From ajamas.rn at gmail.com  Mon Dec  1 07:36:04 2025
From: ajamas.rn at gmail.com (Bob D.)
Date: Mon, 1 Dec 2025 07:36:04 -0500
Subject: [Amps] MFJ 50V SMPS schematic appears in the manual here...
Message-ID: <CA+kZa5q93ZwTgZrsPD4CGi2tXM0ivnbUTBNmtNPCKc-29xujZw@mail.gmail.com>

https://cdn.shopify.com/s/files/1/0289/7782/3843/files/ALS-600S.pdf?v=1586534128

-do not look into LASER with remaining eye!

From ajamas.rn at gmail.com  Mon Dec  1 07:45:26 2025
From: ajamas.rn at gmail.com (Bob D.)
Date: Mon, 1 Dec 2025 07:45:26 -0500
Subject: [Amps] MFJ 50V SMPS
Message-ID: <CA+kZa5o45Fb6Qd8_suffQzrMVxHJcyTuJ4fYkA2CS7OH9YQf9w@mail.gmail.com>

The schematic part numbers are difficult to read. Having the supply at hand
should be enough. I found with one of their 13.8V supplies that once I had
it apart. The only problem was discontinued high side switching
transistors. Part numbers on the actual parts were clear. Looked up spec.
Did a parametric search. Found something close enough.


-do not look into LASER with remaining eye!

From ajamas.rn at gmail.com  Mon Dec  1 07:57:51 2025
From: ajamas.rn at gmail.com (Bob D.)
Date: Mon, 1 Dec 2025 07:57:51 -0500
Subject: [Amps] MFJ 50V SMPS
Message-ID: <CA+kZa5pLNR3bwf=1t4_nk5LVo5As8mAjALdvsYOU3t+ZH7Uo-g@mail.gmail.com>

Looks like the controller pn starts with TL. Likely TL594 or equivalent.
Plenty of application info on line.
For example:
https://www.flywing-tech.com/blog/tl494-pwm-controller-working-principle-circuit-design-and-smps-applications/

-do not look into LASER with remaining eye!

From k5sul at aol.com  Mon Dec  8 15:55:10 2025
From: k5sul at aol.com (Charles K Hardy)
Date: Mon, 8 Dec 2025 20:55:10 +0000 (UTC)
Subject: [Amps] AL-82
References: <1574992284.1070308.1765227310716.ref@mail.yahoo.com>
Message-ID: <1574992284.1070308.1765227310716@mail.yahoo.com>

Does anyone know a source for a bandswitch for the Ameritron AL-82?? Is the same switch also used in the AL 1200 and 1500 as well?
Thanks.Charles K. Hardy? K5SUL

From maflukey at gmail.com  Tue Dec  9 01:01:28 2025
From: maflukey at gmail.com (maflukey at gmail.com)
Date: Tue, 9 Dec 2025 00:01:28 -0600
Subject: [Amps] AL-82
In-Reply-To: <1574992284.1070308.1765227310716@mail.yahoo.com>
References: <1574992284.1070308.1765227310716.ref@mail.yahoo.com>
	<1574992284.1070308.1765227310716@mail.yahoo.com>
Message-ID: <011701dc68d1$42c03aa0$c840afe0$@gmail.com>

https://www.ctrengineeringinc.com/rf-switches-medium-and-high-power/

Matt
KM5VI

-----Original Message-----
From: Amps <amps-bounces at contesting.com> On Behalf Of Charles K Hardy via Amps
Sent: Monday, December 8, 2025 2:55 PM
To: amps at contesting.com
Subject: [Amps] AL-82

Does anyone know a source for a bandswitch for the Ameritron AL-82?  Is the same switch also used in the AL 1200 and 1500 as well?
Thanks.Charles K. Hardy  K5SUL
_______________________________________________
Amps mailing list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps



