SS Rectified Get*Set*Go

[SDS-PAGE]

lth1, did you try the copper cap rectifier with your GSG yet? How does the sound compare to 6AX5? I am ordering stuff for GSG with a 300 mod and was wondering whether or not I should go with the copper cap. Thanks!

[lth1]

I have ordered the copper cap rectifier but they have not arrived. I did receive two GE 6AX5GT and they sound much better than the RCA sidegetter tubes that I was original using. It will be interesting to see if the GSG with the copper cap rectifier with its "normal" voltages will sound as good as the over driven tubes with UF5408 rectification. There is a loud pop on startup when using the uf5408's but I just remove one speaker wire from each side as a temporary solution.

The 300B mod would probably sound better with the higher voltages created with the UF5408 rectification. Maybe Shannon or Ed could jump in here and give much better advice.

After changing the cathode cap from 100volts to 500volts I have not had any more problems to date, still usings the 1100 ohm network.

[TomMcNally]

Running a tube amp with no load on the output can blow
up the transformers ! You'd be better off shorting them.

[EWBrown]

It might be a good idea to wire into the AC primary circuit an Inrush Current Llimiter like the Keystone CL-90 as used with the DIY35 board, this will give it a soft start and should eliminate the power-on "pop".

/ed B in NH

[77seriesIII]

SDS-Page, which weber cap were you getting or are you doing a special request one to fill Ed's SS rectifier for a 300B mod?

[lth1]

I was only getting the weber cap that was a direct replacement for the 6AX5. With the 300B installed I (and as I understand SDS-Page) use the UF5408 or UF4007 diodes, but I did replace the coupling caps with 500v caps, no proplems since, except the pop on startup, will install the CL-90 as Ed recommended.

[lth1]

I was only getting the weber cap that was a direct replacement for the 6AX5. With the 300B installed I (and as I understand SDS-Page) use the UF5408 or UF4007 diodes, but I did replace the coupling caps with 500v caps, no proplems since, except the pop on startup, will install the CL-90 as Ed recommended.

[SDS-PAGE]

That's right. Get WAX5 in liew of 6AX5 if you're using 6B4Gs. WAX5 will drop 45-50V just like 6AX5. I wanted the extra boost in voltage to go with the 300B mod, so I made a solid state rectifier using an empty metal tube with a pair of high voltage diodes that I bought from Radio Shack. Works like a charm.

[77seriesIII]

lth1 and SDS,

Thanks. I'm looking into the 300B version so I was wondering which weber would be the best in that format OR just go with the diode option as mentioned in the GSG SS thread and skip the weber option.

Sidebar the weber name threw me a bit as I have an old Land Rover, hence the moniker and weber is a pretty well known after market carb for older vehicles.

Thanks for the help!

[EWBrown]

If you don't mind adding a little extra componentry, a 6X5 pins out exactly the same as a 6AX5, just use one to power only the 6SL7, and then add in SS rectifiers and a couple extra suitable electrolytic caps for developing the 300Bs' B+. That should get you closer to the normal 300B operating points.

The "extra" PSU circuitry can be mounted off-board, on terminal strips.

The 6AX5 is going to be "overdrawn" by the 300Bs mosst likely, hence the extreme voltage drop.

/ed B in NH

[77seriesIII]

Ed,

Thanks, what you describe is much in line with what I am looking for. Now having said that and understanding my limitations (wife calls me sparky...) How do I do that? I followed the SS creation and will look at the schematic to ID the wires but what do you recommend as additional caps and more importantly how should I inject them into the build?

Thanks!

[SDS-PAGE]

Here is an idea. If you're pretty sure that you're going w/SS rectification, you can just do away with a PCB mount octal socket. You can just solder anodes of diodes to where pin 3 and 5 is supposed to be on the PCB and solder cathodes to pin 8. This way you won't even have to bother punching a hole on the chassis or make a SS rectifier tube. And yes, it would be wise to wire in an in-rush limiter (aka a thermistor) to protect your investment. voila, c'est trop facille, non? -Min

[EWBrown]

The simplest and easiest approach is that addressed in the previous reply. I do subscribe to the "simpler/easier is better" theory in most cases, but also like to experiment and try out some "strange" ideas from time to time. (visualize some of those old fashioned "flying machine" crack-up photos from the early 1900s) :o Yellow_Light_Colorz_PDT_09

If you still want the 6AX5 for supplying the 6SL7 by itself, proceed as follows: (it gets a little complex, but not insurmountable).

The PA-774 secondary wires (two "hot" and the CT) connect at the ten-place barrierl strip, that would be the best place to connect an extra set of leads (using spade or ring lugs) which, in turn, would go to the "external" SS rectifier circuitry, that can be mounted on one or two small terminal strips.

I'd go with two uF4007s or uF5408s, two 100-220 uF / 450 V caps, and use the choke that is already in place, just disconnect it from its two barrier strip connections, and connect it between the + end of the two added external caps.

Connect a 50 ohm (or higher value) 2W resistor to the two barrier strip locations where the choke was connected. Since the 6SL7 by iteslf draws very litle current, a larger resistor could be used, anything 100 ohms to 1K (or even higher) , the actual current consumed by the 6SL7 is around 1.2 mA total. A 1K resistor is going to offer a 1.2 VDC drop, so it is rather insignificant. The idea is to get about 150VDC "resting" voltage at the plates of the 6SL7.

HTH

/ed B in NH

[ecir38]

I took apart and had a look at the diode in SDS-Page's SS rectifier. He used a 1N5399 http://search.digikey.com/scripts/DkSea ... =1N5399-ND which is standard recovery.

lth1, I noticed that the UF5408 and UF4007 diodes are fast recovery. I wonder if this is the cause of your pop at startup.

[EWBrown]

Another "old school" approach to reducing or eliminating the "pop" is to connect a 0.001 uF, 1KV (or higher) ceramic cap across teh power switch terminals. Most mechanical switches have some degree of contact bounce which can generate the pops and other transient effects.

This will absorb the transients and contact arcing. The seemingly high voltage rating is necessary because of the potential for inductive kickback from the power transformer primary winding.

/ed B in NH