[Amps] 572B/T160L tube class C

Alek Petkovic vk6apk at bigpond.com
Sat Aug 21 20:23:04 EDT 2021 

Yeah, The AC mains voltages are all over the place here. Even more so 
these days with everybodies (including mine) solar arrays cramming extra 
power down the lines.

I use common 5W wire wound resistors in the 6.3V filament line. 
Combinations of 0.1 and 0.22 Ohm units, series/parallel to get the 
required resistance at a power rating that will not create too much heat 
in the resistors.

Typically, a FL-2100 runs at 6.9V at the filament pins, with 245V mains, 
so I aim to destroy about 0.6V to 0.7V.

Two tubes in parallel run 8A at 6.3V, so the resistor needs to drop 0.6V 
to  0.7V at 8A. Therefore the resistor needs to be between 0.075 and 
0.0875 Ohms. The power dissipated in the resistors is 5 to 6 Watts, so I 
aim to have at least 20 to 30 Watts capability in the resistor combo. 
This means that they run very cool.

In the above example, 4 x 0.22 Ohms in parallell will give me 0.055 Ohms 
and 4 x 0.1 Ohms will give me 0.025 Ohms. Put those two units in series 
and you have your 0.08 Ohms at 40Watts.

The above example is perfect in theory but in reality, you have to 
solder them into place and usually add a short piece of thick wire into 
the line. This adds resistance, so in my experience. 3 x 0.1 Ohms in 
parallel and and the same again in series, gives you 0.066 Ohms  at 30 
Watts and that is usually perfect to give the nominal 6.3V at the 
filament pins.

The series/parallel combination of 5W resistors can be made compact 
enough to fit under the chassis of the 2100 amplifiers.

The Ameritron 811 amplifiers are not as easy to physically modify but it 
can be done. These amps would be better candidates for resistance wire 
in series, due to they way they are built. Those bloody mother boards 
with everything on them are a pain.

I've also done it with a couple of Dentron Clipperton L amplifiers. 16A 
of filament current that the 4 tubes draw, presents extra power 
dissipation challenges for the resistors and the resulting bundle gets 
big and untidy but there is room inside the cabinet, down one side from 
memory. Those jobs were a long time ago.

Anyway, the result is that the owners of the amps that have been 
modified in this way have never been repeat customers for buying 572B 
tubes, other than to buy spares.

Probably another benefit of adding this resistance is the reduction of 
around 15% of filament inrush current. The Chinese Shuguang 572Bs are 
prone to filament breakage and this may go part of the way to minimising 
that problem.

The Shuguang tubes are sometimes hard to get due to irregular production 
runs. When they are in short supply, the factory rejects seem to find 
their way into the market.🙁

One time, I had a whole box of 10 tubes turn out to be rubbish. Luckily, 
my supplier in China is a personal and family friend, so I got my money 
back on them, in the form of a credit for a new lot of 10 when the next 
production run came in.

I do have a true RMS meter but only got it recently. I have never 
compared the readings against my other meters. I will do it for my own 
curiosity. Thanks.

