New 5F4 build-transformers

[Travst]

Another question, just to make sure I have this right. On the PT, I've noted my assumptions and questionables:

Power Transformer
Black= Common Primary
Red/black= 120volt Primary To power switch
Yellow/black= 125volt Primary Capped off
Green/black= 135volt Primary Capped off

Green and Green/yellow= 6.3 volt Center tapped heater To heaters, but... there are two greens and a green/yellow. Does green/yellow go to ground per the Ceriatone layout? Or, is it capped off?

Blue and Blue/yellow= 24 volt Center tapped Capped off

Red and Red/yellow= 630 volt Center tapped To rectifier, but... there are two reds and a red/yellow. Does red/yellow go to ground? Or, should it be capped?

Yellow= 64 volt tap. To board, change the 68k resistor before the diode for a higher value to lower voltage to 50v.

I'm confused by the "0" markings on the PT. I've done some Googling, but it hasn't cleared it up. I'm assuming it means a center tap that should go to ground in this amp.

[Tom Phillips]

...Green and Green/yellow= 6.3 volt Center tapped heater [B]To heaters, but... there are two greens and a green/yellow. Does green/yellow go to ground per the Ceriatone layout? Or, is it capped off?

Grn/Yel connects to ground. Reference the schematic to understand the voltages and signal flow.

...Red and Red/yellow= 630 volt Center tapped [B]To rectifier, but... there are two reds and a red/yellow. Does red/yellow go to ground? Or, should it be capped?

Red/Yel connects to ground. Again, reference the schematic.

...Yellow= 64 volt tap. [B]To board, change the 68k resistor before the diode for a higher value to lower voltage to 50v.

I think you meant 6.8k. Are you going to implement adjustable bias? I’d recommend that. It is shown in the Weber schematic you posted earlier in the thread. Actual resistance values can be changed to allow you to set a voltage that will give the proper bias current. It’s best to start with the most negative voltage.

...I'm confused by the "0" markings on the PT. I've done some Googling, but it hasn't cleared it up. I'm assuming it means a center tap that should go to ground in this amp.

Conventional schematic terminology uses the zero in two different ways.
It can be the bottom end of a winding with multiple taps.
Or
It can be the center tap. A 350-0-350 winding is the same thing as a 750V center tapped winding.

A good way to learn about this stuff is to read some of the basic material on power supplies from the old days. A Radio Amateur’s Handbook from the 1960’s would be one good source. I’ll bet there are scans posted. I recommend the old books because they will be discussing high voltage power supplies for tube circuits and will include tube rectifier info. No sense in reading material about modern switching power supplies for your purposes.

Cheers,
Tom

[Travst]

Thank you, Tom. I did mean the 6.8k resistor, and I do plan to put in the bias pot. Your explanation made everything clear.

[Travst]

I had one more question that I neglected to bring up. On the PT, the black wire is described as "common primary". After thinking on it and doing some googling, I'm still not sure exactly what the term means. My assumption was ground, but I want to make certain.

[Tom Phillips]

...On the PT, the black wire is described as "common primary". After thinking on it and doing some googling, I'm still not sure exactly what the term means.

This is the same as "...It can be the bottom end of a winding with multiple taps" example I described in post #17. In this case common could also be considered 0. It is "common" because, for the intended application, it is always connected. Then you use one of the other primary winding wires depending on the available voltage supply.
Tom

[Travst]

Thank you, Tom. I will ground it with the others, then.

[Tom Phillips]

NO. This one connects to the neutral side of the AC line supply!

[Travst]

Ah, got it now. I'm glad I waited for a response. I am always checking my assumptions, better to be cautious, I think. Thanks!

[Travst]

Saved again. I have it wired correctly now and have moved on to heater wiring. The board is built and wired, so I'm getting close.

[Travst]

I was temporarily distracted by fixing up an old Reverberocket, but am back on the case now. A couple of progress pics:

[Bruce / Mission Amps]

Wow, that's is really an ugly chassis... does it have a faceplate too? It must.
The proper high current choke filter system on these vintage of Fender clone amps is actually a "Brute Force" PI filter.... not a choke input filter. You'll need around 5Hy @ 200ma for it to work right.
Yes, the screen voltage will be higher then the plate voltage on the power tubes...and it's not that big of a deal as the NET gurus will demand it is.
As recommended, use a 470ohm to 1Kohm 2 watt screen resistors on the sockets like the Fender black face/silver face 6L6 amps have had.
Also, like many guys selling tweed "clone" kits (and I use the term "clone" very loosely) they are going the least expensive way with "over the counter parts". The 4k output tranny is the wrong impedance for a true 5F4. Seems like many vendors are trying to use the black face and silver face Pro Reverb/Bandmaster/Vibrolux Reverb OT for those amps.... it works OK but it's wrong and the real amps idled their power tubes at like 45ma to 55ma each.
Not sure if these reissue black face and silver face OTs were made to have that kind of DC idle current in them. MagComp makes really good iron though.

[Travst]

Hey Bruce, thanks for responding. The choke is a Weber/Heyboer unit, Choke for Tweed Fenders. 5-8H @ 200ma, 125 ohm. As noted above, the PT and OT are old Ballantine units from a theater amp, and I'm unsure of the impedance and how to check it. What should the proper impedance be?

Yes, the chassis does have a chrome faceplate.

[Travst]

I've been working on this build and started testing the completed amp prior to installing the tubes. Everything looked pretty fair with only a couple of voltages that were slightly out of whack in the preamp tubes.

My next step was to install the Weber Copper Cap in place of the 5U4G tube and test without any other tubes installed. I've never used a Copper Cap before, and chose it because the Ballentine PT doesn't have 5v leads. Referencing the Ceriatone layout, I have three wires running to the rectifier at pins 4, 6, and 8-the two reds from the PT at 4&6, and the connection from pin 8 to standby.

Prior to installing the cap, my voltage at pin 8 on the rectifier was 253v. After installing the cap, it jumps to over 400 and feeds that voltage down the line to the preamp tube sockets. I've researched the Copper Caps, but haven't found an answer as to how to tame the voltage or whether I've mis-wired something. I'd appreciate your thoughts on this.

[loudthud]

Was the standby switch on or off when you made the first measurement? Most meters give an average measurement. When there is no filter cap connected, the output of the rectifier looks like an average of about 280V, the peaks are about 400V, that's what the caps charge up to. What you are seeing is prefectly normal.

[Travst]

Standby was on when I first tested. I can't remember if I measured again with it off. What concerned me was getting 400+v at pin 6 on the preamp tubes. I'll double check and then pop some tubes in and measure again. Thanks for the response!