....and, Oh No, NOT Another 102

[David Root]

Yup, sorry about that. This one is a basic Ojai circuit, classic PS. I built a precision PS but several people opined that the classic is better for this vintage of circuit, so I built another classic one. Jelle, I'd appreciate your comment on that. Found a good 40+40 500V can cap for V1/V2 at justradios.com . Not cheap but much less than the AES Mallory cans.

CE chassis, 3 relays, OD, PAB, MB. '73 Twin OT, new M-C Twin PT. Normster's internal buffered loop. Most of the signal caps and resistors are NOS '60s to '80s, as are the pots. Two '72 Stackpole 250KA, rest are old Clarostats with press fit aluminum shafts, easy to cut to length in my drill press. Only the presence pot is an Alpha.

I deliberately used as many NOS parts as I could find that made sense. The orange drops all have the outer foil end marked by the mfr. Some of them are so old they are turning brown. I had to dry them out in a convection oven for 4 days at 225 deg F to get them back into spec. If you store old orange or choco drops in a humid non-A/C environment for 40 years the capacitance goes up way above spec. I now keep them in Mason jars with silica gel desiccant in the bottom. The .01uF bass cap is allegedly the so-called mystery cap. It's 400V and not a 6PS.

No 68pF cap on the master.

Resistors are Electra/Mepco-Electra MFs as you can see, the rest are almost all CFs by Piher and Draloric.

Tubes are a quad of NOS Mesa 415-STR, V1 '58 long plate Mullard, V2 long plate '59 Amperex, V3 (loop buffer) '50 Telefunken long ridged plate, V4 (PI) '62 Telefunken long ridged plate. I recently received a '50s short shiny black plate Sylvania 12AX7 that I/m going to try in V2. It's a gain monster for an old US 12AX7, tests gain of 115 and 110 on my VTV dual triode tester. One post here a while back claimed it had girth to spare and would be good with single coils.

Next amp is a first gen ODS 004 50W w/ old choco drops and a '64 Bassman OT. Stop me before I build again!

[mhartman]

Gorgeous build David!

[rogb]

Wow! Great looking build David - hope it sounds amazing.

102s just falling out of the sky like asteroids at the moment

[dcribbs1412]

Inspiring build David
Some tasty NOS parts
I've used the small solens for internal loops also.
I hope to see discussion on the PPS and classic power supplies.

Thanks
Darin

[David Root]

Thanx guys. We AB'd it against a Sebago Amps (Bill Dunham) Double Trouble, which is 100W hi-plate presumably going for the SRV tone? My pals played a rather pricey PRS and a 25 year old Fender parts guitar with the F-hole semi solid body and a dead straight (!) birdseye neck. Both amps had a quad of NOS Mesa STR-415s. Don't know what Chuck has in V1-V3. Wish I could get $2,600 for a 100W Dumble with no buffered loop and no NOS tubes.

Both sounded quite similar thru my pair of 2x12s w/Celestion Blackbacks vs. a single '80s G12-65 which had a slightly crunchier tone when pushed.

My first Dumble build, a 124 w/o buffered loop, compared well with the other amps but with the differences you'd expect from hi vs. lo plate topology and black plate RCA power tubes..

Normster's internal buffered loop layout in the Files shows Xicon caps but when the Solens are less than a buck each why not?. You'll notice I always use a 0.1 Solen in the PI now because it is not in the signal path so no need for an NOS orange drop.

The main PS rectifier is a TO-220 dual diode, 1200V/8A each diode. Mouser obsoleted them, I'm glad I bought 10 of 'em a while back, also less than a buck each.

[wjdunham]

Thanx guys. We AB'd it against a Sebago Amps (Bill Dunham) Double Trouble, which is 100W hi-plate presumably going for the SRV tone? My pals played a rather pricey PRS and a 25 year old Fender parts guitar with the F-hole semi solid body and a dead straight (!) birdseye neck. Both amps had a quad of NOS Mesa STR-415s. Don't know what Chuck has in V1-V3. Wish I could get $2,600 for a 100W Dumble with no buffered loop and no NOS tubes.

Both sounded quite similar thru my pair of 2x12s w/Celestion Blackbacks vs. a single '80s G12-65 which had a slightly crunchier tone when pushed.

My first Dumble build, a 124 w/o buffered loop, compared well with the other amps but with the differences you'd expect from hi vs. lo plate topology and black plate RCA power tubes..

Normster's internal buffered loop layout in the Files shows Xicon caps but when the Solens are less than a buck each why not?. You'll notice I always use a 0.1 Solen in the PI now because it is not in the signal path so no need for an NOS orange drop.

The main PS rectifier is a TO-220 dual diode, 1200V/8A each diode. Mouser obsoleted them, I'm glad I bought 10 of 'em a while back, also less than a buck each.

Good looking build Dave, glad to see you building and posting again.
That Sebago amp was pretty much a straight 102 with a smaller master bright cap (39pf) and non-shielded wire in a few spots where the original had co-ax. I heard that was a fun session.
Bill

www.sebagosound.com

[jelle]

Great looking build, I wonder what exactly you would like my input on... The difference between the older style power supply vs the Precision one in the 102? In the amp I posted today, I have 500v B+ so that dictated the filterbank design.

I like both, the Precision feels less dynamic, more controlled than the Classic.

[David Root]

Thanx Bill, it's good to be back. After all the complications from my surgery last year, 4 months in hospital, another 4 convalescing at home. Just got back again from my ileostomy reversal, which was done March 4. No complications this time just 20 odd pounds of water retention which will take a while to lose.

I think I have 8 runs of coax but it is not too bright at all and none of that congestion in the mids that Chuck complained about in one 102 he had (not yours!). Maybe I'll try a 39pF on the master, what the hell.

Jelle, yes that's the comparison I was looking for on the main PS types. The opinions I got against the precision PS in older designs were quite vehement as I recall. So why would a precision PS work so well with a 335 in a 102? The eternal questions.......

[talbany]

Dave
Nice build man!!.. Would love to hear some clips.
Tony

[erwin_ve]

Nice built David!
Is the brown cap on the outer right from a certain brand you would share?
Why did you do 2 caps at the presence?

[steve_p]

Interesting note about drying out the vintage 6ps caps in an oven.
I have many that meter quite a bit over tolerance.
I am going to give this a try and see how many drop down closer to spec.

Steve

[David Root]

Erwin, the mystery cap is "manufacturer unknown". I got three of them on Ebay recently, there are probably some left. attached is the Ebay pic.

Presence caps are 2x1uF in parallel, I didn't have a 2uF at the time. Those red ones are 50V radial Black Gates from a build that didn't work out.

Steve, what I did really works. It will take a .13 measuring .1 cap back within spec most of the time. The less the overage the shorter the treatment time.
If the cap measures .15 then you are not likely to get it back in spec although it will drop some.

[Colossal]

Stop me before I build again!

Never!

Looks great David. I like the built-in Loop!

[vibratoking]

How long do you expect the cooked cap to remain in spec??

[David Root]

Good question.

Stored in Mason jars over desiccant, indefinitely.

In service, I guess I'll find out, but the interior of a chassis generally runs pretty warm, so I would expect pretty much the same as a new 2013 cap.

Remember it took a good 40 years or so for these epoxy caps to absorb enough moisture to drive up their capacitance 20 to 40%. Their original environment was Houston, which is pretty extreme humidity situation most of the year.