From sparks06524 at yahoo.com  Tue Dec  9 03:37:25 2025
From: sparks06524 at yahoo.com (Douglas L)
Date: Tue, 9 Dec 2025 03:37:25 -0500
Subject: [Amps] Ameritron AL-800
References: <08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9.ref@yahoo.com>
Message-ID: <08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9@yahoo.com>

Has anyone created a work around to replace the 3CX800A7 tubes in the AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
Eimac versions are greater than $1500 and the Chinese subs, last I looked, were pushing toward $1000/tube. Machlett, Penta and the like are simply rebranded Chinese tubes.
Medical pulls have largely dried up with MRI and other machines going solid state.
Thus the tube pricing has gotten ridiculous.
  Perhaps the only answer is going to solid state amps?
73,
DougWA1TUT


From g8gsq at gmx.com  Tue Dec  9 04:37:38 2025
From: g8gsq at gmx.com (Steve Thompson)
Date: Tue, 9 Dec 2025 09:37:38 +0000
Subject: [Amps] =?utf-8?q?Ameritron_AL-800?=
In-Reply-To: <08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9@yahoo.com>
References: <08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9.ref@yahoo.com>
	<08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9@yahoo.com>
Message-ID: <trinity-5b66dfa6-37c0-49a4-80f8-f13f13c47c73-1765273058268@trinity-msg-rest-gmx-gmx-live-5ff6d7d9d4-jmrl6>


From g8gsq at gmx.com  Tue Dec  9 05:31:28 2025
From: g8gsq at gmx.com (Steve Thompson)
Date: Tue, 9 Dec 2025 10:31:28 +0000
Subject: [Amps] Ameritron AL-800
In-Reply-To: <08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9@yahoo.com>
References: <08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9.ref@yahoo.com>
	<08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9@yahoo.com>
Message-ID: <13e6af91-ec37-4d7c-851b-508a1ada2e91@gmx.com>

https://www.ampleon.com/products/extremely-rugged/75-v/ART4K0FX.html

But not the easiest retrofit ?

Steve G8GSQ

On 09/12/2025 08:37, Douglas L via Amps wrote:
> Has anyone created a work around to replace the 3CX800A7 tubes in the AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
> Eimac versions are greater than $1500 and the Chinese subs, last I looked, were pushing toward $1000/tube. Machlett, Penta and the like are simply rebranded Chinese tubes.
> Medical pulls have largely dried up with MRI and other machines going solid state.
> Thus the tube pricing has gotten ridiculous.
>    Perhaps the only answer is going to solid state amps?
> 73,
> DougWA1TUT
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps



From sparks06524 at yahoo.com  Tue Dec  9 06:02:23 2025
From: sparks06524 at yahoo.com (Douglas L)
Date: Tue, 9 Dec 2025 06:02:23 -0500
Subject: [Amps] Ameritron AL-800
In-Reply-To: <13e6af91-ec37-4d7c-851b-508a1ada2e91@gmx.com>
References: <13e6af91-ec37-4d7c-851b-508a1ada2e91@gmx.com>
Message-ID: <A21C5E48-9064-4266-9C38-AA0B1C484130@yahoo.com>

I wouldn?t say that using an LDMOSFET is a retrofit.
It would basically mean building an entirely different amplifier with a different power supply, different input and output networks, etc.

> On Dec 9, 2025, at 5:32?AM, Steve Thompson via Amps <amps at contesting.com> wrote:
> 
> ?https://www.ampleon.com/products/extremely-rugged/75-v/ART4K0FX.html
> 
> But not the easiest retrofit ?
> 
> Steve G8GSQ
> 
>> On 09/12/2025 08:37, Douglas L via Amps wrote:
>> Has anyone created a work around to replace the 3CX800A7 tubes in the AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
>> Eimac versions are greater than $1500 and the Chinese subs, last I looked, were pushing toward $1000/tube. Machlett, Penta and the like are simply rebranded Chinese tubes.
>> Medical pulls have largely dried up with MRI and other machines going solid state.
>> Thus the tube pricing has gotten ridiculous.
>>   Perhaps the only answer is going to solid state amps?
>> 73,
>> DougWA1TUT
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
> 
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps



