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Old 14th May 2016, 01:04 PM   #1
gcom is offline gcom  Ireland
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Default SSE up and running. Some questions.

Hi all,

I have just go my SSE up and running on the bench and it sounds absolutely great.
Thanks to all here and George for the help, I am just over the moon at the moment..


I had couple of issues in getting it running:

I followed Ty Bowers checkout procedure without the tube in and all the resistances checked out perfectly but when I went to measure the voltages I found the the fuse was popping as soon as I plugged in the power transformer.
After checking over the board and seeing nothing wrong and disconnecting filament wires etc., I decided to pull out the hexfreds and sure enough, that sorted it out.
One of them was reading a short in both directions and the other seemed to be reading a 0.3v drop in both directions.
I did not have the SS rectification switch or jumper wired and I had no rectifier tube in so they weren't really being used
So what did I do to blow them?
Could I have heated them up too much when I soldered them or can static blow them ( they do come in an anti-static bag)?

The voltages are:
Line voltage 243vac

B+ 442 vdc
Traffo 388 vac
12at7 filament 6.8vac
12at7 plates 304,309 vdc
5ar4 filament 5.7vac

As you can see, the filament voltages are a bit high but I did it at work and the line voltage at the factory is high at 243vac
The line voltage at home is only 228vac so that should be just fine.

One thing that concerns me is that the 12AT7 flashes brightly for about half a second around the base of the tube when the transformer is plugged in and then after a few seconds you can see the heaters slowly glowing up at the top of the tube.

Is that the heaters or is something arcing over at the bottom? It doesn't happen at the top where you can see the filaments sticking out.

Is it the high voltage?
Do I need to get a CL-90?

(Another 20 euro delivery charge on a 2 euro part, I've had a few of those already!)

Thanks again for all your help.

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Old 14th May 2016, 02:45 PM   #2
Sodacose is offline Sodacose  United States
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Congrats, George!

Those Hexfreds could have been blown by static or heat. I believe they're also sensitive to the voltage generated by EMF collapse from the power transformer if power is cycled quickly. You have them installed the right way around too, right? I've made sillier mistakes when building.

The 12AT7 flash worries me a bit. Is that at the socket or is this inside the tube envelope? Can you tell whether this is the heater wires? It may just be the current surge with cold heaters.

I would use some kind of thermistor. It does not have to be a CL90 if you have access to other NTC types.
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Old 14th May 2016, 05:02 PM   #3
w5jag is offline w5jag  United States
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The flash is normal start up for many vintage, European manufacture, small signal, dual triodes. Don't worry about it.

As for the diodes, who knows. Many have no trouble with them, others ( like myself ) have no end of trouble with them. When I want to use a solid state rectifier, I use the potted style that plugs into the rectifier tube socket. These are not fancy, but they are convenient and seem bulletproof.

Congrats on getting it going!


Last edited by w5jag; 14th May 2016 at 05:04 PM. Reason: needed some commas
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Old 14th May 2016, 05:14 PM   #4
rmyauck is offline rmyauck  Canada
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CL-90 should help the filaments as you have to think of tubes to being like light bulbs in that regard. The more cycles the lower the life. CL-90 should help bring the voltage up slower helping life I would think.

They are used (suitable size) on aircraft light for that reason as they are expensive to replace. I bet they would help with car headlights etc.

I put a dimmer switch on my bathroom light as an experiment about 14-15 years ago and it's that old!

The light sensor used on screw in bases to turn on lights at night will give the same affect as they slowly bring the voltage up as it gets darker on the ones I've seen.

The GZ34/5AR4 does help with the slow warm up for the rest of the tubes (not the filaments) , but there is a diode mod that I think George puts on his latest PCB's for that amp (last few years) which helps the rectifier tube last. Diodes are put in series to pins 4 & 6 ( be careful of polarity) of the tube.

I forgot to also say that flash can be normal as I've read on various forums like Win W5JAG says!

Yes congrats! a great amp!

Last edited by rmyauck; 14th May 2016 at 05:24 PM.
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Old 14th May 2016, 06:38 PM   #5
rmyauck is offline rmyauck  Canada
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Diode mod info is in this thread:

Sparking Rectifier Tubes
Attached Images
File Type: gif Diode mod.gif (17.0 KB, 347 views)
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Old 17th May 2016, 08:42 PM   #6
gcom is offline gcom  Ireland
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Thanks all for the advice.
Yes, W5jag, they are Nos Sylvania 12at7 and if that is normal that's fine.
The tubes were cheap so I'm not really worried about them as long as they don't blow something else up (my house). They seemed to be working happily enough though.
What is the flash? Is it the heaters or is it across the tube?

Thanks for the comments Sodacose, I will get a Cl-90 the next time I am ordering something, it can only help to take some pressure off the other stuff.
I do have the CL-140 and the diodes in stalled because it was one of the newer boards that I got with that mod on them.
And thank you rmyauk for that link, I was wondering how they worked as well, as they seem to be just a SS rectifier that makes the tube redundant.
But George explains it in that thread.
I can't do any more testing for now as I disassembled it pretty much straight away.
I need to get it into a chassis now, I routed the top plate today out of aluminium.
Bit of a chore.
Next time, I'm going to buy a chassis!
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Old 17th May 2016, 10:21 PM   #7
rknize is offline rknize  United States
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A yellow flash at the base of some tubes is normal. It's the exposed part of the heater element below the cathode heating up more quickly than the rest of the heater stuffed inside the cathode. Once the rest of the heater comes up to temp, the resistance across it equalizes and it glows more evenly.
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Old 17th May 2016, 11:26 PM   #8
mcandmar is offline mcandmar
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What was the reverse voltage rating of the hexfreds? I popped a couple of Cree diodes in a recent build until i realized the 600v reverse voltage rating was too low for my application.

Flash on the 12at7 may be normal depending on the brand of tube, google "mullard flash"
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Old 18th May 2016, 06:26 PM   #9
gcom is offline gcom  Ireland
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Originally Posted by mcandmar View Post
Flash on the 12at7 may be normal depending on the brand of tube, google "mullard flash"
Ha ha! Yes that's it. There's a Youtube video of them doing exactly that.

I just checked the hexfreds they are the 12A version of the IXYS DSEI-12 which is the 1200V 11A version.
I wired it up to a lead and then plugged the lead in.
Probably not the cleanest way to turn something on.

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Old 31st May 2016, 06:30 PM   #10
gcom is offline gcom  Ireland
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A question please about connecting up speakers that are already connected to another amp.
It is very difficult to get behind my gear to connect and disconnect the speakers so I have connected my SSE to my main speakers which are already connected to the main amp in the room which is a Nad C370.

The SSE seems to be working fine with the Nad switched off.
Will everything continue to be fine with the SSE playing as long as the Nad is switched off?
Would it be ok to play the Nad with the SSE switched off?
I imagine that the transformers would generate a high voltage in their primaries from the voltage coming out of the Nad.
Is this correct?
Would it do harm?

Last edited by gcom; 31st May 2016 at 06:32 PM. Reason: Spelling
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