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Title: 811A vs 812A in modulators and RF Post by: K8WBL on October 19, 2009, 07:02:19 PM I have a extra supply of 812A's and wondered if anyone has used them as subs for the 811A's in modulators such as the Globe King series...?
73, Tim K8WBL Title: Re: 811A vs 812A in modulators and RF Post by: W7TFO on October 19, 2009, 07:10:27 PM They can do, but you will have to add some bias as the Mu is lower.
Title: Re: 811A vs 812A in modulators and RF Post by: N2DTS on October 19, 2009, 08:13:17 PM 812's make great push pull rf tubes. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
811a's make great modulators, mostly because they are zero bias. If you use 812's as modulators, they work just the same as 811's but you need a stiff -48 volt bias supply. I was told 812's make better class C rf tubes than 811's because you have much more bias, they modulate better, but when I tried 811's in place of the 812's, they seemed to work exactly the same.... Brett |