SimpleSE CFB problem

[fandersen]

Just finished my SimpleSE using Edcor XPSE25-8-5K opts. Works great in Triode and UL mode, but when I switched on the Cathode Feedback the JJ-GZ34 flashed briefly and the power line fuse blew. I made the switch with power off. The fuse blew when I powered on the amp.

I have inspected the wiring and it all looks correct. I have attached a simple diagram of how I wired the CFB switch, and again it looks correct to me but any advice or suggestions would be welcome.

[Ty_Bower]

I made these drawings for connecting a feedback switch. There are two versions, depending on how the output transformer is phased. Note that my circuit board is stuffed for "below chassis" mounting, so everything might look upside-down and backwards compared to your drawing.

I'm staring at your sketch vs. mine to try and decide if they are equivalent. I think they are.


http://i69.photobucket.com/albums/i4.../feedbackA.jpg
http://i69.photobucket.com/albums/i4.../feedbackB.jpg

[fandersen]

Originally Posted by Ty_Bower

I'm staring at your sketch vs. mine to try and decide if they are equivalent. I think they are.

Looks the same to me.

[Ty_Bower]

Originally Posted by fandersen

...the JJ-GZ34 flashed briefly and the power line fuse blew. I made the switch with power off. The fuse blew when I powered on the amp.

Was the amp still hot when you turned the power back on? That could cause the GZ34 to arc out. Always wait for the tubes to cool completely before turning the amplifier back on. The worst part is that once a rectifier arcs, it's about a hundred times more likely to do it again.

The JJ rectifiers aren't exactly known for their durability, either.

[fandersen]

Originally Posted by Ty_Bower

Was the amp still hot when you turned the power back on?

Yes. I turned it off, flipped the CFB switch, and turned the amp back on.

Originally Posted by Ty_Bower

That could cause the GZ34 to arc out. Always wait for the tubes to cool completely before turning the amplifier back on.

Makes sense. I'm used to SS

Will try again when the amp cools down.

Originally Posted by Ty_Bower

The worst part is that once a rectifier arcs, it's about a hundred times more likely to do it again.

The JJ rectifiers aren't exactly known for their durability, either.

It's my first tube amp so buying the tubes were a bit of hit and miss. Which rectifier tube would you recommend? Also I'm currently using EH EL-34s which sound very nice. Any suggestions for other power tubes to try?

[fandersen]

Works like a charm.

Thanks Ty!

[Ty_Bower]

Originally Posted by fandersen

Which rectifier tube would you recommend? Also I'm currently using EH EL-34s which sound very nice. Any suggestions for other power tubes to try?

Try keeping a Sovtek around as a spare. They don't cost too much. I've used a Sovtek in mine with good success. Word on the street is that the current production Chinese rectifiers (Shuguang) are actually not half bad. Of course, the textbook answer to your question is "Blackburn Mullard". Too bad you might spend weeks hunting for one on eBay and a $100 to get it. No guarantee it's even any good. That said, I'll admit I own a few. They are excellent rectifier tubes, and if you treat them well they will last the life of the amp. Another good rectifier tube that sometimes gets overlooked are the Japanese 5AR4. Look for the telltale crosshatch seams at the top of the glass.

I prefer beam power tubes over pentodes with a suppressor grid. It's a matter of personal taste I suppose. If your power transformer and choke are rated for the current draw, a good KT88 is very nice. They can deliver hefty bass if you've got decent output transformers. Old American 6L6GC sound great. A set of coin base Russian 6P3S-E are a real treat and don't cost much at all, but there's a fair number of duds out there (gassy tubes). The Simple SE is a lot fun in that the tube choices are very versatile. You've got a lot of options.


http://i69.photobucket.com/albums/i4...E/P1100484.jpg
http://i69.photobucket.com/albums/i4...SE/6L6GC_2.jpg
http://i69.photobucket.com/albums/i4...E/P1110492.jpg

[mach1]

Another good rectifier tube that sometimes gets overlooked are the Japanese 5AR4. Look for the telltale crosshatch seams at the top of the glass.

I'll second that. IMHO they are every bit as good as the Mullards at a fraction of the price.

[fandersen]

Originally Posted by Ty_Bower

Try keeping a Sovtek around as a spare. They don't cost too much. I've used a Sovtek in mine with good success. Word on the street is that the current production Chinese rectifiers (Shuguang) are actually not half bad. Of course, the textbook answer to your question is "Blackburn Mullard". Too bad you might spend weeks hunting for one on eBay and a $100 to get it. No guarantee it's even any good. That said, I'll admit I own a few. They are excellent rectifier tubes, and if you treat them well they will last the life of the amp. Another good rectifier tube that sometimes gets overlooked are the Japanese 5AR4. Look for the telltale crosshatch seams at the top of the glass.

I will pick up a Sovtek and look for a Japanese 5AR4.

Originally Posted by Ty_Bower

I prefer beam power tubes over pentodes with a suppressor grid. It's a matter of personal taste I suppose. If your power transformer and choke are rated for the current draw, a good KT88 is very nice. They can deliver hefty bass if you've got decent output transformers.

I have Edcor CXSE25-8-5k opts and Hammond 193J (200ma) choke. Any particular KT88 you would recommend?

Originally Posted by Ty_Bower

The Simple SE is a lot fun in that the tube choices are very versatile. You've got a lot of options.

One of the reasons I chose this as my first tube amp

BTW, how's the Buschhorns coming?

[Ty_Bower]

Originally Posted by fandersen

Any particular KT88 you would recommend?

I picked up a set of the New Sensor Genalex re-issues. I've been very pleased with them. I haven't tried the Electroharmonix KT88, but I've heard reports they are a decent tube too. They're about half the price of the Gold Lion.

BTW, how's the Buschhorns coming?

The Buschhorns are fun. They've been playing music for a few days now. I need to take the drivers back out so I can put on a veneer and finish them.