New Rocket Build - Mix of modern and traditional

[RJ Guitars]

Hello All,
I am putting together another Rocket build for somebody else. I'm not really bringing much to the table that is going to be new except a bit of an updated power transformer. I had Pacific wind some 120/240 mains Wreck transformers with a 5V rectifier tap. The OT is a Heyboer HTS-8093-1 Dynaco style.

For this particular build I'm also going to go with the JJ can caps and it all required a little trickery get everything to fit into the available space. I slid the power tubes slightly to the east to make a little more room for everything. I also added a heat shield to reduce the direct heat hitting the can caps. I've never actually done this or had any indication I needed it but it just seemed like a good thing to include.

I'm just finished with the initial wiring stages of getting all the transformer leads connected and ran some voltage verification tests.
532V AC on the PT Secondary (using the lower voltage taps)
5.4V AC on the rectifier tap
6.9V AC on the heater tap

The pilot light comes on and I get an ever so slight hum on the chassis when I power it up. More photos coming as I progress...

Edit - August 26, 2017 -- I have determined that I had the rectifier wiring wrong... look at the later photos if you have plans to copy my work

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[M Fowler]

Another beauty Bob. I like using the JJ cap cans makes the circuit so much neater looking and I have never had problems with them.

Mark

[RJ Guitars]

I took this a little further today... my 2nd favorite part of amp building, the heater filament wiring. I have been playing with a few different strategies for doing heater wiring. In this case I run one set of leads then switch wire colors and run the 2nd set. Happy to have this task done and getting closer to the fun stuff.

Edit - August 26, 2017 -- I have determined that I had the rectifier wiring wrong... look at the later photos if you have plans to copy my work

[RJ Guitars]

I wired up the power supply and finished off the power tube wiring. I also had a request to add a master volume so I went ahead and punched out the chassis for that. This amp is going into a cabinet that was previously used for an Express and the owner is going to reuse the old faceplate. So I am going to include a "Mid" control and now a MV control to match up with that faceplate. The cut control will say "Presence" and at a glance this will look a lot like an Express or Liverpool.

Edit - August 26, 2017 -- I have determined that I had the rectifier wiring wrong... look at the later photos if you have plans to copy my work

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[telentubes]

Coming along nicely RJ

[dorrisant]

I also added a heat shield to reduce the direct heat hitting the can caps. I've never actually done this or had any indication I needed it but it just seemed like a good thing to include.

Great idea! That is how I fix JTM30s and JTM60s... put in an aluminum plate between the power tubes and the caps just above them... Works every time.

[RJ Guitars]

Here is the latest effort... I mounted up all the parts onto the preamp board. Of course it took longer than it should have but generally pleased with these new boards. This is the first time I've built directly on the board without using any turrets... so far I like it. There is definitely a minimum of extra metal on this board so we'll see if that has any impact on the noise levels... I suspect I won't notice but if nothing else it's good from the simplicity and economics perspective.

[RJ Guitars]

Got a little more done. I wired up the tubes to the preamp board and ran the power supply wires to their apprpriate locations... lemme know if you see something that looks wrong...

Now I am figuring out what tonestack I think will work best... as I run the various options on Duncan's Tone Stack Calculator I always seem to be drawn back to the Marshall Tonestack for a Rocket build. These require very little circuit modification from the Rocket (Vox) Tonestack but additionally provide a more effective mid control. I documented my Rocket Tonestack work in a previous build (http://diyguitaramps.prophpbb.com/topic69.html) and it is becoming the Defacto standard for my Rocket builds until I find inspiration otherwise.

[M Fowler]

Looks great very nice detailed wiring.

[RJ Guitars]

Looks great very nice detailed wiring.

I sorta had to laugh when I read that... just before that post I realized I had near perfect documentation of an error on the rectifier wiring. This is a new PT and I made some assumptions that were wrong and when I went to do some verification measurements before putting any tubes in it, I found a mistake. I corrected it and the amp has now passed it's initial power-up test. I put in a set of not so special tubes and I am getting sound. Seems like I am about to head down the home stretch on finishing this thing up.

[RJ Guitars]

I had a chance to do some preliminary testing on this unit - I played through it at church this morning... I had a backup amp but didn't need it. Late last night I added a master volume control. I used the pre-phase inverter style - something I a friend of mine dubbed the "PIG" control a few years back. Here are my evaluation notes for this first test...

