50 Watt Bass (1986 circuit) Rocks!

[Danhalen]

So after going from lead to bass and everything possible thing in between I could think of in my Metro 50 kitt, I have gone back to stock 1986 specs but with a couple of slight mods:

-100pf bright cap
-Filter can for Phase Interverter and Screens reduced to dual 32
-27k negative feedback connected to 8ohm tap

A while ago (probably couple of years now) I had posted a couple of threads when I was excited about whatever combo of specs I had going at the time. Well this is the happiest I have ever been with the amp (and to think this was the spec I originally planned to build! I was right the first time about what I wanted out of this amp, but now I know for sure). And now I actually have a much better capacity to record the sound of the amp. Which I will do. I was just cranking my '59 LP Jr through it and it really is the tone I imagined in my head when I first got this kit. For the last hour or so I just wailed non-stop. I think it is possibly the best I have ever played because I was so excited about the tone and feel of the amp! I will admit that a lot of that is that I have improved a lot as a player, but this spec really does it for me! Between this amp and my '65 AC 50, I have most ground covered for what I do most of the time. Now I would like to build a JTM 45/100 or a '67 100 Watter in the future when I can afford it... Clips to follow I promise

[54strat]

I converted my old Lead to Bass specs a few years ago. After a while I put the .68 bypass cap back on V-2 for a little more gain and upper mid, then lowered the V-1 bypass to a 5mF to get rid of some extreme low end flub. Still plenty of beef.

[shakti]

It really is a wonderful circuit, and when push comes to shove it probably is the one Marshall amp I would keep above the others.

What you have there should be '68 specs more or less. I've lived without one of these amps for a while, but just fired up a new build yesterday. Mine is a hybrid spec amp - aesthetically it's like a '67 black flag amp. All Piher resistors, mustards and Lemcos, Erie 32+32 in the preamp. Single voltage dropper like the '67 amps, but 270k mix resistors. Then the icing: switchable tube/solid state rectifier. 32uf mains filtering in tube mode, 64 in solid state mode. 32uF for both screens and phase inverter.
I currently have 27k@8 ohm feedback, but wil experiment between that and 16 ohm.

So in tube mode, it's essentially just like an early '67 black flag JTM50, except for a little more PI filtering and a little less feedback.
And in solid state mode, it's essentially just like a mid '68 except for single voltage dropper and 270k mix resistors.

Needs burn-in, but sounds just like it should and super quiet! Will make a separate thread with photos. I still need to figure out how to optimize the bias for each mode, but I have a plan...

[Danhalen]

Those are both interesting specs. My friend was just producing a session and used my 1986 for Wurlitzer and for reamping a recording of a brass section. It sounded awesome for that stuff too!

Have you guys seen this? Sounds awesome!

http://www.youtube.com/watch?v=rUceBH1gKXA" onclick="window.open(this.href);return false;

[somethin'else]

Those are both interesting specs. My friend was just producing a session and used my 1986 for Wurlitzer and for reamping a recording of a brass section. It sounded awesome for that stuff too!

Have you guys seen this? Sounds awesome!

http://www.youtube.com/watch?v=rUceBH1gKXA" onclick="window.open(this.href);return false;

Man, that is sweet, indeed! Stellar tone and playing there.

[Harold]

I converted my old Lead to Bass specs a few years ago. After a while I put the .68 bypass cap back on V-2 for a little more gain and upper mid, then lowered the V-1 bypass to a 5mF to get rid of some extreme low end flub. Still plenty of beef.

Is that the 330μF cap you're referring to?

I'm planning to build a 1964/2100 Bass & Lead head, which is essentially a 1986 Bass with 500pF bright cap and the 56k slope and 500pf treble cap. I'm also planning on adding the V2 .68 cap.

Couple of questions though:
* is anybody jumpering their channels?
* I'd like a master volume, and am thinking about a 2203/2204-stype PrePIMV. Any objections?

[Danhalen]

I converted my old Lead to Bass specs a few years ago. After a while I put the .68 bypass cap back on V-2 for a little more gain and upper mid, then lowered the V-1 bypass to a 5mF to get rid of some extreme low end flub. Still plenty of beef.

Is that the 330μF cap you're referring to?

I'm planning to build a 1964/2100 Bass & Lead head, which is essentially a 1986 Bass with 500pF bright cap and the 56k slope and 500pf treble cap. I'm also planning on adding the V2 .68 cap.

Couple of questions though:
* is anybody jumpering their channels?
* I'd like a master volume, and am thinking about a 2203/2204-stype PrePIMV. Any objections?

