GSG 300B with Transcendar OPTs

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I got this done in about 6 hours. Having right tools makes a lot of difference with metal working. Changed R19 and R20 with 1.5 ohms/5W and put in 4 pin sockets as per Shannon's recommendation. Worked like a charm the first time. Dead silent and everything seems to run cool. I listen to the amp briefly and boy am I impressed right off the bat! I really dig these Transcendar irons. They sound really clean with good solid bass. I really like this 300B amp with Transcendars better than the 6B4G version with James iron. Here are some pictures. Sorry, my camera doesn't do too well indoors:

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I did some voltage testing and I was getting 150V across 300B plate! Beats me how good it sounded with voltage that low. Anyway, I checked my wiring and it looked good. I got suspicious with the rectifier, so I soldered a couple of rectifiers in lieu of 6ax7. I got 378V on the plate, and 64V/59V for the cathode. So, I guess the 6ax5 is toast.
I read Lee's experience with his GSG and blown bypass caps and I don't want it to happen to my amp. Do my numbers look ok for the 300Bs? I like the sound of SS better. -Min

[Shannon Parks]

Congrats! Those operating points look perfect for a 300B:
http://www.emissionlabs.com/datasheets/EML300B.htm

BTW, what brand 6AX5GT was that?

[WA4SWJ]

Nice Amp!

Anyone tried the Emission Labs tubes. Looks interesting.

[TomMcNally]

The GSG looks sweet in the Hammond chassis Min.
What size is the chassis ?


Ed - I found the price on the Emission Labs 300B-XLS,
$ 489 a pair .... I also found a link to a 300B amp for sale
that I patterned mine after .... $ 2995 - wow !

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Thanks guys. The rectifier tube is what supposed to be a NOS RCA that I got from eBay. It tests out ok on my tube tester, but why is it lowering the voltage so much? It actually blew the fuse on the first power up, then it's been consistently lowering the B+.

Think I will stick to those diodes. No fireworks yet, hopefully none to come. The sound is just awesome. BTW, is there some kind of octal plugs to cover up the empty socket?

Tom, the hammond was 12 x 10 x 2, like Terry's. This is more like the size that I would prefer rather than other one that I built 6B4G-GSG on. It looks compact and proportional (except for the tubes) to irons.

IMHO, I think it's worth investing a little more and get your GSG upgraded to 300B. It's an improvement, as I found out.

[TerrySmith]

Min, you could gut out an old metal tube and hide the diodes in there. That way if you wanted to try another tube, you could plug it right in.

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I went through my stash of old tubes and found a couple of metal tubes. One of them says 1N1237. Is this a solid state rectifier? Anyway, how do I open up the metal tubes? They seem to have a tight seal.

[TomMcNally]

Typically, a metal tube has 4 crimped spots around the edge.
You can bend the crimps out with needle nose and a small
screwdriver, and unsolder the pins and pry the top off.

Sometimes it's a glass tube inside of the can, sometimes
the glass glues to the metal. I opened up a supposed
6V6 onetime to make a rectifier in the can with some
diodes, and found a 7 pin socket inside with a 6AQ5
plugged into it !

[TerrySmith]

An old 0Z4 would be perfect to make a SS 6AX5, the pinout is comparable and they come apart easily. Sometimes you can find an aluminum shell 0Z4.

[hembrook]

What did they cost you?

I just ordered some EI outputs from Trafomatic for my 6A5G version of the get*set*go. I am curious how they would compare to your transcendars for price etc.

Thanks

Robert
Mannheim

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Tom, I did find a metal tube socket that you described and it came apart ok. I wanted to use the other one marked "1N1237", but it was tightly sealed with no crimp spots.
The Transcendar OPTs that I used cost $90 BIN on eBay, plus $13 for shipping. I really liked them, considering they cost only a little more than Hammond's 125Es. Excellent performer. There is a 15W version of this pair that has 4 and 8 ohms secondaries. They cost $150 BIN.

[Sal Brisindi]

Min,
First off great job on the amp, looks really nice. As far as your 6AX5, why don't you get a replacement or if you want to keep the diodes below dremel pins 3, 5 and 8 off the tube and leave it plugged in.

Regards,
Sal

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Thanks, Sal! I successfully converted a metal tube into a solid state rectifier. I can now swap between tubes and SS rectifiers with ease. I definitely prefer the SS for the extra voltage I get for 300Bs.

This is purely academic, but if you get the 6ax5 (with those pins cut) plugged and used SS below wouldn't you be wasting power in keeping the filament heated and cause the PT to run hot for nothing? Just a thought. -Min

[jduffy]

Super clean looking. Great job.

That looks like a keeper! You'll never want to let go of that one.