Vintage style 1974 Head Build with Push Pull Extra Gain Stage

[xenrelic]

Here's my second 18watt build based on a vintage model 1974.

When you pull the Normal Channel's volume control it cascades the Normal Channel into the Tremolo Channel via a DPDT switch to kick things up a notch. The DPDT switch basically adjusts the input impedance on V3's input grid for the Tremolo Channel from about 33K to about 500K and adds a 1M resistor between the output of the Normal Volume and the input grid of the Tremolo Channel. Thing kicks ass when cascaded and has such a beautiful clean tone too. I really like how a 10uF for V3's cathode bypass cap sounds when I'm in cascade mode, so I may add a second push pull pot to switch between the 47uf and the 10uF down the road.

Was able to source a Radiospares EL84 output transformer and I had a custom power transformer built by Pacific in Anaheim with the original 300v-0-300v secondary.

180ohm cathode resistor bypassed with a 220uF cap. Sounded best to me. We're biased at about 14W on some N.O.S. Mullard EL84's.

Preamp tubes are all N.O.S. Mullard 12AX7 and the Rectifier is an Amperex EZ81.

Electrical grade Paxoline board material milled on an EZTrak equipped Bridgeport. This material sounds great with every vintage style build I've used it with so far.

Made the Perspex front and rear panels as well as the cabinet logo on Adobe illustrator and had them UV printed and painted them with a vintage metallic gold mix.

Really stoked on the mini box cab. Makes it really easy to transport like a compact model 2061.

[Bieworm]

Did you just write that paxolin boards sound great?

[xenrelic]

Did you just write that paxolin boards sound great?

Yes, yes I did. If you experiment with different board materials in an amplifier circuit you'll find that they slightly affect the tone due to their electrical isolation and humidity resistance specifications. Some board materials have better electrical isolation and humidity resistance than others and therefore affect the circuit less. For instance Paxoline (Paper impregnated with phenolic resin) is seemingly darker/warmer sounding than the same circuit with G10 FR4 (fiberglass impregnated with flame resistant epoxy resin).

The same goes for Fender Fiberboard material and no board at all with everything wired true point to point. The same circuit with the Fender Fiberboard will sound darker/warmer than the one that has no board.

[JMPGuitars]

If the boards aren't faulty, there won't be an audible difference. If a board is faulty, there will be problems.

You can't make those claims without first testing every single component going into the circuits to be within 1% of each other, while making matching amps with opposing board material. Then give them equal break in time. Use the same exact tubes. Make recordings, and do double blind listening tests. etc. etc. etc. However, making everything match 100% to isolate the board material is nearly impossible.

They probably sound fine, but I'm not going to pretend anybody can hear board material. This sounds like another case of not understanding that correlation does not equal causation. I don't mean any offense by this, it's an exceptionally common mistake.

It doesn't matter what material you use as long as it's fireproof and rated for the voltage / application.

[xenrelic]

If the boards aren't faulty, there won't be an audible difference. If a board is faulty, there will be problems.

You can't make those claims without first testing every single component going into the circuits to be within 1% of each other, while making matching amps with opposing board material. Then give them equal break in time. Use the same exact tubes. Make recordings, and do double blind listening tests. etc. etc. etc. However, making everything match 100% to isolate the board material is nearly impossible.

They probably sound fine, but I'm not going to pretend anybody can hear board material. This sounds like another case of not understanding that correlation does not equal causation. I don't mean any offense by this, it's an exceptionally common mistake.

It doesn't matter what material you use as long as it's fireproof and rated for the voltage / application.

I've definitely heard the difference when I was experimenting with different board materials using the same exact parts moved from one board to the other with lead wires that had temporary clips on the end to attach to the turrets. You can call it subjective and perhaps it is, but I prefer the tone of certain materials for certain amps and in these vintage Marshall style builds I tend to learn towards the paper phenolic boards yielding a superior tonal response from my listening results.

That being said, I've done a similar experiment with a high gain single channel build of mine and I did not prefer the paper-phenolic in that amp, I preferred the brighter sounding glass-epoxy FR4 in that one, so not one board material is the best for every application in my experience.

[JMPGuitars]

If the mojo makes you happy, go for it.

[xenrelic]

If the mojo makes you happy, go for it.

I guess the same goes for resistor material and capacitor material. Some people say the material makes no difference and it's all in the value of the component, but the different materials sure do sound different to me. I've even heard a difference between plug ends that used a copper core and ones that were just nickel plated brass and the brass does sound brighter than the copper core plugs.

Considering that on the atomic level everything is energy vibrating at different frequencies, I think it's very much the sum of all of the parts that yields the end result, even down to the insulation and plating of the wire you use, the metal the turrets/eyelets are made of or if you're using a paper layer wound output transformer vs. one wound on a nylon bobbin. It seems that every piece makes a little bit of difference that adds up in how the amp will respond tonally.

[Bieworm]

Although I’m a non believer of things going this deep I am aware some people have a dog’s nose, where I can’t imagine the scent of it. I consider myself very lucky in that regard. I think I can build my amps for way less money and trouble that way. But hey, some swear there is a god, I simply don’t.
No offence man, but I’m not along with this.

[Crabman]

Mojo takes a hold of some folks more than others. I don't buy it. Some time ago I experimented with replacing Sozo caps in my Trinity 18 watt with cheap Chinese poly caps. Couldn't hear any difference .. but just maybe the Chinese caps sounded a bit better!

Change the speaker type and voila .. now we are talking about large tonal variations.

[xenrelic]

Mojo takes a hold of some folks more than others. I don't buy it. Some time ago I experimented with replacing Sozo caps in my Trinity 18 watt with cheap Chinese poly caps. Couldn't hear any difference .. but just maybe the Chinese caps sounded a bit better!

