Peavey Classic 30 --> 36W TMB project

[krash]

I started the build yesterday. Got the chassis drilled and most of the power supply worked out.

Step 1 was to snap off the tube retainer hooks from the chassis, and then drill for the tube sockets. Further chassis tweaks included relocating the output transformer so it's further towards the middle of the chassis (drilled two new holes, reused the two inner holes to mount the outer screws) since it was in the way of where I needed to drill for the turret board standoffs. Drilled for the turret board and put in the stand-offs, and also installed two six-lug terminal strips on the back-side of the chassis (inside) near the power transformer to put the bridge rectifiers & main ps filter caps.

The original Peavey design & power transformer has a 25.2V winding on the PT for the heaters. The original design has the 4 output tubes running their heaters in series from this winding, and a bridge rectifier & 4700uF cap making 18VDC from this winding for DC heater supply for the three 12AX7s in series. After evaluating a lot of options including installing an auxilliary filament transformer, replacing the entire power transformer, etc., I finally decided just to go ahead and wire up the 36watt heaters in this same fashion.

I guess right now I'm a little stumped as to how to route these heater wires, should I route the AC and DC heater supplies together along the front edge of the chassis? Will the DC heater wires pick up hum from the AC heater wires if they are routed nearby? I have tightly-twisted wire pair. I guess I'll find out. I may just start out routing the DC filament wires around the other side of the chassis from the AC filament.

The other big challenge in the Peavey chassis is that the pots are mounted basically right above the tube sockets making either one difficult to access with a soldering iron, particularly when the turret board is in there. The solution I think is to wire up the tube sockets with the wires sticking through the chassis hole and then install them after they're wired, and same for the pots (wire them up with them not installed).

I plan to use a sag resistor and a switch to turn it on and off on the power supply, as well as a half-power switch, mounted in the effects loop jack holes. I will use a stereo input jack with one side going to the normal channel and the other going to the TMB channel so that with it half-inserted it'll be normal channel, fully-inserted it's TMB channel, and use a stereo cable from an A/B/Y switch and I can switch it remotely. I figure this is a lot simpler than using a channel switch relay.

I did evaluate selling the C30 and just building a complete amp but the real kicker for me in this is the form factor. I really like the compact format of the Classic 30 cabinet and chassis. My 1x12 18W combo does not fit in the trunk of my car and only fits standing up in the front seat so it's really not portable. Whatever "gig" amp I have has to be in this <20" wide form factor like a Classic 30. This basically meant I was going to be doing a custom chassis and build my own cabinet from scratch so that was just going to end up being too much work and expense. The Classic 30 has an 18" wide chassis (2" narrower than a regular 18W) and it's a moderately tight fit for a 36W but doable especially with SS rectifier. The other thing about this is that for an amp to take on gigs where there's always a risk of it getting stolen during load-in etc., the pedestrian appearance of a Peavey amp is a definite theft deterrent.

[lastwinj]

My 1x12 18W combo does not fit in the trunk of my car and only fits standing up in the front seat so it's really not portable. Whatever "gig" amp I have has to be in this <.

what kind of car do you have?



also, make a photo record of the build.

germ

[krash]

I have a Mazda Miata.

I have shot some pics during initial chassis assy and have the digital camera on the bench for the whole project. I'll write it up

[Dynaflow_Donnie]

I have a Mazda Miata.

I have shot some pics during initial chassis assy and have the digital camera on the bench for the whole project. I'll write it up

Sounds cool, can't wait to see the write up. I had a miata years ago, great car, handled really well, SMALL trunk, we had to get REAL creative when we grocery shopped years ago, bags behind the seats etc...

Regards,

Dyna

[krash]

The M2 (2nd generation) Miatas have much bigger trunks than the first-generation cars did. I can fit a Classic 30 in the trunk, or my Princeton Reverb fits, my big pedal board fits even along with a solidbody guitar in a gig bag case (and amp in the front seat). Normally I lay the amp back-side-down in the passenger seat, pedalboard in the trunk and guitar double-gig-bag case in the passenger footwell and this is how I gig in this car.

Ayway I think with the amp I am going to try a 12V Zener to give me 12V DC heaters to the preamp tubes in parallel rather than the 18V series/odd arrangement, since I kind of figure mixing and matching tubes you never know which one is going to have lower or higher heater resistance, but for the power amp tubes series heaters is probably ok since it'll normally have matched/same-brand tubes in all 4 spots. I have all of the power supply wired now except the sag switch (thinking 150 ohm resistor in series with B+) and I hope to start building the turret board soon. Tues-Wed is my busy time of the week so it'll likely be Thurs before I get back to building.

[krash]

I just went and rechecked the original C30 schematic and I was way wrong.

The original power supply has -36VDC coming from the low-voltage secondary bridge and capacitors & resistor dividers deriving voltages for bias and the DC supply for the op amp, reverb driver transistor, channel switch relay, etc.

I guess I should fire up the tranny and measure the voltage on that winding.

Maybe a 6.3V filament transformer is my best bet after all. I really don't want to do series heaters in the preamp.

[krash]

FWIW I think I decided to go ahead and put an additional filament tranny in the amp and rip out the DC filament nonsense.

