capacitors

[8urchevy]

Hello everyone. I just joined up and have begun planning my first build. I am in need of advice on a couple topics. First, what type on capacitor construction is preferred as a coupling cap, filter cap, etc and why? I am trying to understand the reasons in types used in different sections of a tube circuit. Also, I see there are several sites online to source parts from, but I am curious as to which are the best to deal with. Finding the values I need is seeming to be a bit of a chore. Thank you.

[Daviedawg]

Welcome to 18 Watt. This is a question no one has a definitive answer to, just an opinion. The electrolytic filter caps should be good quality as they are at the heart of the whole amp. Poor power supply characteristics may result in poor tone. In my view money spent there cannot be wrong.

For the remainder it depends if what you want is a vintage replica or a modern version. That applies to resistors as well. I used orange drop caps. Mainly because first priority was reliability. But I used carbon comp resistors hoping for some old school outcomes.

But I agree with you about sourcing. For me the hardest part of the 18 watt build was making up my buying list. It took me ages to settle on it.

Dd

[JMPGuitars]

For the electrolytics, some people think it's important to stick to 1 brand for 1 build to keep consistent... That's also a matter of opinion. It does look nicer in photos. The Sprague Atom series stuff that looks vintage is one case where spending more doesn't get you anything more than mojo, but they're perfectly fine capacitors.

I made a video comparing capacitors you can view here: https://www.youtube.com/watch?v=kUDhBnMSuG0 - it compares Orange Drop, Mallory 150, and SoZo in three otherwise identical builds. Not 1000% scientific, but close enough for a subjective test like this.

There's plenty of great sources out there. I use Mouser for a lot of the basic components. AmplifiedParts/CE is good, MojoTone, Trinity, GDSamps.com (great transformers & kits), Watts Tube Audio... I also made a list of resources for tools and such in the download section of this site.

[8urchevy]

Thanks guys. Do you use electrolytics for all caps or just in certain areas of the circuits? If you use different types of caps through the circuit could you specify what type and where? This is where I am hung up in my ordering. Thanks again

[JMPGuitars]

Thanks guys. Do you use electrolytics for all caps or just in certain areas of the circuits? If you use different types of caps through the circuit could you specify what type and where? This is where I am hung up in my ordering. Thanks again

Only in certain areas. Before you order anything you should familiarize yourself with reading a schematic/layout. You should also have a specific layout/schematic in mind, preferably from the downloads section of this site.

In a layout, the electrolytics are more obvious, in a schematic the main difference is that you'll see a + symbol notating the polarization of the capacitor. (Just to be confusing, there are some instances where electrolytics and other types are interchangeable, and not all electrolytics are polarized +/-, but I wouldn't worry about that yet. )

Follow the layout/schematic of your choice and you should be fine. If you're not sure about what you should order, link the schematic/layout you're using, and share your questions here. We're happy to help.

[8urchevy]

Thank you JMP. I am very familiar following schematics as I am an electrician, but I reckon my knowledge of amplifiers is limited to knowing what type of caps to use where and why. I actually downloaded a schematic and BOM from here that I am following. Some of the caps have EL, OD or CD after the values. I believe the EL are electrolytic and CD are ceramic disc, but can't for the life of me decipher what the OD is. I appreciate all your guys' help. So far I have the chassis, power and output transformers. They are out of something that I am unsure of. I stripped the chassis down and tested the transformers and they are good. Heavy little suckers.

[JMPGuitars]

Which schematic are you using?

OD to me sounds like Orange Drop, which is just a brand. You don't need to stick with that brand, it's a preference. OD caps are more typical of American voiced amps.

With amp schematics, the types are drawn in. Whether they're American or European symbols is the main difference you'll see here (I've not seen any Japanese schematics with these amps).
This web image shows the common symbol types:

66269f6d858311a73e6e9f28db53afea.gif

The schematics on this site show where the electrolytics are used. They're generally used for filtering and decoupling. You wouldn't want to use an electrolytic somewhere that the schematic doesn't call for one. If for no other reason, because electrolytics have a shelf life.

