I'm tired of anemic guitar amps!

[toobfreak]

JHS Moonshine. Made for guitar, but turns out to be great for adding a bit of anger to a bass.

BTW, OC, I don't care what anyone else here says, you have a great collection of gear and I loved your photos!

 

[Orangecat]

BTW, OC, I don't care what anyone else here says, you have a great collection of gear and I loved your photos!

You should see the guitars and fuzz pedals....

Concept guitar built for this no-name dude:

 

[toobfreak]

You should see the guitars and fuzz pedals....
Concept guitar built for this no-name dude:
View attachment 1155596

Wow! Small world. Devadip.

 

[Orangecat]

Wow! Small world. Devadip.

I spent many years in LA chasing rainbows. Ended up with some really cool gear. Got my 57 tweed champ from Kevin Martin, used all over the big Candlebox album.

 

[toobfreak]

I spent many years in LA chasing rainbows. Ended up with some really cool gear. Got my 57 tweed champ from Kevin Martin, used all over the big Candlebox album.

That is what drew me into the pro music circuit. I've never been much of a player myself--- took guitar at age ten but got interrupted by a health issue, then got interested in percussion. But in the mid-70s, I went backstage to meet a friend whom I was a fan of, while there, met another guitarist who was opening for him, and he and I struck up an instant friendship over our mutual love of hot rods.

In the intervening years our friendship grew, we stayed in touch, I eventually took up a few electronic music projects for him involving one errant effects box that had crapped out on him and another effects box I essentially redesigned from the ground up for him.

 

[Fort Fun Indiana]

I just auditioned the PRS MT100 amp.

Meh.

3 amps in one is pretty cool. But FFS, put a master volume control in the final stage, not just one on each channel.

 

[Orangecat]

I just auditioned the PRS MT100 amp.

Meh.

3 amps in one is pretty cool. But FFS, put a master volume control in the final stage, not just one on each channel.

I used to have a PRS Harmonic Generator head. Lit up pretty, but not so great sounding (solid state). I still have one of those HG412s, though. Great cab.

 

[toobfreak]

Lit up pretty, but not so great sounding (solid state).

No wonder. These days, they've made some advances in forcing transistors to be more analogous, but generally, traditionally, while real music is analogous--- the waveform transitions from zero to its amplitude waveform then smoothly back to zero, transistors tend to truncate the attack and decay slope of every waveform creating nothing but ear-bleeding odd harmonics in the process.

 

[Orangecat]

No wonder. These days, they've made some advances in forcing transistors to be more analogous, but generally, traditionally, while real music is analogous--- the waveform transitions from zero to its amplitude waveform then smoothly back to zero, transistors tend to truncate the attack and decay slope of every waveform creating nothing but ear-bleeding odd harmonics in the process.

Dumble used to say that fragile harmonics survive better in a vacuum tube than in a solid-state crystal matrix.

 

[toobfreak]

Dumble used to say that fragile harmonics survive better in a vacuum tube than in a solid-state crystal matrix.

Well, that is true even if the THD and other figures for solid state suggest otherwise, for complex reasons.

Back in the 1980s, a friend and I proved conclusively that distortion figures are meaningless. Greater feedback improves lowering distortion yet sucks the life out of an amplifier necessary to give it musicality.

We ran tests on circuits producing upwards of 20% THD measured rms, not 0.002% as is common, and the damned thing rocked ass, sounding better than anything in the stores.

 

[Orangecat]

Well, that is true even if the THD and other figures for solid state suggest otherwise, for complex reasons.

Back in the 1980s, a friend and I proved conclusively that distortion figures are meaningless. Greater feedback improves lowering distortion yet sucks the life out of an amplifier necessary to give it musicality.

We ran tests on circuits producing upwards of 20% THD measured rms, not 0.002% as is common, and the damned thing rocked ass, sounding better than anything in the stores.

