Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: terminalgs on April 01, 2017, 09:38:37 am
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Using Hoffman's revibe as an example:
http://el34world.com/Hoffman/files/Hoffman_ReVibe.pdf (http://el34world.com/Hoffman/files/Hoffman_ReVibe.pdf)
Are the capacitors C27 and C28 responsible for the duration of the bias shift that produces the trem effect? (capacitor charge/discharge time)?
Is there bias shift only on V4B?
Are V5B and V4A only there to produce an out of phase oscillation signal to cancel the one that's mixed with the signal on V4B?
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C27 and C28 are just smoothing caps for the LFO tremolo signal. Take a look at page 11 of this pdf for an explanation of the circuit operation...
http://sluckeyamps.com/misc/Amp_Scrapbook.pdf (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf)
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Ah, ok. So this isn't just applying to a push-pull 12AX7 what the tremolo circuit does in --say-- a Princeton 6G2 for example (which applies the wiggle to the bias of the 6V6s). On that circuit (princeton 6G2), there is a .05/200 cap at the junction of the 6v6 grid leak 220K R's., that I figured was charging/discharging DC from the osc. wiggle.
So on the circuit in your scrapbook on pg.11, how does the oscillation signal change the gain on V4A or V4B if it isn't changing the DC bias on the grid (via some charge/discharge cap)? wouldn't the gain stage simply cleanly amplify the osc. signal like in V3B?
neither triode (V4A or V4B) is driven into cut-off by the osc. signal, is it?
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It now dawns on me that I was looking at the harmonic tremolo as if it were a push-pull device. The final stages of V4 are drawn like PP, and there was a phase inverter, BUT there is no push-pull..