From steve at nr4m.com  Tue Dec  9 10:34:14 2025
From: steve at nr4m.com (Steve Bookout, NR4M)
Date: Tue, 9 Dec 2025 10:34:14 -0500
Subject: [Amps] Ameritron AL-800
In-Reply-To: <A21C5E48-9064-4266-9C38-AA0B1C484130@yahoo.com>
References: <A21C5E48-9064-4266-9C38-AA0B1C484130@yahoo.com>
Message-ID: <2340313F-4400-4115-9B60-F028364A489C@nr4m.com>

Have you given any thought to converting to some of the Russian tubes.  
Would justhave to be an easier rebuild than converting to LDMOSFET?s. And, when I last looked those tubes are still less expensive than ?Merican alternatives. 

Steve NR4M 

Sent from my iPhone

> On Dec 9, 2025, at 6:03?AM, Douglas L via Amps <amps at contesting.com> wrote:
> 
> ?I wouldn?t say that using an LDMOSFET is a retrofit.
> It would basically mean building an entirely different amplifier with a different power supply, different input and output networks, etc.
> 
>> On Dec 9, 2025, at 5:32?AM, Steve Thompson via Amps <amps at contesting.com> wrote:
>> 
>> ?https://www.ampleon.com/products/extremely-rugged/75-v/ART4K0FX.html
>> 
>> But not the easiest retrofit ?
>> 
>> Steve G8GSQ
>> 
>>>> On 09/12/2025 08:37, Douglas L via Amps wrote:
>>> Has anyone created a work around to replace the 3CX800A7 tubes in the AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
>>> Eimac versions are greater than $1500 and the Chinese subs, last I looked, were pushing toward $1000/tube. Machlett, Penta and the like are simply rebranded Chinese tubes.
>>> Medical pulls have largely dried up with MRI and other machines going solid state.
>>> Thus the tube pricing has gotten ridiculous.
>>>  Perhaps the only answer is going to solid state amps?
>>> 73,
>>> DougWA1TUT
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>> 
>> 
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
> 
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps



From woodr90 at gmail.com  Tue Dec  9 12:27:41 2025
From: woodr90 at gmail.com (Robert W5AJ)
Date: Tue, 9 Dec 2025 11:27:41 -0600
Subject: [Amps] Ameritron AL-800
In-Reply-To: <08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9@yahoo.com>
References: <08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9.ref@yahoo.com>
	<08CBADD0-9B4C-414D-99D7-EA5FAEACF9C9@yahoo.com>
Message-ID: <CAGuXMYN4Hihrz34U6SErD22QZNECGUJbG5ekCavpKUbU+LjVoQ@mail.gmail.com>

 Doug,

I had several 3cx800 up for sale ->  I think 400 or 450$ each
healthy tubes too.

NO TAKERS.

73 Robert W5AJ

Keep eye on swap.qth.com    and eham.net for the tubes.

I have box of 3-1000 and 4-1000 tubes too but my tester hasn't been fired
up in a LONG time!

On Tue, Dec 9, 2025 at 2:50?AM Douglas L via Amps <amps at contesting.com>
wrote:

> Has anyone created a work around to replace the 3CX800A7 tubes in the
> AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
> Eimac versions are greater than $1500 and the Chinese subs, last I looked,
> were pushing toward $1000/tube. Machlett, Penta and the like are simply
> rebranded Chinese tubes.
> Medical pulls have largely dried up with MRI and other machines going
> solid state.
> Thus the tube pricing has gotten ridiculous.
>   Perhaps the only answer is going to solid state amps?
> 73,
> DougWA1TUT
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>

From g8gsq at gmx.com  Tue Dec  9 12:43:20 2025
From: g8gsq at gmx.com (Steve Thompson)
Date: Tue, 9 Dec 2025 17:43:20 +0000
Subject: [Amps] Ameritron AL-800
In-Reply-To: <2340313F-4400-4115-9B60-F028364A489C@nr4m.com>
References: <A21C5E48-9064-4266-9C38-AA0B1C484130@yahoo.com>
	<2340313F-4400-4115-9B60-F028364A489C@nr4m.com>
Message-ID: <d02f1733-23e2-4c71-a59e-b9360ade2b74@gmx.com>

Unfortunately, plain text doesn't convey the tongue-in-cheek and 
intended humour of my comment (prompted by not long having received the 
info. about the new LDMOS part). Well cared for, tubes will often 
outlive their owners; my 60 yr old 813s probably will.