1) Noise floor was very low (once I added a bottom cover) - no further work needed there.
2) Fit into the cabinet was very good - no further work needed there.
3) Volume control - worked as expected and no further work needed there.
4) Bright switch - after some testing I settled on a 250pF cap - worked well and no further work needed.
5) Cut Control - Worked well and no further work needed.
6) Master Volume Control - Worked well and no further work needed.
7) Tone Stack - I am not so happy with this. Too much interaction between the treble and bass controls and overall not as much bass as I expected from a Rocket build - I'm going to work on this a bit further until I like it.

Overall a very clean tone and sweet sounding amp but I'd like to do a little tonestack work before I'm going to call it as the ultimate. According to my Duncan Amps Tonestack calculator it should have been perfect but I sorta recall that my ears and the expected tone spectrums were not in perfect alignment in the past. I used the MArshall Tonestack but now I need to go back and revisit that a bit more.

As you can see, this cabinet is really nice and this is going to be a very cool amp in somebodies collection...

Stay tuned...

[Mark]

What's new with the tone stack?

I'm surprised you didn't have enough bass, I was using a large bass GE 12AX7 and I was amazed at how it fattened up with volume. It was a bit too much for my taste. I decided to go for something a bit more transparent.

Have you experimented with bass and treble pot tapers. That will effect things such as how easy it is to find the sweet spot.

[RJ Guitars]

Mark,
I've been away from the workbench for a couple weeks so I haven't made any progress since that last post. I think overall I wasn't happy with the actual tonestack values so just tonight I started to read up on things a bit more and discovered a nice web offering from Rob Robinettte on the Fender TMB tonestack. After reading through that post I'm going to go with the Fender 5F6-A values and then listen to it again. Indeed, I may need to try a different preamp tube but usually I have more bass than I need with my Rocket builds. Here is the link tot he page I mentioned: https://robrobinette.com/How_The_TMB_To ... _Works.htm I was especially intrigued by the reasoning behind the mid frequency dip in the Fender design... now I am rethinking things a bit.
rj

[RJ Guitars]

So I went with the Fender 5F6-A tonestack and I was pleasantly surprised that it performs exactly the way the Duncan Tonestack Calculator indicated it would. I used the potentiometer style mid control versus the Variable resistor style. There is a subtle difference in these. The pot style leaves a little signal that doesn't sound that great with all the tone control knobs at zero. The VR style has the signal go to zero with all the tone knobs down which just seemed a little odd to me.

There is one quirk I might work to sort out someday in the future. There is a slight dip in the bass signal right as you max out the treble control. I heard it when I was playing with the controls in some sound testing. I ran the controls through the Tonestack calculator and it did the exact same thing. I think I actually like the tone best with the treble control at about 75% which also allows the best bass response.

The faceplate is little tight up against the front panel so I need to trim things somewhere to put the final finish on things...

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[RJ Guitars]

Well I worked with the faceplate and found enough clearance to get the amp slipped in below the front panel. I think it would probably be better to have a decent gap of maybe 3/32" but I'll leave it as and let the owner decide if he wants to further modify the faceplate. The guy I am building this for asked me to fit the amp into this cab and use this faceplate so the current fit was what was originally intended. It's obviously an Express or Liverpool faceplate so the Presence control is actually a cut control in my build and I also added a MV and mid control to fill in the empty holes.

After getting this into the box I have played through it a bunch. I am again impressed with the clean tones of a Rocket amp, amazing sound coming out of this amp and it's just as clear and quiet as any I have built. In my shop I had to add the bottom cover to get rid of the residual noise and then the amp got deadly quiet with only a slight hiss with the volume control up and no guitar plugged in. I think the can caps are really well matched to this circuit and the grounding scheme is as good as any Rocket that I've built.

I would still like to find a tonestack that doesn't have any interaction between the controls. This seems more noticeable with the addition of the mid control but if it was easy to make a perfect stack I suspect Fender, Marshall, and Vox would have already worked that out. In this case there is a loss of some of the low end if you max out the treble setting... it's easy to work with it and get what I want but it is just feels wrong to me to have the treble control affect the bass tone. I have always been one of those guys that just turns everything all the way up and leaves it that way so I have to rethink things to change my default settings.

I need to call this done and get on with the next build since this has turned out to be one of the better ones in combination of the cosmetic, layout, and sonic performance... I guess it's time to send it on it's way.