[TenTec] Centurion & Tubes
Bob McGraw K4TAX
rmcgraw at blomand.net
Sat Aug 4 09:52:17 EDT 2018
I've often heard hams say that they are operating at reduced power on
their 3-500 amps. Reason, to save the tubes. Well that may not be
accurate and, in fact, may just be the opposite. The 3-500 series
has a coating on the anode {plate} that when heated where the anode is
showing a bit of color is used to degas the tube. Secondly, have you
determined the efficiency of the amp? If not, you should, as one may
not be operating at peak efficiency which means the redundant heat is
dissipated in the amp and the tubes. Tuning, loading and grid current
are the three critical ingredients which keep efficiency high and
contribute to long life of the tubes. Operating at less than rated
power, meaning tuned for less than rated power is most likely causing
the amp to operate at less than peak efficiency. The most critical
component in amplifier operation is GRID CURRENT. Exceeding the grid
current rating will do more to damage a 3-500 than about anything else.
To determine efficiency; Plate volts X Plate current {amps} = DC input
power {watts}. Then; Output power {watts} / Input power {watts} X 100
= efficiency %. This number should be greater than 60%. If not,
something isn't correct. Example: 2800 x .800 = 2240 Then;
1400 / 2240 x 100 = 62.5%
In the above example, the plate voltage is 2800 volts, the plate current
is 800 ma or 0.800 amps, the DC power input is 2240 watts, the power
output is 1400 watts, divided by power input times 100 equals
efficiency in percentage. These values are the correct average for a
pair of 3-500ZG tubes as used in the Tentec Centurion.
My rule, always tune for maximum power output, increase drive and
re-adjust Tune and Load to have maximum output and with rated or
slightly less than rated grid current. If you wish to operate at lower
power, reduce the drive from the transceiver and DO NOT change any Tune
or Load values on the amp.
Today, a pair of 3-500ZG tubes will cost more than a SB-220 is worth.
NOS tubes are always a risky choice.
73
Bob, K4TAX
On 8/4/2018 8:09 AM, Byron Cordes via TenTec wrote:
> I bet there will be a lot of amps (3-500z )Not driven so hard !
> New business for someone , make some tubes ! It probably doesn’t pencil out to good. Sad but tubes are on there way out. I love there glow in the shack!
> Wonder how many 3-500z are sold every year? I have had many amps with original tubes that where 30 years old!
> Yep where moving to the transistor from tube amps 750 Watts from one device under 10 Watts drive . Qrp rigs might get more popular!
> It’s only taking 50 years for high power transistors to come about. Hihi
> Wonder what the next 50 will bring? Look how long it took to improve on the (filter radio) . Ok yes SDR radios might not be the best yet but there they are on there way and much much cheaper to make.
> 🤔
> Byron AC9PA
>
> Sent from my iPad
>
>> On Aug 3, 2018, at 11:34 PM, Rick at dj0ip.de wrote:
>>
>> Well I bought my first transistorized amp about 25 years ago (ALS-600).
>> But I had a problem with it in contests.
>>
>> When operating CQWW DX contest in late November, portable in the mountains
>> of Liechtenstein (HB0), with snow, ice and wind, the antenna blowing in the
>> wind tended to have a wandering SWR, up and down.
>> This would cause the amp to trigger to FAULT. PITA when contesting.
>>
>> So I went back to tube amps, buying 5 more tube amps after that (4 with
>> 3-500z and the Centaur).
>> No more problems with FAULT.
>>
>> About two years ago I decided to dump every piece of equipment which I can
>> no longer comfortably carry!
>> I bought a used ICOM IC-2KL.
>>
>> I have interfacing problems with the IC-2KL and my Eagle, because the Eagle,
>> like all Ten-Tec amps does not have ALC feedback to the amp.
>> Bad decision by Ten-Tec!
>>
>> This is only on SSB. I have to run the Eagle at 25 to 30 watts, otherwise
>> the FAULT triggers on voice peaks.
>> Output is about 350 watts.
>>
>> On CW I use external time-sequence keying and just run the Eagle at 30 to 40
>> watts.
>> Works just fine like that.
>> I can run 500w all day long!
>> This is good enuff for my current (retired from contesting) needs.
>>
>> 73,
>> Rick, DJ0IP
>> (Nr. Frankfurt, Germany)
>>
>> -----Original Message-----
>> From: TenTec <tentec-bounces at contesting.com> On Behalf Of Mcelmer1
>> Sent: 04 August 2018 06:22
>> To: Discussion of Ten-Tec Equipment <tentec at contesting.com>
>> Subject: Re: [TenTec] Centurion & Tubes
>>
>> Rick,
>>
>> Transistor amps were the future at least 10 years ago - good choice on your
>> part. I and several friends have had excellent performance and service life
>> with 3-500, 4CX1000A, 572B etc. Yes, occasionally one gets a lemon. A friend
>> bought a NOS Eimac a few years ago - failed less than 5 days after he
>> installed it.