I'm more of a player/tinkerer than a technician. I just know that tubes feel better and analog sounds better.
I stick to passive electronics, for the most part. Here's a nifty rewire I did on a 50s LP Jr:

 

[scruffy]

I'm more of a player/tinkerer than a technician. I just know that tubes feel better and analog sounds better.
I stick to passive electronics, for the most part. Here's a nifty rewire I did on a 50s LP Jr:
View attachment 1155697

Wow cool, old school capacitor.

 

[Orangecat]

Wow cool, old school capacitor.

It’s a reissue Gibson bumblebee cap. Expensive little bastard.

 

[toobfreak]

I'm more of a player/tinkerer than a technician. I just know that tubes feel better and analog sounds better.

And I can tell you exactly why. Leave it to say that in part, digital is just an estimation of the original sound, reduced to the nearest codification. It takes at least a 20-bit (many say 24-bit) word length in order to even realistically approach true analog resolution. When they were inventing the CD (digital) record, Philips wanted to only go with a 14-bit word but to their credit, the other company involved (Sony) talked them into going with a 16-bit word and the S/PDIF format was invented! The good news is that you can hear the difference between tube and transistor--- a lot of people cannot even do that.

I stick to passive electronics, for the most part. Here's a nifty rewire I did on a 50s LP Jr:
View attachment 1155697

Ah! Nifty! A carbon resistor in a plastic body! Everything looks OK except those two blobby solder joints at top. Looks like you were soldering to a silver oxide battery. Those are cold solder joints and they will be resistive and will likely fail eventually as the metal they were soldered to wasn't hot enough to take the solder properly when applied.

 

[Orangecat]

Those are cold solder joints and they will be resistive and will likely fail eventually as the metal they were soldered to wasn't hot enough to take the solder properly when applied.

Yeah, I was working with an old soldering iron/shitty tip, and playing “operation” trying not to burn the edges of that 50s cavity. Gotta work with what you got.

 

[scruffy]

Well, I turned the amp on, it registered 570 volts, and it didn't blow a 2A fuse. But it popped at me after about 5 seconds, so I turned it back off. Probably a wire hair or a solder blob or something. I should have blown out the chassis with compressed air first. I'll take it to the studio tomorrow and test it outdoors with a long extension cord plugged into a fused power strip, don't want to risk burning down the house. Nothing burned, nothing fried, no melted wires, no visual evidence of any kind, but just in case...

Here's what it looks like now:

That little piece of PC board between the transformers was just a separator till I locked down the PT, I'll remove it tomorrow.

Underside:

Here's the power section:

We're going full wave into two 350 uF caps in series. The strip on top is the bias circuitry. The power chain isn't connected yet, wanted to make sure the B+ is stable first.

My old ham gear used to pop at me like that, the first time I turned it on. It wasn't a very loud pop, just a little one. Best be safe though. I figure, if it didn't blow a tiny fuse it's probably okay.

 

[scruffy]

Yeah, if you zoom in real close in the pic of the underside, on the first filter cap, you can see a tiny little wire hair right next to the red wire. That's probably what popped. I took the pics before turning the amp on. Whatever... it ain't there no more, I checked.

I'll look at the wiring under the magnifier before turning it on again. I'll bet it's fine though. The pilot light came on (and didn't turn off) so the heater wiring is good. B+ persisted even after the pop, so that's good too.

Meh ... y'know, you can tin that stranded wire and you still get wire hairs. Anyway, I need more parts, missing a bias cap and some 1 meg and 10 meg resistors. The reverb send is done except for the 1 meg on the grid. (I re-used the old reverb transformer, it tests good, and I'll check it out with a dummy load before connecting the tank). All the tube sockets still work, no solder plugs or anything. As soon as the amp stays on for 20 minutes i'll start wiring the power chain.

So far so good. By the way, AES is having a Labor Day sale, 20% off all JJ tubes. I'm gonna stock up, cause they ain't getting any cheaper.

 

[scruffy]

Well, that is true even if the THD and other figures for solid state suggest otherwise, for complex reasons.

