Some questions about 70's ODS

[Hendrix]

Hello Dumble-fanatics!

With some experience of building stompboxes and guitars I thought it was time to make an amplifier. I'm using the 70's ODS schematics from the schematics heaven website. Are these schematics okay, by the way?
I've a few more (beginners)questions: What kind of diodes are supposed to be used in the powersupply? The choke is 80 ohm in the schematic, can I use a 90 ohm? (80 ohm choke is hard to get in the netherlands, apparently)What kind of pots do I need for Bias of the poweramptubes?

Thanks and kind regards from the Netherlands!:)
Dennis

[d95err]

(I haven't built a Dumble-style amp, nor am I a guru or expert but here goes...)

A Dumble seems like a very ambitious project as a first tube amp build. I'm sure it can be done, but I would recommend sticking something like the D-Lite, rather than the 70s version. In particular, make sure you're using a well-tested layout, rather than trying to come up with your own.

By using a more commonly built version, you'll find it much easier to get help here on the forum, and to get something out of all those discussions on how to voice and tweak the amp.

80 or 90 ohms should work equally well for the choke. You could also skip the choke ("Robben Ford mod") and use a resistor instead, as in the D-Lite.

Good luck!

[odourboy]

I'd recommend you use schematics found in the 'Dumble Files' section of this forum posted by HiGain.

They are reported to be more accurate than schematics heaven.

[Funkalicousgroove]

There are nothing wrong with the schematic heaven70's schemo's, they are correct-and there is no difference in a D-lite as far as complexity of build.

Start with something that is actually simple like a Champ or 5E3 Deluxe, and make sure you can get it working without an issue, then perhaps build something with reverb and trem like a blackface, then try a dumble, JMHO.

To answer your questions:

1N4007 Diodes will work fine
The choke in that amp was most likeley a Fender and spec'd at 90 ohms, but what you are really concerned about is that it is a 3H and will take the current load.

Now, what Odourboy says about the schematics in the files section is true, they are later models, and will probably yield more of what you are after tone wise, the 70's is kind of harsh and gritty sounding, but the schematics are totally correct.

[Hendrix]

Thanks for the advices, guys!

[oldmacman]

Those schematics aren't exactly right, if you mean the ones that are split up into 4 PDFs.

The one at https://tubeamparchive.com/files/1977_a1_449.pdf is closer.

You'll want the 390pF cap across the 220K grid resistor on CL2, the 44M on the local feedback loop, and don't leave out the 220K resistor before the drive control or the 150K resistor before the level control - they're key to the sound. You might also try changing the cathode bypass caps on CL1 and CL2 to 25 uF.

[heisthl]

Those schematics aren't exactly right, if you mean the ones that are split up into 4 PDFs.

The one at https://tubeamparchive.com/files/1977_a1_449.pdf is closer.

You'll want the 390pF cap across the 220K grid resistor on CL2, the 44M on the local feedback loop, and don't leave out the 220K resistor before the drive control or the 150K resistor before the level control - they're key to the sound. You might also try changing the cathode bypass caps on CL1 and CL2 to 25 uF.

I think you meant to say "220k before the entrance trimmer"
Those 2 resistors are important "tone shapers" but don't feel locked into those values, ideally use a resistance decade box while tweaking to get thes tuned for optimum OD sound with your amp and taste. On some builds adjusting the value of the 150k before the level control (or ratio) can really help smooth out (or mask) some lower mid harshness.