Wanting to Build an EL84 Amp, but which one?

[FlaCharlie]

@FlaCharlie. I used a 50 ohm and 470uf cap for the last filter stage. As suggested. I am going to leave it out initially and add it if I feel it is needed.

So Im looking at parts now. Just for my own sanity and to keep tin foil off my head. What kind of caps am I looking for to build this PS? Polarized Electrolytic whats?

For electrolytics (which are polarized) look for caps rated at 105 degrees for 10,000 hours. Any of the major brands should do fine . . . Nichicon, Panasonic, Cornell-Dublier, Elna, whatever.

If you're going to use one or more film caps . . . for something really small value, like the 'small c" discussed earlier, just get something that would normally be used as a coupling cap rated at 630v.

If you want to use film caps instead of electrolytics, check out the Panasonic EZPE series:
https://www.digikey.com/products/en...ity=0&ColumnSort=0&page=1&stock=1&pageSize=25

 

[macaltec]

Im having trouble finding the caps I need. WJOE doesnt have most of the values I need. Mouser seems astronomically high and not much seems to be axial in the values I need. Im also confused now about the "small c" is supposed to be polarized or not? I thought only electrolytics were polar?

 

[macaltec]

The only non polar cap I see is the coupling cap in the SEUL EL84.

 

[Squidward]

Here's a search on Mouser for a 1.5uF motor run cap:

https://www.mouser.com/Passive-Comp...or-Run-Capacitors/_/N-fb8xk?P=1y92dduZ1z0wqtr

C1 (the "small c") could be a Motor Run or a Film. I'd avoid an electrolytic for that position. If the motor run has an AC rating, multiply it by 1.4 for DC rating. If you use film get one of the 630V rated ones like FlaCharlie said.

You can get motor run caps all over the place. The only disadvantage to using them is their size.

 

[macaltec]

Is it supposed to be polarized?
Im not finding:
220uf 450V
470uf 450V
What about the 40uf to ground in the audio circuit?

 

[FlaCharlie]

Im having trouble finding the caps I need. WJOE doesnt have most of the values I need. Mouser seems astronomically high and not much seems to be axial in the values I need. Im also confused now about the "small c" is supposed to be polarized or not? I thought only electrolytics were polar?

I usually use Digi-Key because of the free shipping option, see my post with link earlier in this thread.

For such a small value cap (the small c) film caps, which are not polarized, are very affordable so there's no need to use an electrolytic, although you could. Motor run caps are film but they are physically large because their normal use puts a lot of stress on them. They can be used anywhere in your PS if you have the room. Here's a good source: https://www.surpluscenter.com/Electrical/Capacitors/
I've never bought any from Digi so I don't know how their prices compare if you take free shipping into account.

I'd probably just use a regular 630v film cap, such as you would use as a coupling cap, in the small c position.

Here are some 220uf 450v with the ratings I suggested: https://www.digikey.com/products/en...tity=&ColumnSort=0&page=1&stock=1&pageSize=25

And a 470uf 450v: https://www.digikey.com/products/en...03a&quantity=&ColumnSort=0&page=1&pageSize=25

These are all what's known as "snap in" style caps. The connectors are short but they're not hard to work with. If you use terminal strips, they are spaced so that you can solder them to the tabs on the strip. You could also mount them in other ways in which case you just put a little bend in the connector and solder a wire to it..

I forget which schematic you're building but I would guess the 40uf would be a cathode bypass cap. Maybe you could post or link to the schematic so we can be sure. Typically, you would use an electrolytic there. Voltage rating would be much lower (if it's a cathode bypass) and you're not as likely to find something in 40uf so go with a 47uf. Again, post a schematic so I know if that's what it's used for in the circuit.

Axial caps are not nearly as common as radial or snap in style and they will be more expensive, usually.

 

[macaltec]

My head is spinning. Thank you all for tolerating me here. I have one simple question I need answered before my mind will allow me to absorb anything else.

Do I NEED to use polarized caps to build my power supply?

 

[FlaCharlie]

My head is spinning. Thank you all for tolerating me here. I have one simple question I need answered before my mind will allow me to absorb anything else.

Do I NEED to use polarized caps to build my power supply?

No, you could use all film caps. But they will take up much more space and be more expensive. The higher values will be much more expensive. Also, you may not be able to get large values (uf) in film.

Compare the prices and dimensions of the electrolytics I linked to the Panasonic EZPE series, which I also linked, or to the motor runs.

