Question about my Vibro champ PT

[dude]

Opened up my 67 Vibro champ and notice that I had changed the filament wiring to the standard later Fender filament wiring but notice that I didn't put the two 100 ohm R's for a center tap. Did have a little hum. Then I notice that the PT had a wire nipped and capped off making me think this isn't the original PT, it's been replaced as the PT has a yellow w/green stripe capped off, as seen in pic. I figured this the the CT ground for the filaments but not sure...? If so, then I don't need the 100 ohms just ground that yellow/green stripe.


The PT looks old, did Fender use some PT's  for Vibro champ with a CT for the filaments (6.3vdc)? Or I assume this was replaced years ago. Searching the numbers on PT, 022772 I get replacement PT's for the Champ. No other markings on this PT.


Anyway to check if that yellow/green stripe is indeed the filament CT or am I getting too anal and just ground it? 

[DummyLoad]

strip off some of the insulation - measure from it to both green leads with an ohmmeter (DMM set to ohms). zero or just a couple of ohms would tell you that's a center tap.


--pete

[DummyLoad]

BTW, they (fender) would have used a champ PT for the vibro champ PT - they added one 12AX7 - 2-3mA added load. meh! 


--pete

[dude]

Thanks, .5 to 1 ohms bouncing around ,has continuity too. It's a filament CT, learn something everyday.
Wonder why they cut this CT wire when replaced, guess the guy didn't feel like lifting the one filament lead from ground and adding it to the tube heaters.   


Wonder if adding the filament CT to the cathode on the 6V6, pin 8, lifting the ground and maybe a more quiet amp?

[DummyLoad]

MAKE SURE that one side of the 6.3V (green wires) isn't grounded. do NOT just hook up that CT before checking! :D


--pete

[dude]

I know thanks for the warning. I changed the wiring, lifted the filament from ground and wired like a Princeton and later Fenders. I did have the two 100 ohm artificial CT but didn't see them right away cause I grounded then to the 6V6 cathode. So, I was OK with filament wiring but now I'm using the PT's filament CT, but no difference.


One last thing while the amps open, the schematic calls for 355v at first node, I have 385v, then goes down the same increments as the schematic but of course 25V higher. Wall current is 120ac here.


Not to get technician, I can't change the first nodes voltage (without Zeners or resistors before) but I could up the two next nodes resistors to drop voltage to the screens and preamp in line with the schematic. I would think doing this would take a little head room out though.
Or would you just leave it, amp sounds good as is. All stock but running a little on the hot side, running a GE 6V6 (cathode R reads 455 ohms) with 350v on the plates. Too hot...?  Raise the cathode R to 500 ohms. Also, some say using a high valve cathode bias cap, high as 1000uf, tightens up the bass...?  Ever heard of that?


I appreciate your advice,
al


     

[DummyLoad]

al, no need to worry - 385V is fine as long as the 6V6 isn't red-plating. 


--pete

[DummyLoad]

1000uF is excessive: 220uF is far more than enough to get subsonic. NFB tightens up the bottom end of any SE or PP amp but tends to make them sound darker if you apply too much. your amp has NFB. maybe try a different speaker or external cabinet to experiment. 


--pete

[sluckey]

Look at page 2. You need to build one of these...

     http://sluckeyamps.com/misc/Amp_Scrapbook.pdf

[dude]

Can I use this PT see pic. Unloaded it measures from CT to one sec 7.1vac, both sec to each 14.2acv.? I use it to break in low wattage speakers, 25 watts to 50 watts.


Not sure about the wiring, in your diagram, (bare with me). My PT has a CT in the middle and two sec on the ends, your diagram has CT tap as 6.3v, top sec with a dot (what is a red dot?) going to primary switch and the other sec going to selection switch. Why a double pole on/off switch, both on's do the same. What is the dotted line, surely not a wire?


