2nd Generation 50W ODS Period correct Layout

[Deric]

Thanks for sharing!!!

One more amp on the "to do" list.

[67plexi]

Great work Tony. Thank you this will be a fun build.

Steve.

[jborders5]

Thanks Tony!

[talbany]

Great work Tony. Thank you this will be a fun build.

Steve.

DOH!! who needs Viagra.. Just stare!

Tony

[Max]

2nd generation "pre-classic" tone stack (1975 – 1978):

Treble: 500KL pot / 510pF treble cap
100k slope resistor
Mid: 250KA pot / .01 mid cap
Bass: 1MA pot / .1 bass cap / .002 soldered between the terminals 2 and 3 of the bass pot and .02 cap soldered between terminals 1 and 2 of the bass pot / 10K tail
Also notice PS cap types are not the same throughout

Hi Tony,

What do you mean by "PS cap types are not the same throughout"? I ask because in your layout they all are marked as 6PS 600V?

When the 2nd generation was manufactured
- pre production ODS with the 3 step OD switch (1968 - 1972)
- 1st generation (1972 - 1975)
- 2nd generation (1975 - 1978)
- 3rd generation (1978 - 1979)
- transition generation (1979 - 1981)

When I posted this info and the according series number ranges in the "70ies circuit Bludodrive" thread I did mean these year dates and series # ranges in the sense of "around" of course. Just as with vintage guitars you will of course always find some very early ones and some very late ones that have been made a bit earlier or a bit later.

These really are WONDERFUL sounding amps and recommend them highly!!

I have posted some clips that have been recorded with such a 2nd generation "pre-classic" ODS 50W in different threads here. Here are the links to these posts:
https://tubeamparchive.com/viewtopic.ph ... 483#136483
https://tubeamparchive.com/viewtopic.ph ... 484#136484
https://tubeamparchive.com/viewtopic.ph ... 960#133960
https://tubeamparchive.com/viewtopic.ph ... 973#134973
https://tubeamparchive.com/viewtopic.ph ... 368#129368

I did also post a song that has been recorded with a 3rd generation "pre-classic" ODS 50W.

https://tubeamparchive.com/viewtopic.ph ... 117#135117
https://tubeamparchive.com/viewtopic.ph ... 120#135120
https://tubeamparchive.com/viewtopic.ph ... 121#135121

These 3rd generation "pre-classic" ODS amps have been built from around 1978 -1979. Their series # range starts around #060 and ends in the low #07X. #075, the Farris amp, is already a transition generation "classic" ODS with all the 4th generation (1981 -1988) "classic" specs (snubbers, "classic" tone stack, OD "trigger" trim pot entrance, ratio control, presence control, dynamic balance control, etc.).

The 3rd generation ODS amps and the 2nd generation ODS amps are very similar in their technical specs. The more important technical differences that are IMO the main reasons for the different tone of a 2nd and a 3rd generation ODS are their different tone stacks and their different kind of coax cables (RG59/U foam 75ohm video cable in 3rd generation).

Here are again the different tone stacks of the 2nd and 3rd generation "pre-classic" ODS amps:

2nd generation "pre-classic" tone stack (1975 – 1978):

Treble: 500KL pot / 510pF treble cap
100k slope resistor
Mid: 250KA pot / .01 mid cap
Bass: 1MA pot / .1 bass cap / .002 soldered between the terminals 2 and 3 of the bass pot and .02 cap soldered between terminals 1 and 2 of the bass pot / 10K tail

3rd generation "pre-classic" tone stack (1978 – 1979):

Treble: 250KA pot / 510pF treble cap
100k slope resistor
Mid: 250KA pot / .01 mid cap
Bass: 1 MA pot / .1 bass cap / .005 soldered between the terminals 2 and 3 of the bass pot / 10K tail

Everything else is technically rather similar in a 2nd and 3rd generation "pre-classic" ODS. The obvious difference in their appearance are the small slide switches for EQ and manual/pedal of the 2nd generation "pre-classic" ODS amps and the small toggle switches for EQ and manual/pedal of the 3rd generation "pre-classic" ODS amps.

Cheers,

Max

[talbany]

Hi Tony,

What do you mean by "PS cap types are not the same throughout"? I ask because in your layout they all are marked as 6PS 600V?

