¿ªÔÆÌåÓý

ctrl + shift + ? for shortcuts
© 2025 Groups.io
  1. DRAKE-RADIO
  2. Topics

L4B Chimney size (K7CBR, VE7RF, WB6KBL)

Joseph K7CBR
 

The new blower moves over twice the air of the factory blower through the same sk406 chimney. I did the direct comparison using a hand held anemometer... held at the same location and distance above the outlet of the SK-406 chimney. I forgot now what the original velocity and CFM values vs. new ones were/are. I measured this to avoid any confirmation bias. It was nice to see Jim (VE7RF) confirming my findings. As I stated a long time ago, it is not enough to have one person just say it/measure it. Even though I was careful to do empirical measurement.

Tuesday, December 10, 2024 at 11:33:34 AM EST, Richard Knoppow via groups.io <1oldlens1@...> wrote:


? ? ? Does changing the idle current affect the distortion? If this is
the grid bias with no drive it is the operating point of the amplifier.
If I understand what you are doing correctly (and I may well not be) the
bias establishes the operating point of the amplifier so increasing bias
toward cut off, i.e. more negative, moves the amplifier toward Class B.
That would certainly reduce dissipation in the absence of drive.
? ? Another thought: Does not the tapering of the chimney at the top
restrict air flow? It should increase velocity at the plate seal but is
a constriction so might reduce overall air flow. Maybe there is
something here I am not getting.


On 12/10/2024 7:46 AM, Jim VE7RF via groups.io wrote:
> On Mon, Dec 9, 2024 at 05:17 PM, Joseph K7CBR wrote:
>
>? ? <Well Senor Jim... I was wondering if you had made the change yet on
>? ? the L4B... .. What was the before and after result? Cooling, noise,
>? ? and so on...
>


--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
 

¿ªÔÆÌåÓý

Joseph
Where did you get your fan motor for your Drake L4B? Part numbers and cost?

Merry Chirstmas
73¡±²õ


On Dec 18, 2024, at 11:16?AM, Joseph K7CBR via groups.io <k7cbr@...> wrote:

The new blower moves over twice the air of the factory blower through the same sk406 chimney. I did the direct comparison using a hand held anemometer... held at the same location and distance above the outlet of the SK-406 chimney. I forgot now what the original velocity and CFM values vs. new ones were/are. I measured this to avoid any confirmation bias. It was nice to see Jim (VE7RF) confirming my findings. As I stated a long time ago, it is not enough to have one person just say it/measure it. Even though I was careful to do empirical measurement.

Tuesday, December 10, 2024 at 11:33:34 AM EST, Richard Knoppow via groups.io <1oldlens1@...> wrote:


? ? ? Does changing the idle current affect the distortion? If this is
the grid bias with no drive it is the operating point of the amplifier.
If I understand what you are doing correctly (and I may well not be) the
bias establishes the operating point of the amplifier so increasing bias
toward cut off, i.e. more negative, moves the amplifier toward Class B.
That would certainly reduce dissipation in the absence of drive.
? ? Another thought: Does not the tapering of the chimney at the top
restrict air flow? It should increase velocity at the plate seal but is
a constriction so might reduce overall air flow. Maybe there is
something here I am not getting.

On 12/10/2024 7:46 AM, Jim VE7RF via groups.io wrote:
> On Mon, Dec 9, 2024 at 05:17 PM, Joseph K7CBR wrote:
>
>? ? <Well Senor Jim... I was wondering if you had made the change yet on
>? ? the L4B... .. What was the before and after result? Cooling, noise,
>? ? and so on...
>


--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998







73¡¯²õ
KK4IZ
Amateur Radio Operator
Warren Bryant?
124 Crestview Dr
Clanton,AL.??35045
Email:?KK4IZ284@...
Cell: 205-389-4170
Joseph K7CBR
 

Hello Clayton,

This was all done so long ago I can't recall, yet that information was posted to the Drake board here. Jim (VE7RF) used a different blower (same housing yet 230VAC) I think. If I had to guess, I order parts mostly from Mouser, DigiKey, and Newark, so likely came from one of those. Know that if you do this, You will need to relocate the inlet, enlarge the discharge port in the horizontal chassis, and make some minor changes to the new blower mounting flange to make it fit properly with the glass chimney. Is it worth the trouble? YES! You only need to do it once. This type of blower (compact air over induction motor) did not exist in this size and style when Drake built this amplifier. I attached photo's from my archive to show you in case you did not see them some years ago. If you have issues locating the part number, I can look inside my L4B this weekend and post the part number here for you. --Joseph

On Monday, December 23, 2024 at 09:29:12 PM EST, Clayton kk4iz via groups.io <kk4iz284@...> wrote:


Joseph
Where did you get your fan motor for your Drake L4B? Part numbers and cost?

Merry Chirstmas
73¡±²õ


On Dec 18, 2024, at 11:16?AM, Joseph K7CBR via groups.io <k7cbr@...> wrote:

The new blower moves over twice the air of the factory blower through the same sk406 chimney. I did the direct comparison using a hand held anemometer... held at the same location and distance above the outlet of the SK-406 chimney. I forgot now what the original velocity and CFM values vs. new ones were/are. I measured this to avoid any confirmation bias. It was nice to see Jim (VE7RF) confirming my findings. As I stated a long time ago, it is not enough to have one person just say it/measure it. Even though I was careful to do empirical measurement.