Well first of all I will say that with the things you have mentioned there, there is no wrong answer. If you like it is good.

That said, I tried the 2100 spec myself and found that I did not like the 56k/500pf combo at all. It was REALLY bright and scooped sounding. I prefer the 56k/250pf for what I like. That being said that, the 33k/500pf tonestack sounds really good in a lead spec amp too. They are both relatively balanced sounding. I have tried lead spec, bass spec and everything in between that I could think of and personally I prefer full bass or full lead spec. Most of the in between versions I tried just lacked something. You can get a lot of variation by experimenting with filtering, negative feedback and bright caps to really dial in the tone/feel you want without changing the lead/bass stuff even. That being said, the best way to figure out what really works for you is to try it. So I say if you want to try that spec go for it you really can't lose! If you don't like it or are curious, then try a different combo of specs. Then you will be a guru. Or something.

[Harold]

That being said, the best way to figure out what really works for you is to try it. So I say if you want to try that spec go for it you really can't lose! If you don't like it or are curious, then try a different combo of specs. Then you will be a guru. Or something.

Thanx!

I added the 250pF to my order to be able to try them all. Let's start with the stock 1986 Bass spec and work our way up to the 33K/500pF spec.

[54strat]

Yes. I was referring to the 330mF bypass cap on V-1. There is a great bypass cap calculator on Pentode Press website. Standard Marshall values of 330mF and 250mF, with an 820 resistor, do not roll off ANY lows. You have to go down to a 10mF before you hear any difference. I tried everything from 10 to 2.2mF and liked 5mF best.

[Harold]

Yes. I was referring to the 330mF bypass cap on V-1. There is a great bypass cap calculator on Pentode Press website. Standard Marshall values of 330mF and 250mF, with an 820 resistor, do not roll off ANY lows. You have to go down to a 10mF before you hear any difference. I tried everything from 10 to 2.2mF and liked 5mF best.

This calculator shows the difference between 220uF and 4.7uF nicely:




I don't need to tell which is which


This is 10uF btw:

[TWANGGG]

It's worth mentioning that when looking at the graphs produced by the calculators on that website(great site, btw) be sure to pay close attention to the left hand dB scale because each graph covers a different range. For instance though the 220uF appears to have a steep rolloff the entire graph is actually only covering .045 dB, so in this case essentially flat.

[Danhalen]

Thanx!

I added the 250pF to my order to be able to try them all. Let's start with the stock 1986 Bass spec and work our way up to the 33K/500pF spec.

That is a rock solid plan

If you are going that route I would definitely give full bass and lead spec a try. Heck might as well! Make sure to at least try the "proper" negative feedback values for each as well. The bass spec with lower than stock negative feedback doesn't sound that great to me, too mushy. And then the 27k negative feedback is too stiff with the lead spec. They balance each other out. All of this is just my opinion of course...

Oh and don't be afraid to set the bass control really low on the bass spec, even as low as 0. With my LP Jr or SG, I tend to run the bass around 1 on my 1986. Or sometimes to record a lead with a real fat, squashy/fuzzy sound I turn it up but for a punchy sound especially when playing chords I keep it pretty low. George has mentioned a bass setting of 0 on bass spec amps as well.

Have fun! Oh and I really will post a clip of my amp for kicks.

[Harold]

Have fun! Oh and I really will post a clip of my amp for kicks.

I hope to wire the build this evening.

Current set-up:
* 47K NFB resistor on the 8 Ohm tap
* 250pF/56K tonestack
* 500pF bright cap on high treble channel
* 820R/4.7uF on V1
* Cathode-lift-bypass on my progressive off/standby/on switch
* Larry's ground layout (slightly modified)
* 1M PrePIMV (2204/2203 style) pot where the standby switch used to be

[Harold]

I hope to wire the build this evening.

Current set-up:
* 47K NFB resistor on the 8 Ohm tap
* 250pF/56K tonestack
* 500pF bright cap on high treble channel
* 820R/4.7uF on V1
* Cathode-lift-bypass on my progressive off/standby/on switch
* Larry's ground layout (slightly modified)
* 1M PrePIMV (2204/2203 style) pot where the standby switch used to be

* 820/680nF V2A cathode "mod".

The amp made it's first sound yesterday evening, but that was using a headphone on my Koch LB120 loadbox because it was already pretty late All controls are working, cathode standby works too and no noises/oscillation/humm/etc.



I was hoping for a little more gain though ...

[Roe]

I had a particularly sweet sounding 1986 in for service recently. it was a rare 1973 model with .68u presence cap and 100k @ 8ohms nfb with 2old filter caps