Spitfire build (Filter caps) ?

[chainsawmillerman]

Greetings,
The schematic I'm looking at calls for 2 22/450v and 2 33/450v for the
filter caps and a choke. It uses a 5ar4 rectifier two el84's 2 12ax7's.The
transformer voltage is 285-0-285. My project amp will have a 6ca4 rectifier
same power and pre tubes and a power transformer that measures 248-0-248
volts.I have several 22uf 400v caps would this value work?I also have a
choke that would work but do I need it?Would there be a benifit in using say
5 of these 22 400 volt caps instead of the 4 caps called for in the
schematic? Should I stick to the schematic?The reason I ask is the voltages
in the circuit seems to be at least 50 volts under 400volts anywhere in the
circuit.Also what is the difference in voltage drop between a 5ar4 and a
6ca4 ? lots of questions I know ,but sure would appreciate some answers,
Thanks,
CB

[zaphod_phil]

Why has this been posted in the Classified Ads section? Is it for sale???

[chainsawmillerman]

thats a good question, thought is was going to the tech group? : ) Whoops!

[Graydon]

Hi guys,

I moved it to the BBQ since it is off-topic. I suppose it is not too far off topic since it is discussing a 2xEL84 amp which is probably close to the 18W in output and basic character.

[RossH]

The schematic I'm looking at calls for 2 22/450v and 2 33/450v for the
filter caps and a choke. It uses a 5ar4 rectifier two el84's 2 12ax7's.The
transformer voltage is 285-0-285. My project amp will have a 6ca4 rectifier
same power and pre tubes and a power transformer that measures 248-0-248
volts.I have several 22uf 400v caps would this value work?I also have a
choke that would work but do I need it?Would there be a benifit in using say
5 of these 22 400 volt caps instead of the 4 caps called for in the
schematic? Should I stick to the schematic?The reason I ask is the voltages
in the circuit seems to be at least 50 volts under 400volts anywhere in the
circuit.Also what is the difference in voltage drop between a 5ar4 and a
6ca4 ? lots of questions I know ,but sure would appreciate some answers,
Thanks,
CB

I'll take a shot at it. Theoretically, your 400V caps would work in this environment. Most people prefer not to run PS caps "too close" to the limit because of spikes and fluctuations in power. If you are only at 248 before the rectifier, you should be OK.

The cap size thing becomes an experiment. Traditionally,the stiffer cap comes first after the rectifier and and it goes downhill from there. Personally , If if I had only 22uf caps I would put 2 of them in parallel to attain 44uf for the first cap and then use 22uf's after that. There is a limit on cap size following the rectifier. Check on that 44uf before you act on that.

You don't need a choke. It might help with filtering if you are going to experiment with "caps available". Study the difference between the 18watt PS and the Matchless PS. 18 Watt uses a resistor instead of a choke. Chokes become less of an issue (although still have an effect) in these smaller amps.

The 6CA4 will not raise the voltage like the 5AR4. And the 6CA4 will have more sag. According to Kenny Fischer the 5AR4 is going to be closer to the 1n4007 diode because it has less sag than its fellow rectifiers. What does that mean to you? More squishy-ness...less voltage. The original 18 uses the 6CA4.

HTH,
~ Ross