Yet another 124 build

[GAStan]

I was able to spend approximately 25-30 hours on this over the weekend beginning Friday evening. Here is it's current state.

20230917_193324.jpg

I am learning a LOT from this build, there is no teacher like experience.

[GAStan]

Mistakenly ordered a lay-down trimmer where I needed one that stood up.

20230917_193437.jpg

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[Stephen1966]

I would be prepared to reflow the solder joints. Some look dry and if they are, they will give you audible problems, crackling, humming, squealing. An example, the bottom of the slope resistor, nearest the sockets. If it's really silver solder you are using, you might want to use a higher melting point with your iron to get it to flow properly. A good joint should look like it has a meniscus around it. If it looks like a biscuit (grainy) it needs reflowing.

[GAStan]

I would be prepared to reflow the solder joints. Some look dry and if they are, they will give you audible problems, crackling, humming, squealing. An example, the bottom of the slope resistor, nearest the sockets. If it's really silver solder you are using, you might want to use a higher melting point with your iron to get it to flow properly. A good joint should look like it has a meniscus around it. If it looks like a biscuit (grainy) it needs reflowing.

The solder is an old spool of Kester 44 I've had around over 20 years. Finally found a project worthy of it. The mix is their basic 63/37 with something like 2% Ag. I'll get the actual recipe this evening. I do have the iron hotter than normal. I'll double check my joints, as well as post clearer pics. Because the 44 is a cleaning optional Flux I decided not to clean, so some of what you see may be the Flux.

I received a week of 8 hour days of solder training in the military in the mid '80s and consider myself to have good soldering skills. However being human I realize I'm not perfect and prone to miss something. Thank you Stephen for taking the time to look closely, critically, at my work.

[Stephen1966]

I would be prepared to reflow the solder joints. Some look dry and if they are, they will give you audible problems, crackling, humming, squealing. An example, the bottom of the slope resistor, nearest the sockets. If it's really silver solder you are using, you might want to use a higher melting point with your iron to get it to flow properly. A good joint should look like it has a meniscus around it. If it looks like a biscuit (grainy) it needs reflowing.

The solder is an old spool of Kester 44 I've had around over 20 years. Finally found a project worthy of it. The mix is their basic 63/37 with something like 2% Ag. I'll get the actual recipe this evening. I do have the iron hotter than normal. I'll double check my joints, as well as post clearer pics. Because the 44 is a cleaning optional Flux I decided not to clean, so some of what you see may be the Flux.

I received a week of 8 hour days of solder training in the military in the mid '80s and consider myself to have good soldering skills. However being human I realize I'm not perfect and prone to miss something. Thank you Stephen for taking the time to look closely, critically, at my work.

Sure, no problem. It might be the light in the photos. I generally take lots of very close-up shots for inspection as well as using a loupe when I can get my head in the chassis. The proof is in the pudding though because a dry joint might not be immediately apparent, you will hear it though and that's where the chopsticks come in.

I meant to ask you as well, you have resistors in series coming off (or rather, feeding) the OD trimmer. Two are in parallel. What's the story there?

[GAStan]

I would be prepared to reflow the solder joints. Some look dry and if they are, they will give you audible problems, crackling, humming, squealing. An example, the bottom of the slope resistor, nearest the sockets. If it's really silver solder you are using, you might want to use a higher melting point with your iron to get it to flow properly. A good joint should look like it has a meniscus around it. If it looks like a biscuit (grainy) it needs reflowing.

The solder is an old spool of Kester 44 I've had around over 20 years. Finally found a project worthy of it. The mix is their basic 63/37 with something like 2% Ag. I'll get the actual recipe this evening. I do have the iron hotter than normal. I'll double check my joints, as well as post clearer pics. Because the 44 is a cleaning optional Flux I decided not to clean, so some of what you see may be the Flux.

I received a week of 8 hour days of solder training in the military in the mid '80s and consider myself to have good soldering skills. However being human I realize I'm not perfect and prone to miss something. Thank you Stephen for taking the time to look closely, critically, at my work.

Sure, no problem. It might be the light in the photos. I generally take lots of very close-up shots for inspection as well as using a loupe when I can get my head in the chassis. The proof is in the pudding though because a dry joint might not be immediately apparent, you will hear it though and that's where the chopsticks come in.

I meant to ask you as well, you have resistors in series coming off (or rather, feeding) the OD trimmer. Two are in parallel. What's the story there?

