# Another Rectifier Question



## keeperofthegood (Apr 30, 2008)

Probably a no-brainer but, if you placed a Silicon diode across at Tube rectifier, doesn't that mean that you essentially have a Silicon rectifier? Wouldn't that essentially take the tube out of consideration?

IF SO! Is there anything special to know first before placing a SS across a TUBE diode?


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## zdogma (Mar 21, 2006)

Probably what you want is a Port Arthur rectifier, a Gerald Weber mod that uses a diode/resistor network to bypass the tube. I've never tried it, but it apparently maintains a lot of the tube feel with better reliability, and can be run without a tube if needed:

http://kendrick-amplifiers.com/Merc...uct_Code=KEN080205Rectimod&Category_Code=0802


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## nonreverb (Sep 19, 2006)

You'll basically have a solid state rectifier then. The diodes will bypass the tube voltage drop and the sag will disappear.


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## keeperofthegood (Apr 30, 2008)

zdogma said:


> Probably what you want is a Port Arthur rectifier, a Gerald Weber mod that uses a diode/resistor network to bypass the tube. I've never tried it, but it apparently maintains a lot of the tube feel with better reliability, and can be run without a tube if needed:
> 
> http://kendrick-amplifiers.com/Merc...uct_Code=KEN080205Rectimod&Category_Code=0802


Ok, this is what was at the back of my mind from an article I read about a week ago. The engineer responding suggesting the resistor was unnecessary. I would think it was for maintaining voltage drop, but the simulation works out ok with and without.




nonreverb said:


> You'll basically have a solid state rectifier then. The diodes will bypass the tube voltage drop and the sag will disappear.


This is the intention really. 

A) If I used a DPDT switch and A/B connected the anode ends of the full wave tube and a pair of 1N4007's OR 
B) If I use a SPDT and A/B connected the cathode end (connected end of the 1N7004') OR 
C) If I used a SPST and just connected the diodes across the tube

What would be the working difference. Options B and C I think would end up the same as option A. Option B would work out the best, would be Tube, Standby, Solidstate and instead of 4 [email protected] I can get [email protected] 

However, I wanted to know if option C was a way to go or not. Actually, I wonder with option B, can transformer power be on the tube plates and the cathode float?


This is a mock-up, unfortunately I don't have mechanical switch models in LTSpice. So, some use of imagination is needed.


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## Dieter Billinger (May 25, 2009)

Be very careful about substituting tube rectifiers with solid state. There are some considerations which you need to be absolutely sure about.
1 - the forward voltage of the rectifier or will it handle the high voltages on the secondary of the power transformer.
2 - the reverse voltage or PRV of the rectifier. The PRV voltages produced by the transformer can be more than double than the primary voltage
3 - It may be adviseable to add a standby switch. The high voltages which appear on the plates of the power tubes prior to the tubes warming up can lead to premature failure of the tubes caused by cathode striping.\
4 - The high DC voltage produced by the solid state rectifiers will be higher than those produced by a rectifer tube. This will affect the biasing of the preamp as well as the output tubes. Can you deal with that or is unwanted harmonic and / or crossover distortion of no concern.

Another word of caution is that nice old tube amps in original condition are worth far more than on the resale market than stuff that has been modified.

best regards
Dieter.


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## madkatb (May 14, 2009)

Check this out as it shows combined solid state and tube rectifiers:
http://www.freewebs.com/valvewizard/fullwave.html
Go to his home page and check his other stuff too. Well written and easy to understand. He has a book out too!


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## keeperofthegood (Apr 30, 2008)

Dieter Billinger said:


> Be very careful about substituting tube rectifiers with solid state. There are some considerations which you need to be absolutely sure about.
> 1 - the forward voltage of the rectifier or will it handle the high voltages on the secondary of the power transformer.
> 2 - the reverse voltage or PRV of the rectifier. The PRV voltages produced by the transformer can be more than double than the primary voltage
> 3 - It may be adviseable to add a standby switch. The high voltages which appear on the plates of the power tubes prior to the tubes warming up can lead to premature failure of the tubes caused by cathode striping.\
> ...


