A Rockster Variant Mutant Donster Monster

[donzoid]

...Gonna call it "Donster"...hopin' its a monster!

It was "going to be" a more standard KT66 Rockster but after all, this is a learning forum for me, and I just couldn't go without some experimentation.

I've been collecting parts one at a time over the last year, most of them off the for sale list right here on TAG. It's not quite beaks and feet, but I have a feeling it should sound pretty good.

I am installing a relay (courtesy of Colossal's fine ready-made boards) to switch stage 2 cap AND lift the extra 220K voltage divider at the PI for a boost to use on leads since I'm gigging steady. I tried to get all of the components onto one board, alas I couldn't do that without cramming too tight, so had to add one extra bit for the power supply, which is a fairly unique design. When I get the money for a reverb transfo, the tube socket is all wired for it and until that arrives I will use the extra stage of V2 as an RJ boost control; Shuguang kt's, diode rectumfried, and a PPIMV...both transformers are used Heyboers from Moose.

[M Fowler]

Doesn't that switched 220k voltage divider at the PI entrance lower the amps gain, speaking volume wise too much?

The bypass cap boost I don't use a relay just cliff jack and Marshall style foot switch/ otherwise just a mini SPST switch on the front panel. But having the relay is nice especially Colossals.

[donzoid]

Mark, when playing around with that 220K at the PI, I found that I liked having it in "most" of the time because it retained a lot of the chimey jangly quality of the vox sound in my 18watt Rocket. I have that on a switch in that one, so I can add more gain (and less chime) by lifting that divider back out. So the idea was to lift the resistor, AND add a 22uF cap to the 2.2uF I have in there all the time at V2 (at the same time using that relay).

EDIT: that should read V1b, not V2 in the last sentence.

My hope is, it will get me about 2 or 3dB (just enough between both) to push the leads out front!

I may add another relay for the 'verb but not sure yet cause even when I use verb, it's never really overbearing more of wet down subtle kind of use.

[M Fowler]

The Normster and rjguitar reverb is very subtle which what I like so I keep my reverb on all the time no reverb switch on my amp.

A different reverb pan would certainly allow one to get a more Fender swampy decay if one wanted that.

On a Rocket reverb V1b I put a DPDT switch center off so I had
(10uf down- off - 22uf up) on the switch for greater flexibility to boost the gain. Yours should work great.

[matt h]

This Donster will monster.

And it shall monster hard.

[Bob S]

I likes the Donster Monster.
Soviet K caps - nice.
I'm betting it will sound killer.

[matt h]

I managed to manipulate, er, persuade Donzoid into rolling with a few of my slightly-off-beaten-path suggestions for this thing... so I may be a little invested in its success. haha

[JoeCon]

I've only built three amps so far, a Rocket, Liverpool and KT66 Rockster. And the Rockster is the best one for me. With just a slight twist of the vol control it cleans up so nice and then...voom on 10 great lead tone.
I started with the straight circuit but couldn't resist tweaking it for my ear.
Went with an .001uF coupling cap off V1. V1s bypass is a 10uF, V2s is a 1 uF.
And all the .047s were changed to .002 to tighten it up. PPIMV too.
Edcor 280-0-280 PT and a 5K OT.

[donzoid]

Joe - are you talking about the vol. control on your guitar, or on the amp? I was curious how this one will behave compared to an Express (which runs the whole range of clean to mean on guitar vol. pot).

[donzoid]

Updated build pics.

Got most of the relays connected, pots installed and got the master vol. started. I had a 500K dual pot (several actually) so I strapped a 470K across them so they measure about 250k.

I hope to be able to bring up power tonight and start checking volts. Thanks for all your comments. This thing will have to be awfully really good to compete with the big dogs (like Tardis). Hey at least I'm building this one sober from start to finish! LOL.

BobS, those PIO's were cheap, and I have been wanting to try them in a build, so hopefully based on the cork-sniffin' home stereo crowds positive reviews, they will sound decent. They are certainly built well...

I should mention: the switch I have mounted out there in the midst of everything is for swapping the secondaries from the 260-0-260 to the 300-0-300 taps coming out of the PT. Certainly NOT on-the-fly, but I wanted to be able to compare them.

[JoeCon]

Zoid

Yes very sensitive volume control on guitar, which makes it so easy to find good sounds. Iturn ot down to 7 on the guitar set up my sound on the Rockster and that little twist to ten gets you right into solo territory.

Here's an early pic of mine...

[donzoid]

Thanks Joe, that's what I was hoping you'd say. I used your build as a reference among several, because I wanted the same or similar type of turret layout!

When I built the Express I kinda went into shock. I was decades-used-to using my volume pot on Marshalls and with those it's 2 positions...vol on 2.5 or 3 for clean with grit, and all the way up for everything else.

But with the Express I had to actually "use" the pots because there is a huge difference between 2, and 3, and 5 and 5.5, 7, etc.

Now that I am used to it, I really like it, and glad to hear the Rocket/Rockster does it too! I'm even thinking about switching several of my guitar pots out for the special tapers to give me more control.

[donzoid]

OK, she's alive! Started up with an old pair of 6550's since I only have the one set of KT66 and didn't wanna risk them.

So far everything is functional except the boost control (the one that uses the spare triode, which I plan to use for reverb anyway but still looking for a suitable transfo here) isn't playing well with the tone controls. So I'm going to have a closer look again at my integration. And its pretty woofy when the relay gets engaged so the V1b bypass cap that is part of that relay's function will have to get dropped a bit - say to 10 or lower, until I find a sweeter spot.

All of this is on the "High secondary" selector side of my switch, set to 300-0-300 with FRD's I'm seeing 392v at B+ and 363 at the plates. I am also going to try the 260-0-260 setting at some point today so I can chart both and compare...

So I am gonna review it all, post up voltages and get those KT's in there!

[donzoid]

KT66's installed, very boisterous! Can't wait to A/B this next to the 18watt el84 flavor.

Note the plate volts went up a few with the KT's, and the power rail B+ is a little high down at the preamp end. All these are charted by the high setting of the sec. so today I will be checking the lower setting. Screens are pretty darn close to the plates, but no redplating apparent.

I installed a 500k trimmer pot where the PI 220K feed was to try to dial that in. Once I find the right value, I'll replace it with a fixed value. So far that seems to be right around 330K to my ears...clips to come soon.

[donzoid]

Hmmm...pretty tasty tone on the lower secondary setting. Creamy and smooth. I'm liking it with about 338v at the B+ reservoir.

Question for anyone looking: Why is this beast (on either sec. setting) rampantly oscillating ONLY when I pull the signal (guitar) cable? Its pretty darn quiet with the cable in, and even with the guitar turned up almost all the way on its vol. pot. Pull the instrument cable and whoa! I have to back the gain knob to about 30% to get it to stop when that cable is unplugged.