GSG 300B with Transcendar OPTs

[Sal Brisindi]

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

Yes,
That is a true statement, wasted heat but if there was a working tube in there the filament would have been on anyway. Purely aesthetics, but it looks like you worked out a solution. Great job.

Regards,
Sal

[lth1]

Here is a photo of the SS rectifier that I made. I have one with UF5408's and one with UF4007's. I have not received the Weber diodes to date.

http://cgim.audiogon.com/i/vs/i/f/1195494688.jpg

How did you get rid of the start up surge and resulting pop when using your rectifier.

Since I have both 8 and 4 pin sockets, I would like to reduce the filament going to the 4 pin socket inorder to install a 300B without changing R19,20. Can I put a resistor from J3, J4 to the socket to reduce the voltage, and if so what value?

Lee Hankins

[SDS-PAGE]

How did you get rid of the start up surge and resulting pop when using your rectifier.

Since I have both 8 and 4 pin sockets, I would like to reduce the filament going to the 4 pin socket inorder to install a 300B without changing R19,20. Can I put a resistor from J3, J4 to the socket to reduce the voltage, and if so what value?

Good job on the SS rectifier tube, Lee!. Mine doesn't look as fancy as yours. It's just a metal tube with diodes inside. I did paint it black and polyurethaned it, so it looks presentable. It works great though.

I don't hear pops either when I turn it on or off. The amp operates and sounds with no glitches at all. The PT runs cool for most part. Don't know what I did right to make it so. Everything is stock except for R19, R20, and UX4 sockets.

As far as putting in extra resistors, you could probably do it, but wouldn't it be just easier to get a pair of 1.5 ohms 5W resistors? I would prefer to use least number of components possible. It's one less thing to worry about if I had to troubleshoot.

For resistor values, could you use: voltage drop needed/current=resistance. Power=IV=RxRxI.

[lth1]

If I change R19,R20 then I would not be able to use the 8 pin sockets. I am trying to make things plug and play for the 6B4G and 300B tubes. I could put in a switch with .75 and 1.5 ohms resistors but it seems simplier to just reduce the 6.3 volt filament current to 5 volts at the four pin socket, if possible.

Are we over driving the 6SL7 with these SS rectifiers?

[SDS-PAGE]

If I change R19,R20 then I would not be able to use the 8 pin sockets. I am trying to make things plug and play for the 6B4G and 300B tubes. I could put in a switch with .75 and 1.5 ohms resistors but it seems simplier to just reduce the 6.3 volt filament current to 5 volts at the four pin socket, if possible.

I see. Could you tell me how you made that SS rectifer using an old tube base? Where did you get the metal top? Thanks. -Min

[lth1]

Took an old rectifier and removed all the glass and leads. Revoved the solder from all of the pins, bent the rectifer leads 90 degrees so that they go down into the pins (3,5,& 8). The two negative ends are soldered together (8), one cut shorter (I wrapped wire around the two leads and soldered), only one lead can go into the pin 8. The other leads go into pins 3 and 5.

I machined the aluminum top which is made from an aluminun tube with a 1.25" solid round stock epoxied to the top.

[Shannon Parks]

Are we over driving the 6SL7 with these SS rectifiers?

No problem at all. I think they are well within their rated plate voltage of 300V 99% of the time. Plus that 270k plate resistor helps.

[RobertWStephens]

Hello! I have been lurking on this forum for a while and am getting ready to put together a get*set*go project. Where can you buy the Transcendar OPT's if they are not listed on Ebay? Peace. Robert

[TomMcNally]

Hi Robert -

I don't have any personal experience with the
Transcendar OPT's ... but here is a link to
the seller on eBay .... http://search.ebay.com/_W0QQsassZggaet

[EWBrown]

The next G*S*G, I'll be building it up as a 2A3 version, using separate 2.5V 3A filament transformers for each tube. I'll start out with AC filaments and if the AC hum is negligible then I won't bother with rectifying the filament voltage - I've had good "quiet" 2A3 results in teh past, using a 50 ohm WW pot as an AC balance control.

This gives the advantage of being able to use "standard" 2A3s or the J/J 2A3-40, which is really a 300B with a 2.5V filament (40W plate dissipation, and it can be run hard at 450V B+ is desired) . No extra sockets, or complex filament adaptation circuitry needed.

Still undecided whether to use James 6112HS or the 10W 3K Transcendar OPTs... I have all the parts on hand and the Hammond black steel chassis are on their way to me..

J/J 2A3-40s can be found at www.eurotubes.com or here:

http://cgi.ebay.com/Factory-Matched-Pai ... dZViewItem

In either case they're ten bucks more per MP than are the J/J 300Bs.




/ed B in NH

[TerrySmith]

The Hammond 302AX is a specific design for 2A3 amps. It has two 2.5v windings, one each 6.3v and 5v. With this transformer, and some minor cut&jumpering, you could use different rectifiers such as a 5U4, 5AR4, or the cool looking russian 5U3C, and the endless choices of 2A3's.

Angela has 'em for $90.99

[EWBrown]

THanks! I'll check it out. I know there is a similar "special" 300B power trannie with separate 5VAC filament windings

/ed B in NH

[ecir38]

Found this link for the transcendar's for those that might not want to deal with ebay. Not much of a site but has a sales email available.

http://www.transcendar.com/

[77seriesIII]

Ed,

How far along are you on the 2A3 mod to the GSG? That idea has gotten me thinking...never a good thing. Anyway took a look at the 5U3C tube : http://thetubestore.com/russian5u3c.html and the bit o glass is sharp! So waht are you thinking of doing?

Erick

[lth1]

Ed,

I just don't understand why one would want to go to the additional trouble to build a 2.5v 300B (2A3-40) in the Get Set Go when everything is already there for a 5v 300B. They both are going to sound the same, the 2A3-40 is not a true sounding 2A3, according to reports it sounds just like a 300B, which it is.

Lee Hankins