So I have a Howler now :) : low productivitiy day

[mikepukmel]

So are you using a Fender chassis or an exact clone? I ask because Leo & Co. usually oriented the transformers to minimize the hum.

The hum could be coming from the AC filament supply. One way to check that is with a 6VDC power supply which could be from 4 AA batteries, or even try the 5VDC output from a USB portable power pack. I believe that if you disconnect the AC filament supply with the tubes hot you can hear if the hum disappears as the signal fades out.

If you decide to go with a DC filament supply you can leave the power tubes on the AC supply... the Boogie Mark IIIC schematic as I recall shows a nifty way to get DC for the preamp tubes.

I did not look up earlier threads with you discussing the hum issues so I have no idea what you already tried.

Steve A.

P.S. We usually encounter the initial problem in this thread after replacing an OT so our first thought is to reverse the leads going to it from the power tubes...

Its an inexpensive clone chassis. I have collected a bunch of period chassis images, and the relative positioning on most stuff seems reasonable, but its not an exact copy, cloned from an original. Most noticeable: the output jacks in the original amps straddle the phase inverter, and the standby switch is right behind the hole in the chassis where the output transformer wires go through. So, in the original amps, the standby wires drop to the chassis, go around the output trans wiring hole, and over to the back of the board, then up to eyelets on that side of the board.

On this chassis, the jacks and switches are quite a bit farther towards the preamp side of the chassis. So the output jacks are over the tremolo tube, the standby switch is over the phase inverter. There wasn't enough room to route the dirty signal wiring wiring to/from the standby switch along the chassis, away from the phase inverter and output trans wiring, so I twisted it and routed it in the air. Otherwise, it would run very close to either the phase inverter socket wiring or the output transformer wiring, neither very good. Probably worse if closer to the phase inverter wiring?

The reverb transformer is in similar relative positioning, and mounted 45 degrees. The OT and PT seem to be similar relative positioning compared to the originals.

*** thanks for the tips on the filament wiring. Looking for how to try DC filaments on this amp for a test run.

[Steve A.]

Its an inexpensive clone chassis.*** I have collected a bunch of period chassis images, and the relative positioning on most stuff seems reasonable, but its not an exact copy, cloned from an original.** Most noticeable:* the output jacks in the original amps straddle the phase inverter, and the standby switch is right* behind the hole in the chassis where the output transformer wires go through.** So, in the original amps, the standby wires drop to the chassis, go around the output trans wiring hole, and over to the back of the board, then up to eyelets on that side of the board.**

On this chassis, the jacks and switches are quite a bit farther towards the preamp side of the chassis.* So the output jacks are over the tremolo tube, the standby switch is over the phase inverter.** There wasn't enough room to route the dirty signal wiring* wiring to/from the standby switch along the chassis, away from the phase inverter and output trans wiring, so I twisted it and routed it in the air.** Otherwise, it would run very close to either the phase inverter socket wiring or the output transformer wiring, neither very good.* Probably worse if closer to the phase inverter wiring?

The reverb transformer is in similar relative positioning, and mounted 45 degrees.** The OT and PT seem to be similar relative positioning compared to the originals.

*** thanks for the tips on the filament wiring.** Looking for how to try DC filaments on this amp for a test run.

The orientation of the laminations on the iron can be very critical as well as the actual placement.

So did you already try the chopsticks method for checking the lead dress as a possible source of your hum? It is best to get the lead dress issues resolved before the final trimming of the wires. When leads cross it is usually best for them to cross at right angles to reduce parasitic interactions.

As you go through the circuit the leads going to the grids become less sensitive to noise — the signal going into the phase invertor is not going to pick up crap like the signal going into the initial gain stage since it is not being amplified as much.

Steve A.

[mikepukmel]

The orientation of the laminations on the iron can be very critical as well as the actual placement.

So did you already try the chopsticks method for checking the lead dress as a possible source of your hum? It is best to get the lead dress issues resolved before the final trimming of the wires. When leads cross it is usually best for them to cross at right angles to reduce parasitic interactions.

