1962 Vibrolux 6G11 Power Transformer

[keithb7]

Hi folks. I have a 1962 Fender 6G11. Layout and schematic below. A previous owner had converted it to SS diode Rectification. I am changing it back. It needed a proper spec transformer again.
I ordered a new Classictone 40-18041. The wiring diagram for it, is also attached. I have a couple of questions. I am not 100% sure on the wiring so I thought I would ask:

See Classictone PT wiring diagram: What is the orange wire on the primary side for? Other amp uses?

I assume Red/Green is a bias tap, not used in the 6G11?

This Classictone transformer has a centre tap off the secondaries, red/yellow. Correct? Same is the original, also red/yellow shown on the layout? Correct?

This Classictone PT has a center tap for the heaters, so I do not need a artificial, dual resistor center tap off the heaters, correct?

Last question: The Classictone PT diagram show 650V of the secondary side, just the one red wire. I assume that is split to 325V AC per red wire headed to the rectifier. Correct?
Thanks very much.


http://www.ampwares.com/schematics/vibrolux_6g11.pdf

http://www.davidsonamp.com/sf/images...6g11layout.gif

http://www.classictone.net/40-18041.pdf

[g1]

Correct on all your questions.
Orange is shield, connect to chassis. (stated on sheet)

[keithb7]

Thanks. Orange is shield, connect to chassis. Which is ground. Ok. I will ground the orange wire. I assume to help quiet things up maybe?
It's pretty quiet right now. Fired it up, about to check voltages.

[keithb7]

Installed the new transformer and I have a few questions about voltages. Any help appreciated.

Wall voltage: 120.7 VAC
Red wires off PT: 336.5 VAC. Original spec 330 VAC
B+ at Pin 8 on GZ34: 444 VDC. Spec 365 VDC
6L6GC Plate volatge, pin 3: 440 VDC. Spec 365 VDC
Bias voltage -53.5 VDC. Spec -36V
Plate current at PT CT: 13 mA

Seems it's biased too cold? To adjust bias, do I change the 33K resistor on the bias board. parallel to the cap? Suggested value? Thanks, Keith

[g1]

Yes, lowering the value of the resistor in parallel with the bias filter cap will increase your idle current and also lower your plate voltage somewhat.
The schematic you linked shows 43K and -45V, not 33K and -36V. You could add parallel resistors or try lower values till you get the bias where you want it. These amps stock are generally biased fairly cold, nowhere near 70%, more like 50 to 60% range.

[keithb7]

Thanks g1. I settled on a 30K resistor and now have 414V on the plates, and 46 mA current draw. -39 V bias voltage. I believe I am now in the 65% dissipation range.

The differences in the values I posted earlier are the 6G11 and the 6G11-A. Both two schematics are available. 6G11 shows a 43K resistor and -45V bias.
The 6G11-A lists a 33K resistor at -36V bias. I could only locate a 6G11 layout, not a 6G11-A.
I am happy with the amp tone with a 30K bias resistor. It sounds great. Thanks for your assurance that my questions were on the right track.

[g1]

As long as you are happy with the trem sweep you should be good. On this style trem you can lose sweep as you increase idle current.

[keithb7]

I just experienced that, yes you are quite correct. I have the run the trem depth a little higher up the dial for sure. But on 10 setting is too much, so it's all I'll need.