Scott 222C

[thefragger]

Thanks Blast! Still waiting on the electrolytics--backordered until October (Nichicons! who doesn't keep a huge stock of those?!).

Sigh.

I still have to drill new holes for the multicap brackets and then I think I should be good...

 

[Blast]

Oh, yeah, I see now that your JJ electro isn't screwed down. Still waiting on the bias supply electros, huh?

And, I meant if the amp runs for 30 minutes WITHOUT REDPLATING. Not if it'll run for 30 minutes before, oh I don't know... smoke, or an explosion, or something....

 

[wank]

Love this thread. The transformers look dead sexy.

 

[Blast]

Oh, yeah! They're sex on fire!

 

[thefragger]

(Alice Cooper) Schooool's out! for! winter! Schooool's out! until! the New Year!


I'm working on this ol' girl again.


Also, apparently the power supply that's been built in this chassis isn't the one that's laid out in the schematic; ah, bliss..

 

[tube-a-lou]

Hi,
Love what you doing with your amp. I just got Scott Lk72 it's pretty bad, but
got it for a good price, did polish it with Weiman polish and came out pretty
nice, I'll leave it as is, because it needs a power Transformer and a recap, but
I'll take my time and do it right.

 

[thefragger]

Thank you, and it's key to take the time to do it right, definitely!

Well, tonight I got as far as I can! I need a handful of caps and a 33R 5W resistor before I can fire this puppy up! I also have to build my VARIAC into a proper case...

Then it's little things, lie replacing the RCA jacks and swapping the screw-down posts with binding posts. SO CLOSE!


Photos tomorrow

 

[thefragger]

Does anyone have any thoughts about installing an inrush current limiter, and what part I might use? I'll go digging through my drawers tomorrow to see what parts I have.

I'm extremely excited with how close to finishing the chassis!

 

[tube-a-lou]

Thank you, and it's key to take the time to do it right, definitely!

Well, tonight I got as far as I can! I need a handful of caps and a 33R 5W resistor before I can fire this puppy up! I also have to build my VARIAC into a proper case...

Then it's little things, lie replacing the RCA jacks and swapping the screw-down posts with binding posts. SO CLOSE!


Photos tomorrow

Hi,
I saw on line some screw down binding posts for the Dynaco amps,
I just Google Dynaco Parts for sale, I think the Company's in New Jersey.
They look good and they include the panel to fit. I just polished the RCA
jacks with my Dremel tool they came out good , I was surprised they had
a little rust on them on they clean right up, for the inside I use flitz polish
and Q-tips and shine them up and they do make the amp sound better!

Thanks

 

[jonw]

Flitz works great as a polish but.........
Be sure and wipe the polished metal down with IPA to remove any protective coating the Flitz left.

Most metal polishes contain a protective coating to keep things protected from tarnishing.

I use a Q-tip.

 

[tube-a-lou]

Yes, I always use my contact Cleaner after I polish the contact's

 

[thefragger]

Thanks for the tips!!

I found the extra caps I needed but I need to go out and get a 33R 5W resistor and I won't be in for a few days--update to follow!

 

[thefragger]

Wahoo!!! I think I'm done... I wasn't able to get out to the store to grab a 33ohm resistor, but I paralleled twp 20 ohm resistors and then put another in series to achieve 30ohms (each individual resistor rated at 2W), so I hope that'll work until I can get to the shop. Got all the caps installed (aside from four in the tone control section that I missed when I was doing an inventory).

Later today I'll be working on building my VARIAC and I'll have photos uploaded.

 

[thefragger]

Alright, with 2A fast-blow fuse locked and loaded, I hooked up the amp to the VARIAC and eased 'er up to 120 from 0. Max current draw at the top, not tubes loaded, was 0.110A--nothing blew up, fuses are all good, no magic smoke--excellent!

Next I tested the tube heater supply--the unloaded voltage after the resistors was -78VDC, so I rolled in some 12AX7s I had kicking around (some newish Sovteks) and remeasured; loaded the voltage ran up to -49.5V and the amp's current draw creeped up to 0.178A. A little high. I suspect that I should remove the cobbled-30ohm-equivalent resistor with a proper 33ohm 5W model as even within the five minute window and only the four tubes loaded, the group-of-three began to get a little warm.

Photos to follow. I promise!

 

[thefragger]

Amp

Test Setup--DMM attached to the binding posts on the VARIAC

Main Power Capacitor

Negative Tube Supply

Third Cap--two 32u/500V in the big can and two 27u/35V underneath

GLOWING TUBES!! Overvolted a wee bit, though

Thermistor installed under vent holes

Cap that was hiding

​

 

[tube-a-lou]

Hi,
Wow that's looking real good!

Tube

 

[KGBMAN]

Nice pics!

 

[thefragger]

Hi,
Wow that's looking real good!

Tube

Nice pics!

Thank you, thank you!


Now, I've hit a wall--new 5AR4 tubes are inexpensive and plentiful, but also have problems and fair prematurely. I've been reading and a common mod is to put a solid-state bridge rectifier before the 5AR4 tube, using the tube's naturally warm-up time as a slow ramp-up of the B+, while the diode bridge prevents the mains traffo from being destroyed by arcing! Sounds like a winning idea to me that's fully reversible.

 

[Blast]

I'm using Sovtek 5AR4's in two Scott 222C's (and a 299A) with no problems whatsoever...

Ask yourself, "What would Herman do?"

 

[kpaxfaq]

I'm using Sovtek 5AR4's in two Scott 222C's (and a 299A) with no problems whatsoever...

Ask yourself, "What would Herman do?"

Honestly with a 100% restored amp in proper operational condition just buy a 5AR4 from a reputable tube seller (McShane cough McShane) and be done with it! Sometimes I think we all over-think this stuff.