Change the speaker type and voila .. now we are talking about large tonal variations.

That's cool that you like the more transparent and modern tone of the Chinese Poly's. It's definitely a thing and VOX uses them in their newer AC amps from the Chinese factory. I personally think they sound too transparent and harsh, but there's a lot of people that love them. Fender uses a lot of that stuff too now, but from that Illinois Capacitor (IC brand) company now owned by Cornell Dubilier. I think it makes the reissue amp sound too bright and harsh in the overdrive, but you can get some great clean sounds from them when using the reverb and the right speaker combination.

I hear quite a bit a difference between Polyester Film and Foil SoZo caps and other types like polypropylene and metallized polyester. Mainly in the warmth and character of how the amp responds to playing.

SoZo Mustards, old school Mustards and those Fender Blue Molded caps sound like they have a distinct warmth and overdrive character, not too harsh but pleasing overdrive like the difinitive 60's and early 70's tones when the amp is pushed, plus the cleans are soulful and lush with vibrant tone.

6PS Orange Drops have a lot of the same qualities as the SoZo's but more detail and tighter response, slightly more hifi, but still great warmth and soulful feel to them. Slightly sharper in the overdrive character, but that can work to our benefit when placed early in the signal path as the V1 coupler to the next gain stage or for the tone stack if you want to edge out some muddiness that you might find with SoZo's in that area.

CDE DMT Capacitors have all the tonal warmth of standard Polyester Film and Foil, but damn they seem to have managed to get them to sound a bit more transparent and hifi, not as much coloration as the previously mentioned. Very cool for the phase inverter input grid capacitors if you want to dial back the coloration a bit before the plate couplers pass the signal to the power tubes.

Metallized polyester caps like the Mallory 150M's immediately sound brighter and tinny compared to the Sozo's, but that creates a meaner texture for more aggressive overdrive tones with more transparent clean tones. I definitely hear the late 70's through the 80's rock tones with them. These can help out as the phase inverter plate couplers when mixed with SoZo's or 6PS if you need a bit more transparency there for higher gain stuff that can get muddy as it hits the phase inverter. Polycarbonate is very similar, transparent but not as tinny, has rounder feel and works really great for the plate output couplers on the phase inverter for high gain stuff.

Polypropylene film and foil sounds more hifi than polyester film and foil and metallized polyester, more full sounding than metallized and more modern than polyester film and foil with crisper highs and tighter bass response. Great blend of rock and metal with a very distinct and lush clean tone. Not over the top aggressive, but it can definitely handle more aggressive types of music well with little hints of warmth that you'd find in the early 70's, just a bit different. These caps remind me of the late 90's when people were using a lot of Mesa amps.

Metallized polypropylene has a similar character to the metallized polyester but more aggressive texture for even higher gain metal stuff. Outstanding note separation great bass response too for extra higher gain tones, not as tinny sounding as the metallized polyester, I can tell there's a hifi edge and character to it that the polyester does not possess. I can see this style of capacitor being very popular for high gain djent style metal amps of the current era.

Then there's stuff like the Sprague Paper In Oil that have this wild vibrant organic tonal coloration to them that makes me feel like I'm playing guitar through an old McIntosh tube amp. That's a strange bird for sure and I bet 50's style music dudes, surf rockers and blues player would love those capacitors for their tonal coloration.

I've even tried newer capacitors for the hifi range like Poly Films with Oil Impregnated Paper rolled with Copper or Silver Foils and these I didn't like as much as the Sprague Paper In Oil capacitors, but damn they sound pretty cool and have amazing note separation and add some warm dimension to the tone. Early Sprague's have more coloration character though.

[JMPGuitars]

I won't disagree with you there; capacitors can certainly impact the sound. Generally not as much as a speaker change will though.

My experience has been that good quality caps sound good. As you said, different types do affect the sound differently, but for me, it isn't generally drastic change as long as the quality is good.

I made this capacitor comparison test a decade ago. It's not quite scientific, but it gives you an idea:


For me personally, I liked the Mallory caps the best on that test. I still think the biggest benefit for the SoZos is knowing which is the foil side for people who don't have a scope.

Thanks,
Josh

[xenrelic]

I won't disagree with you there; capacitors can certainly impact the sound. Generally not as much as a speaker change will though.

My experience has been that good quality caps sound good. As you said, different types do affect the sound differently, but for me, it isn't generally drastic change as long as the quality is good.

I made this capacitor comparison test a decade ago. It's not quite scientific, but it gives you an idea:
https://www.youtube.com/watch?v=kUDhBnMSuG0

For me personally, I liked the Mallory caps the best on that test. I still think the biggest benefit for the SoZos is knowing which is the foil side for people who don't have a scope.

Thanks,
Josh

I hear pretty significant differences in that test between each type. Actually preferred the fuller clean tones with the Orange Drops. The Mallory caps had the most raging and bright drive tone though. Sometimes I like to put Mallories, or actually Ero MKT1813 caps to be more precise throughout the preamp, Sozos on the tone controls and then beef up the last output couplers with the 716P Orange drops. This gets a really great tonal combination going on.

You don't really need an oscilloscope to determine the outside foil. A simple audio interface with a DAW that has a level meter will work too. You can just crank the preamp on your audio interface to a readable level while holding the capacitor and switch the hot and ground clips on the capacitor leads until you see on the level meter which orientation is quieter and then mark the outside foil to whichever lead the ground clip is on with the quietest orientation.

[JMPGuitars]

That's a cool tip! I've got a nice scope, so I've never tried anything else. If you feel like it, start a new thread with the title something like "Capacitor Foil Direction Without a Scope" - and include some how-to photos.

Re: my demo- yeah, lots of people had different opinions on what they thought was better. That's all subjective; to each their own.

Thanks,
Josh