HRP_50

[maint_tech]

So I drew a schematic.
Mostly the DBM/Mark Fowler HotRodPlexi, some minor changes.
Bass pot using all 3 legs, Hammond Iron, Presence wired to keep DC off the pot, PS dropping R's changed because I tried to use Duncan's PSU designer...
Anything that should be changed before I work a layout and commit a chunk of G10 to the drill press?
Edit: Schematic and added layout. Pretty slow going this time of year with hunting deer and hen-of-the woods, finishing the garden, and that whole going to work every day thing...
Joe

[xtian]

Wow, that looks like a lot of fun to drive. But, THREE treble peakers?!? Two with 1000p caps?

[bepone]

dc heaters are mandatory for first two stages, and why is there half of 5751 for the first stage? for good signal/ noise ratio first stage must have as much as possible gain. and here is opposite approach. + it is wasted half tube?

[maint_tech]

Wow, that looks like a lot of fun to drive. But, THREE treble peakers?!? Two with 1000p caps?

Well, it has been described as a harmonic monster. Might have to wear a mask just to keep my face on when I fire it up.

+ it is wasted half tube?

Yes but that is not so uncommon as in some TrainWrecks, eh?

[bepone]

if you connect this 5751 in parallel (paralleled sections) then you can have some good job there, noise going down and gain up

[Reeltarded]

I would delete all peaking until the amp is built and then make only as much as it needs as early as possible

I would not plan to use a lower mu tube.. You aren't actually making much gain. You are leaving lots on the table. A stock JCM800 uses three and the CF.. right?

Me H

[Reeltarded]

Even with the peaking as you have it, this amp will sound about the strength of the normal II input on an 800. Motown.

[maint_tech]

All good input to think about.
Design is not mine, just following on what others have done, still have to finish the layout.

[Reeltarded]

I cant look at the pdf and do this at the same time.. but here is how I would approach (generally) your scheme

As mentioned plan on no peaking until you get the amp running then add what you need early in the circuit (as early as you can but not all in one place)

12ax7 V1 and if you leave it as no normal plexi input try 150-180k plate on first stage. This is still small in a similar circuit.

TS. Slope resistor 33k swap to 47-56k. That will make a beautiful dip for an apparent lowend lift, consider a smaller treble cap.. but it's all good.

I don't use DC heaters on much more insanity. It would be fine to do so, but this is a very small murder.. you will easily get away with it.

[Littlewyan]

That is going to be BRIGHT with all of those treble peakers! As Reeltarded said, start with none and add them early in the circuit if needed. I built a 4 gain stage amp recently which only had a peaker after the first stage and it has a fairly balanced tone. The EVH 5150 doesn't have any peakers at all, it uses smaller coupling caps instead. The AFD100 has two and is considered a very bright amp. Just to give you some examples.

I also agree on the DC heaters, they're not essential for a build with this level of gain. I would elevate your heaters though just to give the cathode follower a helping hand.

You may need some plate bypass caps to cut some fizzy high end, if you have any.

[Reeltarded]

I built a 4 gain stage amp recently which only had a peaker after the first stage and it has a fairly balanced tone.

The EVH 5150 doesn't have any peakers at all, it uses smaller coupling caps instead. The AFD100 has two and is considered a very bright amp. Just to give you some examples.

The 4 stage thing is interesting and we probably share a lot of recent experience. I made the last three BLOATED and RIDICULOUS and the first stage is ANGRY, BRIGHTLY PEAKED, and PEEPY LIL COUPLER. (500p)

[Littlewyan]

So many ways to skin a cat! Mine is now a CAE 3+ lead channel but with reduced coupling caps on the first and second stage, a .68uF cathode bypass on the last stage and Marshall tonestack. Gives me a polished classic Marshall tone. I tried just having a smaller coupling cap on the first stage but I never could get it to sound right, not in this configuration anyway.

[M Fowler]

So I drew a schematic.
Mostly the DBM/Mark Fowler HotRodPlexi, some minor changes.
Bass pot using all 3 legs, Hammond Iron, Presence wired to keep DC off the pot, PS dropping R's changed because I tried to use Duncan's PSU designer...
Anything that should be changed before I work a layout and commit a chunk of G10 to the drill press?

Joe
HRP_50_V1.0.pdf

Joe looks good. Just build it and then if you need to do any changes you want. Many guys are using the HRP50 and 100 and none have asked for changes.

Mark

[maint_tech]

Added the layout I intend to use to original post, modified the skat a bit too. Managed to fit everything on a 17" board, had a local tin bender make a 20" chassis.
Faceplate and BOM next.
Joe

[pdf64]

I think it’s better to connect an OT secondary safety resistor directly across the winding, rather than via the impedance selector.

A 7k6 primary on the OT?