the point on the performance curve where the fan is operating near optimal efficiency. Thus there is a bit of "specmanship" involved since the stated CFM and the lowest dB noise are often derived from different points on the curve.

- Glenn W9IQ
Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KM1H
Member

Posts: 5106




Ignore
« Reply #13 on: July 17, 2019, 09:29:12 AM »

Mouser has fans rated by noise in decibels (lower the better). Buy the most quiet fan. Tubes are not dependent upon a lot of air flow for better plate dissipation, just needs air flow to cool the cabinet.

The fan has nothing to do with improving dissipation as glass tubes cool by convection/infrared radiation. The actual purpose of the fan is to keep the plate cap seal and side glass from softening from excessive dissipation of overrated tubes since they are not true to RCA 811A specs and construction. Excessive tuning time is the biggest tube killer in those amps unless 572B's are used and then the transformer becomes the weak link when abused.

Even the Collins 30L1 had a small fan but those RCA tubes lasted for decades when run properly.

KM1H, re-read my post. My post did not state higher flow fans provide better tube cooling.

Try re-reading my post as it was generic to the tubes and not specific to you but may have possibly added to your understanding of amps in general. Glenn has been trying also but it seems to no avail.
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K6BSU
Member

Posts: 39




Ignore
« Reply #14 on: July 17, 2019, 10:11:21 AM »

I was not happy with the fan noise from my Kenwood transistor tx/rx (no model number given to avoid dissing a good radio).  I simply added a series dropping resistor in the fan circuit.  The resistor value selected to reduce noise, but with reliable start-up,  This did not seem to affect the radio.  The over-temp thermistor still operated normally, but not called on to protect the finals..
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