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

[Junior]

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.



Many thanks

[Ty_Bower]

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.

[Junior]

Originally Posted by Ty_Bower

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


Connection for 8 ohm


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.

[rknize]

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.

[Junior]

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.

[rknize]

Originally Posted by Junior

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.

Originally Posted by Junior

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.

Originally Posted by Junior

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.

[Junior]

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.



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

[rknize]

That looks fine, assuming the phasing ends up being right for CFB.

[Junior]

Originally Posted by rknize

That looks fine, assuming the phasing ends up being right for CFB.

if nothing is wrong with the Hammond 1629SE datasheet then the connection is rite.
if the amp gets louder then phasing need to be switch. will report back once i hook it up accordingly.

thanks

[Junior]

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.