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Old 7th May 2011, 02:11 PM   #1
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Default SSE triode/UL wiring help please

Hello,

I have had my SSE working beautifully for the past week wired in triode mode, i.e. T3-PRI and T2-PRI 01 and 02 shorted, as per the initial recommended Tubelab wiring diagram.

This morning I was trying to sort out triode/UL switching.

As often happens I got confused straight away, as there seems to be a discrepancy between the actual PCB and the wiring diagram. Looking at the connections for V21, you see that on the PCB, T3-PRI 01 connects to the plate and T3-PRI 02 connects to the screen. The wiring diagram, however, has the centre connection of T3-PRI going to the plate, and the furthest right hand connection going to the screen. It's as if the plate and screen connections have been swapped around.

Of course this is no problem in triode config as the two terminals are shorted.

Anyway, I figured that for the switch wiring, the common pin would connect to the screen (T3-PRI 02), with ON-1 [triode] going to the plate (T3-PRI 01) and ON-2 [UL] going to the screen tap on the OPT.

So I wired it this way and turned it on. It seemed to work normally in triode mode but turning beyond half way results in noticeable distortion that wasn't there before. Switching to UL mode whilst playing (a big no-no?) causes a horrible sound from the speakers as the connection is broken and remade. Once in UL mode, there is a tiny increase in volume, barely perceptible.

Gut feeling says I've got it wrong somewhere along the line....sorry for the ramble.....anything strike anyone as obvious? Is switching between modes whilst playing a Bad Thing? Given that output power seems to roughly double when UL is in use, should I notice more than a barely perceptible increase in volume? Any other qualitative sound differences I can listen for to tell if it's wired correctly?

Thank you, as always.

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Old 8th May 2011, 01:34 AM   #2
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The schematic doesn't have the pcb connections labeled, so I would assume that the schematic is made with ease of reading in mind, not matching the pcb. What you explain appears to match the wiring diagram and my amp. Not sure about the new appearance of distortion in triode connection. That seems strange. It goes away again when you short out the connections and disconnect the switch?

You should not switch while power is applied. Your switch probably isn't rated to break 400 or so volts dc (very few are). The awful noise is awful. Power down, wait for sound to stop and then flip the switch. The only other consideration here is if you are using a NTC inrush limiter. If you switch off your amp, change connection, then turn it back on your inrush limiter isn't limiting (already hot). The nice thing is that your tubes are also already hot, so that's not a problem. The only issue could be if you are using the limiter to protect a tube rectifier from working too hard to fill empty filter caps. Wow, that was a long aside... sorry about that.

My amp gets a little bit louder, but not way louder. Remember, every doubling of power is only about +3db. Another thing to listen for is bass. When I turn it over to UL if I don't also switch on cathode feedback I get bass that's kind of... how do I explain... um, rude? But maybe that's also due to using the CXSE OPTs.
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Old 10th May 2011, 06:36 PM   #3
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Thanks for the comments - no apology needed for the digression, t'was very interesting!

I had a closer listen in triode mode with the switching in place and the distortion is awful - clearly I've done something wrong. The sound in UL is fine, although no obvious changes compared to triode mode that I could hear.

I haven't been able to find where I've gone wrong yet so in the meantime I've disconnected all the tri/UL switching and it's back to its sweet self again.

I'm going to enjoy it as-is for the time being and revisit the switching at a later date after I've digested some more of the old threads.
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