Back in the 1980s, a friend and I proved conclusively that distortion figures are meaningless. Greater feedback improves lowering distortion yet sucks the life out of an amplifier necessary to give it musicality.

We ran tests on circuits producing upwards of 20% THD measured rms, not 0.002% as is common, and the damned thing rocked ass, sounding better than anything in the stores.

Without NFB the amp sounds more aggressive but you get speaker flap. Plus your presence control doesn't work any more.

Little things can make a big difference. Those carbon comp resistors are notorious for changing value, you can wake up one morning and realize your amp just doesn't sound the same. I took a 100k resistor out of a Fender once that read 62k on the meter. That's why I use metal oxide, they're rock solid and cheap. Plus a 2 watt mox is about a third of the size of a 2 watt carbon. (Even a 3 watt mox is way smaller than a 2 watt carbon). You'll see when I post pics of the PI, it wouldn't even fit with carbon resistors.

 

[toobfreak]

Yeah, if you zoom in real close in the pic of the underside, on the first filter cap, you can see a tiny little wire hair right next to the red wire. That's probably what popped. I took the pics before turning the amp on. Whatever... it ain't there no more, I checked.

If it ain't there no more, you can be sure it didn't just walk away on its own. I always like using one of those magnifiers on an articulated arm over my work with one of those circular fluorescent tubes for light, then scratch and pick at anything that looks suspicious with a plastic probe.

By the way, AES is having a Labor Day sale, 20% off all JJ tubes. I'm gonna stock up, cause they ain't getting any cheaper.

If they have any Sylvania or Tung-Sol 6550s, I'll take a matched set of four.
(BTW, all your work looks great so far! I like how you are taking a systematic, progressive approach to building and testing it).

 

[toobfreak]

Without NFB the amp sounds more aggressive but you get speaker flap. Plus your presence control doesn't work any more.

You always need at least a little neg FB to keep the amp stable. Naturally, like putting exhaust & mufflers on a race car, as soon as you apply it though, you lose a little of the grit the amp is capable of. Mind you, I don't do guitar amps and stuff like that as a rule. Not my bag. Musicians are looking for character in their amps, whereas home playback equipment is merely looking for fidelity to the original signal--- so if that grit was ON the recording, it can reproduce it, but with no actual characteristic sound of its own.

Little things can make a big difference. Those carbon comp resistors are notorious for changing value, you can wake up one morning and realize your amp just doesn't sound the same. I took a 100k resistor out of a Fender once that read 62k on the meter. That's why I use metal oxide, they're rock solid and cheap. Plus a 2 watt mox is about a third of the size of a 2 watt carbon. (Even a 3 watt mox is way smaller than a 2 watt carbon). You'll see when I post pics of the PI, it wouldn't even fit with carbon resistors.

That was actually one of my first thoughts looking at your pictures, the fact that you used 1% metal film instead of carbon. A lot of my gear originally came from the 1970s when carbon types were prevalent, and yes, those damn things are 5% or worse when they are made then heats shifts them further.

In fact, early in this thread, I posted some pictures of probes I made to reach and plug into the jacks on one amp for setting the bias on the output tubes. What I didn't say was that last I checked, even with the trim pots all the way to the end, I still can't quite reach the speced bias for the tubes, thereby running them hotter than they need shortening their lives, so at some point, I will need to go back to the schematics and replace a few parts to get the part specs back in line. In fact, if I do this, I might as well redo a whole bunch of parts in the amp (or at least check their values) to see how they hold up to factory requirements.

Then I should machine new handles for the rack faceplate to replace the rather girlie generic ones that are on the amp now.

One nice thing is that long ago, a buddy wisely got me to buy my own tube tester--- it is a table top unit that is basically similar to the ones they had in stores (does anyone remember there being floor-standing tube testers in most department/ pharmacy stores)? So when I have a tube issue, being able to test the tube right there on the spot comes in real handy, and it takes me at least 30 tubes to fire up my music system, NOT including any tubes in my radio (tuner) or in my RTR deck.