Rich you now said:
"4. disregard the users' manual's ok of more than 500mA of anode current.
No 3-500Z/8008 manufacturer has Ever rated this tube at more than 400mA."
This 500 mA is a EIMAC IVS rating - the same as beeing used for the 8873,
8875 and 8874. These tubes are rated 350 mA max anode current but have been
used up to 500 mA in many amplifiers in the past. With no harm if you are
careful - my old HENRY K2000 still uses the original 8873 tubes with almost
full output. But the question is, if the now avaiable emission, after more
than 20 years usage, does give flat-topping?
The IVS system is a trade -off beetween tube life, distorsion and economy.
If you are not on the air all the time this IVS system is cheaper.
Eventually distorsion will increase to the point where the amp will be the
dominating factor in the transceiver + amp system. Because, as far as I
understand, 13 volt finals in transceivers have more distorsion than 28 or
48 versions and may in most cases dominate the system total distorsion. If
you on the other hand use one of the high voltage transceiver finals such as
the excellent low distorsion TS 950 ( 48 volts ) or one of the old COLLINS
rigs , you have to use negative feedback ( as in the SB220 ) and, as you
say, limit your anode current to max 400 mA in a 3 -500Z. In order to match
the low distorsion transceiver.
Have not seen any distorsion measurments with 500 mA anode current- so
maybe you are right in your statement? Better ask EIMAC, maybe.
Hej daa de Hans
See also Ham Radio 1/1971: " Intermittent Voice Operation of Power Tubes"
by W6SAI
----------
>Från: measures <measures@vcnet.com>
>Till: "AMPS" <amps@contesting.com>
>Ämne: [AMPS] AL-80 / SB-1000 circuit improvements
>Datum: mån 28 feb 2000 16.22
>
>
>To owners of SB-1000s and AL-80s: :
>
>The B+ to gnd bypass cap. (C-23 in SB1000) at the base of the HV RFC
>(RFC-3) is 1000pF. At 1.8MHz, 1000pF has -j88 ohms of reactance. It is
>my opinion that 88 ohms is not a sufficient bypass. My unsolicited
>advise is to:
>
>1. parallel more C with C23 to keep RF away from PS components during
>160m and 80m operation.
>2. add a glitch protection resistor in the B+ lead.
>3. add 200a-pk glitch diodes to protect the meter movements.
>4. disregard the users' manual's ok of more than 500mA of anode current.
> No 3-500Z/8008 manufacturer has Ever rated this tube at more than 400mA.
>
>Might not the designer improve his credibility if he corrected his
>misstatement?.
>
>good luck.
>
>- Rich..., 805.386.3734, www.vcnet.com/measures.
>end
>
>
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>
>
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