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Check my SSE's Triode/UL and CFB Switch Connection

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Hi to all,
Am in the mid of building my SSE.
I had read the assembly manual again and again and again many times trying to understand each and every connection especially on the Triode/UL Switch and CFB Switch.

I had so far manage to figure out the connection on the Triode/UL Switch but am having problem understanding the CFB. Perhaps the reason is due to the fact that I am using Hammond 1629SE OPT and wishes to have the luxury of having 4ohm and 8ohm speaker binding post for my use. Please help to check if my understanding on the Triode/UL Switch and CFM switch is correct as illustrated in the attached picture.

Connection.jpg


Many thanks
 
If you are not using feedback, the 0 ohm connection at the speaker binding post should be tied into your star ground for safety purposes.

The feedback connection should not connect to both the 4 & 8 ohm taps - only choose one or the other. Choosing the 8 ohm tap will give you "more" feedback, while choosing the 4 ohm tap will give you "less". Wiring both together (as your diagram implies) will short out a section of the secondary, almost certainly causing "bad things".

The phasing of the feedback connection (whether it's green-to-green and black-to-black, or green-to-black and black-to-green) depends on the specific output transformer. I've got no experience on the Hammond 1629, so I'll refrain from comment here.
 
If you are not using feedback, the 0 ohm connection at the speaker binding post should be tied into your star ground for safety purposes.

The feedback connection should not connect to both the 4 & 8 ohm taps - only choose one or the other. Choosing the 8 ohm tap will give you "more" feedback, while choosing the 4 ohm tap will give you "less". Wiring both together (as your diagram implies) will short out a section of the secondary, almost certainly causing "bad things".

The phasing of the feedback connection (whether it's green-to-green and black-to-black, or green-to-black and black-to-green) depends on the specific output transformer. I've got no experience on the Hammond 1629, so I'll refrain from comment here.

hi Ty,
thanks for the reply.

hi all and Ty,
please bear with me on my poor understanding on electrical connection as i am mechanically trained.

to simplified my connection query, i had breakdown to simply 8 ohm and 4 ohm individual connection for speaker output. in order for me to have a choice of choosing with or without feedback, is the below connection correct?

Connection for 4 ohm
Connection4ohm.jpg


Connection for 8 ohm
Connection8ohm.jpg


is both the connection correct?
any suggestion/solution/recommendation is welcome to get my project going as it is at my final stage.

thanks in advance.
 
For the CFB, either of those last two should be correct, but note that you will have to check the phasing. You'll know if it is right or not when you throw the CFB switch. If the amp gets quieter, you have it right. If it gets louder, you need to reverse the phasing of the secondary. If you do need to reverse it, you won't be able to use both the 8 and 4 ohm taps.
 
hi rknize,
am not sure if i get it rite and thus shall repeat it here. (thanks for the patience and do correct me if i am wrong).

first, you mean that both the connection (connection for 8ohm and connection for 4ohm) is correct. is that rite?

i have to watch out the phasing. what phasing mean is that the part after the
cathode feedback switch (green line and black line) connects to. it was shown as green to 0ohm and blck to 4/8ohm in the above diagram). i might need to reverse it if the amp gets lounder when CFM is ON. is that rite?

lastly, i won't be able to use both the 8 & 4 ohm tab. i do not wuite understand this part. mind explain it in another way?

thanks for the patience.
 
first, you mean that both the connection (connection for 8ohm and connection for 4ohm) is correct. is that rite?

That is right. You don't need to move the CFB to whichever tap your speaker is connected to. Either tap will work. The 4 ohm tap would give less feedback than the 8 ohm tap. When faced with a choice like this, I usually go with whatever the designer did. I'm pretty sure George's speakers are 8 ohm and so I would use the 8 ohm tap for CFB to start.

Later to can experiment with the 4 ohm tap if you want. Unfortunately you can't use the 16 ohm (which would give you more feedback than the 8 ohm) because of Hammond's goofy secondary wiring.

i have to watch out the phasing. what phasing mean is that the part after the cathode feedback switch (green line and black line) connects to. it was shown as green to 0ohm and blck to 4/8ohm in the above diagram). i might need to reverse it if the amp gets lounder when CFM is ON. is that rite?

I'm speaking in terms of the output transformers. It depends on which direction Hammond wound the secondary relative to the primary. You want the feedback to be "negative" such that the output is reduced when CFB is enabled. You are reducing the gain of the output stage so that, in effect, it gives the output tube/transformer combo some extra headroom. If they have trouble driving the load (speaker) the feedback loop adds some of that gain back to compensate. If the feedback is "positive", you are actually increasing the gain of the output stage and reducing headroom. This leads to instability and other bad things.

