Hammond AO-43 for 5E3 build

[g-man]

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[sluckey]

I think it would make a great donor for a 5E3.

[g-man]

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[dude]

But an original  5E3's  B+ was around 350/360v, that AO-43 PT would be around 400 B+, still ok...? Sure it would work fine as the deluxe reverb is around 400v, but isn't "part" of the grind and break-up in 5E3 contributed to lower plate voltages..? Just asking.

[sluckey]

...that AO-43 PT would be around 400 B+

You can't just say that PT will give a certain amount of B+. It all depends on the LOAD. I used that same PT in a fixed bias Plexi6V6 and got 400V. I also used that same PT in a cathode biased Supro and got 350V. Cathode biased amps tend to run hotter than fixed bias amps, at least at idle. I think that PT will be a fine candidate for a 5E3.

[dude]

OK, got it. I was thinking the 6V6 fixed bias load for 400v, like you mentioned. Learning everyday, 5E3 is cathode biased, that makes a lower load, therefore lower B+...?

[sluckey]

5E3 is cathode biased, that makes a lower load, therefore lower B+...?

Just the opposite. The cathode biased 5E3 is a heavier load (more current) than the typical fixed biased 6V6 amp, so the B+ will be sucked down more (sag) due to the heavier load. Think about it... We obsess about biasing our fixed biased amps at 70%, but our cathode biased amps typically run at about 90-100%.

[dude]

Thanks for the clarification. I can't hear much of a difference in a fixed biased amp at 70% to 80%, maybe a little more headroom.  I usually bias a fixed biased amp around 85/90% but as long as no red-plating after a good beating, I leave it on the hotter side. Maybe I'm cooking the tubes but that little bit of cleaner headroom seems to give me a better tone but really I know it's all bull, back in the days of Leo, there was no 70% bias...?


Basically for me, as long as the tubes are not redplating or close to it, you can (smell the heat), I'm good to go, for me anyway. Others I'll keep with the 70/80% rule. I usually biased cathode amps hot but to me they don't have that brownish tone if too hot, fixed, the other way around. But what heck do I know,