On another note, I have one Cetron 572B that was pulled out of an FL-2100 and never had its anode cap correctly soldered. It's essentially brand new while it's neighbor suffered a very punishing life doing the work of two tubes. Anytime I've tried to get it to play nicely with a partner, it's tried to hog the majority of the work and cherries its plate red before its partners. I mentioned this in case someone has one brand new Cetron, I may have your match...
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Winter Project or Scrap? Bandit 2000A Amp
- Thread starter FlatlandBusa
- Start date
The Cetron 572B is made so it can be used horizontally as long as pins 1 and 4 are in the vertical plane. RCA tube manual says this rule applies equally to the 811A, since the filament and grid are the same. The filament wire is suspended in the shape of the letter "W". Naturally it will sag somewhat as it gets hot enough to light up. So long as the sag doesn't move it closer to the grid wires, no problem. Keeping the "W" in the vertical plane keeps any slack from touching the grid wires.
Mohawk linears were built with the 572B tubes turned 90 degrees the wrong way. Rather than drill out rivets, turn the tube sockets a quarter turn and fix the problem that way I just recommended turning it on its side. This stood the tubes vertically and solved the filament-sag problem. Cheaper fix.
73
Mohawk linears were built with the 572B tubes turned 90 degrees the wrong way. Rather than drill out rivets, turn the tube sockets a quarter turn and fix the problem that way I just recommended turning it on its side. This stood the tubes vertically and solved the filament-sag problem. Cheaper fix.
73
The spec sheet for either tube specifies putting pins 1 and 4 in the vertical plane when mounted sideways. This keeps the filament wire from sagging against the grid.
Some chinesium tubes are not built with this critical alignment, and must be mounted vertically.
American-made tubes are usually aligned correctly on the inside.
73
Some chinesium tubes are not built with this critical alignment, and must be mounted vertically.
American-made tubes are usually aligned correctly on the inside.
73
I have said the same thing about plate transformers for years, right up until last month. I had a guy with a base amp and it ran fine, made all the watts, no issues. But it stunk. Smelled like burning plastic. Now he had this since new for over a year and the trans was new. I came over, and gave it a look see, expecting to find brown resistors, or an arcing air variable, or swollen and arcing electrolytics... I saw nothing . I even ran it in a dark room to try to diagnose it visually . Sometimes you can spot a blue flash of an arc easier in the dark. Nothing.
I took the box home to delve deeper basically, the plate trans must be melting some insulation deep inside and when its on for a while it starts to stink. Still runs though.
Its certainly an oddity. A replacement transformer is in the works.
I bought a pair of Cetron's NOS in 2000 and installed in my FL-2100. One tube lost the filament within 5 mins.
Yep, new old stock, but it's still be sitting in a box for 40 years.
I bought my last NOS tubes over ten years ago from a well know retailer and had to fight to get two of them replaced.
One lasted about ten seconds the other was shorted on arrival because it had a blog of solder floating around in the envelope.....
73
Jeff
That sucks. Although, unless the vacuum seal was compromised and burned the filiment open, many times this is just a cold solder joint on one of the tubes two filiment pins. Mechanical shock can also be a culprit for developing cracks in filiment wires. I once dropped a 8877. It still worked great for several days and then the filiment opened. After that, when I turned the amp on, one sharp bang on the RF deck would Arc the filiment back together and it worked until I turned it off. That went on for months before completely failing.
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