Tuesday, December 10, 2024 at 11:33:34 AM EST, Richard Knoppow via groups.io <1oldlens1@...> wrote:


? ? ? Does changing the idle current affect the distortion? If this is
the grid bias with no drive it is the operating point of the amplifier.
If I understand what you are doing correctly (and I may well not be) the
bias establishes the operating point of the amplifier so increasing bias
toward cut off, i.e. more negative, moves the amplifier toward Class B.
That would certainly reduce dissipation in the absence of drive.
? ? Another thought: Does not the tapering of the chimney at the top
restrict air flow? It should increase velocity at the plate seal but is
a constriction so might reduce overall air flow. Maybe there is
something here I am not getting.

On 12/10/2024 7:46 AM, Jim VE7RF via groups.io wrote:
> On Mon, Dec 9, 2024 at 05:17 PM, Joseph K7CBR wrote:
>
>? ? <Well Senor Jim... I was wondering if you had made the change yet on
>? ? the L4B... .. What was the before and after result? Cooling, noise,
>? ? and so on...
>


--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998







73¡¯²õ
KK4IZ
Amateur Radio Operator
Warren Bryant?
124 Crestview Dr
Clanton,AL.??35045
Email:?KK4IZ284@...
Cell: 205-389-4170




IMG_4788.JPG
IMG_0138.JPG

 

We both used the? EBM-PAPST? (German made)? squirrel cage blower from the Ameritron AL-1500/AL-1200/ AL-82 amplifier.? ? They came in both a 115 and also a 230 vac version.? Ameritron used the? 115 vac version...and used pri xfmr / buck boost taps to get 3 x different speeds from the blower.

Ameritron used to sell the 115 vac blower for $138.00? then the price went up to $168.00? ? ? At Mouser / Digikey, the 115 vac version was almost $200.00? ? ?For whatever reason, the 230 vac version? at Mouser / DK is $102.00 to $112.00 range.? ?I bought the 230 vac versions, since I needed 4 of em? (for 4 x L4B's).? ?Thought here was..... I have never run those amps on 120 vac.?

The mod however does require metal work, since the blower exhaust dimensions are bigger than the drake blower.? ?The new blower has flanges on the exhaust and one of em has to be cut off in my bandsaw.? ?The intake opening is bigger than oem, and slightly offset too.?

I did not have the anemometer, but guesstimated the airflow? on the papst blower to be a bare? minimum of double.? ?My estimate was? between 2.25? and 2.5 X? more airflow.? ?By using a? drop resistor in one leg, any speed can be obtained.? The drop resistor can also be shunted on TX.? ?Then it's quieter on RX....and extended RX.? That's an experiment in progress.?
?
 

It's an EBM-Papst blower... model # is? G2S097- DB61-08? (115 vac version).?

The 230 vac version is? #? G2S097- DB03 - 01?

They both weigh 1.81 lbs, and both are galvanized.?
26 cfm @ 0"? ?and 20 cfm @ .4"?
37 dba
Ball bearings.? ( field replaceable)??
22 watts.?

Eimac 3-500Z cooling specs ( using tapered chimneys and a? PAIR of tubes)? is 20.6 cfm @ .052"? ? for 400w? CCS diss.? ? And? ?26.0? cfm @ .082"?
Joseph K7CBR
 

Yes this looks spot on! Thanks Jim... I also attached another view with the old suppressors installed with the factory straight wall chimney's.
the tapered version is what Eimac recommends, along with grids grounded at the chassis. I am not being critical about anything Drake did.
Just showing what my own iteration for the L4B is. I am 100% happy with it, and after all the work, never has suggested excess heating is an
issue. I use no auxiliary fans or blowers with it at all as it flat does not need it. I used a bias scheme similar to Jim's also giving 100ma of grid
current at idle.

On Tuesday, December 24, 2024 at 11:46:05 AM EST, Jim VE7RF via groups.io <jim.thom@...> wrote:


It's an EBM-Papst blower... model # is? G2S097- DB61-08? (115 vac version).?

The 230 vac version is? #? G2S097- DB03 - 01?

They both weigh 1.81 lbs, and both are galvanized.?
26 cfm @ 0"? ?and 20 cfm @ .4"?
37 dba
Ball bearings.? ( field replaceable)??
22 watts.?

Eimac 3-500Z cooling specs ( using tapered chimneys and a? PAIR of tubes)? is 20.6 cfm @ .052"? ? for 400w? CCS diss.? ? And? ?26.0? cfm @ .082"?

005.JPG
IMG_0138.JPG
IMG_4788.JPG

 

That shoulda read...... Eimac 3-500Z cooling specs ( using tapered chimneys and a? PAIR of tubes)? is 20.6 cfm @ .052"? ? for 800w? CCS diss.? ? And? ?26.0? cfm @ .082"? for 1000w CCS diss.?

The ebm blower is more than up to the task.?

1 - 7 of 7