Metropoulos Forum

Is it true one should stay below 450v on the plates?

I don't know if it's true but I have used RFT with plate voltages up to 520V.
Maybe I did'nt wait long enough for them to melt...They're still in a '70 Superlead I sold last year, 480V on the plates and still sound great.

I remember looking at the reference information when I bought these and according to the performance chart (if that is what you call them) it should be capable of much higher plate voltages. Am I wrong?

I think that old rumor has been blown out of proportion by the internet. I did some searches over at "Vintage Amps" forum on the RFT's and there had been reports of failures and decline in quality control in the later years of production (1980's). It seems that there are incidents of certain batches that exhibited internal arcing at high plate voltages and that you must weed through the inferior batches to find ones that would safely operate at higher voltages. Again, I think this is likely just a few random cases that were blown out of proportion. Many companies such as Telefunken, Siemens, Lorenz and others commonly branded RFT's for resale. With so many of these in the market over the years I would feel pretty confident that you can run them without problem. The main thing would be to properly bias them and be sure you are using screen grid resistors to limit current dissipation and you should be just fine. I would definitely trust RFT's over any of the newer production tubes made these days!

danman wrote:I think that old rumor has been blown out of proportion by the internet. I did some searches over at "Vintage Amps" forum on the RFT's and there had been reports of failures and decline in quality control in the later years of production (1980's). It seems that there are incidents of certain batches that exhibited internal arcing at high plate voltages and that you must weed through the inferior batches to find ones that would safely operate at higher voltages. Again, I think this is likely just a few random cases that were blown out of proportion. Many companies such as Telefunken, Siemens, Lorenz and others commonly branded RFT's for resale. With so many of these in the market over the years I would feel pretty confident that you can run them without problem. The main thing would be to properly bias them and be sure you are using screen grid resistors to limit current dissipation and you should be just fine. I would definitely trust RFT's over any of the newer production tubes made these days!

Cool, thanks for the info. I just bought an Orange VT1000, I'll give them a test before trying them in my Metro plexi 100.

Old ancient thread but I just wanted to add my $.02. I have been running a matched and burned in set of NOS Siemens RFT EL34s in my 2204 with a b+ of 476v for almost 7 years and they have not drifted and they still sound amazing. I think the seller I got them from burned them in at 450v and warned me not to bias too hot so I took his advice and they have served me well.