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Rectifier problems


 
2/17/2003 9:49 AM
Jim
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Rectifier problems
Hi guys  
 
I have just completed my 5e3, save for the covering. I tried it out the other day and had a problem with the rectifier. The amp sounded fine, and fired up first time no problem. After about 10 seconds however there were some random flashes in the rectifier tube and what appears to be arcing inside. It sorta looks like someones welding inside the tube!!!  
 
This also happens when I switch the Standby switch to the on postition, so the amp is muted. It happens at the moment the switch is activated, not after.  
 
It's one of those small problems which need to be sorted out, as it's driving me mad and I want to play!!!!  
 
Cheers  
 
Jim
 
2/18/2003 5:12 PM
quayhog
email

try a different rectifier.  
You may also have too much filtering at the first stage filter.
 
2/19/2003 10:33 AM
Jim
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I'm using a nos Mazda 5y3 which are supposed to be very good. Anyone used these before?  
 
What tube would you suggest quayhog?  
 
Sorry to be lame, but when you say TOO MUCH filtering at the first stage filter, what do you mean. Are we talking the filter caps?  
 
Cheers  
 
Jim
 
2/19/2003 8:45 PM
quayhog
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The RCA manual suggests no more than 20uf capacitor value for the first stage of the capacitor input type of circuit which is what the 5E3 is. If you used too much it can cause rectifier tube failures.  
 
The 5Y3 series of tubes are only good for 125ma. What tubes are you using. 2 6V6 draw 90ma + a little more for the screen. Its possible to exceed the capacity of the rectifier if you are using 6L6 of KT66 tubes.  
 
Try another 5Y3, 5V4, 5AR4. These each draw only 2amps on the heater and will work in the socket.  
 
Jonathan Horne  
Quayhog amps
 
2/20/2003 1:45 PM
Jason A
email
Re: Rectifier problems--Some info for you
Jim,  
 
Personally, I have never had an arcing rectifier, and that sounds really odd. When you wired the socket up, did you connect the wiring properly? 5.0V filaments [yellow] to pin #2 and #8 and the PT secondaries [red] to #4 and #6? Double check this. Also, as far as filter capacitance on the 5E3 should be 16-20uF @450V-500V.  
 
Angela Instruments has some very nice NOS Phillips JAN 5Y3GT's for around $7-8 each. They are also guaranteed for 1 year--not too shabby. However, I personally prefer a nice RCA 5V4GA instead. Both sound nice. The 5V4 gives a bit more voltage than a 5Y3 [about 20-30VDC] and slightly more power and tightness [noticable enough], and the 5Y3 gives a little less tightness and power with more compression. Each plate of the 5Y3 [there are 2] is rated for 125 ma and each plate for the 5V4 [there are 2] is rated for 175ma. Also, the 5Y3 has a directly heated cathode [the filament is also the cathode] and the 5V4 has an indirectly heated cathode [the cathode is seperate from the filament]. Many people in the audio world state that directly heated cathodes have a reputation for cathode stripping when applying high voltages to the plates if the cathode/filament is not up to operating temperature. Indirectly heated cahtode have less of a tendency to do this. I personally can't vouch for the validity of this because with over the last decade and 50 or so builds, I have never had this problem.  
 
Jason
 
2/20/2003 1:55 PM
Jason A
email
Correction!
Jim,  
 
After reading what I wrote, I think I made a mistake in describing a 5V4 having an indirectly heated cathode. A 6CA4/EZ-81 [noval rectifier] has an indirectly heated cathode--it has a seperate pin specifically for the cathdode connection instead of tapping off of the filament for B+. Unfortunately, I was thinking about a G.W. article when I replied to your post. Haha. Somebody please correct me if I am wrong regarding the 5V4?!  
 
No flames please.  
 
Jason
 
2/24/2003 1:17 PM
erndawg
The 5V4 is an indirectly heated rectifier. The cathode is pin 8.  
N.B. Have seen many arcing rectifiers. This is the typical failure mode for infant mortality in new rectifiers. *Many* of the original Sovtek 5AR4/GZ34 failed this way. Very unusual in Mullards, but I have seen it happen.
 
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