you may gain some degree of reliability with tubes powered up softer than with typical bridge rectifier, but the pulsation will be with larger amplitude... imho going from half-wave rectifier to full-wave rectifier not going to be beneficial.
Converting Solid State to Tube Rectification on a Preamp
I am looking to convert my Preamp from a Bridge Rectifier to a Tube Rectifier. Any members have done or knows how to do this. Your help are much appreciated!
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What preamp do you have? I have switched back and forth on several preamps from solid state to tube rectifier, but each of them was a DIY unit where I had intended to have this flexibility when I built it. A commercial preamp with solid state rectifiers may not be as easy to modify. For example, you need a power supply for the heaters of the tube rectifier. An all solid state preamp is not likely to have this capability. A tube preamp will already have a 6v or 12v supply which might be able to supply the voltage needed for a tube rectifier, but it may not have the current capability to handle a rectifier tube as well as the signal tubes. If the preamp has a 6v supply and has enough current capability, you could theoretically use a 6v indirectly heated rectifier tube such as a 6X4, but the resulting B+ voltage will be lower than with a solid state rectifier. That may or may not be a problem. Of course, if you have the skills to build an outboard power supply for your preamp, you can basically build anything you want. You can use a different power transformer that has a slightly higher voltage output to account for the losses with a tube rectifier, and the new transformer can have the proper voltages for the rectifier tube as well as signal tubes. |
By the way, a typical tube rectified power supply uses a dual-element rectifier tube and a power transformer with a center-tap secondary wiring. This is a full-wave rectifier. A solid state power supply often uses a full-wave-bridge (4 diodes) that can be fed by a power supply winding that does not have a center-tap. This allows some savings in transformer cost. But both types of power supplies are full-wave. So the issue is not full-wave vs. half-wave. |
@salectric I might be lost in translations, but full-wave bridge superposes 4x(as signal is phase split by 180deg) half-waves thus pulsation is substantially smoother than to the conventional full-wave method or tube rectification. Literally saying that you’re dealing with 4 superposed half-waves as opposed to 2 superposed half-waves. Pulsation of bridge is nearly 4 times lower in magnitude and closer to the perfect DC. |
If you haven’t already, try some ultrafast/soft recovery HEXFREDs first. Much simpler, and may satisfy your desire for improved sound. ie: (http://www.partsconnexion.com/rectifier_diode_fred.html) &(http://www.partsconnexion.com/rectifier_bridge_hex.html) There’s a blurb on potential benefits, on this page: (https://www.caryaudio.com/upgrades-and-modifications/) |
I have a Blue Circle 21 preamp. Output tubes are 6sn7 with a solid state bridge rectifier. I want to replace that solid state bridge rectifier with a tube say 6x5. I will be using the existing 6v for the heater or running on battery for the heater. My questions are: 1) curently the unit is running on a bridge rectifier, if i convert it to tube, then it has to be half wave rectifier. To run the preamp at full wave, a pair of two 6x5 are needed? 2) if i do make that change to a single 6x5 tube rectifier, with the preamp does it matter if i do run it in a half wave or full wave?? 3) does anyone knows how to do this, if you can help me out?? Much appreciated!! |
@salectric
A solid state power supply often uses a full-wave-bridge (4 diodes) that can be fed by a power supply winding that does not have a center-tap.Is it possible to use two 6X5 or one 6X5 with 2 Schottky Diodes, and add a heater transformer to make use of the existing power transformer? |
@zipost Do you have the schematics of your Blue Circle 21 preamp? and what is the B+ voltage? BTW, I also found a BC21.1 with outboard power supply on usaudiomart. http://www.usaudiomart.com/details/649027319-blue_circle_211_tube_preamp_with_bcg31_power_supply_fre... |
So, it can be done, the question is why you want to do that! Well, if it's to me, than perhaps I can assume some degree of masochism as tubes get blown over 10 times faster than diode. I think the best bridge approach with vacuum tubes can actually be done with 2 triodes as each triode can be represented with equivalent 2 diodes. |
Imhififan... the voltage on the secondary power transformer is around say 350v. As an option on this preamp; Blue circle website do sell a separate power supply, pretty sure it will work with my preamp. But i do not want to take that route. why would i change a solid state rect. to tube??? I am curious to see if a tube rect will outperform a solid states in my preamp. All members feeback are much appreciated! |
To my experience upgrading current rectifier with better parts is quicker, smarter and cheaper approach with larger outcome. Just modifying for tube rectifier seems to be more like spiritual masturbation. Tube rectifier maybe more safe for especially power tubes as it rises up operational voltage substantially slower than semiconductor. In preamp you may be better off with solid state sonically. There are upgrades to SS rectifiers you can research for more quiet designs with higher quality semiconductors and for a lot less money. I've done in the past replacements of separate diodes by integrated low-noise bridge on tube power amplifier. It's available in Newark.com and look for proper parameters of Semicron bridge models specifically designed for tube electronics with high operating voltages. Also another cheap trick is to throw over the AC terminals Jensen film in oil cap of few thousand pf -- these you can get at partsconnexion. |
why would i change a solid state rect. to tube??? I am curious to see if a tube rect will outperform a solid states in my preamp.Using four rectifier tubes like 6AX4 to create a full-wave bridge and a 6V 5A power supply for heaters should work, This is a schematic for your referance: http://1.bp.blogspot.com/_ZXzBbxBRjUc/TVKRXcVOklI/AAAAAAAAAGc/i_zXDoVqTHw/s1600/6CB5A-PSU-Graetz-6AX... maybe add some high DC voltage rating spdt relays control by a switch so you can select between tube or solid states rectifier. |
Oops! one more thing, as mentioned by salectric: the resulting B+ voltage will be lower than with a solid state rectifier, that may or may not be a problem. |
if i decided to do just a half wave rectifier using a single tube 6x5, is that possible? Also, with the secondary measure at 350v, that is more than enough for a single 6x5 plate voltage?Sorry I don't have an answer for your question, but if you really want to use a single 6X5 with the existing transformer, check out this link: http://www.antiqueradios.com/forums/viewtopic.php?f=13&t=176225 |