100w 2nd Gen. ODS build

[DSull89]

Thanks Ian, I really appreciate the input. I’ll just get my hands on some 100R’s and stick to the formula here. No big deal. Looking forward to hearing what this thing can do.
-Dan

[ijedouglas]

Same here

[DSull89]

Some more progress…

[dbharris]

Those Jupiter caps sound great in my 2nd gen. I think you'll like them.

Looks like you need to flip the orientation of your screens filter cap.

-Dan

[DSull89]

Doh! Thanks for pointing that out, Dan! Will rectify that tomorrow. What sound difference did you notice with the Jupiter’s? I believe I got them after looking at your build pics. Lol
-Dan

[dbharris]

Doh! Thanks for pointing that out, Dan! Will rectify that tomorrow. What sound difference did you notice with the Jupiter’s? I believe I got them after looking at your build pics. Lol
-Dan

For me, it is more how the power supply feels via low end response when you are playing loud. The bass stays firm and immediately responsive while being "clear" sounding.

Btw, for a 100W amp you have about half the filtering that HAD would normally use. The layout in the files section is for a 50W and shows the 100uf B+ filters in series. But a 100W would often have 220uf in series.

-Dan

[DSull89]

I wasn’t aware of the filtering issue, I based my choice of filter values off of the only gut shots of a 100w 3rd Gen I could find which were Charlie Wilson’s photos of #54…

[martin manning]

My guess is HAD’s thinking on the reservoir capacitance evolved over time. For reference, the BF Twin had 2x70uF, maybe they were actually nearer 100uF. He may have started there. #124 had 2x 300. Maybe that was for a particular player, or maybe he decided it wasn't necessary, since the later amps were 2x 220. Interestingly the '65 Twin Reverb reissue has 2x 220.

[DSull89]

Thanks for all the info and suggestions, everybody! So from what I’ve read here on the forum, the 100uf filters would give a looser low end response overall. Is that a typical characteristic of 2nd Gen’s?

Thanks,
Dan

[dbharris]

Yes, that is correct. But you may love the amp setup like that. I would just play it for while before considering any changes.

-Dan

[DSull89]

That’s my plan, thanks for the reply, Dan! Those Jupiter’s were pricey, therefore in they go. Lol
-Dan

[Max]

I wasn’t aware of the filtering issue, I based my choice of filter values off of the only gut shots of a 100w 3rd Gen ...

Here are two links to pictures of the inside of two ODRS amps in 2nd generation chassis:
One has a 100W power amplifier (“Guts of Dumble Lowell George Sister Amp”) https://www.instagram.com/kittyhawk_dum ... jNOPROGIw/
The other one has a 50W power amplifier (“Guts of vintage Dumble Overdrive Reverb Special 50 Watts”) https://www.instagram.com/kittyhawk_dum ... kBV09Ofai/
And both apparently have the same filter capacitors for their power amplifiers (2 x TVA 1620 / 100UF - 350VDC).

[DSull89]

Thanks, Max! Great info! Had another question about cap orientation. I found an old Elmenco spec sheet for that designates the stripe on the cap as “ground”. Did I orient my caps correctly? I’ve seen some variation on a number of build threads here.

-Dan

[martin manning]

If you look at the eyelet board layouts in the Dumble files section https://ampgarage.com/forum/viewtopic.p ... 08#p365408 you will see a line | on the caps that indicates the end that has the lowest impedance to ground in the circuit. It was common practice in RF applications to orient the outer foil lead of the cap in that direction to minimize noise pickup. In the past the outer foil lead on caps was correctly marked, but in current production any such marking is likely to be random. I added a comment in the first post of the eyelet board thread about that. We don't know if HAD was following that convention or not.

[DSull89]

Thank you, Martin! I missed that detail on your board layouts, thanks for clarifying. I’ll be more diligent in the future. Looks like I’ve got some caps to flip.
-Dan