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previous: Eth That tiny capacitor always confused... -- 9/21/1999 6:19 PM

Re: Cap across driver tube

9/21/1999 7:11 PM
SpeedRacer	Re: Cap across driver tube I suppose I'm guilty of "Leo did so will I" engineering.. I've always used it when building those circuits. Never noticed a big tonal shift or anything. Talking to Ed Pennypacker once he mentioned that the longtail circuit in the 5F6-A had a tendency for osc around 47kHz and the acap took care of this; he even used bigger caps in some deisgns here (I think either the MiG50 or 100 uses 120pF?) Guitar amps "get away" with some of this stuff BC their OT's are (typically) bandwidth limiting devices (HF and LF rolloffs are often in the audible range). When the amp saturates, the -fb loop loses its ability to "correct" things and you get more rolloff at HF & LF. I think the HF point at which the phase will be 360 out and things get ugly is far enough out that it's not a problem in a guitar amp. maybe I'm dead wrong there? anyone?anyone? Bueler?

9/21/1999 7:11 PM

SpeedRacer

Re: Cap across driver tube

I suppose I'm guilty of "Leo did so will I" engineering.. I've always used it when building those circuits. Never noticed a big tonal shift or anything. Talking to Ed Pennypacker once he mentioned that the longtail circuit in the 5F6-A had a tendency for osc around 47kHz and the acap took care of this; he even used bigger caps in some deisgns here (I think either the MiG50 or 100 uses 120pF?)

Guitar amps "get away" with some of this stuff BC their OT's are (typically) bandwidth limiting devices (HF and LF rolloffs are often in the audible range). When the amp saturates, the -fb loop loses its ability to "correct" things and you get more rolloff at HF & LF. I think the HF point at which the phase will be 360 out and things get ugly is far enough out that it's not a problem in a guitar amp.

maybe I'm dead wrong there? :-)

anyone?anyone? Bueler?

Replies:

Trace Some amps have a very high top end ... -- 9/22/1999 1:48 AM