Guitar Gear Forum

I just finished designing, prototyping, tweaking and finalizing what I'm calling the 5E3M Deluxe Micro. It's a 1 to 2 watt two tube (12AY7 preamp & 12AT7 parallel single-ended poweramp) version of the 1957 classic Fender tweed Deluxe tube guitar amp.

The preamp is an almost exact copy of the 5E3 Deluxe's Bright Hi channel so it really sounds like a Deluxe but volume is kept lower and the inclusion of a Master Volume allows for really low volume practice.

I used two of Merlin's (the ValveWizard) B9A prototyping boards to build the amp. It uses a $14, 3.5 watt Fender reverb transformer for the output transformer. Power transformer voltage is pretty flexible and will work with anything between 190-0-190V to 300-0-300 volts.



The amp really does sound like a micro Deluxe and it sounds absolutely killer through a Weber 12A125A 12" AlNiCo speaker. I'm not a good enough guitar player to post sound clips but I hope to get a friend to cut some clips so people can hear it.

Preamp on the left, Poweramp on the right.



The details of the design and build are here: http://robrobinette.com/Deluxe_Micro.htm

Excellent first post! Would love to hear clips!

to the greatest show on (virtual) earth

Merlin's B9A development boards are about $7 each which includes shipping from the UK. The US distributor was out of stock so I ordered directly from the ValveWizard here: http://www.valvewizard.co.uk/developmentboard.html

Very nice. I've been thinking of trying out some of the B9A boards in a rack a pre.

The one detail I missed on the B9A boards is the fine print on the backside, "Fit tube this side." I put the tube socket on the front of the board then after having problems firing up the amp and finally noticing the fine print I had to put a second set on the correct side

Sweet! Got any clips recorded?

Here's an optional EZ 81 tube rectifier for the Deluxe Micro

Here's the complete Deluxe Micro with tube rectification.

Welcome to the fold brother! This is the best guitar/amp site on the net.
I checked out your website... Wow! You like to keep busy!

Speaking of my website I also have a "How Tube Amps Work for Non-Techies" webpage: http://robrobinette.com/How_Amps_Work.htm

This is an annotated 5E3 Deluxe schematic I did that lists the function of every component and shows the signal flow.

You are a smart dude - I'm going to have to read that link again when I'm not drunk....

Yup - great resources on those pages. I really like the functional / signal flow diagrams and component labeling - really helps put things together!

Here's an AA1164 Blackface Princeton Reverb Tremolo & Reverb Add On Circuit using the Merlin B9A boards

some sweet stuff in here. that circle alignment pcb is genius.

I played around with the Deluxe Micro's B+ voltage and it seems any 190-0-190V (285V B+) to 300-0-300V (430V B+) transformer will work. Some of the Blackface amps push their 12AT7 reverb driver with 460V at the plates so B+ voltage isn't critical. The lowest Blackface reverb drive voltage I found was 390V.

Using my Firefly's Hammond 269EX 190-0-190v power transformer I only got a B+ of 285V and the V1 plates were at 110V. The Micro Deluxe sounded good but not as good as with a B+ closer to 400V.

I hooked the Deluxe Micro's heaters to a dedicated 6.3V transformer then used a variac to control the HT from a 375-0-375V transformer so I could vary the amp's B+ voltage.

I tried everything between 230 to 460V B+. At 275V of B+ I got 270V at the power tube plates and 103V at the V1 plates. With a low B+ like this the amp loses some headroom and sparkle.

The amp sounded great with a 460V B+ with plenty of clean headroom, extra clarity and chime but I'm not sure how long the 12AT7 power tube will last. I believe the sweet spot comes from 290-0-290V of HT which gave me a B+ of 400V and 395V at the power tube plates and 150V at the V1 plates.

Deluxe Micro on the left, Firefly at center.


I also took some time to compare the Deluxe Micro to the Firefly 3.0 I just built. The DM sounds very tweedy compared to the modern tone of the (unboosted) Firefly as it should. The DM makes my Tele sound like Tele.

I'm still trying to get a good player to record some clips.

I took voltage measurements with my preferred B+1 of 400v. The B+1 powers the single-ended output transformer. I get 393v on the power tube plates with 11.94v at the single 2.2k power tube cathode resistor.

