Re-using a 65 re-issue Twin Reverb PT

[dwp]

Well, I just gutted my first re-issue, (had issues) 65 Twin Reverb, am now looking at the power supply realizing there's no center taps on anything. This a first for me, I have a couple questions please:
1.     do I need to keep/re-install the hum balance pot, or will the two 100ohm resistors suffice on the heater circuit?
2.     should my bridge rectifier be with four 4007 or four 5408 dioides?
3.     should I switch the negative (ground) instead of the positive for standby off the bridge rectifier? (per fender schem)

I'm not building a Twin Reverb back in this thing, more 5F8A with a twist or two. Any other noise issues I have to look forward to with no center taps?

Thanks in advance, dwp
 

[bigsbybender]

I've built a few amps out of reissues and "modern" Fender tube amps. It's a shame how different the Twin Reverb Reissue is than the original 1965 model.  The Bassman and Deluxe Reverb Reissue are much closer to the original than the Twin Reverb.

1. do I need to keep/re-install the hum balance pot, or will the two 100ohm resistors suffice on the heater circuit?

No need for the Hum Balance pot.  A pair of 100ohm resistors is what I recommend.

2.     should my bridge rectifier be with four 4007 or four 5408 dioides?

It doesn't matter.  Either one will handle the job.

3.     should I switch the negative (ground) instead of the positive for standby off the bridge rectifier?

Hmmmm. Either will work... I've always used the Positive.

[eleventeen]

1: Yes, keep the dual 100 ohm structure. You're more likley than not to need it or at least want it.

[edit; sorry, I didn't quite understand your question: The resistors alone are fine; no special need to the balance pot]

2: Either diode is fine, traditionally diodes are doubled or tripled up (in series) in Fenders and lots of other amps. I've never understood why. 1N4007 claims to be good for 1 amp.

[edit: Are you sure a bridge is the right choice vs a voltage doubler?]

3: My vote would be to switch the positive leg of the supply, because

a: It is certainly more "traditional" with tube circuitry to remove "B+"
b: once you have the filament hum balance deal in place, the filaments are effectively at ground (thru the 100 ohm resistors) If the plates (in standby) remain at a heightened B+ (heightened because current flow has been stopped through the output tubes) and the cathodes are at "ground" but they are not at zero volts because that leg has been disconnected, you'd have to convince me that you wouldn't do goofy and possibly destructive and maybe even dangerous things to the 6L6's letting the heaters remain at or near zero volts, while the cathode tries to float up towards B+. I could see exceeding the heater-tocathod ratings of the 6L6's. I don't know offhand if this PT has an independent bias tap or if bias is derived from one of the outer HV legs. If you also shut off the bias, the 6L6 tubes could really puke if you don't get the placement of the stdby switch just right.
c: Depending upon exactly where you place the stdy switch, when you turn power back on, the inrush current has to go through the dropping resistors before reaching full value. That would be a plus in my book.

My .02.

[dwp]

thanks all for your responses. I got this hull as a gift, tubed it up once to make sure the Iron was good, then gutted it without really looking at things. I just went and got the board out of the trash, am looking at it in wonderment. (that a word?) everything is miniature, and some kind of shared cap thing going on in the cap can, chucked it too.
     The schematic shows switching the ground right off the rectifier bridge. I had to check the diodes on the board, miniature too. not 4007's I do believe. and the CR-1/CR-2, etc spots on the board don't match the schematic either, is a flip. It worked for them.

When you say doubler, that just two diodes, (or string) just tied together at the DC end? what about a ground reference since I don't have a center tap?
Am thinking the bridge is easiest for that reason. All input appreciated as always.
yup, Tweed 5F8A ahead. with a gain stage mod, via relay, just placed the order. Doug's Hotswitch except two stage with pot controls maybe?
got some holes to fill with knobs on the front.
Thanks again, dwp

[sluckey]

Bridge is what you want.