73, Alek, VK6APK



On 22/08/2021 12:43 am, Carl wrote:
> Interesting Alek and thanks for the input. Have you come up with a 
> specific resistance for the various 572B amps rhat would make it 
> easier for others?
>
> Around here the 120/240V lines can vary from about 118-126/236-252 at 
> times due to population increase and frequent storm rebuilds along 
> with rerouting distribution.
>
> I have Liberty Utilities fairly well trained by now to keep the pole 
> pig tap across the street at 236-242. Increases lighting life also.
>
> At one time there were at least 3 Chinese 572B producers. Except for 
> Shuguang the others didnt want the headaches of dealing with hams and 
> concentrated on the Audiophool market where profits were much higher.
>
> I picked up a nice variety of resistance wire from a surplus 
> electronics shop about 40 years ago to deal with Dentron and others. A 
> Clipperton L, MLA-2500, and DTR-2000L get rotated thru the vintage TX 
> benches, mostly on AM and a little CW and SSB.
>
> Be very sure to use a TRUE RMS meter for measuring right at the tube 
> sockets. Most of the cheap imports dont qualify. I currrently use a 
> military surplus Fluke FM76 from when they dumped a load on the market 
> many years ago.
>
> Carl
> Ham since 1955
>
> ----- Original Message ----- From: "Alek Petkovic" <vk6apk at bigpond.com>
> To: <amps at contesting.com>
> Sent: Friday, August 20, 2021 10:08 PM
> Subject: Re: [Amps] 572B/T160L tube class C
>
>
>> Over the years, I've imported around 200 572Bs from China.
>>
>> They are definitely not as good as the US ones but they have proven 
>> to be very serviceable, when treated right.
>>
>> The single biggest proviso that I drummed into everybody that I ever 
>> sold them to is to make absolutely certain that the filament voltage 
>> stays at 6.3V. The Chinese tubes fail very quickly with filament 
>> voltages of around 7V+, which are the rule in both Yaesu, Ameritron 
>> and Dentron amplifiers when connected to Australian 240V+ mains 
>> voltages.
>>
>> It is a very simple thing to add appropriate resistance to the 
>> filament circuit to bring the voltage back to 6.3V. I've modified 
>> very many amps in this way for many hams. The result has been that 
>> all those amps are running happily on Chinese tubes, which are 
>> lasting many years.
>>
>> 73, Alek, VK6APK.
>>
>>
>> On 21/08/2021 8:00 am, Stan Gammons via Amps wrote:
>>> I agree. I've had so so luck with the Chinese ones. They are nowhere
>>> near the quality of the American made tubes. When America made lots of
>>> tubes; I think we made the best tubes in the world. But, I'm a bit 
>>> biased :)
>>>
>>> 73
>>>
>>> Stan
>>> KM4HQE
>>>
>>>
>>> On 8/20/21 6:52 PM, Carl wrote:
>>>> The Chinesw 572B and 811 (it is NOT a real 811A, not even close) 
>>>> are mostly
>>>> all junk looking for a trash can. They sometimes let a good one 
>>>> sneak thru.
>>>>
>>>> Best bet is to pay the freight for a real NOS Cetron or United 
>>>> Electronics,
>>>> the only USA real manufacturer who private labeled them for others.
>>>>
>>>>
>>>>
>>>>
>>>> ----- Original Message -----
>>>> From: "Jeff Blaine" <KeepWalking188 at ac0c.com>
>>>> To: <amps at contesting.com>
>>>> Sent: Thursday, August 19, 2021 10:33 PM
>>>> Subject: Re: [Amps] 572B/T160L tube class C
>>>>
>>>>
>>>>> How much service do you expect from a new set of tubes? It's one 
>>>>> thing to
>>>>> know "it can do it, if I want" - but then not actually need the
>>>>> capability. It's another thing if you are saying "I want to run a 
>>>>> 572b
>>>>> 24/7 at full output."
>>>>>
>>>>> About 10 years ago I was working on a SB200 which was initially 
>>>>> setup to
>>>>> run RTTY. I did quite a lot of profiling of those using the 
>>>>> Chinese tubes
>>>>> of the era. Watching very carefully to respect the Pd max of the 
>>>>> tubes, I
>>>>> found a typical 25% drop in Po over about 100 hours of testing. The
>>>>> testing was typically 3-15 minutes key down 100% carrier per 
>>>>> interval.
>>>>> Plus on-band rag chew, contesting & DX (this was pre FT8).
>>>>>
>>>>> Carl is about a million times more experienced than I am but I 
>>>>> think maybe
>>>>> the Pd spec vs. actual was a bit optimistic for the Chinese tubes 
>>>>> I had
>>>>> because this drop off seemed excessive. However my abuse of those 
>>>>> tubes,
>>>>> compared to typical ham use, was really bad. Also the SB200 
>>>>> positions the
>>>>> tube horizontally which may be a factor as is the generally poor
>>>>> circulation even with my augmented cooling.
>>>>>
>>>>> In the end, I abandoned the 572b and went with the GI7T which was an
>>>>> excellent performer by comparison although it required quite a lot of
>>>>> changes to the SB200. Unless there is a specific reason to use the 
>>>>> 572b,
>>>>> if I were building a high duty cycle amp in the future, I would 
>>>>> probably
>>>>> want to use a metal/ceramic type tube instead of a glass one.
>>>>>
>>>>> Good luck!
>>>>>
>>>>> 73/jeff/ac0c
>>>>> alpha-charlie-zero-charlie
>>>>> www.ac0c.com
>>>>>
>>>>>
>>>>> On 8/19/21 8:50 PM, Carl wrote:
>>>>>> That tube was designed for AM BCB service by Taylor but didnt 
>>>>>> catch on
>>>>>> there or for AM hams as the T-160L in the late 50's.
>>>>>>
>>>>>> It was later bought by and designated the 572/T-160L for Unitrd
>>>>>> Electronics alone.
>>>>>> They couldnt keep up with demand and sold production rights to 
>>>>>> Cetron who
>>>>>> had a much larger production facility.
>>>>>>
>>>>>> UE then became the 572A and Cetron the 572B. The step top 
>>>>>> (shouldered)
>>>>>> glass was Cetron and the round top was UE.
>>>>>>
>>>>>> At some point the T-160L was dropped for both.
>>>>>>
>>>>>> You may also find a 572B with the round top and the Cetron name, 
>>>>>> those
>>>>>> were built by UE as the demand was even too much for Cetron alone at
>>>>>> times....such as the SB-200 and the Clipperton L.
>>>>>>
>>>>>> I have examples of both (no Taylor T-160L) as well as other versions
>>>>>> including OEM named such as Dentron, Waters, plus Raytheon, GE, and
>>>>>> several others who did not build their own. The top shape ID's the
>>>>>> source.
>>>>>>
>>>>>> I cant remember ever seeing an actual T-160L spect sheet or the 
>>>>>> tube.
>>>>>>
>>>>>> Carl
>>>>>> Ham since 1955
>>>>>>
>>>>>>
>>>>>> ----- Original Message ----- From: "Fuqua, William L." 
>>>>>> <wlfuqu00 at uky.edu>
>>>>>> To: <amps at contesting.com>
>>>>>> Sent: Thursday, August 19, 2021 8:56 PM
>>>>>> Subject: [Amps] 572B/T160L tube class C
>>>>>>
>>>>>>
>>>>>>> I am looking for full power data for the 572B/T160L operating ICAS
>>>>>>> class-c CW and AM.
>>>>>>> The only thing I have found thus far is in an ARRL handbook, but 
>>>>>>> it is
>>>>>>> obviously the 811A specs.
>>>>>>> Not the full 160W plate dissipation specs.
>>>>>>>
>>>>>>> 73
>>>>>>> Bill wa4lav
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> Amps mailing list
>>>>>>> Amps at contesting.com
>>>>>>> http://lists.contesting.com/mailman/listinfo/amps
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