With a plate-to-cathode voltage of 381v and the 12AT7 rated at 2.5w of idle dissipation I get 2.7ma of cathode current (no current loss to screens), 1 watt of dissipation which is 40% of the 2.5w rating so it's running a little cold. I will parallel in another cathode resistor to see if I can bump up that dissipation closer to 60 to 70% and check how that affects the amp's tone.

With a B+1 of 400v I get a B+2 of 311v after the 27k dropping resistor which feeds the 100k load resistors which drops 155 and 150v on the 12AY7 V1A and V1B plates with 2.33 and 2.5v on the cathodes.

I'm battling some noise/distortion on some chords at max volume (and max master volume) so I'm going to try a 500KA master volume pot (current is 1MA) to attenuate some more driver output.

This is so much freakin' fun

I strapped a 1M resistor across the Master Volume pot input terminal to ground to simulate a 500K pot to increase attenuation of the signal coming from the driver with no effect.

I added a parallel 10k resistor to the 2.2k power tube cathode resistor which dropped the cathode resistance to 1.8k and it bumped the bias from 40% to 48% but the power tube overload distortion is actually worse.

My next step is to remove the 10k cathode resistor I just added and bump up the 470k power tube grid stopper to 750k. I may revisit the power tube bias after I get the overload issue solved.

I also tested the headphone output for the first time. It works really well for clean tones and you can even dial back the Master Volume a whole bunch and get some preamp tube overdrive.

It's easy to add the headphone output to this 1 watt amp because all you need is a stereo TRS jack (1/4 or 1/8") and a 10 ohm 2 watt resistor. The resistor parallels the headphones (which are anywhere from 32 to 600 ohms) to load the output transformer with approximately 8 ohms.

The headphone resistor also loads the output transformer with 10 ohms when no speaker is plugged in so it can prevent damage to that expensive $15 transformer.

I tried a 12AU7 as the power tube and I don't know if it didn't like the 2.2k cathode resistor or what but it couldn't handle high master volume settings. It would pop and motorboat when pushed. The bad thing is I forgot I had an AU7 in V2 and started modding the preamp to solve the overdrive problem.

Today I decided to try a 12AU7 power tube again and when I pulled V2 I realized it was already an AU7 so I put a 12AT7 back in V2 and everything was sweet again. Nice attention to detail.

I reversed all the mods I had done chasing the AU7 overdrive problem. I settled on one change and that's using a 500KA pot for the master volume instead of the 1MA I originally planned.

I still need to plug in the tone generator and do some scopin and probin and measure the power output but the little amp is sounding pretty good.

we're gonna needs some clips!

But this is awesome.

I finalized the design and added a "How the Deluxe Micro Works" section to the webpage http://robrobinette.com/Deluxe_Micro.htm.

We already have a successful second build from a fan of my website. He used a turret board for his build. I'm hoping he will post some clips.

I did some more tweaking to the amp design and the little Deluxe Micro sounds fantastic. It's absolutely killer tweed with a 12AY7 in V1 and it gets snarly mean with a 12AX7. I made four design changes during the test and tweak phase. The first was to drop the Master Volume pot from 1M to 500K to attenuate the signal from the driver stage to the power tube. The second change was to increase the power tube grid stopper resistor from 330K to 470K, again to attenuate the signal from the driver stage and reduce power tube blocking distortion. The third change was to add a Master Volume Bright Cap to add some brightness to lower Master Volume levels. This really made the Master Volume more useable. The final tweak was to drop the power tube cathode resistor from 2.2K down to 870 ohms which boosted the clean power output from 135 milliwatts up to 720 and max power with distortion climbed to 1.33 watts. The amp sounds a little more lively too. I also changed my recommended power transformer to the ClassicTone 40-18027. All the diagrams on the Deluxe Micro webpage reflect these changes: http://robrobinette.com/Deluxe_Micro.htm

Tonight I put the Deluxe Micro through its paces with pedals and fx. Hooked up a POD 400HD and tried everything. I also tried a Seymour Duncan tube overdrive, Boss PS-6 Harmonist and boosted EQ.

The amp's two volume controls allow you to use pretty much anything with good effect. The main volume controls how hard the preamp is pushed and the master volume controls how hard the power tube is pushed so you can keep both tubes happy no matter what's plugged in. This little amp makes me smile when I play it.

I know, this thread is useless without sound clips.

For comparison I measured the output of my my Firefly (2 x 12AX7 preamp and 12AU7 self-split push-pull power tube) puts out 154 milliwatts of clean power and 1.12 watts max with distortion.