>>
>> Auf Wiedersehen,
>>
>> Mike
>> W8TRN
>> ----- Original Message -----
>> From: <Rick at dj0ip.de>
>> To: "'Discussion of Ten-Tec Equipment'" <tentec at contesting.com>
>> Sent: Friday, August 03, 2018 21:36
>> Subject: Re: [TenTec] Centurion & Tubes
>>
>>
>>> I put my 25 year old NOS into my AL-80A and let it cook for a while, then
>>> slowly applied power.
>>> I slowly ran the output power up until about 400w out.
>>> It increasingly was showing a light blue inside.
>>> Then pop, boom, BANG. Blew the fuse in the house.
>>>
>>> I sold the amp, and sold the tube for 20 bucks.
>>> Now I run a transistorized amp.
>>>
>>> 73,
>>> Rick, DJ0IP
>>> (Nr. Frankfurt, Germany)
>>>
>>> -----Original Message-----
>>> From: TenTec <tentec-bounces at contesting.com> On Behalf Of Stan Gammons
>>> Sent: 04 August 2018 04:28
>>> To: tentec at contesting.com
>>> Subject: Re: [TenTec] Centurion & Tubes
>>>
>>> Hi Bob,
>>>
>>> The 3-500 is subject to going gassy. IF and that's a big if, I put the
>>> old Eimac 3-500 in the amp (best I can read the date code on it, it was
>>> made in 1979); I'll bring the amp up with a variac. The variac I have is
>>> 110/120 volts, so I'd have to re-wire the amp since it's wired for
>>> 220 volts. Yes, when a tube flashes over; it's fireworks for sure!
>>>
>>>
>>> 73
>>>
>>> Stan
>>> KM4HQE
>>>
>>>> On 08/03/2018 09:08 PM, Bob McGraw K4TAX wrote:
>>>> A comment on 3-500 type tubes. These types of tubes have an extremely
>>>> high vacuum. NOS units are subject to air leakage into the envelope
>>>> around the pin seals. The coated anode in the 3-500Z and 3-500ZG
>>>> serves as the getter to burn the extraneous air out of the envelope.
>>>> It is a very incorrect belief of many hams that having the filament on
>>>> for a few hours will burn the air out. This is not true with this type
>>>> of tube thus having only the filament on serves no useful purpose.
>>>> The only correct way to burn the air out is to have the tube
>>>> operational and with enough voltage and current to cause the anode to
>>>> show color. It is this heat and chemical action of the anode coating
>>>> that removes the extraneous air from the envelope.
>>>>
>>>> Other smaller tubes may have a getter that is ignited by external
>>>> microwave energy. Once the getter is ignited, it is consumed, and any
>>>> leakage from that point forward will only deteriorate the tube.
>>>> Again, having the filament on for some hours does no good in this regard.
>>>>
>>>> External anode tubes, such as the 3CXxxx and 4CXxxx types, are
>>>> different designs and thus running the heater will remove any remnants
>>>> of air leakage as the getter is part of the cathode coating.
>>>>
>>>> If you intend to prepare a 3-500ZG or such, a filament supply, an
>>>> adjustable bias supply, and an adjustable HV supply, with proper
>>>> metering for each supply is the correct way to static burn in this
>>>> type tube. The values are adjusted such that anode does show color.
>>>> Just putting the tube in an amplifier and hitting the switch will
>>>> most likely produce a flash, bang, pop and the smoke may then exit the
>>>> box.
>>>>
>>>> 73
>>>>
>>>> Bob, K4TAX
>>>>
>>>>
>>>>> On 8/3/2018 8:30 PM, Stan Gammons wrote:
>>>>> I think most/all of the 3-500's are made in China now. One can still
>>>>> find some Eimac's that may still be good after all these years. The
>>>>> near 40 year old one I have may still be good. Need to put it in my
>>>>> L-4B some times and see. This is what we get for outsourcing so much
>>>>> of our manufacturing to China. I've said for many years that that
>>>>> was a bad idea. At one time Amperex tubes were made in France. Don't
>>>>> know if that's still the case. I'm thinking no. Maybe we can talk
>>>>> CPI/Eimac into making 3-500's here again? Probably not, but might be
>>>>> worth a try.
>>>>>
>>>>> 73
>>>>>
>>>>> Stan
>>>>> KM4HQE
>>>>>
>>>>>
>>>>>> On 08/03/2018 08:12 PM, Bob McGraw K4TAX wrote:
>>>>>> Yes, thanks to the new tariffs we can expect tube prices to go
>>>>>> through the roof. Most tubes are made in China and branded under a
>>>>>> US company. a.k.a. RF Parts.
>>>>>>
>>>>>> Bob, K4TAX
>>>>>>
>>>>>>
>>>>>> Sent from my iPhone
>>>>>>
>>>>>>>> On Aug 3, 2018, at 5:03 PM, Carter <k8vt at ameritech.net> wrote:
>>>>>>>>
>>>>>>>> On 8/3/2018 4:45 PM, Greg S via TenTec wrote:
>>>>>>>> There will be a price increase SOON. RF Parts apparently will no
>>>>>>>> longer be importing Chinese tubes.
>>>>>>> Hmmm...bad news, as I thought China was the *only* one making
>>>>>>> 3-500s. If not China, who else?
>>>>>>>
>>>>>>> Carter
>>>>>>> K8VT
>>>>>>> _______________________________________________
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>>>>>>>
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