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Reviews Categories | Electron Tubes | Eimac 4CX1500B Help

Reviews Summary for Eimac 4CX1500B
Eimac 4CX1500B Reviews: 1 Average rating: 5.0/5 MSRP: $(missing—add MSRP)
Description: Eimac's 1500Watt broadcast tetrode
Product is in production.
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G4TCB Rating: 5/5 Jan 23, 2011 13:48 Send this review to a friend
A great performer  Time owned: more than 12 months
I managed to get hold of a 4CX1500B from a retired broadcast engineer. As the socket for that valve was horrendously expensive, I opted to fabricate a base for it. Lying around in the shack was my beat up old test chassis, which I used to test various valves that I had come across, so rather than make a chassis up for a valve that could be faulty, I mounted the valve in the test unit.
I cobbled together 380v 1 amp supply, for the screen, and sat the EHT of 2400v on top of the screen supply, giving 2780v on the anode. To avoid anything nasty happening to the screen grid in case of a fault condition I inserted a 1200 ohm sacrificial resistor in the screen circuit, with a 47k pull down to ground. The grid bias was controlled with an 85A2 gas stabiliser to give just over 100Ma standing current.
Having tested the insulation of the valve, and finding it good, I ran the heaters for 12 hours to regenerate the vacuum. On running the valve in , I slowly increased the output power, to find the gain was about 18db. In the process of testing the output, I flashed over the PA tuning capacitor, the anode current went through the roof, and the screen resistor blew. I thus tested albeit inadvertently the safety feature. I replaced the tune capacitor with a vacuum capacitor. The valve suffered no ill effects, and has taken the place as my main linear amplifier. The test chassis has never been tidied up,
as when I discovered how well it worked, I decided there was no way I could improve it. For the way it worked straight away, with no fuss, perfectly clean signal, and high gain, this venerable broadcast tetrode must be given 5 out of 5.

Pete Holland G4TCB.

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