DUAL RECTIFIER TUBES

[TIMBO]

Hi guys, I bought an other Fi Sonic similar to the one I restored. This amp also suffered the same PT burnout that was caused by the undersized 6CA4 heater flashover.
I replaced the 6CA4 with a GZ34 in the other amp as the replacement PT had extra 5V tap.

This amp also has extra taps 1X6.3v@3A and 1X5v@3A with 1X6.3v CT@3A used for the heaters

I was thinking with the extra 1X6.3v@3A I could add an extra 6CA4 and split the power/preamp or do a dual rectifier setup.

Some thoughts. Thanks

[jazbo8]

Unless you are after originality, I would replace the VR with SS and use larger filter capacitors - the amp will run cooler, the components will last longer - if you want some sag, just add a resistor before the first filter cap.

[jjasilli]

Can't find earlier thread.  What s is amp's power consumption?


6CA4 is a high voltage, hi current tube; and takes a large enough 1st filter cap, 50mF.  Not sure why there's a problem with rectifier tube type.  Unless the stock PT can't handle all the 6V heater draw.  OTOH a 50mF cap may really be way higher.  Maybe better to use 30 - 40mF.


Preamp should draw little B+ current.  So a separate rectifier for that has no real benefit. 

[TIMBO]

Hi guys, This is the other amp http://el34world.com/Forum/index.php?topic=15917.msg154591#msg154591

[jjasilli]

Hi guys, This is the other amp http://el34world.com/Forum/index.php?topic=15917.msg154591#msg154591

Thanks for re-posting, Timbo.  Good thread!  Looks like PRR addressed the power consumption issue in the last tread.  Also in the new companion thread Sluckey is suspicious of the 6CA4 matching with EL34's.  Does the amp have 6L6's or EL34's?


What is the plate voltage?  Cathode or fixed bias?

[jazbo8]

Not sure why there's a problem with rectifier tube type. 

Nothing execept for the extra heat it generates and the voltage drop.

[tubeswell]

The 6CA4 forward current supply is about 150mA, compared to about 250mA for a 5AR4 or 5U4G, which is why a 6CA4 won't hold up with EL34s as well as a 5AR4 or 5U4G will.


@ Timbo, I'm not sure what you mean by 'extra taps' at 6.3V and 5V. Are these in fact separate windings? or are they just taps off the same winding? To run a pair of rectifiers off the same winding, you need to sum the current draw of the rectifiers to get the current draw rating needed for the winding. Running two rectifiers off a single 3A winding with 5V and 6V taps won't work.

[TIMBO]

Hey tubeswell, The replacement has 1x 6.3v CT @3A 1x 6.3v @3A and 1x5v@3A

[tubeswell]

You're good to go

[jjasilli]

Tubeswell:  I'm seeing 6CA4 cuurent handling as 500mA per plate X 2= 1 Amp total.  Is this wrong?


But heater : cathode is 500V.  Probably OK for 6L6's, but EL34's might run at higher voltages than a 6CA4 lijkes to see.

[sluckey]

Tubeswell:  I'm seeing 6CA4 cuurent handling as 500mA per plate X 2= 1 Amp total.  Is this wrong?

I think you are referring to peak plate current. The actual working dc current is only 150ma. IMO, this 9-pin rectifier is better used with 9-pin output tubes, but if you gotta pair it with an octal, I would use nothing bigger than a 6V6. Here's a screen shot of RC-30...

[tubeswell]

What Steve said.


The 6CA4 is in a miniature nine pin envelope (similar to an EL84), and everything is packed in snugly with less capability to dissipate heat. It won't last as long as a 5V octal rectifier if you run it at full bore.

[TIMBO]

Hi guys, Thanks for all the good info.
What I was trying to get at is, is it worth adding another 6CA4 either in parallel as per FENDER or split the preamp and power amp to have its own rect tube.

The PT has a low output so using a rect tube will give me about 360v OR using a SS rect about 400v.

[Willabe]

The PT in that amp say's 5v@3A so, you could go with 2x6CA4 (1A heater) rec tubes or use 1xGZ34 / 1x5V4  / 1x5U4.

Splitting the power amp and pre to use 1x6CA4 each wont help much. The pre amp will draw like only 10mA's? So the 6CA4 that supplies the PP power tubes will still be over worked with either a pair of EL34's or 6L6's.

You'd have to go with 2x6CA4 in parallel but then you need 2 - 8 pin sockets and the space for the 2nd socket.

Seems easier/cheaper and you'd have more space going with a single 1xGZ34/5V4/5U4.


                      Brad   

Edit; 1 of my tube books says 5V4@175mA, 6CA4@150, so maybe not much use here in this amp?

[TIMBO]

Hey Brad, I don't fully under stand the workings of a parallel rect tubes and if they would work in this amp. It's just that I saw Fender do it and I thought it possible for this one. I do have room for another socket and I even have a matching socket. Thanks

[sluckey]

There's nothing magical or complicated about using dual (parallel) rectifiers. Just connect the second tube to the first tube, pin for pin. You will now have 300mA working current capacity.

If I had only two choices with the PT you have, I'd forget dual 6CA4s and just ream out the single recto hole to accept a 5AR4/GZ34 tube. GZ34s have been used with EL34s forever. I've never seen any amp using 6CA4s with big bottles.

Here's something you may want to consider... Those EL34s use 1.5A heater current each so a pair will use up one of your filament windings. Now if you decide to use parallel 6CA4s they will eat up 2A, leaving only 1A available for the rest of the tubes. You would be able to heat three 12AX7s but if you need to heat any more tubes you will exceed the current rating of your second heater winding.

Using EL34s with that PT just begs for GZ34 (or 1N4007s) rectifier IMO. If you were to drop back to 6V6s, then the 6CA4 would be fine and you wouldn't need to do any metal work.

[Willabe]

It's just that I saw Fender do it and I thought it possible for this one. 

Fender used it on a Tweed Bassman for a tighter bass sound before reliable/inexpensive SS diodes.

I'd go with what Sluckey's saying.


                          Brad