AFD 36 39

[Smokebreak]

I started in on one of these the other day. I had converted my very first amp, P1ex, into a SE version of this a while back, and was impressed enough to do a big one.

MC 50W iron, Ebay chassis. I'm not real sure what is "the" circuit to cop, so I've got a lot of components mounted and some switches. I'd also like to have a JCM800 channel, and will try to do that via switching jacks, hi/lo. I'm looking forward to some experimenting. I also can't stop watching the Ritz recording, though that was a different amp I believe. Nonetheless, once again inspired by the gutter rock. That's where I learned all my rockstar moves, anyhow.

[Smokebreak]

Do i really have to put input shield on plate? Won't a small pf between grid and plate suffice for Miller effect?

[Darkbluemurder]

That should be the same effect. However I shy away from using a plate-to-grid cap on the input gain stage - if that cap shorts you have the plate voltage on the signal input.

Cheers Stephan

[Smokebreak]

Right. I'll try it in different spots for a minute at least. I'm really interested in what shielding the input signal with 200v sounds like Very nice schematic you have Stephan, I have a 470k/390k on my board to try out your circuit .
Anyone tried the Aro/ Staalhoofd thing? 5 stages??

[Reeltarded]

36 is pretty ripping. 39 is sweet bit nobody has the balls to wire it up as it really goes. No master and two gains.



Do it.

[M Fowler]

I built the DBM #39 as Darkbluemurder's schematic showed and the amp is fantastic, the owner loves it.

He has compared it to Splawn Nitro and Quickrod but loves the #39 more

Good job Stephan and thanks for providing the schematic.

Mark

[Smokebreak]

36 is pretty ripping. 39 is sweet bit nobody has the balls to wire it up as it really goes. No master and two gains.



Do it.

Same circuit though, right? Just lack of MV in original? No way Jose

I finished the wiring and spent all morning troubleshooting low output. Did all the usual stuff. Stage 3 is plate>cc>470k divider>grid. I forgot to solder the lower leg to ground and passed over it 10 times thinking " oh the amp will just be meaner, I'll wire it when I get her running". DOH the grid had no ground reference. All is well I'm gonna put in the switching.. more in a bit.

[Smokebreak]

Amp is waaay too bright and lacks ass, using the scheme on Metro p.140. For my taste at least

[mhartman]

I built the preamp section of my last build based on my take of the AFD 36/39 circuit (after reading far too many posts over on Metroamp).

https://tubeamparchive.com/viewtopic.ph ... sc&start=0

If you want a decent starting point, either work from the layout on Metroamp or check out Ceriatone's AFD #35 Layout (freely available). They will get you in the right direction -- but there is much tweaking to be had from there.

[Smokebreak]

Thanks man! Yep I've been working off the Ceriatone layout, the A-Wai schematic from Metro, and DBM #39, making sure I've got all the elemnts of each on switches. Right now I'm running the Metro and it's really scooped

Edit : well it sounded bad through a V30, but glorious through a gold go figure

[Reeltarded]

They kick ass through 75s. Way to trebly thouh, yah.

[Smokebreak]

I've got this thing right where I want it now. It took a lil of this and that to tame the brightness and get the mids cookin, but I'm really excited about it now.
Cathodes are 2.7k/.68, 10K, 10K, 820r
I've got switches on stages 2,3,4 for parallel

stage 2 switches in 3.7K/.68u or .1u or stock
stage 3 switches 3.7K/.68u or .1u or stock
stage 4 switches .68 or stock

I've got 2 inputs wired to do hi/lo 3 or 4 stages, so the high is the AFD and the lo is a JCM800, but the lo isn't dependent on a pot for the grid leak like a JCM800, which was important to me for some reason..

So for AFD input, I like it best stock, with only 1st stage bypassed. Adding the .1u to the 2nd stage cathode gets into slash-ville. Anything else bypassed at the same time is just a hissing mess.

For JCM800 input, switching in 3.7K/.68 on 2nd stage(now the 1st stage) gets it to typical stock 1st stage 2.7k/.68 JCM800 value. I added a 470K/2n7 peaker after this stage, so it's basically stock JCM800 at this point(besides the 2n7, which just sounds better) I can switch in 3.7K/.68 on the next stage(10K) and now it's cali-modded 80's style.
I could honestly live without the .68u on the next 820r stage.
There's a handful of other switching combos(1st 3 stages all 2.7k/.68 yikes!) but these are the ones I find most useful.

All peakers/dividers are 470k/2n7, treble cap is 500p, largeish caps across 1st 2 plate resistors. 22k/4ohm,.68, 5K NFB/pres

Pics are before some of the mods

[M Fowler]

Looks good and sounds like fun.