The Much Anticipated (?) Bluesmaster Build Thread

[Raoul Duke]

Hot dog! That’s it!

Everything is working as it should now and sounds pretty good! Amp is dead quiet, no oscillations even with OD and PAB cranked. Definite Marshall character and really full (vs scoopy) cleans. Going through a NOS 1989 EVM12S that I got a deal on from an on-line stereo/hi fi store.

HRM sounds pretty good with Tony’s settings - I really don’t want to mess with it. The pot for the lift definitely makes a difference and I turned it up just slightly from the 68k pre-set after playing with it a few turns.

I’m going to noodle a bit more, then get to the FET.

[martin manning]

I currently have it going to the OD relay NO2 per the board plans - but nothing connecting to that cap on the board. I think I’m going to try a jumper from OD relay NO2 to that cap.... Going to try the simplest way first and jump relay to board.

That's it. The Eyelet board plan relay connections say NO2 Cl Vol CW, Cl 2 CCap, meaning Clean Vol CW and Cl 2 CCap are connected to NO2. You were missing that jumper. It's shown in the layout, indicating it has to go somewhere.

Glad you figured it out, not easy since you are going through two transforms, OD normally on to OD normally off, and to the Hoffman relay board.

[Raoul Duke]

I had a feeling it was in my interpretation of the three references combined with the variables you mentioned - that’s why I kept reviewing and looking for possible misinterpretations. I remembered that I was confused by those connections initially, so I figured it warranted some digging before tearing into other things.

As always - I appreciate all the help I get here to include the “passive assistance” provided by others’ build threads and pictures! Really invaluable to someone who lacks the basic theory knowledge (like me). I’m always learning from you guys.

This thing sounds great - and definitely different than my 102 or 2nd Gen - which was what I was hoping for. Just have to put the aluminum flat stock on the cab and that’ll be ready; but I plan on keeping it on the bench for a few days just to keep an eye on it. Also, I have to mention how I’m always surprised by the differences in preamp voltages dependent upon the given tube and position - and how they interact both voltage and sound-wise. Below is the combination I like today, lol.

I also tried Ian’s choke polarity experiment and found that it did make a difference in clarity and harmonic content. Subtle, but definitely noticeable. Now I have to check the other amps when I’ve got time.

Here’s where we’re at currently as it starts to break in:

B+1: 474
B+2: 473
B+3: 436
B+4: 349
B+5: 309

V1a: 194 Tung Sol 12AX7 long plate
V1b: 198
V2a: 221 GE 12AX7 long plate
V2b: 224
V3a: 275 Ruby/JJ HG
V3b: 265

V4: 473 plate/41 bias JJ 6L6GC x 2
V5: 473 plate/39 bias

FET: 17.4 - 7.1 (R1-18k, Rs - 1k6)

Thanks again guys

[martin manning]

I have to mention how I’m always surprised by the differences in preamp voltages dependent upon the given tube and position - and how they interact both voltage and sound-wise. Below is the combination I like today, lol.

Tubes will typically have so much variation in current that the voltages will shift when pulling current through the large dropping resistors, which shifts the operating points. If you had all matched tubes with matched sections, that wouldn't happen.

I also tried Ian’s choke polarity experiment and found that it did make a difference in clarity and harmonic content. Subtle, but definitely noticeable. Now I have to check the other amps when I’ve got time.

I'm still skeptical. Data sheets generally do not make any distinction, and this is not a thing that gets any attention, even among the Hi-Fi nuts.

[Raoul Duke]

My collection of random tubes is anything but matched, lol. I just try to get my power tubes closely matched and wing it with the rest.

As for the choke thing - I hear you Martin. I’m always a bit skeptical of these types of things but I definitely heard a difference with this circuit. Over time I’ll try with the other two amps and maybe it’ll be as obvious - maybe it won’t. Maybe it just depends on the circuit (and the ears) on the day? I don’t know - but in this case - one orientation was definitely preferable to the other for me.

I’m always in awe of the stuff I learn from you fellers; and I greatly appreciate it!

[dbharris]

Glad you got everything working!

