Rectifiers

[jcmusic]

Hi Guys I am new here so take it easy on me! I have an old Baldwin organ amp updated and modded by Will Vincent. The amp uses 4-6L6 power tubes, 2-12AX7 drivers, and 2-5U4's. Will has suggested that I use a 5V4 rectifier because of the slow start up, problem I have with that is the voltage drop. The 5U4's drop is about 50v, the 5V4's is about 17, isn't this going to make the amp sound more aggressive??? Does anyone have any advice on which rectifier I should use try, etc????

Jay

[kevinkr]

Originally Posted by jcmusic

Hi Guys I am new here so take it easy on me! I have an old Baldwin organ amp updated and modded by Will Vincent. The amp uses 4-6L6 power tubes, 2-12AX7 drivers, and 2-5U4's. Will has suggested that I use a 5V4 rectifier because of the slow start up, problem I have with that is the voltage drop. The 5U4's drop is about 50v, the 5V4's is about 17, isn't this going to make the amp sound more aggressive??? Does anyone have any advice on which rectifier I should use try, etc????

Jay

Have you measured the actual voltage drop across your pair of 5U4, IMHO that drop really only applies when the tube is loaded to somewhere near it's rated current, probably not the case here. You may be much lower than you think, I swag 20 - 30V range at a couple of hundred mA load current with both 5U4s.

Also it isn't necessarily true that a slightly higher plate voltage is going to result in a more aggressive sound, it could, but you need to try it first. I've generally found it possible to achieve slightly better linearity on higher plate voltages which should result in less aggressive sound.

I don't think the B+ arriving 10 - 15 seconds before the tubes are warmed up is any sort of issue with the tubes in this amplifier.

I'm assuming this is a guitar amplifier since you didn't spell it out, but my comments would apply equally to a hifi or acoustic instrument amp as well.

[boywonder]

Are the voltage drops that you mentioned above actual drops measured in the amp or are you looking at the data sheets?

Do you happen to know the B+ voltage and current draw of the amp?

Running a higher B+ voltage (less drop across the rectifier) will result in more output power, shorter tube life, and the possibility of exceeding the plate dissipation of your output tubes, although if the tubes are operating rather conservatively, it may work fine.

That being said, Duncan amps lists the following data for the two tubes:

5U4 Tube drop = 44V @ 225mA DC

5V4 Tube drop = 25V @ 175mA DC

Which a 19V difference, and maybe less when the currents are equal.

TDSL Tube data [5U4]

TDSL Tube data [5V4]

[jcmusic]

Originally Posted by kevinkr

Have you measured the actual voltage drop across your pair of 5U4, IMHO that drop really only applies when the tube is loaded to somewhere near it's rated current, probably not the case here. You may be much lower than you think, I swag 20 - 30V range at a couple of hundred mA load current with both 5U4s.

Also it isn't necessarily true that a slightly higher plate voltage is going to result in a more aggressive sound, it could, but you need to try it first. I've generally found it possible to achieve slightly better linearity on higher plate voltages which should result in less aggressive sound.

I don't think the B+ arriving 10 - 15 seconds before the tubes are warmed up is any sort of issue with the tubes in this amplifier.

I'm assuming this is a guitar amplifier since you didn't spell it out, but my comments would apply equally to a hifi or acoustic instrument amp as well.

Kevin,
Thanks for replying, no I have not measured anything I was going by what I read in tube data sheets. Yes it is a high-fi amp that will never be pushed do to the efficency of my speakers. When I tried a 5Y3 in my 45 amp it mellowed it out alot, too much in fact I had to use a 5U4G tube in it.

Jay

[jcmusic]

Originally Posted by boywonder

Are the voltage drops that you mentioned above actual drops measured in the amp or are you looking at the data sheets?

Do you happen to know the B+ voltage and current draw of the amp?

Running a higher B+ voltage (less drop across the rectifier) will result in more output power, shorter tube life, and the possibility of exceeding the plate dissipation of your output tubes, although if the tubes are operating rather conservatively, it may work fine.

That being said, Duncan amps lists the following data for the two tubes:

5U4 Tube drop = 44V @ 225mA DC

5V4 Tube drop = 25V @ 175mA DC

Which a 19V difference, and maybe less when the currents are equal.

TDSL Tube data [5U4]

TDSL Tube data [5V4]

Boywonder,
I was looking at data sheets no actual measurement. No I don't know what the B+ voltage is, the man who modded the amp made the suggestion to try the 5V4 tube.

Jay