PT Hummmmm

[Blind Lemon]

I could use a second opinion. Here ya go.

You can hear the PT hum on SB, without the speaker plugged in and no tubes

You can hear it through the speaker with it jacked in and on SB w/o tubes (induced into OPT)

Both center taps grounded to the PT bolt.

Disconnected it on the out put side, except diode rect and still have hum.

Transformer orientation is the same as the Trainwrecks except the choke and I changed that to no avail.

BTW, I have done a few builds with these transformers and quality has been first rate.

BL

[dynaman]

Does the hum disappear when standby is turned on? Is your OT's B+ connection before the standby switch?

[Blind Lemon]

No when you turn the SB switch to the on position it gets louder.

No the B+ to the OP is after the SB switch.

BL

[Structo]

My D'lite PT buzzes a bit but it is more of a mechanical buzz as I don't hear it through the speaker.
It is a Heyboer PT.

The only thing I can suggest is to make sure the bolts holding the laminations together are nice and tight.

[Blind Lemon]

The lam bolts are German tite.

I hate to think about moving these transformers around. Build has be completed, I do not like the unused holes in the top of the chassis or extended wire.

This transformer layout have work well for all the Rocket style builds I have done.

BL

[David Root]

Try disconnecting the B+ line right after the rectifier diodes. Maybe a bad diode?

[dynaman]

You saying you can hear a hum through a speaker with the standby off and no tubes in the amp?

Pic and schem?

[Blind Lemon]

Yes, the PT is inducing the Hum into the OPT. The OPT has no juice running through it because the amps on SB and no tubes are installed.

Also If the secondary's are only hooked up to the diode rect and nothing else the PT still has a hum.

re:

You can hear the PT hum on SB, without the speaker plugged in and no tubes

You can hear it through the speaker with it jacked in and on SB w/o tubes (induced into OPT)

Both center taps grounded to the PT bolt.

Disconnected it on the out put side, except diode rect and still have hum.

Transformer orientation is the same as the Trainwrecks except the choke and I changed that to no avail.

Single channel AB763 no trem. Have built a couple with no problems.

I'll get pics tomorrow.

BL

BOOMER SOONER

[tubeswell]

Unfortunately the laminations on some PTs sing more than others - nothing much you can do about it when it happens to you except change PTs.

[Blind Lemon]

I'm going to move the iron around today and see if that helps.

BL

[Blind Lemon]

I've isolated the PT, even built a shield to see if that would help. Still vibrates/hums. Guess I'm going to try a new one.

BL

[Blind Lemon]

Update: New PT came in.

So I started to pull the installed transformer out and I'm still having a hard time believing it's the transformer. I have the cap board out and I'm looking again at the wiring. Every thing is correct, 2 center taps together first stage filter cap separated from the rest. I am looking at the diode rect and wonder if the noise is coming from there so I disconnect from it and turn the amp on, nope. You see this started because I was looking at that new PT and really didn't want to cut the leads on it, I'm still not for sure for sure. You know. I'm still looking at it, tracing wires and looking at the grounding, I look at the center taps again. Yep thats right, but the CT's come out of opposite sides of the PT. That don't make any difference coming out of different sides of the transformer. Oh well I'll move the filament CT to another leg of the transformer away from the others. Bullshit, it sounds quieter, I'm hearing stuff or not hearing stuff because I'm listening to hard. Ok, I put the amp back together and plug it in, its not the quietest amp I have built but its 100% better. I've got a couple here that are a little noisier than this one now.

Don't know if this will help anybody, but there it is.

BL

[TheGimp]

Could one of the wires you thought was a CT be a shield ground wire?

[Phil_S]

If you pull the old PT off the chassis, completely disconnected, and apply a/c to the primary, I think you'll find out it if vibrates. I realize, this isn't the same as having a load on it, but it tells you something.

If you know what the mA load is on the secondary, you can hang an appropriate wattage resistor on the high voltage secondary while it is uninstalled and see if a load makes a difference.

To be clear about the resistive load (sorry if you already know this), the smaller the R value, the higher the mA draw, so going too low will smoke the PT. So, for example, your PT is 300-0-300, that's 600VAC. If your known load is 100mA, then use Ohm's law to solve for the correct R. V=I*R. 600 = 0.1 * R. R=6000. So you find a 6K ohm or larger R. In this example, V*I = 60W, so your R needs to handle that much and I suggest three parallel 25W 25K (about 8K) resistors would provide enough load and wattage. I would not crank it to the wire and use 6000 ohms.

Anyway, maybe you don't feel the urge now that you've reworked it. I want to mention, though, that using a transformer bolt, which many people do without incident, is not recommended and is probably against the electrical code. The ground should be on a dedicated bolt. That's my 2 cents on the ground, FWIW.

[Blind Lemon]

As I said above this is a grounding scheme I have used in the past. I've built quite a few Rockets this way and all have been dead quite.

I think it shows that grounding is not aways an exact science.

BL