As you go through the circuit the leads going to the grids become less sensitive to noise — the signal going into the phase invertor is not going to pick up crap like the signal going into the initial gain stage since it is not being amplified as much.

Steve A.

Thanks got a chopstick at the ready. Putting a plan of attack together on which wires to move.

[mikepukmel]

The noise seems to be almost all (>99%??) coming in through the reverb circuit. Did Leo's suggestion, swapping the tank around, back and forth, got it to what seems to be the best spot, but still some hum when I turn up the reverb control> Turn it all the way down and the amp is about silent.

[mikepukmel]

Sometimes it pays not to get everything super nice and neat before a sound check. like not cutting OT leads until your sure of phase. And as you've noticed color code will not always match up.

nosaj

As someone very new to the internals of these cool amps (GEEZ wish I had gotten into more tech stuff back in the day!! Aaaand, we had guys with tons of broken amps to sell for cheap, all brands. ) I tried forever to find a post or article SOMEplace that said "If you use a Hammond NNN Output Transformer on a Fender AB763 Deluxe circuit, the blue wire goes here, and the brown wire goes here". I thought Hammond should know this but their tech guys wrote "There's no way to know in advance, you'll know if you got it wrong the first time you fire it up.". I can't believe that Hammond doesn't know the orientation of the two sets of leads!

Thanks for the help tracking this down. Now on to the reverb noise. . . The great news (fan TAS tic news) is that w reverb off, the amp is almost dead quiet.

[g1]

"If you use a Hammond NNN Output Transformer on a Fender AB763 Deluxe circuit, the blue wire goes here, and the brown wire goes here". I thought Hammond should know this but their tech guys wrote "There's no way to know in advance, you'll know if you got it wrong the first time you fire it up.". I can't believe that Hammond doesn't know the orientation of the two sets of leads!

The orientation is dependent on the connection to the PI tube, also the connection to the output jack (for single impedance OT's).
So it really is the safest default to suggest what they suggested.

[mikepukmel]

The orientation is dependent on the connection to the PI tube, also the connection to the output jack (for single impedance OT's).
So it really is the safest default to suggest what they suggested.

Cool, thanks. And, as an added benefit, that horrible honking seems to have assisted in the break in (and not blowup, luckily) of the speaker. Shoulda done this months ago!

[mikepukmel]

I get lost here. So, you have a phase inverter in the circuit. You know that one side is in phase with the output of the previous stage, and one side is out. Follow both signals through the power tubes (single or pair). Shouldn't there be a way to mark the output transformer leads so that if you send a positive (charge flowing in) signal to lead A of the primary side, then lead D or E on the secondary will have the in phase signal?

[Enzo]

Most data sheets put a dot by the start end of each winding.

But really, you have a center tap and two plate leads. You have a 50/50 shot of getting it right. SO we don't trim the blue and brown wires to length, we try the system out with them tacked to the sockets. if it howls, reverse them at the sockets. If it works right off, trim the wires and solder them in place.

[mikepukmel]

Most data sheets put a dot by the start end of each winding.

But really, you have a center tap and two plate leads. You have a 50/50 shot of getting it right. SO we don't trim the blue and brown wires to length, we try the system out with them tacked to the sockets. if it howls, reverse them at the sockets. If it works right off, trim the wires and solder them in place.

Got it, thanks Enzo.

[g1]

I get lost here. So, you have a phase inverter in the circuit. You know that one side is in phase with the output of the previous stage, and one side is out. Follow both signals through the power tubes (single or pair). Shouldn't there be a way to mark the output transformer leads so that if you send a positive (charge flowing in) signal to lead A of the primary side, then lead D or E on the secondary will have the in phase signal?

If we're talking about an OT that was designed for a particular model, then that should be. But was this Hammond specifically for this version of the deluxe? And did the person you spoke to at Hammond know that, or was he speaking generally?
I mention this because there is another curve ball, where the feedback gets applied. Some designs apply the feedback to another stage where it could be opposite phase, and opposite wiring would be correct.