Nevertheless, a single transistor rated at 3-4kW output is an intriguing 
prospect and would have been the stuff of science fiction when I started 
out in RF design.

Steve G8GSQ

On 09/12/2025 15:34, Steve Bookout, NR4M wrote:
> Have you given any thought to converting to some of the Russian tubes.
> Would justhave to be an easier rebuild than converting to LDMOSFET?s. And, when I last looked those tubes are still less expensive than ?Merican alternatives.
> 
> Steve NR4M
> 
> Sent from my iPhone
> 
>> On Dec 9, 2025, at 6:03?AM, Douglas L via Amps <amps at contesting.com> wrote:
>>
>> ?I wouldn?t say that using an LDMOSFET is a retrofit.
>> It would basically mean building an entirely different amplifier with a different power supply, different input and output networks, etc.
>>
>>> On Dec 9, 2025, at 5:32?AM, Steve Thompson via Amps <amps at contesting.com> wrote:
>>>
>>> ?https://www.ampleon.com/products/extremely-rugged/75-v/ART4K0FX.html
>>>
>>> But not the easiest retrofit ?
>>>
>>> Steve G8GSQ
>>>
>>>>> On 09/12/2025 08:37, Douglas L via Amps wrote:
>>>> Has anyone created a work around to replace the 3CX800A7 tubes in the AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
>>>> Eimac versions are greater than $1500 and the Chinese subs, last I looked, were pushing toward $1000/tube. Machlett, Penta and the like are simply rebranded Chinese tubes.
>>>> Medical pulls have largely dried up with MRI and other machines going solid state.
>>>> Thus the tube pricing has gotten ridiculous.
>>>>   Perhaps the only answer is going to solid state amps?
>>>> 73,
>>>> DougWA1TUT
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
> 



From sparks06524 at yahoo.com  Tue Dec  9 16:41:46 2025
From: sparks06524 at yahoo.com (Douglas L)
Date: Tue, 9 Dec 2025 16:41:46 -0500
Subject: [Amps] Ameritron AL-800
In-Reply-To: <d02f1733-23e2-4c71-a59e-b9360ade2b74@gmx.com>
References: <d02f1733-23e2-4c71-a59e-b9360ade2b74@gmx.com>
Message-ID: <4BC00D0A-25CF-4F7F-950C-A4FC0DF2E491@yahoo.com>

You?re right about the fairly rapid advances in technology. Back in the 1970?s I was an assistant engineer at WELI radio, a 5 KW AM station in New Haven, Connecticut.
Our main transmitter was a 1955 vintage RCA BTA-5H. It took up three 60? by 48? racks, one for the driver and RF output, one for the modulator and one for the power supply.
  I recommended a then new design Nautel all solid state transmitter. Despite using 5 (I think) one kw modules, the whole transmitter was in one rack.
  However the chief was suspicious of an all solid state rig and went with a Harris MW-5, that only used one tube which I believe was a 4CX10,000a.
  It?s been almost 50 years and I think that station still has the Harris as a backup transmitter.
Doug/WA1TUT

