NEC CQ-301 AMP

[G4SSX]

Hi All
I have bought a pair of QY 4-400 very cheap and i was wondering if i can use them in my nec cq-301 Linear My Linear is the same as a Heathkit 220,so i need Help.I waqnted to know what the standing carrent is four 2 3-500zg and also for the 2 QY 4-400 .My Manual does not tell me that at the moment the standing currant for 2 3-500zg is 0.06.
So any Help Please
Many Thanks
73 de Wolf G4ssx

[W9GB]

The NEC CQ-301 manual can be found at MODS.DK
http://www.mods.dk/manual.php?brand=_other

It is only 12 pages with schematic, so it really is a minimal document.

Cosmetically, the amplifier looks somewhat like the Kenwood TL-922(A) HF amplifier, which also uses dual 3-500Z glass RF tubes.

w9gb

[W9GB]

Wolf -

Here is an earlier eHam.net Q&A about this same question!
http://www.eham.net/ehamforum/smf/in...pic=282.0;wap2

The 4-400 is a TETRODE glass tube, and normally requires a screen supply (voltage).
Your NEC amplifier does NOT have that screen supply and the 5-pin socket
would require rewiring to operate as a true TETRODE.
http://www.g8wrb.org/tetrodes/

The 3-500Z and the 3-400 are TRIODE glass RF tubes. Your NEC CQ-301 was designed for a TRIODE.
http://www.g8wrb.org/triodes/

ADVICE?
Electrically they can be interchanged, you need to check socket wiring, and height clearances.
Current draw (mA) can be an issue, it depends on your NEC CQ-301 power supply.
4-400a tubes have been used interchangeably with 3-400, 4-250, 3-500z tubes.
While the QY 4-400 may work -- it is not ideal.

Go buy the proper 3-500Z glass RF tubes for your NEC HF amplifier.
Given the age of this amplifier, you may be well advised to check / replace the HV electrolytic capacitors.

w9gb