Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on December 18, 2011, 03:39:54 pm
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Hi !
Just finished a 2204 50W lead ( 1983 ) clone ( or almost ) and everything is fine, clean, humless and LOUD . ( I have built it in a TRAYNOR YBA1A from 1963 ). The only bug I had was the voltages at the PI ( 82K side ) that was reading 400 V from both sides of the resistor!!!!!!!!! Two hours later, I realized I have forgotten to fit in the MV coupling cap.......... :BangHead: The trannies are not original but the one I used are close to the Marshall specs, the OT I used being a 4.3K from Hammond ( 1650N model ). The PT delivers 50V less on the EL34' plates than the original from Marshall, but I have adjusted the B+ rail resistors to get all other voltages from the Pi to the first 12AX7 pretty much the same.The OT from Marshall is 3.4K , so .9k less than the one I used . Here is a curious thing: I used the 4 OHM tap with 4 OHM speakers arrangement that should have given the ultimate load match. When I plug in a 16 OHM speaker cab into the 4 OHM tap, it seems to be an ideal load impedance beacause, the sound is much stronger and the harmonics are richer. (same speakers but different series/parallel hook up). Here are some useful voltages to know: plates: 415V, screen grids 413V, bias: 40mA.
Definitely I don't undestand quite well the load calculation. All I have to do for now, is try different loads and see what sounds best. I guess that when it sounds best, the load is at its best too.
Colas