> On Dec 9, 2025, at 1:00?PM, Steve Thompson via Amps <amps at contesting.com> wrote:
> 
> ?Unfortunately, plain text doesn't convey the tongue-in-cheek and intended humour of my comment (prompted by not long having received the info. about the new LDMOS part). Well cared for, tubes will often outlive their owners; my 60 yr old 813s probably will.
> 
> Nevertheless, a single transistor rated at 3-4kW output is an intriguing prospect and would have been the stuff of science fiction when I started out in RF design.
> 
> Steve G8GSQ
> 
>> On 09/12/2025 15:34, Steve Bookout, NR4M wrote:
>> Have you given any thought to converting to some of the Russian tubes.
>> Would justhave to be an easier rebuild than converting to LDMOSFET?s. And, when I last looked those tubes are still less expensive than ?Merican alternatives.
>> Steve NR4M
>> Sent from my iPhone
>>>> On Dec 9, 2025, at 6:03?AM, Douglas L via Amps <amps at contesting.com> wrote:
>>> 
>>> ?I wouldn?t say that using an LDMOSFET is a retrofit.
>>> It would basically mean building an entirely different amplifier with a different power supply, different input and output networks, etc.
>>> 
>>>> On Dec 9, 2025, at 5:32?AM, Steve Thompson via Amps <amps at contesting.com> wrote:
>>>> 
>>>> ?https://www.ampleon.com/products/extremely-rugged/75-v/ART4K0FX.html
>>>> 
>>>> But not the easiest retrofit ?
>>>> 
>>>> Steve G8GSQ
>>>> 
>>>>>> On 09/12/2025 08:37, Douglas L via Amps wrote:
>>>>> Has anyone created a work around to replace the 3CX800A7 tubes in the AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
>>>>> Eimac versions are greater than $1500 and the Chinese subs, last I looked, were pushing toward $1000/tube. Machlett, Penta and the like are simply rebranded Chinese tubes.
>>>>> Medical pulls have largely dried up with MRI and other machines going solid state.
>>>>> Thus the tube pricing has gotten ridiculous.
>>>>>  Perhaps the only answer is going to solid state amps?
>>>>> 73,
>>>>> DougWA1TUT
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>> 
>>>> 
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>> 
>>> 
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
> 
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps



From kg7hf at comcast.net  Wed Dec 10 13:00:21 2025
From: kg7hf at comcast.net (Paul Decker)
Date: Wed, 10 Dec 2025 13:00:21 -0500 (EST)
Subject: [Amps] Ameritron AL-800
In-Reply-To: <mailman.1.1765386002.12068.amps@contesting.com>
References: <mailman.1.1765386002.12068.amps@contesting.com>
Message-ID: <1742500658.1722179.1765389621952@connect.xfinity.com>

> > Has anyone created a work around to replace the 3CX800A7 tubes in the
> > AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?

The 3cx400U7 and 3cx800U7 are usually much cheaper alternatives and in many cases can be NOS. The datasheet lists the working B+ as lower, but I suspect that is simply due to the higher frequency rating of the U7

The only issue is changing out the base which seems daunting at first. There is an "RCA like" plug connector that fits the base really well so that only the grid ring needs to be figured out with some simple finger stock and a metal plate. 

Someone with talent could design an adapter board that would work well too! 

Paul
KG7HF


From sparks06524 at yahoo.com  Wed Dec 10 19:01:26 2025
From: sparks06524 at yahoo.com (Douglas L)
Date: Wed, 10 Dec 2025 19:01:26 -0500
Subject: [Amps] Ameritron AL-800
In-Reply-To: <1742500658.1722179.1765389621952@connect.xfinity.com>
References: <1742500658.1722179.1765389621952@connect.xfinity.com>
Message-ID: <7741B558-A0A0-418F-8C42-828B795CFD4D@yahoo.com>

Checking the specs, the 3CX800U7 is rated at 350 watts output with an efficiency of only 33%. That?s less than half the rated output power of the 3CX800A7.
I wonder if it was derated for typical UHF service?
If not, it?s a poor substitute for a 3CX800A7.
Doug/WA1TUT