When planning/ordering I didn't correctly plan for the #124 OD trimmer. I just ordered 220k resistors. Got 10 from Mouser due to bulk pricing. Doing the math 346k + 220k = 566k in #124. With the 250k trimmer I need 316k additional to match #124. So I paralleled the 220k for 110k which I added to the 220k I had for 330k, as close to 316k as I could get with what I have on hand.

Today I'm ordering tubes so I'm also ordering some resistors, 270k and 47k which will get me really close to where I need to be. +/-5%.

[GAStan]

Speaking of tubes I'm getting/have a variety of 12AX7 and 7025 for the preamp and PI.

Genelax Gold Lion 12AX7 gold pin
Mullard 12AX7/ECC83 new production
TAD 7025 Red Base High Grade
EH 7025
Tung Sol 12AX7 re-issue
And more I can rob from other amps.

I'm ordering an Apex Matched quad of Sovtek 6L6WXT+ for power. Description says they are modeled after the RCA black plates. Thought I'd give them a try. This is my first experience with 6L6 so nothing to compare them to-either I'll like them or I won't. My other big amp has a quad of 6V6.

The amp construction should be done this weekend, ready to smoke test. I didn't order power tubes before because of no way to test them and didn't want to go past the warranty period.

[Stephen1966]

The solder is an old spool of Kester 44 I've had around over 20 years. Finally found a project worthy of it. The mix is their basic 63/37 with something like 2% Ag. I'll get the actual recipe this evening. I do have the iron hotter than normal. I'll double check my joints, as well as post clearer pics. Because the 44 is a cleaning optional Flux I decided not to clean, so some of what you see may be the Flux.

I received a week of 8 hour days of solder training in the military in the mid '80s and consider myself to have good soldering skills. However being human I realize I'm not perfect and prone to miss something. Thank you Stephen for taking the time to look closely, critically, at my work.

Sure, no problem. It might be the light in the photos. I generally take lots of very close-up shots for inspection as well as using a loupe when I can get my head in the chassis. The proof is in the pudding though because a dry joint might not be immediately apparent, you will hear it though and that's where the chopsticks come in.

I meant to ask you as well, you have resistors in series coming off (or rather, feeding) the OD trimmer. Two are in parallel. What's the story there?

When planning/ordering I didn't correctly plan for the #124 OD trimmer. I just ordered 220k resistors. Got 10 from Mouser due to bulk pricing. Doing the math 346k + 220k = 566k in #124. With the 250k trimmer I need 316k additional to match #124. So I paralleled the 220k for 110k which I added to the 220k I had for 330k, as close to 316k as I could get with what I have on hand.

Today I'm ordering tubes so I'm also ordering some resistors, 270k and 47k which will get me really close to where I need to be. +/-5%.

I understand. Yes, with a build like this when you are trying to cost things as you go, you have to be a little conservative in your estimates, because wrong components do arrive, resistors don't give you the values you expect, and so on... it is like ordering lumber in a way. If you estimate the total cost is going to be x dollars, you have to add y dollars to compensate for any poor luck or accidental choices you made along the way. I've never actually figured out what the overspend on projects like this is, but it's always more than the value of the components that end up in the actual build. From a BOM, at a conservative estimate though, you might expect the cost to be 20% higher.

Cost overruns are a problem for larger scale manufacturers though. In a no-compromise build of your own, to suit your tastes and perform to your satisfaction, you might as well say goodbye to a kidney. Because that's what it takes sometimes, to make us happy. Still, if you have a good/great amp - a real dream machine - who needs kidneys. Not saying money is no object, but you can certainly afford to experiment with a project such as this.

It's nice if you get great NOS parts, but every departure from the original is a step into the unknown and sometimes, modern easily available in-production parts are just as good. Usually a whole lot cheaper as well. You don't need to reinvent the wheel with these amps for them to sound awesome is my point.

[Stephen1966]

EH7025s are great in V1 and V2 positions but I would wouldn't use them or EH12AX7s for the PI - apparently they don't like the high currents. JJs are robust and perfectly fine to my ear.

[GAStan]

Sure, no problem. It might be the light in the photos. I generally take lots of very close-up shots for inspection as well as using a loupe when I can get my head in the chassis. The proof is in the pudding though because a dry joint might not be immediately apparent, you will hear it though and that's where the chopsticks come in.

I meant to ask you as well, you have resistors in series coming off (or rather, feeding) the OD trimmer. Two are in parallel. What's the story there?

When planning/ordering I didn't correctly plan for the #124 OD trimmer. I just ordered 220k resistors. Got 10 from Mouser due to bulk pricing. Doing the math 346k + 220k = 566k in #124. With the 250k trimmer I need 316k additional to match #124. So I paralleled the 220k for 110k which I added to the 220k I had for 330k, as close to 316k as I could get with what I have on hand.