[8urchevy]

Thank you. That is extremely helpful. I should have known the OD was orange drop. Blonde moment I guess. I now have what I need to proceed with my order. The schematic I got from this site is the 18watt schmatic 08-28-03. I hope that helps. It has pedalmonkey.com on the bottom of it.

As variation of this schematic I want the higher gain channel to be switched with a pedal instead of the second input. I also plan on adding a reverb tank to it as well. I have a feeling this is going to be a lifelong passion of building amps. lol

[Daviedawg]

That is the standard schematic as it were, to give a close to original amp. It will give you a very good amp.

Will your reverb be valve or solid state driven? If valve you will need to consider the effect on your power supply, especially the transformer.

I considered the same option but in the end chickened out and built a stand alone clone of the Fender 63 reverb. But you should not take that as advice against doing it. I look forward to hearing how it progresses.

Dd

[8urchevy]

There isn't any numbers or markings anywhere on the power or output transformers I have. If I were to add reverb the additional current draw is definitely a consideration as I would want it tube driven. With no ID on the transformer I think I will play it safe and leave the reverb out.

[Crabman]

A decent source of inexpensive capacitors and resistors can be found here:

https://www.justradios.com/

Your filter capacitors will generally be electrolytic and cathode bypass and coupling are usually poly types. Whether you opt for polypropylene or polyester comes down to preference.

I am at a point where I have removed the venerable Sozo caps from my Trinity18W build so that I have flexibility to swap in different values of cap at various points in the circuit from a collection of much cheaper polyester caps that I acquired from Justradios. I can confirm that I can't detect any detrimental effects to the tone by swapping brands. So the Sozo mojo may just be hype .... I may have to record it and convince myself that way to be sure.

[AussieTim]

Hi Guys
I,m planning out a couple of builds the first is a rehash of a homemade 18 watt amp that I have acquired. My first build was a 5E3 that worked out pretty good and an overhaul of a 1960s Australian built Bassking by Rex amplifiers which after replacing the caps and corroded jacks resistors etc sounds a million dollars {anyone interested in old Australian amps this is a good site, https://ozvalveamps.org/}
All that aside the questions that puzzle me is about capacitors, which type to use and where. JMPs post and youtube clip has been a good find. I am still a bit confused and at the forefront of this confusion is usage of Silver Mica capacitors I know one guy who swears by them but have not heard much about them apart from them being offered by most amp part suppliers.

[crgfrench]

FWIW:

Filter Caps:
1) Sprague Atom Electrolytic TVA1803
2) Tube Amp Doctor Electrolytic (I believe F&T manufactures these)

Coupling Caps:
1) Mallory 150 series
2) Sprague(now CDE) Orange Drop 715 series

Bright Cap:
1) Xicon Silver Mica

Tone Cap:
1) Mallory 150 series
2) Sprague(now CDE) Orange Drop 715 series

Cathode Bypass Caps:
1) Sprague Atom TVA1308
2) Fischer & Tausche (F&T, via Tube Amp Doctor -- some values available non-polarized)
3) Mojo Dijon

Power Tube Bias Resistor:
1) Ohmite Brown Devil Wirewound air-core
2) Dale Wirewound solid core
3) Xicon "Cement" Wirewound Ceramic (I never tried these)

Boutique builders also seem to like Sozo and Solen caps but I have never tried them.

[JMPGuitars]

All that aside the questions that puzzle me is about capacitors, which type to use and where. JMPs post and youtube clip has been a good find. I am still a bit confused and at the forefront of this confusion is usage of Silver Mica capacitors I know one guy who swears by them but have not heard much about them apart from them being offered by most amp part suppliers.

Look at the layouts on this site. You'll see where different types are used. I usually use Mallory 150M or SoZo caps for all my tone/coupling caps, except where the silver micas are called for (usually on the tone knob(s)). Look at this layout as an example: files/JMPGuitars_18_Watt_Lite_2b_Layout.pdf

Filter caps are generally polarized electrolytics. I usually use F&T, JJ, or Sprague Atom for those...Nichicon also makes some good electrolytics.