> On Dec 10, 2025, at 1:01?PM, Paul Decker via Amps <amps at contesting.com> wrote:
> 
> ?
>> 
>>> Has anyone created a work around to replace the 3CX800A7 tubes in the
>>> AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
> 
> The 3cx400U7 and 3cx800U7 are usually much cheaper alternatives and in many cases can be NOS. The datasheet lists the working B+ as lower, but I suspect that is simply due to the higher frequency rating of the U7
> 
> The only issue is changing out the base which seems daunting at first. There is an "RCA like" plug connector that fits the base really well so that only the grid ring needs to be figured out with some simple finger stock and a metal plate.
> 
> Someone with talent could design an adapter board that would work well too!
> 
> Paul
> KG7HF
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps



From kg7hf at comcast.net  Wed Dec 10 19:26:57 2025
From: kg7hf at comcast.net (Paul Decker)
Date: Wed, 10 Dec 2025 19:26:57 -0500 (EST)
Subject: [Amps] Ameritron AL-800
In-Reply-To: <7741B558-A0A0-418F-8C42-828B795CFD4D@yahoo.com>
References: <1742500658.1722179.1765389621952@connect.xfinity.com>
	<7741B558-A0A0-418F-8C42-828B795CFD4D@yahoo.com>
Message-ID: <1164940429.1706572.1765412817972@connect.xfinity.com>

I'm not sure. I see at 450 MHz it is 46% efficiency

But typical operation at 150 MHz is listed as:

3CX800A7 ? Typical Operation (Measured Data to 150 MHz)

Class AB2, Cathode Driven

Parameter	Value
Plate Voltage	2200 Vdc
Cathode Bias Voltage	+8.2 Vdc
Zero-Signal Plate Current	150 mAdc
CW Plate Current	500 mAdc
CW Power Input	1100 W
Peak Envelope Power Input	1100 W
Two-Tone Plate Current	313 mAdc
CW Grid Current	16 mAdc
Two-Tone Grid Current	16 mAdc
Peak RF Cathode Voltage	64 V
Peak Driving Power	70 W
Useful Power Output (CW)	750 W
Useful Power Output, PEP	**1100 W
Cathode Input Impedance	54 Ohms
Resonant Load Impedance	2700 Ohms
Intermodulation Distortion (IMD)	
? 3rd Order Products	?36 dB
? 5th Order Products	?32 dB

> On 12/10/2025 7:01 PM EST Douglas L <sparks06524 at yahoo.com> wrote:
> 
>  
> Checking the specs, the 3CX800U7 is rated at 350 watts output with an efficiency of only 33%. That?s less than half the rated output power of the 3CX800A7.
> I wonder if it was derated for typical UHF service?
> If not, it?s a poor substitute for a 3CX800A7.
> Doug/WA1TUT
> 
> 
> > On Dec 10, 2025, at 1:01?PM, Paul Decker via Amps <amps at contesting.com> wrote:
> > 
> > ?
> >> 
> >>> Has anyone created a work around to replace the 3CX800A7 tubes in the
> >>> AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
> > 
> > The 3cx400U7 and 3cx800U7 are usually much cheaper alternatives and in many cases can be NOS. The datasheet lists the working B+ as lower, but I suspect that is simply due to the higher frequency rating of the U7
> > 
> > The only issue is changing out the base which seems daunting at first. There is an "RCA like" plug connector that fits the base really well so that only the grid ring needs to be figured out with some simple finger stock and a metal plate.
> > 
> > Someone with talent could design an adapter board that would work well too!
> > 
> > Paul
> > KG7HF
> > 
> > _______________________________________________
> > Amps mailing list
> > Amps at contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps


From kg7hf at comcast.net  Wed Dec 10 19:38:32 2025
From: kg7hf at comcast.net (Paul Decker)
Date: Wed, 10 Dec 2025 19:38:32 -0500 (EST)
Subject: [Amps] Ameritron AL-800
In-Reply-To: <1164940429.1706572.1765412817972@connect.xfinity.com>
References: <1742500658.1722179.1765389621952@connect.xfinity.com>
	<7741B558-A0A0-418F-8C42-828B795CFD4D@yahoo.com>
	<1164940429.1706572.1765412817972@connect.xfinity.com>
Message-ID: <2027046026.1707098.1765413512909@connect.xfinity.com>

Sorry, I hit send too soon.
This is in the CV-2108 cavity.  I'm fairly certain the 3CX800A7 is not measured at 850 MHz. 