Max
Typo. wanted to say
" Notice cap types are not the same throughout" Referring to the .002 ceramic on top and wiper of bass pot and .01 deep switch..edited

Thanks for chiming in with info and clips very helpful as always..

Right now I am a little behind on work but hopefully in the near future I can do another revision of the layout to a 3rd generation pre-classic tone stack. Shouldn't be too difficult..

Take Care!!
Tony

Tony

[pancac]

thanks Tony for this great job. just a question there is an output preamp , but not a power amp in , right? so impossible to use with effect post OD
jean marc

[Max]

Hi Tony,

What do you mean by "PS cap types are not the same throughout"? I ask because in your layout they all are marked as 6PS 600V?

Max
Typo. wanted to say
" Notice cap types are not the same throughout" Referring to the .002 ceramic on top and wiper of bass pot and .01 deep switch..edited

Hi Tony,

thanks for the clarification.

in the near future I can do another revision of the layout to a 3rd generation pre-classic tone stack. Shouldn't be too difficult...

You are right, the differences are not that large. And this would be very interesting of course (and again very, very generous indeed!) and a great opportunity for everyone here to compare the two different "pre-classic" flavors of a 2nd and a 3rd generation "pre-classic" ODS. So I will try to look for some more 2nd and 3rd generation "pre-classic" clips.

All the best,

Max

[mat]

Thanks for sharing!!!

One more amp on the "to do" list.

+1 to that

[stevlech]

Thank you, Tony!

[Max]

thanks Tony for this great job. just a question there is an output preamp , but not a power amp in , right? so impossible to use with effect post OD
jean marc

Hi marc,

IMO there are at least four ways to deal with this:

Mono fx:
preamp out > Dumblelator > fx in > fx processing > fx out > Dumblelator > separate power amp (Odyssey, Dynaco etc.) > separate cabinet

Stereo fx:
Preamp out > stereo Dumblelator > stereo fx in > stereo fx processing > stereo fx out > stereo Dumblelator > separate stereo power amp or two mono power amps > two separate cabinets

The Larry Carlton setup: http://mr335.tv/?channel=rig&videofile= ... lification

The original "loop mod":

Alexander Dumble did modify some of his 1st, 2nd and 3rd generation ODS amps that he had originally built with only a preamp out with a "loop" or "insert" as he sometimes labeled this. To accomplish this he added a second jack or he replaced the preamp out jack with stereo jack. Then he connected the "loop jack/s" with twisted wires (I did never see a coax for this kind of mod AFAIR). AFAIR he used three twisted wires for this: two for the signal and one connected to ground to work as some kind of shield AFAIR. And AFAIR this ground shield wire was connected only at one point to ground at the jacks. AFAIR this is how this kind of "loop mod" was done in the amps I am familiar with, which had such a kind of "loop mod".

Cheers,

Max

[Max]

Nice!

Do you have a serial number range for this circuit?

Hi ic-racer,

In addition to the range, which Tony (talbany) posted already, an example: The 2nd generation ODS 50W of Steve Lukather (picture attached again) has the series #048.

Cheers,

Max

[talbany]

You are right, the differences are not that large. And this would be very interesting of course (and again very, very generous indeed!) and a great opportunity for everyone here to compare the two different "pre-classic" flavors of a 2nd and a 3rd generation "pre-classic" ODS. So I will try to look for some more 2nd and 3rd generation "pre-classic" clips.

That would be great..Hopefully I should have some time this weekend to work on the 3rd generation..Any clips and other info you post on the next revision would be very much appreciated..THX

Tony

[ToneMerc]

Great work Tony. Thank you this will be a fun build.

Steve.

DOH!! who needs Viagra.. Just stare!

Tony

Steve, looks like you need some vintage resistors to go with those yellow TVA's.

I have both the 1/2w 180K piher and the 1.5w 1M (brown)RN75, I just can't find them

Mike

[Structo]

The light blue look like Mepco or Electra's.

I was searching for those but found they really aren't that great of resistors due to tolerance and drifting problems, but they do look correct.
I guess that depends whether or not you are building a replica or a modern tonal approximation of the amp and want it to sound good and last long time.

I haven't contacted this guy but he claims to have a lot of those resistors, caps and stuff.
His website is old fashioned and hard to navigate but if you really want something he may have it.

http://www.33audio.com/