Monkeymatic Penta (Matchless Clubman inspired)

[xtian]

Got most of the components, and about ready to start on a Matchless Clubman-inspired build. There are two schematics available, marked as 1993 and 1996, attached.

On the '93 version, look at the Treble control. This looks wrong. It would allow C5 to be grounded. Wouldn't that drop volume to zero?

On the '96 version, it shows 10K grid resistors, versus 1.5K on the '93. I'd normally use 1.5K on Marshall style. Opinions?

Last, which arrangement for the screen supply looks better? The '96 version has an additional, shared 1K/25W resistor.

[xtian]

No one has built a clubman? Woah. Well, then. I'll build it, and it will be the most awesome amp on the planet, and then you'll all want to build one, too. So, there.

[LeftyStrat]

The treble controls are functionally equivalent, just different order.

Not sure why the grids we're bumped up, maybe to remedy some blocking distortion?

I'm very interested in your build. If you have Merlin's preamp book, you might check out the parallel tubes section, he mention's the Clubman.

Also, this design is a prime candidate for his pentode/triode morph.

[trane34]

FWIW I had a clubman briefly a long time ago before I started building. Matchless amps always seem too bright to me by themselves but cut through really well in a live setting (thinking of a show I saw with Robert Cray through a clubman). I mostly am a bedroom player so I moved on from it. Will you be using terminal strips?

[vibratoking]

On the '93 version, look at the Treble control. This looks wrong. It would allow C5 to be grounded. Wouldn't that drop volume to zero?

Nothing fundamentally wrong with grounding C5. The closer it gets to ground, the more the highs are dumped to ground. Lows and mid frequencies are relatively unaffected. If the top side of C5 was grounded then you'd drop the volume to zero and screw up the bias of V1-1.

On the '96 version, it shows 10K grid resistors, versus 1.5K on the '93. I'd normally use 1.5K on Marshall style. Opinions?

I'd start with the 1.5k if it were me. I try to stay away from big grid resistors and up them as a last resort.

[hitchcaster]

here's mine.... I think there are 3 versions. I've got the first version 93' pictured version Ala Robert cray. overseas I've got a 95' ef86 version. u really have to roll tubes in these Amps otherwise they can suck, well except the el34's which they tend to burn thu depending on how they are biased. if it was me I'd copy the layout etc. exactly.

[xtian]

Wow, hitchcaster, thanks for the photo! Rare as hens' teeth!

I put in another couple of hours on the layout. Still pushing parts around…and around. Will get settled eventually.

In progress work attached.

[Gaz]

LOL: "Copy the layout." I think you'll be fine.

My only comment is that you shouldn't worry to much between the difference between 1.5K and 10K power tube grid stops, the math says you won't be able to hear the difference. I think the benefit of the 10Ks is they may help reduce blocking slightly when the thing's maxed out.

[ampmike]

Matchless amps gut shots are things of beauty!!I wander how many employes he has and how many leave per day.I have a badcat that is true pt to pt like that and its an inspireing thing to play.Ive heard Nashville is flooded with matchless.You look like you have a great start,Go for it,I do agree with the post above,When I played one in a music store it didnt knock me off my feet but Im sure in a live setting with a band it would.Mikey

[dorrisant]

Very interested in this build... curious as to what you think of the tone stack.

I would use the 1.5ks on the screen grids and maybe try the screen grid voltage divider... ?

Tony

[xtian]

The screen resistors: on the '93 schematic (mislabeled by me as 96) it shows 1K 12w resistors. How could there be that much current here? I see, on the same schematic, a 25v drop across these resistors, making 0.625 watt. Is the 12 watt spec an insurance if the tube fails and the screens start to conduct ALL the current from the cathode?

Answered my own question: yes.

[Gaz]

If it were me, I'd want those suckers to blow,especially since there's no HT fuse. Otherwise the PTs likely to go up in smoke. I don't understand the rationale either.

[xtian]

Oh, well, I just finished reading lots of explanation why you don't want to use a resistor as a fuse. Upshot is, unreliable, and may set other stuff on fire.

And I will use an HT fuse.

[Gaz]

Yeah, I always think it's a good idea. I built an amp once with no HT fuse (like almost ever Fender), but used 5W screen resistors like Marshall instead of lower wattage Fender uses. Screen short of some kind, and the PT fused before the screen resistor did. An HT fuse would have saved the PT. I copied my design from the Trainwrecks since I figured Ken knew very well what he was doing. I believe he did, but I think upping the screen resistors with no HT fuse was a mistake plan and simple.

I'd love to hear any other theories on the Clubman screen supply design.

[Luthierwnc]

I made one a few years back but couldn't get it to sound right. The parts found their way into other builds but every now and then I'll reconsider the project. I had a hard time getting it to stay clean long enough. Real ones I've heard stayed cleaner longer than mine.

I used the EF86 version but the older power section (without the big pre-screen resistor). Get an assortment of plate and screen resistors for the pentode since you can't be quite sure what kinds of voltage you'll get with an off-the-shelf power transformer. If I did it again I might try a 5879.

Good luck, sh