300B SS rectifier with CL-90

[badassbob]

Where can I get the tube base to add in the diodes? I dont have any junk tubes laying around, so Ill have to buy something. Anybody have any good links? Is it the UF4007 diode I need?

[TomMcNally]

Angela has a wide variety ...

http://angela.com/octalsocketsandaccessories.aspx

Of course, with the minimum order, you'll be paying a lot.

You could just tack solder across the bottom of the pc board.

[Shannon Parks]

Yes, I just strap mine across the PCB and leave off the socket. My most common diode laying around is the 1N4007, but UF4007s and 1N5408s work fine, too. I've even picked up HV diodes from Radio Shack.

Shannon

[EWBrown]

If you already have the tube socket soldered onto the PC board, just solder two rectifier diodes (UF4007 or 1N4007) to the appropriate pin locations - anodes to 3 and 5, cathodes joined together at 8.

If you were to leave the 6AX5 tube plugged in, the diodes, with their much lower forward voltage drop, would essentially "bypass" the rectifier tube's action, and it would consume only 6.3VAC @ 1.2A the filament power.

HTH

/ed B

[badassbob]

Just got a bunch of CL-90s yesterday...did a group buy over on Audiokarma . I can just wire one between the switch and fuse? Thats what Ive gathered from above anyway.

[badassbob]

Ordered up some 1N5804s and some empty sockets today...will report my impressions once I get her fired up.

[Shannon Parks]

Did you get 1N5408s or 1N5804s?

Shannon

[badassbob]

My bad, typo LOL. I got 1N5408s.

[EWBrown]

CL90 can go between the switch and fuse, on teh primary side of the power trannie. I usually wire it up (in series) as "hot" line -> fuse -> CL90 -> switch -> trannie primary. The neutral side should be directly wired to the other side of teh primary.

The 5408s are also perfectly good, IIRC they come in the UF5408 form, as well.

Usually, for no real reason, other than my own preferences, I use the 4007s for may currents of 200 mA, and 5408s for more than 200mA and under 1 amp. (I like to have lots of safety margin)

Then I have some oddball 1000V @ 6A rectifiers for the really "hefty" current requirements, and huge capacitance values .

/ed B

[badassbob]

Excuse the newbiness again...but whats the advantage of running a higher B+ on the 6B4G? Im more curious about the difference in sound, but wanting to see if theres gonna be any "gotchas" involved. I wired in my CL-90 the other day. Its situated between the tube socket and OPT, as I didnt have a place to add a terminal strip to keep it away from everything. Seems to be working fine where its at. Its not flopping around, as I used solid core wire in the build, so the rigidity of it helps keep the thermistor in place.

[EWBrown]

The SS rectification is more suitable for use with the 300Bs, most 2A3s (OK, 6B4Gs) may not take well to the overvoltage, except for the J/J 2A3-40s which are effectively a 300B with a 2.5V filament. These have a 400 watt maximum plate dissipation, as does the 300B.

To use these 2A3-40s in a GSG would require adding two 2.5VAC, 3A filament transformers and a few additional conenctions.

Triode-strapped 6AV5GAs work very well in this amplifier, with SS rectification, they just need to be pushed beyond their overly timid published ratings, in order for them to truly perform. .

/ed B

[badassbob]

I was just looking at the Sovtek 6B4G datasheet, and it shows max plate voltage at 450V. I run the Sovies...so the SS rectifier should work well shouldnt it? Damn Ed, youre quick on the trigger tonight LOL. Good stuff. Thank you all for the assistance...more knowledge here than you can shake a turkey leg at

[EWBrown]

For some strange reason, I got locked into thinking "2A3" rather than "6B4G"

I corrected my previous posting , for future reference, and to eliminate confusion

The Sovtek single plate 6B4Gs (and 6A3s, and 2A3s) can take more power dissipation than the earlier vintage USA and Russian made two-plate versions of the 6B4G / 6A3 / 2A3, these were basically two parallel connected 45s inside the globe, and 15W was their maximum safe PD (thypcally they were operated at 250VDC across the tube, at 60 mA, but the Russian Sovtek "single plates" can go up to at least 18W, or even 20W, with grater P-K voltage.

So the SS rectification should be OK, though you should watch the increased plate current, the value of the cathode resistors may have to be increased from 900 ohms total, to 1100-1200 ohms total, , in order to keep the plate current within safe limits.

There is no 40 watt PD version of the 6B4G that I know of. 300Bs with a voltage dropping resistor would work, as explained earlier up the topic.

With the triode strapped 6AV5GAs and SS rectification, I am pushing the 6AV5GAs to between 18 and 20 watts PD with no ill efects (they are published at 11 watts, which is really timid, and overly conservative, depending on the brand and interior structures, some of these can be pushed up to nearly 40W PD, without melting down.

A triode strapped 6AV5GA behaves very similarlyto a 6B4G, just needs a different connection scheme to its socket, in order to work in this circuit.

/ed B

[badassbob]

Ok fellas, gonna be ordering some JJ 300Bs sometime over the next month. Since I plan on using a SS rectifier, would it be a good idea to change out the cathode resistor to 1100 ohms instead of the 900 ohms in the standard BOM? If I decide to stay with the 6AX5, would I be safe keeping the 900 ohm cathode resistor in place? Thanks in advance!

[Shannon Parks]

You can leave the 900 ohm cathode network in there for the SS GSG. The reasoning being:

- 6AX5GT & 900 ohms is safe operation for NOS 6B4Gs
- SS rectifiers & 900 ohms is "hot rod" operation for modern 6B4Gs (i.e. Sovtek 6B4G) and 300Bs

Shannon