[bitsandvolts]

The thing about a C30, is that it's a pretty damn cool amp in it's own right...a few mods on the input section (Steve Aloha's website has a bunch of mods) and the amp sounds downright great for what it is.

However, this sounds like a cool undertaking, to say the least...let us know how you make out...

[krash]

Well I have not modified the board or robbed parts from the orig. amp so other than getting the power transformer soldered back in etc, it's returnable to stock.

However, while it's a decent little amp, worth about 2x what you will pay for one, it's not in the league of an 18W for tone. It has a good clean tone right out of the box and also has a decent overdrive tone and I've used it a lot, but the range of "grit" in between Boogie lead tone and Vox clean is not really usable.

Anyway, I just want something with more personality to it.

[krash]

- got the turret board about 90% assembled last night, while my wife was watching a horrid depressing chick flick in the same room. boy it was nice to be soldering rather than having to consciously suffer through that nightmare missing 2x 0.0047uF caps that will make the turret board complete. looks like I ordered 0.047uF's. Boy that'd make this a bassy amp!

- i also ordered the wrong parts for the power tube cathode bypass caps (radial? axial? who's counting?), and ended up putting in 220uF's for now. that value is a bit large, is it not? originally planned 100uF's. i guess when I order more 0.0047uf's i'll get some radial caps to experiment with cathode bypass in the power stage. anyone have comments on this? res. is 125ohm per pair, B+ around 330V, so far 100 ohm screen res.

- got the B+ power supply wired and untested ... decided to abandon the DC/AC combo series heaters a la Peavey, in favor of an auxiliary 12.6V CT filament transformer so that should get the heaters hooked up easily.

- should get to wiring up tube sockets, pots & jacks this weekend, at least until i run out of parts.

- i'm thinking of putting in a half-power switch and some sag resistor switching ... DPDT switch for half-power, when in half-power mode it puts a 150 ohm resistor in series with B+ and lifts cathode ground on the outside tubes. for the sag switch, it would add ANOTHER 150 ohm res. in series (whether in half or full power). any comments on this? i have the holes in the chassis for the switches and figure this may give me some flexibility. is 150 ohm about the right value? for a sag resistor or a B+/half-power switch?

- the 36W TMB turret board i got from turretboards.com does not match the current, or even recent, layout drawings even though it is supposed to be the "Richie" design. so buyer beware! it's usable but you have to apply a little ingenuity to it. at first i thought it was just backwards (turrets inserted in the wrong side of the board), but it's just mostly different.

- man i just heard the clips of the hayseed 30 ... some of those are killer (mostly the cleans, just a hair of overdrive). i wonder if there's a way to capture some of that in the "normal" channel of a 36W? any suggestions?

[breakfastbuddy]

what do you do with the little ot thats in there ? must you buy a new one ? is it a 4k one ?

[krash]

I'm using the original OT (for now).

[krash]

updates, pics ... scroll past the Princeton Reverb etc. info (unless you dig that too) the C30 stuff is like the last 60% of the page.

http://prophetsandpoets.com/josh/guitar ... jects.html

it's almost finished, waiting for three parts from Mouser and then I'll be ready to give it a shot.

Either it's going to blow up in my face or it's going to rock right out of the box That's my bet. I am very confident of the signal wiring but not 100% sure on the power supply.

[krash]

OK for anyone interested:

the amp plays and works and sounds really good. I have only played the Normal channel since I am still awaiting two components (1M pots) that are required to get the TMB channel working. It's got a little bit of grit when cranked all the way, and it's chimey and shimmery clean with good bottom end. Really a great clean tone from that channel. Sure blows away the original Peavey amp's clean tone. I don't even have choice tubes in it yet!

Here is the schematic of the amp as it is right now:

http://prophetsandpoets.com/josh/images ... B-0506.gif

I will probably tweak a couple of cap values in the TMB channel for voicing whenever I get that channel working. Once I get it all finalized I'll go ahead and do a layout drawing too so the conversion project is sort of finalized.

I'm pretty thrilled with the tone of the normal channel right now. I am running this into an Eminence Private Jack in the Classic 30 stock cabinet.

The plate voltage is around 327V with the bridge rectifier and the Peavey iron. The amp is approximately as loud as my GDS 18W with Red Fang but with a lot more clean headroom and much more authoritative bottom end.

[Dynaflow_Donnie]

Glad to hear it Krash. Good to hear you've tamed it, can't wait to hear how the TMB channel works out. I'm thinking of doing likewise with my 50 watt crate stealth, so I've been watching this closely.


Regards,

Dyna

[krash]

I just played it A/B with my GDS combo. It breaks up when maxed just about like the GDS vibrato channel does on about 3 or 4.

You can definitely hear a similar character in the tone of the two amps. The ex-Peavey has pant-leg-flapping bottom end when cranked but the GDS gets a lot more compressed and spongy.

I would have to say the Normal channel of the GDS when cranked is louder, but it's a LOT more compressed sounding and has a whole different character to it compared to the ex-Peavey. The GDS has a +4dB more efficient speaker so it should make up for the 1/2 power. When they are set to a cleanish tone, you can hear the family resemblance. But when you crank the GDS, it definitely has a whole different character.

I needed an amp with a killer clean tone to add to the stable and this definitely does the trick.