70's circuit updated late '80's

tubedogsmith · Post by **tubedogsmith** » Wed May 06, 2020 2:04 pm

As anyone seen anything like this. The first and second preamp tubes have plate values on #1 of 180K with a 1k cathode, 130k with a 2k2 both caps 25uf25v. Tube 2 is 220k with a 2k2 cathode, 100k with a 1.8k, both caps 5uf/25v. So, with this in place the voltage on the first half of each tube is running low voltages, 130v to 160. the amp sounds pretty good like this but real squishy and soft, lower volume as well. I swapped the cathode resistors out to 180k with a 2.2k, 130k with a 1.8k, 220k with a 3.3k and 100k with a 1.3k like the other OD specials I've seen and all fell into shape. much louder, clearer, bolder sounding and all the voltages feel into the line I'm used to. So, have any of you seen a circuit like the one I'm speaking of? I don't have the original amp here as I didn't think I'd need it and then this.

fred.violleau · Post by **fred.violleau** » Mon May 11, 2020 7:12 pm

Maybe Max, Tony, or Jelle could chime in since they have an encyplodic knowledge of these amps !

Fred.

martin manning · Post by **martin manning** » Mon May 11, 2020 7:33 pm

What amp was this, an ODS replica of some sort?

dcribbs1412 · Post by **dcribbs1412** » Mon May 11, 2020 8:30 pm

Sounds like a version of Ultra Phonix's plate values discussed in this thread:
https://ampgarage.com/forum/viewtopic.p ... x&start=30
How does it sound?
Any pics?

tubedogsmith · Post by **tubedogsmith** » Tue May 12, 2020 11:16 am

The amp is an original late ‘70’s model that was updated by Dumble in the mid/late ‘80’s. I’m curious if anyone has seen the cathode and plate circuits setup as explained, basically backwards.

mojotom · Post by **mojotom** » Tue May 12, 2020 12:43 pm

Thanks Tubedogsmith !

ODSR 60 is the only one I can think of, supposed to be 180k/1k and 130k/1.8k on the clean side. Low plate on the OD side.

beasleybodyshop · Post by **beasleybodyshop** » Tue May 12, 2020 3:06 pm

Yeah sounds like ODSR #60. Ive built that circuit and it sounds great! kind of dark and compressed in a good way. Lots of sustain

Aaron · Post by **Aaron** » Wed May 13, 2020 12:16 am

Here’s a little clip of an ODS #60 I built a few years ago.
The overdrive on this amp was so dynamic. Was one of my favourites, I used vintage Fender Bassman Ten transformers on this build.

https://youtu.be/EtvPAKYpMSo

https://youtu.be/hs8qBk1wA28

Aaron

tubedogsmith · Post by **tubedogsmith** » Wed May 13, 2020 12:54 am

Thanks. Glad to hear I’m not crazy.

marcos · Post by **marcos** » Wed May 13, 2020 10:58 am

#121 is set up in a similar way. Don´t ask me how I know

tubedogsmith · Post by **tubedogsmith** » Wed May 13, 2020 10:59 am

Is there a schematic of ODSR #60 floating around? Those clips really sound great.

Aaron · Post by **Aaron** » Thu May 14, 2020 12:11 pm

Traced from ODRS #060 photos. The only change I did from the schematic is the 470k LNFB resistor on the last triode should be 4M7.

Aaron

tubedogsmith · Post by **tubedogsmith** » Thu May 14, 2020 11:25 pm

Thanks much, really appreciate that.

The Amp Garage

70's circuit updated late '80's

70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's

Re: 70's circuit updated late '80's