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@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@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@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
>>>>> _______________________________________________
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>>>>> Amps@contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>>
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