In order for the feedback to be negative, it needs to have the opposite phase from the output tube itself. That means that when the tube plate swings high the feedback loop swings low. So if you find that hooking up the CFB to the 8 ohm tap makes the amp get louder you will have to reverse the secondary wiring. The 8 ohm tap becomes the ground and the "common" becomes the 8 ohm tap. You will then have to connect CFB loop and the positive speaker terminal to the common and the safety ground and negative speaker terminal to the 8 ohm tap.

lastly, i won't be able to use both the 8 & 4 ohm tab. i do not wuite understand this part. mind explain it in another way?

If you have to reverse the secondary as described above, how do you do the 4 ohm tap? Unfortunately, due to the way impedances work, the 4 ohm tap is not in the "middle" of the winding between the common and the 8 ohm tap. Instead it's about 25%. You can use it, but it will be more like a 6 ohm tap.

I'm looking at Hammond's "not easy wire secondary" to see if there is a way to reverse the phasing for 8 ohm and get a workable 4 ohm tap out of it, but it's not obvious.
 
hi rknize,
thanks for the patience and guidance once again.

now i understand the phasing part. this explain why the 8ohm tab was connected to the common ground (we want negative feedback). initially i am being confused with the wiring part which George had prepared.

as for the 4ohm and 8ohm tab, am configuring the CFB to the 8ohm tab. and since the 4ohm tab is there will make an extra speaker bind post for 4ohm output too but less the CFB. just wish to have another choice so that i can play around with it to "see" if there is any difference.

SECTransformer.jpg


hope to finish my amp so that i can enjoy some music. keep my finger cross so that nothing goes wrong. will post some pictures to share thereafter.

cheers
 
manage to hookup according to the above diagram with both 4ohm and 8ohm tab.
no audio/sound amplifier.

unhook the CFB.
still no audio/sound from the amplifier.

while doing the above, the filament of the 5AR4, 12AT7 & EL34 lighted up with nice glow but no sound despite i crank the volume up to the max.


anyone here able to give me a head up on where to start the trouble shooting?

i had the intention to dismantle all the parts and start from scratch again.
 
Time to measure some voltages. Please use George's advice the hook up the meter with clips with the amp powered off. If you have more than one meter with clips, use them all.

1) B+ This is the voltage (from ground) at R1, R4, C2, R14, R24, and the red wire of your OPT.

2) Across R17 or R27 (one meter probe on each leg of the resistor). This is the output tube bias voltage.

3) Across R13 or R23. From this we can measure the input/driver tube plate current.

Also check that your input wiring isn't shorted somehow. Some pictures of your wiring might help.
 
Time to measure some voltages. Please use George's advice the hook up the meter with clips with the amp powered off. If you have more than one meter with clips, use them all.

1) B+ This is the voltage (from ground) at R1, R4, C2, R14, R24, and the red wire of your OPT.

2) Across R17 or R27 (one meter probe on each leg of the resistor). This is the output tube bias voltage.

3) Across R13 or R23. From this we can measure the input/driver tube plate current.

Also check that your input wiring isn't shorted somehow. Some pictures of your wiring might help.

hi rknize,
did not have a good sleep last nite due to obvious reason :(

this morning had a qucik check on all my wiring (signal in, OPT and pwr trans).
you know what, i left the high vlotage center tap (red/yellow) of the pwr trans disconnect.
looking back to the wiring diagram prepared by george, with the center tap disconnect is as good as putting the amp in standby mode forever (is the rite?).
how stupid of me to have left that out.

will try to power it up tonite and hope all goes well and i do not have to go thru the steps in measuring the above mentioned voltage.
 
Yup, that pretty much puts the amp on standby. :)


connect the HV's CT and powered up, there is some spark on the 5AR4 and see smoke from the Sup capacitor. i thought that i had fried my 5AR4. lucky enough it is still working but not the capacitor. the capacitor is some cheapo made in China product. should not have used it.

currently running the amp. without the SUP capacitor.
will post some pictures to share :)

thanks to rknize for the help.
 
the seller was telling me that it was a motor run cap.
but there is a red and green wire thus i assume that the red is plus and green is minus.
connect it accordingly.
lucky enough i see smoke first and not explosion.
shall go get a real motor run cap the metal can type.

had attached the failed capacitor for reference.
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.
 
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did not suffer from any hum since it was up and running.
nice piece of PCB from George taking care of the grouding.

the built was from plywood and i had it veneer walnut.
i had a rough hand and the joints are not seemless as you can see some glue residue :)
hope i can improve my skill for my next project since i also bought the Tubelab SE :)
300B or 2A3 will be my next project but for the time being shall enjoy some music first.....
 
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