-Dan

[Raoul Duke]

Thanks Dan! As usual, I couldn’t have done it without you guys
Sounds like an exaggeration; but I learn a hundred new things every time I build one of these. This time was definitely educational.

[ijedouglas]

I'm still skeptical. Data sheets generally do not make any distinction, and this is not a thing that gets any attention, even among the Hi-Fi nuts.

Perhaps you should try it instead of constantly knocking these real-life experiments with data sheet theory? Your data sheets also state that there is no difference between resistor types and makes. Frankly, I'm sick of this. If you don't believe it or refuse to try it, good for you, whatever... Marc clearly heard a difference, as have numerous other folks, I applaud him for trying it for himself and making up his own mind.

[martin manning]

Frankly, I'm sick of this. If you don't believe it or refuse to try it, good for you, whatever... Marc clearly heard a difference, as have numerous other folks, I applaud him for trying it for himself and making up his own mind.

I have never said that I don't believe it makes any difference (and I can think of some reasons why it might), I only said I'm skeptical. That's my personal opinion at this point in time. I'm not knocking anyone who claims to have found a preference one way or the other.

Who are the numerous other folks? Can you point me to some independent discussion on this topic? Anybody?

[Raoul Duke]

Still sounds great today (IMHO).

Tried a Celestion G12K-85 with it. It’s a pretty full range and neutral speaker for a Celestion and I figured it might work well with this circuit. Turns out it definitely gives the OD channel more “bark” for lack of a better word; but the clean isn’t quite as full as the EVM-12S. I’m lucky enough to have two cabs to “A/B” these, so that’s what I’ll do as the amp and I get used to each other.

Other observations/questions:

- The PAB isn’t quite as pronounced as my 102. Is this a function of the lift pot adjustment?

- I have the FET biased at a little over Vd/Vdd=2 because of what I have on hand. If everything sounds good and there’s no noticeable voltage problems, how concerned should I be about finding the exact right value? Am I risking anything running it like it is?

Just tidying up stuff now…

[martin manning]

- The PAB isn’t quite as pronounced as my 102. Is this a function of the lift pot adjustment?

Indeed.

- I have the FET biased at a little over V1/Vdd=2 because of what I have on hand. If everything sounds good and there’s no noticeable voltage problems, how concerned should I be about finding the exact right value? Am I risking anything running it like it is?

You can put that voltage ratio where you like, somewhere between 2 and 3, with lower distortion when it's nearer to 2.

[Raoul Duke]

Thanks Martin!

I figured a little over 2 was ok - as long as it was at least 2? Truthfully, the whole FET “sausage” still eludes me as far as understanding the second and third order effects of this part of the circuit. I do know that it definitely helps my single coils sound better through the amp - so I want to get it right

Oddly (or maybe not?) todays reading was 17.1 and 7.5, so I imagine there’s always going to be some fluctuations based on wall voltage, component drift or break-in etc?

Thanks again! I truly appreciate every learning opportunity I get here

[Raoul Duke]

Small little detail I’m looking for advice on:

When I switch stand-by to “stand-by” during power down, I sometimes get a “pop” through the speaker. Is this something that can be solved with a capacitor on the switch or is it indicative of a different problem I should be chasing? I’ve searched and seen a few similar solutions here - just wanted to be certain there wasn’t something more I should look for.

The power switches on this build are Carling 2FA53-73 which seem pretty common.

Any advice is appreciated! Thanks!

[martin manning]

A 1kV 10n cap across the standby might help with the pop and increase the life of the switch contacts.

The better way to shut down is to turn the AC off first. That way the power supply caps will drain through the still hot tubes.

[Raoul Duke]

Hey, didn’t even think of that Martin. Conditioned through the years to reverse the “power-up” process without a second thought.

Sometimes the simplest answer isn’t obvious; but for me the obvious is usually the least simple, lol. Sounds like a fortune cookie

Thanks for the advice Martin! I’ll definitely use the latter and may try the former as well just for insurance - knowing I’ll likely revert to old habits a percentage of the times I power the amp down without even realizing it.