ampage
Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

 
Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

6L6s and 5U4 Cu cap in a 5E3?


 
9/1/2004 11:16 PM
Cliff
email
6L6s and 5U4 Cu cap in a 5E3?
I built a Tweedy a couple years ago and want to try the Paul C mod and run with 6L6s. I read elsewhere that I could change to 6L6s by simply putting in a 5U4 Coppper Cap retifier. I decided to check here first. I see some mention of modifying to 6L6s, but I've done a search and can't come up with anything definitive, especially with regard to using a 5U4 Copper Cap. I know just a little about this stuff...enough to get in trouble. I know that 6L6s draw double the filament current. The JJ 6L6s that I will use run cooler than some other tubes. Would this help offset the higher filament current? Can the Mission Amp tranny hold up to the higher current? Do I need to change the cathode bias resistor? If this topic has been talked to death already, maybe someone could point me in the right direction so that I can read up on it. Thanks much.
 
9/2/2004 4:38 AM
ted m
email

Hi Cliff,  
I think I'll start collecting answers since I don't know if anyone keeps archives here, but many folks don't notice much or any sound change with the Paul C mod in a Cathode biased amp like the deluxe, where you would in say a princeton. While talking to Paul C (he makes a pedal called the TIM), he also couldn't see how this mod, which somehow is wrongly being named after him, affects any tone in a properly designed 5E3.  
 
6L6's should run fine, Bruce often recommends a 10W cathode resistor instead of the stock 5W, and a 5V4 Copper Cap equivalent (WV34 I think it is), yes, 6L6's can draw 0.9 amps vs 0.45 amps for 6V6's, but using a copper cap relieves the PT of taking power from the 5V taps so you should be fine.  
 
Watch the temps, and blow a couple of fans in the back if anything is getting overly hot.  
 
My Cu Cap 5U4s, and 5V4 equivalents are *very* close in B+ measurements, but maybe there is a fluke with them or the differences are in sag at load.
 
 
  Thursday
Book Of The Day The Ultimate Tone, Volume III by Kevin O'Connor
Have you ever wondered if there is a better way to build a Bassman, Champ, Plexi, an 800, AC-30, Bulldog or Portaflex? Or you wanted to build an SVT with off-the-shelf parts? How about a master-volume amp that doesn’t change tone with the master setting? Everything you need to know is right here, including: proper grounding techniques, wiring methods, and mechanical considerations. Eighteen chapters cover the “iconic” amps everyone knows and loves, with schematics and layouts for each, along with the technical history of the product. Eyelet-board and chassis-mounted tube socket construction is used throughout, for easy servicing and modding. TUT3 is very accessible even if you cannot fully read a schematic and is a "must have" if you are going to build an amp for your self.

Note: The Ampage Archive is an Amazon Associate site. A small commission is paid to the site owner on any qualified purchase made after clicking an associate link such as the one above.
 
9/2/2004 4:59 AM
Cliff
email

Ted - Thanks very much for the reply. Interesting...the so-called "Paul C mod" doesn't affect a 5E3 circuit. I'll do a little more research in the 5V4 vs. 5U4. I already own a 5U4, so I guess I'll give it a try and watch it closely. If I may be so ignorant, can you confirm which resistor in the circuit is the "cathode resistor". Just want to be sure. Thanks for your help.
 
9/2/2004 2:41 PM
ted m
email

Hi Cliff,  
The cathode resistor is most likely going to be the sandbox power type -- squarish in it's diameter, and rectangular in length, and white or off-white color, and labelled 250 or 270 ohms / 5W, bypassed with a cap.
 
9/2/2004 3:16 PM
Bruce /Mission Amps
email

Yes, the PT can handle a 5U4 rectifier and two cathode biased 6L6s with the two 9 pin tubes as a total load.  
I prefer to use a WeberVST Copper Cap WU4 or WV4 but a real glass tube rectifier is OK.  
The tranny will get very warm but I've run them on a test bench setup at around 150% of their max rating with temps you'd never see in a real amp and, I've never blown a filament winding.  
Use a 10 watt 270 to 300 ohm cathode biasing resistor and lower the 5K1 dropping resistor between the two fist filter caps down to around 2700 to 2200 ohms.  
 
Bruce
 
9/2/2004 11:57 PM
Cliff
email
Calculating current
Thanks for the help, Ted and Bruce. I'd like to measure the current draw when I put in the 6L6s. Is this correct? I'll use the equation I = V/R. To get V, I measure the B+ voltage and subtract the voltage drop across the cathode bias resistor. R = the value of the cathode bias resistor. Not sure at all about this.
 
9/3/2004 12:33 AM
Bruce /Mission Amps
email

Current would just be the voltage across the cathode resistor divided by the value of the cathode resistor in ohms.  
IE:  
22v/270ohms = .0815A or, about +40.5ma each tube.  
Bruce
 
   Page 1 of 2 Next> Last Page>>