4-4-0 build - done 2-14-15...happy Valentine's Day!

[hans-jörg]

Johnnyreece,
may I give you a small tip: put the grounding of the bias (2x1 Ohm) to the power amp grounding point, or bias circuit grounding point. Will be much more quiet.

Hans-Jörg

[johnnyreece]

Thanks for the heads-up! I'll do just that! I was sticking, somewhat, with the 4-4-0 layout, and that's where they put it. I'm starting to get to that point now, so I'm glad you chimed in. I just made the turret boards yesterday. Need to purchase the guts now; caps, resistors, etc. I might have enough on-hand to do it, but it would be a mish-mash.

Any suggestions on coupling caps? I'll most likely stick with metal film resistors. I keep kicking back and forth about trying Sozos in here.

[RJ Guitars]

I know the circuit likes the cde orange drops. If you don't have them or other (sprague) polyester orange drops then try the Sozos... my 2 cents.

[johnnyreece]

Okay, finally decided on caps, and I'm gonna give the Sozos a try. In the meantime, I started populating my board with some of the stuff I have on hand. Here's what it looks like so far (try not to be too jealous of my *so* in style countertop):

[IMG768]http://i218.photobucket.com/albums/cc165/moto_xxx199/Amp%20designs/5B8A0F15-ABC0-42FB-A15B-D5626C4D19CB_zpsfimveunv.jpg[/img]

Hopefully, the rest of my stuff comes in this week, and I start making real progress soon.

[sliberty]

Looks like you plan to ground the power tubes (via the bias plugs) and the output jack along with the input jack and preamp grounds. You might consider putting a ground lug near the power tubes, and taking both of those grounds to that point instead. Of course you can always do this later if you decide to stick with the current grounding until you hear the results. Maybe you won't need it.

[Edit - I see someone else also picked up on grounding here with a slightly different proposal]

[johnnyreece]

Looks like you plan to ground the power tubes (via the bias plugs) and the output jack along with the input jack and preamp grounds. You might consider putting a ground lug near the power tubes, and taking both of those grounds to that point instead. Of course you can always do this later if you decide to stick with the current grounding until you hear the results. Maybe you won't need it.

[Edit - I see someone else also picked up on grounding here with a slightly different proposal]

Yes, but thanks for catching it! Mostly, I was sticking with the 4-4-0 layout, but that is one thing I will vary, after advice from folks much wiser than myself. I'll eventually update my layout to match, after all the final tweaks are said and done. I'll be dropping the B+, as well. Hopefully, those are the only two big changes. The dropping string may change, since I'm lowering plate voltage for the first stage, but hoping to keep the rest where they're designed to run. I might run the 6J5 right up on their max plate voltage, or a teensy bit over, to help keep from having to modify the string *too* much. It'll be an experiment, for sure!

[romberg]

I found the 4-4-0 grounding scheme to be an elegant piece of engineering. If it did not have a cap can it would look like something out of Merlin's book complete with a single wire connecting the circuit to the chassis for ground reference only.

In particular, I've run the power tube cathodes to the test points and then to the associated supply cap just like the 4-4-0 does in two amps. One uses el34s. It works fine. There is only milli amps/volts running in that wire.

Mike

[RJ Guitars]

...I might run the 6J5 right up on their max plate voltage, or a teensy bit over...

Tubes tend to sound best on the ragged edge of self destruction... Go Johnny Go!

[johnnyreece]

...I might run the 6J5 right up on their max plate voltage, or a teensy bit over...

Tubes tend to sound best on the ragged edge of self destruction... Go Johnny Go!

I just wish there was a little more data I can track down on these tubes in this situation. Tons of discussion about preamp; none yet (that I've found, anyway) in power amp designs.

Edit: There don't seem to be any Class AB specs for this tube. I'm going to leave the voltage alone on this and see if it can withstand 350 or below. From what I've seen on other tubes, you can usually squeeze a few more volts into it in AB. If I cook a couple tubes...well...thanks to RJ, I've got a few more and will try dropping the B+. Until then, I'm waiting for parts!

[johnnyreece]

Just to update, so far, here's what I have learned on this project: If you're going to use Sozo caps, buy them in bulk so when you actually get them, you'll have plenty. The .022's have been back ordered for the past month. I've got everything else (well, except the cab, I guess...) ready to go for this. I'm about to just toss in some Mallorys and call it a day.

[stephenl]

Hi Johnny,

I have a Heyboer OT that Cliff Chappell had designed for the 440. I ended up converting the amp to a 6V6 Express. 22K primary and 4, 8, 16 secondaries. It's beefy, about the size of a good 20watt. The bass response is a big improvement over the Hammond 125. PM me if your interested.

[johnnyreece]

Here it is as it sits now. Hard to get too motivated until my backordered parts arrive. Sorry for the crappy cellphone pic, but it's not exactly like there's anything revolutionary here.

[IMG768]http://i218.photobucket.com/albums/cc165/moto_xxx199/Amp%20designs/1491488C-3332-48F9-ABDA-5EC2A91F93A3_zpsqifhqfpm.jpg[/img]

[johnnyreece]

Started working on the cab. Going to be tolexed with a curly maple faceplate. I don't think Mike is going to be out of a job anytime soon...Going to sand/route shortly. Then I'm going to review Taylor's tolexing guide. Wish me luck!

[IMG768]http://i218.photobucket.com/albums/cc165/moto_xxx199/Amp%20designs/3330E0BE-B3AC-4372-8902-ABBB3909015F_zpsijhyt9ad.jpg[/img]

After looking at this, I wish I had done it Komet-style; with cleats for the front panel, rather than 'Wreck-style. Oh well. Live and learn! It's too bad I never do the same thing twice...

[johnnyreece]

One more pic tonight. Front panel stained and five coats of Tru Oil.

[IMG768]http://i218.photobucket.com/albums/cc165/moto_xxx199/Amp%20designs/998A8C48-C4F6-4B13-A893-5BBBE182C2D7_zpsoqrsarxo.jpg[/img]

[johnnyreece]

Cab is tolexed. My first tolex ever. Not terrible; not great. I learned a few things, if I ever do this again. Don't mind the messy shop area...

[IMG768]http://i218.photobucket.com/albums/cc165/moto_xxx199/Amp%20designs/BB0C3E7F-2049-466C-9877-199875052269_zpsex822jej.jpg[/img]