# 6X5 rectifier tube - Question for the techs



## Lincoln (Jun 2, 2008)

After the thread on Herzog's a while back, I pulled an old amp out of hiding with the thought of making it into a Herzog. Looking at it for the first time with my new semi-educated eyes I could see it was basically a Fender champ circuit. One thing that caught my attention was the power supply - it had no 5 volt winding but it did use a tube rectifier. The 6.3 volt wires feed all the tubes. Was that common? I looked up the 6X5 and see it's made for 6.3 volts.......but......

How/why did almost all amps end up with a separate 5 volt winding to heat the rectifier tubes rather than just run a 6 volt rectifier tube? There must be a good reason. Isolation?


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## dtsaudio (Apr 15, 2009)

Early rectifier tubes had directly heated cathodes. That is, the cathode and filament are the same connection. It therefore required it's own filament tap, because its filament voltage was not referenced to ground, but on the high voltage. Why it was 5V I don't know, possibly to keep from confusing it with the 6.3V tap on the transformer. Later tubes like the 6X5 were made as more compact lower current rectifiers, and allowed for the use of the same filament tap. These were indirectly heated tubes where the filament is not the cathode, but a separate element. There are however a number of indirectly heated rectifiers that have 5V filaments. Probably to utilize existing transformers with 5V taps.


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