As you can see, they are not available in such high values. BTW, motor start caps should not be used, only motor run caps.

 

[macaltec]

Here is what I am going to build.



Are there any polarized caps on this schematic? I know what the symbols say but I have been second guessing what I thought I knew all afternoon.

 

[Squidward]

You can use a non-polar cap in a polar position. The opposite is not true.

The schematic calls for one non-polar cap, the coupling cap. You must use a non-polar cap there.

The rest of the cap positions show a polarity relative to ground. As you can see, if you have a polar cap, you should put the negative leg to the ground side of the circuit.

If you have a non-polar cap and you wish to use it in one of those positions, you may use it in any orientation that you wish.

Motor run, film, PIO, and other caps are often non-polar. Electrolytics are often polar.

 

[macaltec]

Thanks guys. Squid, that is especially direct and helpful info. I will be saving a screenshot of it for future use. I was really hung up the "polarized detail". I will attempt to put it out of my mind. Perhaps a tin foil hat is in order.

 

[Squidward]

The design you are building really only has two critical cap values: the coupling cap and the "small c" in the power supply. The rest of the values can be used as estimates.

The 40uf. driver C+ power supply could be 22uF, 33uF, 40uF, or anywhere in that ballpark.

The 330uF cathode bypass cap could be 220uf, or 440uF if you had those around and wanted to try them.

The power supply stages could be 100uf-330uF. Hell, if I were building it I'd be tempted to use a ~60uF motor run for each of these stages, myself. If I heard hum later I could easily bypass my motor run with a higher value electrolytic. Then you could brag you had an electrolytic bypass cap. Audiophool minds would be blown!

 

[FlaCharlie]

Here is what I am going to build.

View attachment 1439110

Are there any polarized caps on this schematic? I know what the symbols say but I have been second guessing what I thought I knew all afternoon.

There are three caps shown in this part of the schematic. The 40uf cap is a polarized electrolytic and is part of the power supply but, as I said, just use a 47uf 450v part. You could use a film cap here if you want.

The 330uf, which is the cathode bypass cap, doesn't need to be high voltage. I'd go with 25v, although you could probably get away with 16v. It's shown as a polarized electrolytic but you could use a film cap there too.

The 0.22uf is the coupling cap. That needs to be a non-polarized cap. Either 400v or 630v should do fine.

@Squidward is correct about most of the values not being critical.

 

[macaltec]

I am starting to see how these values can be manipulated. I am typically a detail guy, if it says 100.234987uf them Im gonna flip out when I cant find one.

Im trying not to order from more than 2 or three places. Only thing I havent found is the 200K Carbon Comp fb resistor.

 

[Squidward]

If you fuss with the 200K value, keep this in mind: higher value is less feedback. 180K and 220K are close enough. Resistance is also additive, 100K + 100K = 200K.

Sometimes buying 10 100K resistors is cheaper than alternatives, as well.

 

[macaltec]

OK, I have the PS more straight in my brain and the components for the audio circuit sorted out. I saved a bunch of money (insert GEICO joke here) by having the iron for my LCLC PS and my Dad wants an amp and seems to have an open wallet (which is very rare). So, I am going to build this amp for me and the RH84 for him.

 

[Squidward]

Let us know when you want to know how to implement the UL/triode switch for the KG-84.

 

[macaltec]

Damnit, where is the switch in the schematic?

I am down to asking what kind of wire and where to buy it? How many different colors and sizes. Solid or stranded? Special insulation, copper, silver. That kinda stuff. I am already placing orders with Mouser, WJOE Radio, Tube Depot and Edcor.

 

[FlaCharlie]

OK, I have the PS more straight in my brain and the components for the audio circuit sorted out. I saved a bunch of money (insert GEICO joke here) by having the iron for my LCLC PS and my Dad wants an amp and seems to have an open wallet (which is very rare). So, I am going to build this amp for me and the RH84 for him.

Sounds like a plan. Transformers are typically the largest single expense when building from scratch.

 

[Squidward]

Get a DPDT (2P2T) switch rated at 250VAC or higher. Don't skimp on the switch, I've had them smoke before. Connect the output to pin 9 (G2) of the EL84 with a 100 ohm resistor. Connect one input to your 1.2K resistor, this is the UL side. Connect the other to your EL84 screen (pin 7), this is your triode side. Do this for both channels.

The only extra parts you need are the switch, and resistors.

If you're not sure about which switch to buy, run it past us here.