Using 20uf filter capacitors instead of 16uf with 5Y3GT

[tubedood]

Hi all!

Is it ok to use this setup in my tweed Princeton 5F2-A project for the filter caps? Stock would be 16-16-8-8 (450vdc)... I happen to have a few 20uf so either 20-20-8-8 or even if its a benefit I can do 20-20-10-10. Is that too much capacitance for that 5Y3?

As always thanks for your time and valuable suggestions!

Dale

[mozz]

22uf is even good.

[tubedood]

Cool... I was concerned with that whole First node capacitance thingy with the 5Y3

[Justin Thomas]

Champs have been running with 20-20-20-20 or 40-20-20-20 for decades. Just use a nice quality 5Y3-GTA.

Justin

[tubedood]

Thanks guys! This goes hand in hand with my earlier question of using the GZ34 in place of the 5Y3.. I will stick with the 5Y3 for now! The tube I am going to use is an old GE... from 1958! Hopefully its up to the task. I will use the 20-20-10-10 caps to start with. What benefits are the extra capacitance providing us? A google search has so many opinions its hard to get a feel of what one can expect regarding power filter caps.

Dale

[Chuck H]

+1 on Justin's post. You can go higher. Really. Remember that caps from back in the day were rated at something like +80% to -20%. Today's caps are almost invariably close to spec. I've used 47uf for an input filter in silver face Champs without consequence to the 5y3 where the plate voltage was eating the 6V6's for lunch. I didn't find a max spec for the 5y3 but the highest value "typical operating conditions" spec I saw was 32uf. And that was a vintage spec sheet. So... 32uf + 80% (typical vintage cap spec) would be 57uf. I'm sure no spec sheet says that, but I do know I've used 47uf without a problem. In fact, considering modern caps are typically close to spec and any single ended amp can really use the filtering I would recommend it

[tubedood]

Great to hear Chuck... I'm glad I asked this. My turret board I made mostly to the 5F2-A layout except I added a few extra turrets to set it up with a few preamp bypass caps to switch between (off topic but should I have that feature on V1A or B? Per the schematic V1B presently only has the cathode resistor and the feedback loop). That gives me 4 filter caps to work with. Whatcha all think is a good quartet of capacitors in there? I can always pick up something if I need it!

I am all ears
Dale

[Justin Thomas]

And, please ignore that last Quote on Chuck's signature! He took it out of context...

PS: I like F&T caps. Not hideously expensive, smaller than Atoms, and I do appreciate the classier "dressed-up" look. I don't know that they're "better" than other brands, but, they ARE German, so...

Jusrin

[cerrem]

F&T caps have a good track record for reliability as well as sounding good in guitar amps...
20uf should be fine....
If you look up the data sheets for the rectifier tube....it will show the safe operating ranges and limits to what filter capacitance works at given operating conditions....
The data sheets are derived from PEAK currents....
In-Rush current into a empty filter cap is one major concern.... This is where both Peak current and time duration are of concern...ie conduction angle will start at 45 degrees then decrease over several cycyles till steady state... This is where rectifiers can fail quickly...
Then in steady state operation, too big of a filter cap will shorten the conduction angle of the rectifier tube...this will make for very high current peaks during re-charge....that can also shorten the life of rectifier..

[tubedood]

So with a tube complement of 1 12ax7, 1 6v6 and the 5Y3 providing the power I will increase the 16-16-8-8 to … Hmmmm 20-20-10-10? 20-20-20-20? Should my dropping resistors stay the same as stock.. with a 10K 2 watt between the two big and 2 small pairs of filter caps and a 22K 3 watt between the 2 smaller filter caps?


Thanks again for listening to my questions!

[Enzo]

You are focusing too hard on the numbers. 16 or 20 is irrelevant. As CHuck mentioned earlier, in those days the caps had tolerances like +80/-20%. That means a 16uf cap could measure anywhere from 28uf to 12uf and still be on spec. Modern 20uf caps are probably fairly close to 20uf.

Changing the cap value should have no affect on the dropping resistors. All the cap does is smooth out the DC, it doesn't change the voltage of it.


20-20-10-10 or 20-20-20-20, use whichever you have on hand.

The first two section are usually for the plate and screen nodes, and so would have to most reaction to sag. the later ones are for the preamp and are largely there to decouple, so the value is less important. At least in my view.

[tubedood]

Understood Enzo thanks. I never knew that the caps from yesteryear were so wide in the tolerance! I will check what I have, I am sure I have enough to put the amp together with considerably more filtering than the original 16-16-8-8,

Thanks guys

Dale

[Enzo]

Look at your 5F2A schematic, upper right in the notes. All voltages + or - 20%. There is nothing precision in a guitar amp. it is good to keep that in mind.

[SoulFetish]

There is nothing precision in a guitar amp. it is good to keep that in mind.

especially my playing these days

[Chuck H]

And!..

If you don't build/repair much and have electrolytic caps "on hand" you should take into account something I mentioned earlier. Electrolytic caps actually have a shelf life. They age faster unused than they do in circuit. I buy fresh caps for every build. If I did repairs I would literally write dates on my electrolytics and toss them after two years. Doing otherwise (IMHO) means risking problems that you don't want to have for the $$$ new caps cost. I literally have two electrolytic caps in my inventory right now. If they don't get used by December I'll toss them in January. Freshly purchased caps is NOT a guarantee, but it's likely better than using electrolytics you know to be many years in a drawer unused.