Typical Operation ? Class AB2 Cathode Driven (850 MHz)

FM / CW
Heater Voltage (warmup or standby) . . . . . . . . 13.5 / 13.5 Vac
Heater Voltage (during operation) . . . . . . . . . 12.0 / 13.5 Vac
Heater Current (at 13.5 volts)* . . . . . . . . . 1.5 / 1.5 Aac
Plate Voltage . . . . . . . . . . . . . . . . . . . . 1500 / 2000 Vdc
Cathode Bias Voltage* . . . . . . . . . . . . . . +10.0 / +8.2 Vdc
Plate Current* . . . . . . . . . . . . . . . . . . . 500 / 500 mAdc
Grid Current* . . . . . . . . . . . . . . . . . . . . 25 / 20 mAdc
Driving Power* . . . . . . . . . . . . . . . . . . . 25 / 25 W
Useful Power Output* . . . . . . . . . . . . . . 260 / 325 W
Power Gain* . . . . . . . . . . . . . . . . . . . . 10.9 / 11.2 dB

> On 12/10/2025 7:26 PM EST Paul Decker <kg7hf at comcast.net> wrote:
> 
>  
> I'm not sure. I see at 450 MHz it is 46% efficiency
> 
> But typical operation at 150 MHz is listed as:
> 
> 3CX800A7 ? Typical Operation (Measured Data to 150 MHz)
> 
> Class AB2, Cathode Driven
> 
> Parameter	Value
> Plate Voltage	2200 Vdc
> Cathode Bias Voltage	+8.2 Vdc
> Zero-Signal Plate Current	150 mAdc
> CW Plate Current	500 mAdc
> CW Power Input	1100 W
> Peak Envelope Power Input	1100 W
> Two-Tone Plate Current	313 mAdc
> CW Grid Current	16 mAdc
> Two-Tone Grid Current	16 mAdc
> Peak RF Cathode Voltage	64 V
> Peak Driving Power	70 W
> Useful Power Output (CW)	750 W
> Useful Power Output, PEP	**1100 W
> Cathode Input Impedance	54 Ohms
> Resonant Load Impedance	2700 Ohms
> Intermodulation Distortion (IMD)	
> ? 3rd Order Products	?36 dB
> ? 5th Order Products	?32 dB
> 
> > On 12/10/2025 7:01 PM EST Douglas L <sparks06524 at yahoo.com> wrote:
> > 
> >  
> > Checking the specs, the 3CX800U7 is rated at 350 watts output with an efficiency of only 33%. That?s less than half the rated output power of the 3CX800A7.
> > I wonder if it was derated for typical UHF service?
> > If not, it?s a poor substitute for a 3CX800A7.
> > Doug/WA1TUT
> > 
> > 
> > > On Dec 10, 2025, at 1:01?PM, Paul Decker via Amps <amps at contesting.com> wrote:
> > > 
> > > ?
> > >> 
> > >>> Has anyone created a work around to replace the 3CX800A7 tubes in the
> > >>> AL-800, the AL800H, Alpha, Ten-Tec and other amps that used this tube?
> > > 
> > > The 3cx400U7 and 3cx800U7 are usually much cheaper alternatives and in many cases can be NOS. The datasheet lists the working B+ as lower, but I suspect that is simply due to the higher frequency rating of the U7
> > > 
> > > The only issue is changing out the base which seems daunting at first. There is an "RCA like" plug connector that fits the base really well so that only the grid ring needs to be figured out with some simple finger stock and a metal plate.
> > > 
> > > Someone with talent could design an adapter board that would work well too!
> > > 
> > > Paul
> > > KG7HF
> > > 
> > > _______________________________________________
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> > > Amps at contesting.com
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