A couple of questions...

[5thumbs]

Hi Gang,
I have built 3-4 5E3s, 4-5 5F2As, A Princeton Reverb and a couple of other designs from the different forums. I guess the bug has bit! ha! anyway, here are a couple of questions:

1. Is there any difference in wiring a standby switch to one leg of the B+ winding as opposed to the center tap of the B+ winding. I see it both ways on various schematics.

2. Does the 6.3 filament winding need to have a center tap? Some schematics go to the trouble of wiring in a resister "center tap" and some just show the 2 green wires going straight to the jewel light with no center tap.

Any light you can shed on why one way is better than the other (in layman's terms! ha!) would be greatly appreciated.

You guys are the best!

Thanks,
Tim

[Chuck H]

1. Is there any difference in wiring a standby switch to one leg of the B+ winding as opposed to the center tap of the B+ winding. I see it both ways on various schematics.

I haven't seen a standby on one leg of the hV wind. It seems to me this would be half wave rectified at the PA. If what you mean is standby after the rectifier as opposed to standby at CT then I would say there is no advantage I know of for doing it either way.

2. Does the 6.3 filament winding need to have a center tap? Some schematics go to the trouble of wiring in a resister "center tap" and some just show the 2 green wires going straight to the jewel light with no center tap.

There are two common styles of filament winding in vintage amps. One way does not require a CT and is not humbucking. The second way with a CT is more complicated and is humbucking. If you look over the schems you'll see the difference in wiring. The non humbucking scheme is simple and easy and usually only used on lower end models and small single ended amps that can't take advantage of the humbucking scheme because they don't use two anti phase power tubes. But I have used the CT scheme effectively with single ended amps anyway. It still serves to quiet hum in the preamp and if you add a DC elevation it can quiet the power tube hum also making for the lowest hum single ended amp you ever heard.

Chuck

[Tonewood]

This stuff has worked well for me:
The Valve Wizard

I have had very good results with the 2 -100 Ohm resistors to the cathode as seen here:
The Valve Wizard
Good luck.

[Chuck H]

I will note that referencing the filament CT to the top of the cathode resistor worls just fine for most cathode biased amps. But EL84 amps require so little bias voltage that there isn't much elevation. In that case a voltage divider off the B+ rail (I build mine into the "bleeder" resistor circuit) works better.