Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: catnine on July 14, 2011, 04:44:08 pm
-
Since I use 5Y3 rect and my res cap is 47uf and the other two are 22uf and it is just a SE champ the large value first cap may take a bit more time to charge but it will hold the charge longer , is that about right? I did add a 47 ohm 5 watt resister in series between the pin 8 of the 5Y3 and the B+ to the first cap to slow the in-rush at power up to save the 5Y3 . Also from what I understand there is a time constant if that is the proper term .
Is it fair to say that once the cap is charged and being a larger value that this cap is not working the PT any harder or the 5Y3 for that matter. It has no hum and so far the PT only gets warm not even close to hot at all.
I'm just trying to learn a bit more , I have noticed fender amps with 5Y3's with three 30uf caps or some with two 16 uf in parallel which is close to 32uf and others with 16uf or 20 uf all the way down the power rail. ie , some use a larger res/first cap and smaller for the 2nd and 3rd and they tend to be the lower powered fender amps , some larger powered amps with parallel 16 or 20uf caps for the first cap .
All I know is a 73 SF champ I had used a 40/20/20 uf cap can and when I built my 6G2/5E3 which I could use either 6L6's or 6V6's and the 6L6"s gave me a 5E5 power section and on the 5E5 they used a parallel 16uf so I installed a 30uf res cap . Did fender calculate this at all or toss in what ever was on hand at the time within reason?
-
Fender used the RCA tube receiving manual as a guide and then experimented to see how far he could push the threshold.
You do not need that 47 ohm resistor as the 5y3 is not going to explode without it.
However,47uf is rather large as a first filter cap.That's why you don't see much more than 30uf in most older amps,and for good reason;they don't need that much filtering to be quiet with a tube rectifier.
And a 5Y3 is rated for a maximum of 30uf anyway.Do you need more? Not likely.
Slow charge?Whatever for?
-
See if you can contact bigdaddy. He's a champ expert.
-
Fender used the RCA tube receiving manual as a guide and then experimented to see how far he could push the threshold.
You do not need that 47 ohm resistor as the 5y3 is not going to explode without it.
However,47uf is rather large as a first filter cap.That's why you don't see much more than 30uf in most older amps,and for good reason;they don't need that much filtering to be quiet with a tube rectifier.
And a 5Y3 is rated for a maximum of 30uf anyway.Do you need more? Not likely.
Slow charge?Whatever for?
The 47 ohm resister was recommended by Bruce on mission amps so that using the 47uf cap the resister would not allow the 5Y3 to deal with the initial in-rush of current . I really only used the 47uf because my 73 Sf had a 40 uf and I was going off of that since the 73 was the best sounding champ I ever had . I did put a 30 uf cap in it's place a while back but the amp sounded thinner.
-
Quote:"I did put a 30 uf cap in it's place a while back but the amp sounded thinner. "
I highly doubt that.You would have great difficulty hearing the difference between a 30uf and 47uf filter cap if at all.
You need to do stuff that makes your amp and tube live a long life instead of trying to reinvent the wheel.There are so many amps from the 50's that have 5Y3 tubes and they are still working.
sounded thinner. Please.
Change some coupling caps,larger cathode bypass cap on V1 and use a bigger speaker to get more bass.
-
What he said. :icon_biggrin:
-
There's no harm in adding a 47 ohm resistor in series. It's functioning as a mild current limiter. A 5Y3GT is rated for 125mA. If you are gonna run it at close to it's limit, then you want a smaller 1st stage cap. 20uF is what is shown as a typical value. A Champ draws what.... 40ish mA? That's an easy load for a 5Y3GT. 47uF isn't gonna hurt the rectifier at this current load, but it isn't really necessary because you aren't causing excessive ripple. A 47 ohm current limiting resistor isn't really necessary either because you are in no way stressing the rectifier. There's the rub with tube rectifiers. As load increases, you typically wanna add more filtering so as to reject ripple but tube rectifiers have capacitive limits. Look at some hifi tube circuits. You might find a SS rectifier with 1000uF. You won't find a tube recto in any current hifi tube gear.
A Champ is always gonna sound thin because it's simply a low power amp. Your best solution is probably a over-rated speaker that will reject cone breakup. A little more B+ to the preamp tubes will get you a little more punch. To me, the lower the wattage, the harder it is to make sound good. Probably because louder amps saturate your ears and everything starts to sound the same. A good power supply is worth it's weight but often times with geetar amps, we only want just enough.
-
All I'm saying is my 73 SF champ sounded fine and did come with a 40/20/20 uf cap can so this is what I went by not the fender schem. When I did a complete recap on the 73 SF champ I replaced it with the same 40/20/20 uf cap can and for the same make as well. I never gave it a second thought , that is what fender for what ever reason installed in the 73 champ at the factory , you can tell if they were replaced by the solder on the chassis and the rest of the circuit , mine was dead stock . I was after using the same value componants that the 73 had. I used the fender schem for the layout and the other values of resisters and other caps and have the old parts still from my 73 . I was trying to reproduce the 73 the best I could and knew nothing about what a 5Y3 could handle or not I just copied you see.
Now yes I have read about what value cap a 5Y3 is rated for . The AB764 bronco uses a 40/20/20 uf cap can too per the schem . I am not saying anyone is wrong here what I am really asking is is it worth all the effort to replace that one cap , I do have a 30uf and a 22uf F&T cap but they were easy to install when the eyelet board was sitting on the work board out of the amp , but now that it is installed you really have to move things around and be real carefull ,there are four leads in that eyelet and everything is real close in there so is it worth it in the end ?