27-12-2016, 10:36 AM
(27-12-2016, 01:33 AM)Nowhere-Man Wrote: I have been trying to find about differences between the Mullard ECH81 and the Rohre ECH81. I found that the Rohre standardises with a 33 K feed to oscillator anode. Certainly in the Valve Museum cover of the valve this resistance is shown. Then I got to looking up the Mullard data in my Butterworth book. It only lists the Mullard. Of course, a few weeks ago I didn't know this distinction existed. I'm also interested in the 6U8A which is also a mixer (RCA?) Anyone know of any differences with ECH81 even with regard to audio tone?
Hi.
I'm sure you still have a lot to learn young man regarding how things are done. Any Pro-Electron, US and Russian valve with the same type number "should" conform to the original spec no matter who made them, Mazda, Pinnacle and others were often re-badged Mullard/Philips valves.
It's a bit like a car tyre eg a 165/13 with its V or R ratings will conform to that spec whether its a Michelin or Goodyear.
The HT feed resistors to the ECH81 are not universal but in many cases around the value you have stated.
The mixer stage has no relevance on audio tone, it can be changed by characteristics of the IF stages and the bandpass of the IF transformers and of course the audio stages themselves.
