Pedal Mule 30 - Prototype build

[RJ Guitars]

Wow, tough days in TAG forum world lately... this amp generated tons of interesting conversation when the concern was about ethics and such, but not too much curiosity in the actual build, or so it might seem. Whats up with the build threads these days... are we a dying breed?

Anyway, I soldered a few more wires tonight and renewed my love for a pair of octal output tubes as I went to work on the quad of EL84's. There sure are a lot of wires in a pretty small amount of space but it went pretty quick and smooth.

On my previous post nobody caught me with no ground wire on the IEC socket... I noticed it as I began to look things over to measure voltages. For the curious the dropping string on the power supply should look a bit interesting.

[BLT]

Just figured you hadn't got to ground yet. Those noval pins do fill up fast. I've been following this build all through the process of sourcing materials, the rancor and objections to proceeding, and the subsequent calming of nerves, so I'm glad that you are going to proceed come hell or high water. I'm in the process of converting an old 6AQ5 amp to something a little more Spitfiresque. Your build would be somewhere in the distant future, but that doesn't mean I'm not interested. It's in line with the EL84 type amps that I really enjoy.

[johnnyreece]

It seems the TW section has been filled up with discussion of RESONANCE, man! I may not have noticed the IEC wire, but I DID notice the one flathead screw amidst the Phillips. I'm curious how this turns out, as my brother frequently has me build things for him, and he's getting quite a pedal board. He might be interested in something like this going forward.

As far as interest in build threads, I noticed my own thread mostly generated discussion from me. That's okay, though. I don't want everyone TOO interested, or 6J5's may skyrocket in price.

[Mark]

Correction Johnny, the stupid resonance thread that should have been moved into the garage. Somehow I don't see us building what they propose.

[didit]

Power on RJ. To my somewhat tired eyes everything looks great. Looking forward to hearing (literally) your results. You may recall I picked up two of your A470 types last September. One was to build something rocket-like but the other was/will likely be following in this form. You are in undiscovered territory. Though I do recall Mark Fowler has a build on this mould too. No final reports that I've seen however.

As time permits between work & travel etc I'm definitely tracking how this goes.

Best .. Ian

[RJ Guitars]

The end is nigh... below is a photo from where I stopped yesterday. I actually finished up all the major stuff and got to hear the amp tonight... more photos tomorrow after I get a chance to clean it up a bit.

A few items that I wasn't expecting. The first was that I had a bad hum coming from one of the positions on my deep switch (I decided not to swap resistor values on the feedback like my schematic shows but may have to revisit that idea)... I was planning to choose between a couple bias cap values on V1. Mostly it makes things hum when I get too small a cap.

After I sorted out the hum the second thing I noticed was this amp is surprisingly loud. Loud enough to feed back with my strat. The final thing was that my suspicions about this amp not sounding especially nice might be wrong...

more to come soon!

[DocJames]

Hi RJ, I'm always interested in the builds you are taking on. Glad you got this all worked out and I look forward to see more pictures and possibly some audio?

[johnnyreece]

The final thing was that my suspicions about this amp not sounding especially nice might be wrong...

Those are the kind of surprises that don't happen nearly often enough.

[M Fowler]

Glad your getting close to finished on this amp Bob.

[johnny riff]

greetings.. while you're messing with a TW.. try a split load PI.. 2 pre tubes .. octal or 9pin..

[johnny riff]

maybe fowler could tell you about the one he built.. seems like he's built everything else...hehe
with all do respect.. the mule is a mule.. been there years ago.. i thought lets keep moving. all the best

[RJ Guitars]

Finally... I have all the parts in the right places and I'm calling it done.

I started with a 100pF bright cap but I could scarcely hear any impact so I kept going up... eventually I liked it at .022uF. With that value it has some bright boost and also gives it just a little bit of a mid boost as well.

I added a 100K feedback resistor and that added some really nice flavor. This is switched in and out using the deep switch.

Both of these mods really added good stuff... I wouldn't build it again without them.

After making all the mods and cleaning it all up I brought it in the house and gave it a work out. Nice sounding amp with enough bass to wake the dead... but the bass control works really nicely. It does kill all the volume if you run it to zero...

One final item that still needs attention before I declare this ready for prime time. I still hear some power supply hum. It's faint but will give me a bit to work on. I am suspicious that there is not enough filtering on the power supply.

A few pictures as it is now...

[davesi]

Bob, on my last Rocket, I decided to pay attention to RA and grounded the HT CT, mains and screen filters and power tube cathodes to the first star. I would have grounded the filament CT there as well but I like the resisters to ground better. It is the quietest Rocket I have built. I hate hum.

[RJ Guitars]

Hum no mas!

[xtian]

Hum no mas!

What did you do?