Agreed 

I am going to use the 1N4007's they have a 1.2Kv reverse and 1 amp forward current. Using the two prior to the the tube will allow me to play with that tube more safely (only 1 1N4007 is needed at it is only 350VAC) so I can try out damper diodes for example (dampers have peek currents in the amps, fly-backs usually under 1ma).

The issue of the higher voltage, when I posted and asked about that seemed to be a moot point with the feeling expressed of "don't worry about it". What I would want to do is find the idle current, the tube voltage drop, and then apply a suitable wattage/ohmage resistance to the SS circuit if that is indeed a problem.

Using options A or B would by their nature give me built in standby. Hence the on/off/on nature of the switching. In the off position, the amp would be in stand-by. However, I need to know, can I remove the cathode from the circuit and let it float safely or should I do the switching on the anode side of the tube? I may also be able to buy two SPST switches for less than a single SPDT or DPDT switch, I have to look into that. If that is the case, then option C would be the better cost effective choice (with a stand-by switch added in a different spot in the power supply, either before the first filter cap or after the second filter capacitor or the center tap of the power transformer that may be a later question unless someone has an idea on that now).

What I am doing is a re-work of the 5C1 amplifier circuit. This is part of the amp builders project and some pre-set options that we are working forward from, and I have some lead-in questions and am asking them here one at a time. The basic original circuit will be there, but will be augmented with some new choices. SS/Stand-by/Tube for one, and a power switching method that will ensure the filter caps are always drained when power is removed from the amp without using bypass resistances, and a line filter/3wire power lead in instead of the death cap. I wouldn't do this to an original 5C1 as that would be uncool (yes, I like originals to be originals) but for a clone well  The other goal is up-gradability. The 5C1 has lots of wiggle room for upgrading. Adding a dual triode stage for a tone stack, adding a dual triode for a reverb tank, adding a dual triode for a tremolo are all easily done within the base confines of the 5C1 circuit. The power transformer being chosen has more than enough wiggle room to handle a lot more than this. Two 6.3 volt windings at 3 amps each, and two 350 volt windings at I think it is 1 amp or 2 amps each should more than suffice for any up-building.

Hmm... so, that is where it is at. Is there any downsides to any of the three options, and is any of the three options simply a better one over the others?



What I have been working through this week-end are the two conditions of "substitutions for rectifier tube" and "switching for solid state OR tube rectification". I also have budget constraints. So, the other thread on rectifiers was about how I could wire up for use of a lower cost tube but be built compatible to have a higher priced tube used later by simply plugging it in. The 6X5/6AX5 sells for 2 to 3 dollars, where-as the 5Y3/5Y4 sells for 15 to 50 dollars. Across 25 amplifiers, that adds up fast @[email protected]


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## keeperofthegood (Apr 30, 2008)

madkatb said:


> Check this out as it shows combined solid state and tube rectifiers:
> http://www.freewebs.com/valvewizard/fullwave.html
> Go to his home page and check his other stuff too. Well written and easy to understand. He has a book out too!



Already have and plan to buy his book. That is a great site. He doesn't address the question I am asking here though, that of option switching between tube and solid state  but the hybrid power supply is a good idea and I have incorporated that idea in this.


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## nonreverb (Sep 19, 2006)

Option B would be my recommendation...it incorporates all the functions you need...


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## keeperofthegood (Apr 30, 2008)

nonreverb said:


> Option B would be my recommendation...it incorporates all the functions you need...


Thank you  Will go with this option.

Speaking of rectification, here is an oddball that I cannot think of having seen done elsewhere:










and a detailing of the "rectifier"










Was this a "normal" practice, was this a kludge, will this work well, would this lend a different character to how a tube sags? Could you "tune" the amount of sag with this??  Some fun questions for sure!!


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