For resistors I use Xicon or Dale.

Thanks,
Josh

[AussieTim]

Hi I have decided to build a Trinity Siii amp from scratch Ive bent up the chassis getting my BOM together and making the turret board. Im using some parts from an amp I purchased as an unfinished project but Ive decided to strip it down and start again has GDS trannys and some good orange drop caps etc.
One thing I have noticed that the plexi and the siii are very similar apart from about 3 to 4 capacitor values, is switching between capacitors a viable option? if so how do I go about it? do I use relays and switch in extra values or would it be better to switch a whole lump of the circuit. Just curious as whether this is a viable idea

[zuceno]

Things I feel an urge to speak about -

I don't remember why - but I do remember being told that using electrolytics as stage coupling caps is a BAD IDEA. I use polyester there, more out of habit than anything else.

Nobody mentioned that there are alternatives to using electrolytics - paper in oil types, and big PTFE types. These score over electrolytics by not deteriorating with age, although the paper in-oil types can be electrically leaky. OTOH they tend to be big and heavy things, a 20uF PIO smoothing cap can resemble a motorcycle battery in size and shape. And they are expensive, compared to electrolytics.

When you have a non-polarised cap, there is nonetheless a "way" to fit it into the circuit. Turn an amp up and put a guitar lead into it. At the guitar end, hold one cap connection and touch the other to the tip of the jack plug. The amp hums. Turn the cap around, hold the connection and touch to the jack plug tip. This time, the hum is either louder or quieter than the first time. When you have worked out which way round the hum is least, mark the end of the cap which was between your fingers, and put the signal in that end when you build.

[JMPGuitars]

One thing I have noticed that the plexi and the siii are very similar apart from about 3 to 4 capacitor values, is switching between capacitors a viable option?

Caps in parallel are added together. For example: 1uF + 1uF in parallel is 2uF. So let's say a specific discrepancy is that one circuit has a 2.2uF cap, and the other has a 1uF cap. You could put a 1uF in the circuit, and another 1uF on a parallel switch to add the values together to get close to the 2.2uF in the other circuit.

That's the theory of it. The reality of it is that you're better off testing different values and sticking with what you like. There's very few instances that you might actually want to keep something switchable in there (and you probably don't want 10 switches on the amp). Then you also need to consider noise issues including switch noise, and potential unwanted oscillations if the placement of the leads and switch aren't ideal.

Thanks,
Josh

[AussieTim]

Thank you Josh I appreciate the time and effort that you put into answering posts on this forum, as well as the quality of your replies.
Multiple switches is one reason I am rebuilding from scratch. While they are fun to look at and play with the result is waaayy too much sizzling bacon noise which seriously detracts from the tone of the amp.
Having said that I was still wondering if a limited range of switching done well would be a benefit. I am going to laser engrave the fascias so at this point I am not completely committed to the final look and features, at the moment I am pretty sure that it will be a fairly standard build, but I am at the research phase asking lots of questions reading lots of forums and books and gathering my BOM before settling on the final build

[JMPGuitars]

Having said that I was still wondering if a limited range of switching done well would be a benefit. I am going to laser engrave the fascias so at this point I am not completely committed to the final look and features, at the moment I am pretty sure that it will be a fairly standard build, but I am at the research phase asking lots of questions reading lots of forums and books and gathering my BOM before settling on the final build

It could be fine if it's one or two switches, and you set them up well (whether or not you need shielded wire you'll find out). Either way, you should experiment with the values of the caps in question and see what you actually like before deciding on whether or not you should bother with switches.

BUT- simply changing the cap value between two schematics may not be what you're looking for. Take a look at the Superlite TMB schematics and you'll see a bright/fat switch which you may find much more useful. I've used that in lots of builds, and I included it in my new design for an EF86 amp I'll be sharing soon.

When you say you're going to laser engrave, do you mean pay somebody or do it yourself?

Thanks,
Josh

[AussieTim]

I have access to a laser engraver at the school that my wife works at, she works as the supplies and equipment coordinator in the tech studies area which can be useful at times.