Today I'm ordering tubes so I'm also ordering some resistors, 270k and 47k which will get me really close to where I need to be. +/-5%.

I understand. Yes, with a build like this when you are trying to cost things as you go, you have to be a little conservative in your estimates, because wrong components do arrive, resistors don't give you the values you expect, and so on... it is like ordering lumber in a way. If you estimate the total cost is going to be x dollars, you have to add y dollars to compensate for any poor luck or accidental choices you made along the way. I've never actually figured out what the overspend on projects like this is, but it's always more than the value of the components that end up in the actual build. From a BOM, at a conservative estimate though, you might expect the cost to be 20% higher.

Cost overruns are a problem for larger scale manufacturers though. In a no-compromise build of your own, to suit your tastes and perform to your satisfaction, you might as well say goodbye to a kidney. Because that's what it takes sometimes, to make us happy. Still, if you have a good/great amp - a real dream machine - who needs kidneys. Not saying money is no object, but you can certainly afford to experiment with a project such as this.

It's nice if you get great NOS parts, but every departure from the original is a step into the unknown and sometimes, modern easily available in-production parts are just as good. Usually a whole lot cheaper as well. You don't need to reinvent the wheel with these amps for them to sound awesome is my point.

This build HAS been a bit more costly than anticipated. I'm fortunate in that I earn a good wage and am nearing retirement so while I'm not not a spinster I'm not extravagant either. This build has been in the middle cost-wise so quality modern production has been chosen over NOS. The goal is a good sounding solid amp that will hopefully be a lifelong fixture in my teenage son's music room. A Dumble ODS style build, IMHO, suits that goal well. Now my 28 year old son wants a tube amp too...

[GAStan]

Here is the label of the solder I am using. It has 2% silver and .35% antimony. These give it additional strength.

20230919_170333.jpg

This solder is extremely shiny. The issue is trying to photograph it, it's like trying to photograph chrome. You don't capture the chrome surface so much as you do the reflection. Add this to the very irregular surface of a solder joint with the end of stranded wire in it and it is very tough to get a picture that clearly shows you need.

I re-inspected all of my solder joints and they look fine. It was when I tried to take pictures to show this that I discovered what I just described.

20230919_165934.jpg

Here is some of my typical work. The amount of solder is about right, nice concave surface with solder wetted to the edge of the solder pad and well up the leads. But, to me anyway, first glance at this picture they appear to have an excess of solder convex in shape. I did clean the Flux from this board, you can see some white residue.

[martin manning]

Happens all the time, especially when flash is used, which creates all kinds of artifacts.

[GAStan]

It lives!

It's pretty loud!

Set FET trimmer to min, od and PI balance trimmers to mid.

Using a light bulb limiter I brought it up sans tubes. B+=462, 458, 431, 364, & 358. Bias has -62 available, set it for that.

Tubes in, let heaters do their thing a couple of minutes then out of standby. Dummy load hooked up prior to powering on. B+=462, 459, 436, 294 & 285. Heaters at 7.3??? Will that be ok? Wall voltage is 125. Set bias at 30mA (one tube) for now, 55-60% of 25W at 462v. 4x6L6 tubes.

Got 2x12 4ohm speaker, shut down amp and hooked it up. Nothing plugged in to input, all controls at 0. No 60hz hum! No obnoxious feedback, my lucky day. But definite noise, static like white noise. Manipulated all controls with no effect on noise, just a couple of clicks first time I tried each of Mid and Bright switches but subsequent operation of these two controls resulted in no clicks heard.

Lightly tapped each tube. V1 slightly microphonic all others silent.

Plugged in a guitar and tried it out-wooohoooo it works! I'm the only one here now so cranked it UP. Loud, feedback at will. Too soon to comment on tone but clean is clean OD has crunch. Unplugged guitar, static is gone but slowly comes back.

Our cat just came in meowing at me, PO'd that I woke her from her nap.

I'm STOKED!! Need to calm down a bit before I put my hands back in the amp to check out plates voltages etc...

[alberto.chanfreau]

Congratulations Glen, for great progress so far... We do feel your passion and excitement. Thanks for sharing!

Re your last statement, yes, you are right! Better if you may continue with baby-steps... (better thorough than faster, at current stage) Good luck, man!

[GAStan]

Congratulations Glen, for great progress so far... We do feel your passion and excitement. Thanks for sharing!

Re your last statement, yes, you are right! Better if you may continue with baby-steps... (better thorough than faster, at current stage) Good luck, man!

Alberto Thank You.