Do I wire my PT the same as yours, regarding the order of the three wires coming out on the sec side so just copy your wiring?   Forgive my ignorance. Looks like there is only one switch in picture of PT just can't understand why two switches are in drawing.

[mresistor]

That's the exact transformer you need and is same as in Sluckey's drawing..  the switch is double pole double throw and is showing the two poles.. in different locations in the circuit ,, it is one switch and sluckeys drawing is showing you how each half of the switch is being used.   The red dots are phase dots and if you read about Sluckey's Buckaroo you will see he has written a tip in red regarding phasing. 

[sluckey]

That's exactly the same PT that I used. Ignore the red dots. Those are for phase reference. The switch is a DPDT center off. One side of the switch turns the Buckaroo on. The other side of the switch selects either 6v or 12v. The dotted line is a mechanical link between the two halves of the switch. It indicates that the two halves are operated together with only one bat. Sometimes the schematic is less cluttered when you split the sides of the switch rather than showing all 6 lugs together with wires running everywhere. Didn't work for you though!   

If you don't have a DPDT with center off (ON-OFF-ON) you can use two separate switches, SPST for ON-OFF and SPDT to select 6V or 12V.

[dude]

Ok, starting to sink in, it’s me reading the schematic wrong. One switch DPDT, one receptical out, one 120 vac input, wall current. His is a layout I found, same as your schematic, correct? My dumbness

[sluckey]

Can't say. None of your pics posted. Try again, or just link to the post rather than the pics.

[dude]

[dude]

https://robrobinette.com/images/Guitar/5E3P_Build/Buckminister_Bucking_Transformer.png. This layout has just a single pole switch, correct but basically same as yours? Also the his layout has two recepticals, your one. Only need two if you want to bypass it he step down pt?

[sluckey]

Still nothing. I've never seen a link to the forum with the word "blob" in it. What kind of device are you using? Do you look at your post to see if it posted correctly?

[dude]

The link shows up and opens on my PC and iphone, here it is again.https://robrobinette.com/images/Guitar/5E3P_Build/Buckminister_Bucking_Transformer.png
Might have to copy and paste.


I know it's me not reading your schematic correctly on the switch, I think I got it now. This layout is the same as your schematic except using SPST switch and he has a bypass receptacle, your did not. If what I said here is correct then I got it. I'd rather be able to have the DTDP as I can turn the PT off.


I'm make the bucking PT and post pictures of my wiring to make sure I blow myself up    . Let me know if both your and the lays are basically the same, except differences I mentioned.
 

[sluckey]

I see the link to rob's site just fine. But look at replies 12 and 14. Those are the ones where you tried to post images but all I see are x. Those image links all have the word "blog" in them. What's that about? What do you see?

Both our circuits are nearly identical. They both accomplish the same thing. Here's R. G.'s take on the same thing. My circuit was inspired by R. G.'s circuit...

[dude]

Those posts l screwed up, thanks for the  info, guess I never saw a DTDP switch in a written schematic, l got it.

[mresistor]

I like and built Sluckey's version because you can switch it off.   (center position)

[dude]

Well, I finally got around to putting together Sluckey's Bucking Transformer.  Funny, we had the same Radio Shack PT laying around and the same small case. I have no idea where I got the small sheet metal case, probably same place as Sluckey, wherever that was, probably Radio Shack, many moons ago  .


I put the switch on the side instead of one of the ends, total pain in the butt stuffing all that wire in that small box without causing issues. But I used what I had on hand, the switch was a 15 amp on-off-on and it was huge. Anyway it works.


My wall current is 121.3, pretty high, the Bucking PT cuts either 7.3V or 14.6v off the line voltage. The PT is the same one Sluckey used (6.3-0-6.3) but for some reason cuts 7.3vac on each side. Is that because it's unloaded? And once an amp's is drawing current that cut will drop to 6.3 or 12.6 ...?


Thanks for the info on Bucking Transformer.


al