Trans Orientation

[trem]

Can you guys take a peek at this.?
Is there anything fundamentally wrong with the way I have the PT, Choke, and OT placed on the chassis.?
Looking at the Hammond OT there are 2 power tube sockets on the left.
On the right, from top to bottom is the Preamp, Tremolo in the middle, and the last on the bottom is the PI.
Is it "bad" to have the PT and choke in that position.?
Thank You

[tubegeek]

The only criticism I would apply is that the choke - that's the item with the brown kraft-paper insulation, right? - is oriented similarly to the power transformer and nearby it. You might want to put it further towards the empty corner, and possibly turn it 90 degrees, but only if you get 120 Hz rectified hum pickup.

[trem]

I was afraid somebody was going to say that. I realize I have the lams of the Choke and the PT running the same way.
The handful of amps that I have built, I have always kept the trannies at 90 degrees. These existing holes just happened to line up, so I used them. To be honest, I have never heard an amp, or one I built, have a noise issue that was related (so I think anyway) to the transformers coupling do to orientation. I am not really sure how often it happens, or how critical it really is. This is the first time I have installed them the "wrong" way. I believe I have room to move it, so I guess I would be foolish to tempt fate (at my level of ability anyway).
Thank You

[tubegeek]

Listen like this first - I basically agree that it's not necessarily going to cause any problem.

[Chuck H]

Obviously you want to maximize space between trannies to minimize inductance. On something the size of an amp chassis that's a relative consideration because priority is maximizing space between trannies and amplifier circuits. So... Better to have the choke oriented like the PT than to have it oriented like the OT since the OT can pass inducted hum into the audio path. And the choke (ideally) has any AC output at a low impedance via the decoupling of filters. More important to have the choke away from the amplifiers than to have it away from the power supply.

[trem]

10-4
Thanks Again

[clyde1]

I always keep the choke and PT quite close together, almost touching at times, with the orientation determined by available real estate only and there doesn't seem to be a hum issue. The OPT is another matter.

[trem]

I always keep the choke and PT quite close together, almost touching at times, with the orientation determined by available real estate only and there doesn't seem to be a hum issue. The OPT is another matter.

That is interesting.
I just do not have the experience of many builds to say if it is problematic or not.
Thanks for your input.

[Steve Conner]

It's not. The choke doesn't emit a great deal of hum field, and it isn't particularly sensitive to hum picked up from the PT either.

An exception is if you use a choke-input filter, then the choke becomes a buzzing, stray-flux-spewing monster. Another reason to avoid choke-input filters IMO.

[Chuck H]

You know, we got side tracked talking about the choke. I also think your layout would be better if you change your tube designation. Make the preamp tube the lower right, the PI the middle and the trem tube upper right. That way the input and preamp are further from the PT (less hum) and the the OT and output (more stable) and the PI is closer to the powr tubes. The trem almost doesn't matter WRT location because it's just a voltage oscillator and not in the signal path. So let that tube be close to the OT and power supply. That's probably closer to where the bias circuit will be anyhow. This layout change just makes sense to me.

[trem]

It's not. The choke doesn't emit a great deal of hum field, and it isn't particularly sensitive to hum picked up from the PT either.

An exception is if you use a choke-input filter, then the choke becomes a buzzing, stray-flux-spewing monster. Another reason to avoid choke-input filters IMO.

I seem to have a great intuition for making the wrong decision(s). Choke input is exactly what I had in mind, just because I have the choke. So what is the best way to use this little 5H choke.?
Did Fender use a Pie Filter typically.? On a BF/SF they typically had the rectifier, then the first filter cap (sometimes caps in series) for the OT, then the Choke, and the the next filter cap for the power tube screens. Would I be better off doing something like that.?
You know, you guys are at a disadvantage (what's new). You do not even know what I am building. I better draw a quick schem before this gets out of hand. I really need to learn how to use on of those schem programs.
Anyway. I have a real mutt of an amp in progress. Let me do the best I can with a schem, and I will ask for your advice then.
Thank You

[trem]

Chuck H -
Let me try to incorporate your improvements into a hand drawn schem. Hope I can get it on one piece of paper.
Thank You

[Chuck H]

Other than changing the choke input there shouldn't be any change to the schem. Just a change to the layout. For the chassis your working with I think this is probably the most stable layout. Yes, many amps use a Pi filter type filter for the screens and subsequent preamp, omitting the power tubes from the choke feed. That choke looks too small for an input choke to my eyes. Anyhoo... This is what I would do. It looks like there may be some plugs and/or controls already on the right hand side of the chassis. But I would ignore that and drill or punch new holes as needed. Whenever an amp is built with a poor layout and the builder posts because of stability problems (that can't be fixed without radical modification at that point) it always bugs me. Hopefully we've nipped it this time.

[trem]

Here is a rough schem of what I am trying to do.
1. Where would be the best place to use that choke with a 6X5 rectifier.?
2, Can I use the tremolo circuit in this Ampeg Schem with the phase Inverter I have.? Would I just install it at the "high side" of that 22k resistor.?
Thank You
I may have an error(s) those 47k are plate resistors. I probably have the feed to the power tubes from the wrong side of the plate resistors.

[Chuck H]

Yup, A couple of errors. No reason to make corrections until you have a final schem that you feel is correct.

I wouldn't use that PI with a bias vary trem. The Ampeg PI offers more isolation for the PI grids WRT the oscillator. For that matter, why not use a LTP? You really won't need the small amount of extra gain offered by the paraphase.

In the B+ rail, the choke would replace the resistor between the plate and screen nodes.