Need help with PT issue

[PeteG45]

This was also posted on the TDPRI because I'm really excited to continue with my build and I really need an answer. Sorry if that's a problem.

OK so I bought a Weber W022772 PT for a 5F2A type amp that I'm building. I also purchased the end bells that allow the PT to be mounted without cutting the oblong hole in my home made chassis.

The problem is that the end bells don't quite fit. The inside diameter of the end bell mounting plate will place enough pressure on the plastic tape that surrounds the windings to break the tape if tightened.

The original screw and washer arrangement is:

screw-star washer-nylon washer-original end bell-laminations-original end bell-nylon washer-washer-nut

This allows the original end bells (which are slightly larger on the inside) to fit tight to the laminations.

My question is can I move the nylon washer to go between the end bells and the laminations? This will create a 0.075" gap between the end bells and the laminations and I don't know if it's acceptable to have a gap there.

[Bruce / Mission Amps]

Yes, but I'd be careful... the electrons or flux lines could pour out of the air gap and leave a mess.

[PeteG45]

I get that your response was humor and sarcasm but I really am/was a little concerned.

I didn't know if the bells completed some kind of shielding around the transformer. I enlarged the openings in the mounting plates so that the copper tape clears. I'm going to have to go to the hardware store tomorrow and replace the 4 screws that hold this thing together.

The end bells really aren't a good fit. There isn't really enough room inside to accommodate the wires and the mounting plates openings are about 1/8" too narrow on both sides. I really wish that Weber would redesign these with a little more volume inside the bells for wire and enough opening to clear the transformer that it's supposed to fit.

[Steve Conner]

The end bells are really just cosmetic, it doesn't matter how you mount them. If you only need them for the mounting feet, you could take a hacksaw, cut off the part that has the feet on and throw the rest away.

If the transformers are visible or can be touched (ie inside an open backed combo) then it's good form to have the end bells on, so they look neat and the high voltage wires are covered up. But I've built things where I couldn't get any end bells and had to let it all hang out.

One exception might be if the exposed windings or wires were very close to a preamp tube, then an end bell might provide some electrostatic shielding. But so would a socket with a tube shield.

And watch those flux lines! If they get on the floor, it can cause a trip hazard.

[PeteG45]

Thanks for the info on the real purpose of the bells, that was really what I was asking.

I got everything buttoned up and tested my filament heater voltages and my B+ voltage and they all look good. Since the PT will be on top of an exposed chassis I think that the end bells are a necessity.

I know that there has to be a flux capacitor joke in here somewhere.

[Bruce / Mission Amps]

No sarcasm was intended... just having a little fun.
However, you have two potential areas of concern.

1. Scrape all that white paint or powder coat junk off under your grounded wires or you'll have no or little ground even if you are using star washers.

2. take the hi-V red/yellow center tap wire off the ground point of the 6.3v filament center tap (G/Y) and move it to the exact same place the first main filter cap has it's negative lead connected and then ground it.

[PeteG45]

Bruce,

Yeah I forgot to scrape off the white primer under the ground points, I'll definitely go back and take care of that.

With the red/yellow and green/yellow center taps can I just run the first filter cap ground to the same point?

The mention of sarcasm was just to let you know that I got the joke about the flux spilling out. I didn't want you to think that I was a total idiot.

[PeteG45]

I got it together last night but I have two problems that I believe are related. The top input works and the bottom input does not and there is some hum. At first I had it wired like you see in A and then I did some research and wired it into B (the difference is in the connection from the tip on the top jack to it's connection to the bottom jack via the black wire). The bottom input is dead either way. Can someone take a look and see if either of these are correct? I checked my resistance and continuity between the G and ground and between the tip and pin 2 on V1 and everything looks OK.

[PeteG45]

I just found that the connection to the tip of the failing jack is bad at the jack. I've got to run to Lowes, we're painting the dining room, yay . I'll fix it when I get back and report back in.

I'd still like to know which input connection is correct; Fig A or Fig B.

[TD_Madden]

jack setup.

[PeteG45]

Thanks for the jack setup. That is how I found it on most of the other Tweed amps online.

I fixed the jack and 'viola' everything works. The hum is not bad up to about 2/3 of full volume. The hum is definitely less when the voicing switch is in the middle which bypasses both voicing caps. Based on that I'm wondering if I should use a different switching mechanism for that switch. When it's in the middle position the amp is very quiet. Any suggestions?

The amp sounds great. Very dynamic and the tweed voice and the Marshall voice are beautiful. The middle position which is supposed to be black faced Fenderish is leaving me a little flat but it might grow on me. I'm still using the speaker from my ValveKing 112, I'll get the Weber Signature 12B installed in a little bit and give it a try. I really would like to get the tweed and Marshall voices as quiet as the black face voice. Maybe if I eliminate the resistors on the switch. Hmmm...

[PeteG45]

My plan was to flip it over and poke around with a chopstick to see if I could locate the source of the noise. Before I did that I installed the Weber Signature 12B into the cabinet. This is an 8 Ohm speaker and it replaced the 16 Ohm speaker from my Peavey ValveKing (which is now back in the ValveKing). So I was running an 8 Ohm load into a 16 Ohm speaker (second mistake) now I'm running an 8 Ohm load into an 8 Ohm speaker.

What a difference! The noise is all but gone. You can hear a little (I mean little) hiss and a little bit of additional noise when the amp is turned all the way up. This thing is incredible! I can't turn it up enough yet to get any crunch because it's late and my wife, who has been pretty understanding so far, would kill me. I'll post photos soon.

Wooo Hooo!

[PeteG45]

Photo of the front: